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Chapter 4 RESULTS AND DISCUSSION

4.1. Introduction4.2. Study of thermal properties4.3. Study of electrical properties4.4. Study of mechanical properties4.5. Study of FRLS properties4.6. Calculation steps4.7. Conclusion

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4.1. Introduction

The ideal, that is, an ever-continuing search for a polymer

composition that produces no smoke at all and shows zero affinity for fire

shall always remain. This chapter deals with the experimental results

obtained during the course of the work and a systematic study of the

observations.

The experimental work comprises preparation of polymer

‘compounds’ of varying compositions and study of various properties of

these compounds. The study of various properties can broadly be organized

under four headings: study of thermal properties, study of electrical

properties, study of mechanical properties and study of FRLS properties.

Polymeric materials can be classified in a variety of ways: (i) based

on their origin, into natural and synthetic and, (ii) based on their physical

properties, into elastomers, plastics and fibers. Elastomers (or rubbers) are

characterized by a long-range extensibility that is almost completely

reversible at room temperature. Plastics have only partially reversible

deformability, while fibers have very high tensile strength but low

extensibility. Plastics can be further subdivided into thermoplastics (whose

deformation at elevated temperatures is reversible) and thermosets (which

undergo irreversible changes when heated). Elastomers have elastic modulii

between 105 and 106 N/m2, while plastics have modulii between 107 and 108

N/m2, and fibers have modulii between 109 and 1010 N/m2. In terms of

elongation, elastomers can be stretched roughly up to 500 to 1000 percent,

plastics between 100 to 200 percent, and fibers only 10 to 30 percent before

fracture of their material is complete.

Polymers can also be classified in terms of their chemical

composition; this gives a very important indication as to their reactivity,

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including their mechanism of thermal decomposition and their fire

performance.

The main carbonaceous polymers with no heteroatom are polyolefins,

polydienes and aromatic hydrocarbon polymers (typically styrenics). The

main polyolefins are thermoplastics: polyethylene and polypropylene, which

are two of the three most widely used synthetic polymers. Polydienes are

generally elastomeric and contain one double bond per repeating unit; the

common examples are ABS (Acrylic Butadiene Styrene terpolymers) and

EPDM (Ethylene Propylene Diene rubbers). The most important aromatic

hydrocarbon polymers are based on polystyrene.

The most important oxygen-containing polymers are cellulosics,

polyacrylics, and polyesters.

Nitrogen-containing materials include nylons, polyurethanes,

polyamides and polyacrylonitrile.

Chlorine-containing polymers are exemplified by PVC. It is the most

widely used synthetic polymer, together with polyethylene and

polypropylene. It is unique in that it is used both as a rigid material

(unplasticized) and as a flexible material (plasticized). Flexibility is achieved

by adding plasticizers or flexibilizers. Through additional chlorination of

PVC, another member of the family of vinyl materials is made: CPVC, with

different physical and fire properties from PVC.

Fluorine-containing polymers are characterized by high thermal and

chemical inertness and low coefficient of friction. The most important in the

family is PTFE [108(i)].

4.2. Study of thermal properties

Solid polymeric materials undergo both physical and chemical

changes when heat is applied; this usually results in undesirable changes to

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the properties of the polymer. A clear distinction needs to be made between

thermal decomposition and thermal degradation. Thermal decomposition is

‘a process of extensive chemical species change caused by heat’. Thermal

degradation is ‘a process whereby the action of heat or elevated temperature

on a material, product or assembly causes a loss of physical, mechanical or

electrical properties’.

In the context of fire, the important change is thermal decomposition,

whereby the chemical decomposition of a solid material generates volatile

gaseous fuel vapors, which can burn above the solid material. In order for the

process to be self-sustaining, it is necessary for the burning gases to feed

back sufficient heat to the material to continue the production of gaseous fuel

vapors or volatiles. As such, the process can be a continuous feedback loop if

the material continues burning. In that case, heat transferred to the polymer,

ΔH2, causes the generation of flammable volatiles; these volatiles react with

the oxygen in the air above the polymer to generate heat, ΔH1, and a part of

this heat is transferred back to the polymer to continue the process [108(ii)],

as shown in the figure 4.1.

Figure 4.1. Polymer combustion feed-back loop

However, both, the chemical and the physical aspects of thermal

decomposition of polymers are important. The chemical processes are

responsible for the generation of flammable volatiles while physical changes,

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such as melting and charring, can markedly alter the decomposition and

burning characteristics of a material.

The dependence of thermal decomposition on heating rate is due to

the fact that the rate of thermal decomposition is not only a function of the

temperature, but also of the amount and nature of the decomposition process

that has preceded it.

Materials that are stable at high temperatures are likely to be better

performers as far as fire properties are concerned. However, there are several

reasons why the relevance of TGA studies to fire performance is being

questioned: heating rate, amount of material and lack of heat feedback are

the major ones. For example, it is well-known that heating rates of 10-100

K/s are common under fire conditions, but are rare in thermal analysis. More

seriously, TGA studies are incapable of simulating the thermal effects due to

large amount of material burning and resupplying energy to the decomposing

materials at different rates. However, analytical TGA studies do give

important information about the decomposition process, even though

extreme caution needs to be exercised in their direct application to fire

behavior.

Differential thermogravimetry (DTG) is exactly the same as TGA,

except that the mass loss versus time output is differentiated automatically to

give the mass loss rate versus time. DTG is the best indicator of the

temperatures at which the various stages of thermal decomposition take place

and the order in which they occur [108(iii)].

The major reason why thermal decomposition of polymers is studied

is because of its importance to fire performance. Early on, comparisons were

attempted between the minimum decomposition temperature, Td (or, even

better, the temperature for 1% thermal decomposition, T1%) and the Limiting

Oxygen Index. The conclusion was that, although low flammability resulted

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from high minimum thermal decomposition temperatures, no easy

comparison could be found between the two. There were some notable cases

of polymers with both low thermal stability and low flammability. From the

considerable amount of work done in this area, it can be safely deduced that

thermal decomposition cannot be a stand-alone means of predicting fire

performance. A high LOI does not always mean a high T1% or vice-versa.

But, whatever the degree of predictability of fire performance data

from thermal decomposition data, its importance should not be

underestimated: Polymers cannot burn if they do not break down.

Table 4.1. Thermal Stability and Flammability of Polymers

Polymer aTdbT1%

cLOIPolypropylene 531 588 17.4

LDPE 490 591 17.4

HDPE 506 548 17.4

Poly(vinylidenefluoride) 628 683 43.7PVC 356 457 47.0

aTd: Minimum thermal decomposition temperature from TGA (10 mg sample, 10 K.min-1 heating rate, N2 atm.), bT1%: Temperature for 1% thermal decomposition, cLOI: Limiting Oxygen Index

More complete and detailed surveys of polymers and their thermal

decomposition are available in the literature [108(iv),(v)].

Thermal decomposition of PVC has been one of the most widely

studied, given its commercial importance and range of applications. Between

225-275oC, HCl gas is evolved almost quantitatively, by a chain-stripping

mechanism. It is very important to point out, however, that the temperature at

which HCl is evolved in a measurable way is highly dependent on the

stabilization package used. Thus, commercial PVC compounds have been

shown, in recent work, not to evolve HCl until temperatures exceed 250 oC

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and to have a dehydrochlorination stage starting at 325oC. Between 425-475 oC, hydrogen is evolved during carbonization, following cyclization of the

species involved. At temperatures above 475oC, the char (resulting from

dehydrochlorination and further dehydrogenation) is oxidized, leaving no

residue. Dehydrochlorination stabilizers include zinc, cadmium, lead,

calcium and barium salts and organotin derivatives [109-112].

In the present work, thermograms were recorded for different

polymer compounds with a view to understand their thermal behavior and

the thermal rating values and kinetic properties like activation energy and

rate constant were calculated. In a few cases, glass transition temperatures

were also measured using Thermo Mechanical Analysis (TMA) apparatus.

Thermal stability-time was measured in the relevant cases.

4.2.1. The thermal stability-time recording procedure

The thermostat is set at 199.9oC. The previously weighed (~ 50 mg)

samples (in small pieces), taken in sample tubes, are places in the designated

‘cavities’ on the thermostatically controlled heating chamber. Three small

pieces of ph paper are rolled into cylindrical shape and inserted into the top

portion of the sample tubes. Every fifteen minutes for the first one hour, and

every five –minute intervals thereafter, the ph paper pieces are examined and

rated visually for any color change. The color change indicates

decomposition of the sample evolving HCl vapors. The observations are

tabulated.

Figure 4.2. The sample tube used for thermal stability-time test

4.2.2. Studies on PVC K-70 compositions

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Seven samples were prepared using fixed concentrations of K-70

grade PVC, CaCO3, martinal, Mg(OH)2, Sb2O3, tribasic lead sulfate (TBLS),

calcium stearate and paraffin wax and variable concentrations of the two

plasticizers, DOP and TOTM and the two additives, glass and cenospheres.

The objective of the study was to examine the comparative effect of

the two plasticizers, DOP and TOTM, and the additives glass and

cenospheres on the thermal stability of the compositions.

Table 4.2 gives details of the seven compositions prepared using the

various ingredients.

Table 4.2. Compositions of the PVC systems with DOP and TOTM as plasticizers with 100 phr PVC

SlNo

Components (in phr units)(a) (b) (c) (d) (e) (f

)(g) (h) (i) (j) (k) Sample

Code1 30 06 16 28 4 2 8 0.6 0.4 09 09 PM012 12 24 16 28 4 2 8 0.6 0.4 18 - PM023 24 12 16 28 4 2 8 0.6 0.4 18 - PM034 06 30 16 28 4 2 8 0.6 0.4 09 09 PM045 - 36 16 28 4 2 8 0.6 0.4 - 18 PM056 36 - 16 28 4 2 8 0.6 0.4 18 - PM067 - 36 16 28 4 2 8 0.6 0.4 18 - PM07

(a).DOP, (b). TOTM, (c). CaCO3, (d). martinal (e). Mg(OH)2,(f). Sb2O3, (g). TBLS, (h). calcium stearate, (i). paraffin wax, (j). glass, (k).cenospheres

TGA studies were carried out for all the samples using the

thermogravimetric analyzer, using different heating rates. From the

thermograms, the T5% (temperature at 5% weight loss) and T10% (temperature

at 5% weight loss), were noted. However, for the present purposes, only T5%

values would be sufficient and these are presented in table 4.3.

Table 4.3. TGA and Tg data and kinetic properties for PM01 through PM07

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Heating rateβ (o C . min –1 )

T5%

PM01 PM02 PM03 PM04 PM05 PM06 PM07T

GA

2 205 206 204 264 267 252 2584 219 214 213 274 288 256 2818 225 234 235 286 293 273 28912 - 236 243 291 303 285 295

Thermal rating, θ (o C)

107.5 91.7 91.75 162.3 120 109 155

E (Kcal. K–1. mol–1)

29.13 24.00 23.55 36.22 21.74 21.74 23.48

Tg (o C) - - - - 110.1 83.14 79.38

From the above table, it is clear that PM05 shows the highest value

for T5% for all the rates of heating carried out. The composition PM03 shows

the lowest value for T5% for lower heating rates. However, no regular trend in

the variation of T5% is discernable with different heating rates.

Using Ozawa’s method and Toop’s equation, respectively, the

activation energy for thermal decomposition, E, and the thermal rating, θ,

were calculated (the details of the equations are dealt with later in this section

and also in Chapter 5).

In table 4.2., first, let us consider the two compositions, PM01 and

PM04. In these, the quantities of plasticizers, DOP and TOTM, are reversed,

concentrations of all other ingredients remaining same in both. From table

4.3., it can be seen that E and θ values for PM01 and PM04 are 29.13

Kcal.K–1.mol–1 and 36.22 Kcal.K–1.mol–1 and 107.5oC and 162.3oC,

respectively. The data suggest that TOTM, compared to DOP, at the same

level of phr, imparts better thermal stability on the polymer system

considered. Further, incidentally, it is for PM04 that the θ value, at 162.3 o C,

is maximum, compared to that of the other compositions listed in the table

4.2. Thus, from standpoint of thermal stability alone, TOTM seems to be a

better plasticizer than DOP in this context.

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Considering the other two comparable compositions, PM02 and

PM04, the distinguishing feature, again, is plasticizer concentration: PM02

having TOTM concentration double that of DOP, and PM03, having the

concentrations of the two plasticizers reversed. In these two cases, E and θ

values appear to be nearly same and somewhat low, probably because glass

additive, at 18 phr, has made a difference, masking the otherwise possible

difference in θ value, and also by lowering the thermal rating value to some

extent.

A closer look at the table 4.2. would reveal that whereas the four

compositions, PM01 to PM04, contain two plasticizers, the remaining three

compositions, PM05, PM06 and PM07, have only one of the two

plasticizers, DOP or TOTM, and at higher loadings (36 phr). Among PM05

and PM07, the two differing only in respect of glass/cenosphere

concentration, the additive glass has led to higher thermal stability compared

to cenospheres. Between PM06 and PM07, the composition PM07, having

TOTM as plasticizer, has a larger θ value than the composition PM06,

having DOP at the same concentration. This observation reinforces the

inference made above: thermal stability is better with TOTM compared to

that with DOP.

The most desirable combination from thermal stability standpoint is

that of PM04, which contains two plasticizers and two filler additives,

probably suggesting that there is some synergism at work here.

For the compositions PM05, PM06 and PM07, the glass transition

temperatures (Tg oC) were recorded. The composition PM07 has the lowest

Tg of the three, possibly suggesting that the absence of DOP and the additive

cenospheres could be the reason for the lower value.

A set of five compositions, PM08 to PM12, were prepared using two

specially procured PVC resins: CP 172 SG and K6701. The former is a

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specialty emulsion polymerized resin made for the manufacture of sintered

battery separators. Its carefully controlled particle size and shape enable the

production of separators with minimum thickness and optimum mechanical

properties. A recent study [113] suggests that while both the samples CP 172

SG and K6701 are usable for LT PVC cable sheathing, only sample K 6701

can be used for insulation.

The two resins were mixed in different ratios, as given in table 4.4.

The anti-oxidant bisphenol-A has been added here; only DOP is the

plasticizer used. The objective was to investigate the thermal behavior of

these resin samples, when the polymer matrix contained no flame-retardants

or filler additives and contained only the plasticizer DOP, calcium carbonate

filler, stabilizer tribasic lead sulfate, stabilizer lubricant calcium stearate and

the anti-oxidant bisphenol-A.

Table 4.4. Compositions of the PVC systems (Specially procured PVC resins)

Sample Code

Components (in phr units)

a1 a2 b c d e f g h i j k l m

PM08 100 -35

- 20 - - - 5 0.1 - - - 0.1

PM09 - 10035

- 20 - - - 5 0.1 - - - 0.1

PM10 50 5035

- 20 - - - 5 0.1 - - - 0.1

PM11 30 7035

- 20 - - - 5 0.1 - - - 0.1

PM12 20 8035

- 20 - - - 5 0.1 - - - 0.1

(a1). PVC6701, (a2). PVC CP 172 SG, (b).DOP, (c). TOTM, (d). CaCO3, (e). martinal (f). Mg(OH)2, (g). Sb2O3, (h). TBLS, (i). calcium stearate, (j). paraffin wax, (k). glass, (l).cenospheres, (m). bisphenol A

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Table 4.5. TGA and Tg data for PM08 through PM12

β(o C . min –1 )

T5%

PM08 PM09 PM10 PM11 PM12

TG

A

2 202 207 204 207 2114 220 220 222 222 2278 224 248 242 240 23912 262 263 260 244 241

Tg (o C) 141.11 139.88 139.98 138.93 139.62

Though the thermal stability in the first three cases, that is, PM08 to

PM 10, is almost same, it shows a decrease in the latter two cases, if one

were to consider the higher heating rate of 12o C.min –1. However, it is not

possible to arrive at any significant correlation between the compositions and

their thermal behavior, as the T5% readings at different heating rates given in

the table 4.4. clearly show an erratic trend. As no meaningful deductions

were possible from TGA studies, the transition temperature studies were

carried out. The data show that all the five compositions have virtually the

same Tg value and the value is considerably higher than that of the pure PVC

resin (75 – 85 o C). In the light of these observations, the two resins were

considered ‘not suitable’ for further investigations and no other properties

were evaluated for them.

Nine more compositions were prepared using DOP and TCP (in place

of TOTM) as plasticizers; Sb2O3 was not included; zinc borate, a smoke-

suppressant, was included. Different ratios of various additives were tried

out, taking the concentrations of only DOP, martinal and glass as variables

and keeping concentrations of all other components constant. The

compositions are given in table 4.6.

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The compositions PM13, PM14 and PM15 differ only in the

concentration of one component, glass. The next three, PM16, PM17 and

PM18, differ only in the concentration of martinal. Similar observations can

be made for the other compositions as well.

Since some processing issues came up hindering smooth blending

operation, and proper blending required 4 to 6 phr of additional DOP than

originally intended, further investigations were not taken up for these

compositions. Only electrical properties were recorded.

Table 4.6. Compositions of the PVC systems with different additives

Sl. No.

Components (in phr units) Sample Code

(a) (b) (c) (d) (e) (f) (g) (h) (i) (j) (k) (l)

1 100

36 8 14 24 3 1 10 0.2 0.2 10 0.5 PM13

2 100

36 8 14 24 3 1 10 0.2 0.2 15 0.5 PM14

3 100

36 8 14 24 3 1 10 0.2 0.2 20 0.5 PM15

4 100

36 8 14 28 3 1 10 0.2 0.2 10 0.5 PM16

5 100

36 8 14 32 3 1 10 0.2 0.2 10 0.5 PM17

6 100

36 8 14 26 3 1 10 0.2 0.2 10 0.5 PM18

7 100

30 8 16 26 3 1 10 0.2 0.2 10 0.5 PM19

8 100

36 8 16 26 3 1 10 0.2 0.2 10 0.5 PM20

9 100

36 8 14 26 3 1 10 0.2 0.2 15 0.5 PM21

(a). PVC, (b).DOP, (c). TCP, (d). CaCO3, (e). martinal (f). Mg (OH) 2, (g). zinc borate, (h). Ca/Zn stabilizer, (i). calcium stearate, (j). stearic acid, (k). glass, (l). bisphenol A

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After a thorough consideration of the functions of each of the

constituents, suitable alterations were made in their relative proportions, and

three compositions, PM22, PM23 and PM24, formulated. These are given in

table 4.7. These compositions showed better performance on the whole; TGA

data were not recorded as it was not considered necessary. Electrical,

mechanical and FRLS properties were recorded.

Table 4.7. Compositions of the PVC systems with different ratios of additives

Sl. No.

Components (in phr units) Sample Code

(a) (b) (c) (d) (e) (f) (g) (h) (i) (j) (k) (l)

1 100

30 8 16 34.3

4.3 1 10 0.2 0.2 10

0.5 PM22

2 100

30 8 16 34.3

4.3 1 10 0.2 0.2 20

0.5 PM23

3 100

30 8 16 34.3

4.3 1 10 0.2 0.2 30

0.5 PM24

(a). PVC, (b).DOP, (c). TCP, (d). CaCO3, (e). martinal (f). Mg (OH)2, (g). zinc borate, (h). Ca/Zn stabilizer, (i). calcium stearate, (j). stearic acid, (k). glass, (l). bisphenol A

On further considerations, a batch of five compositions, PM25 to

PM29, with cenospheres, the inert filler, as the only variable, were prepared.

DOP and TOTM were the plasticizers used. These compositions showed

impressive results in all the aspects studied.

Table 4.8. Compositions of the PVC systems with cenospheres as filler additives with 100 phr of PVC

Sample Code

Components (in phr units)

a b c d e f g h I j k

PM25 - 36 16 28 4 3 8 0.6 0.4 - -

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PM26 - 36 16 28 4 3 8 0.6 0.4 - 6PM27 - 36 16 28 4 3 8 0.6 0.4 - 12PM28 - 36 16 28 4 3 8 0.6 0.4 - 18PM29 - 36 16 28 4 3 8 0.6 0.4 - 24

(a). DOP, (b). TOTM, (c). CaCO3, (d). martinal (e). Mg(OH)2, (f). Sb2O3, (g). TBLS, (h). calcium stearate, (i). paraffin wax, (j). glass, (k). cenospheres

The TGA thermograms were recorded for each of these five

compositions and using the thermal data, the kinetic parameters for the

thermal decomposition and the thermal rating values were calculated.

Table 4.9. TGA and Tg data and kinetic properties for pM25 through PM29

β(o C.min –1)

Sample Code

PM25 PM26 PM27 PM28 PM29T5% (o C)

TG

A

2 270 260 263 265 266

4 279 272 273 279 280

8 294 289 289 289 293

12 300 293 298 299 299Thermal rating,

θ (oC )183 148 153 162 184

E (Kcal. K–1. mol–1)

44.31 31.04 31.96 35.18 38.89

Tg (o C) 82.13 66.55 - 77.63 -

4.2.2.1. Energetics of the reaction

Using different heating rates, a series of curves (shown in the figure

4.2.) are recorded, the 5% loss temperatures shifting to lower values with

reduced scan rate.

The temperatures at 5% weight loss, as noted in table 4.9, are used to

calculate the activation energy, E, using the following equation (Ozawa’s

method):

- log β – 0.457 E/R ( 1/Tp ) = constant or

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- log β = constant + (– 0.457 E/R) (1 / 103). (1/Tp *103).

The slope (m) = (– 0.457 E/R) (1/103)

Knowing the slope, the activation energy, E, is calculated.

4.2.2.2. Evaluation of thermal condition

Reports on the application of thermal analysis for estimation of

thermal life of wire enamels from the decomposition reactions are available

in literature. The mathematical expression based on life theory and

thermogravimetric theory is given by Toop:

log tf = E/2.303 Rθ + log E p(xf)/ βR

where log p(xf) = -2.315 – 0.457 E/R Tf

E = energy of activation, R = gas constant, Tf = temperature at which specific change is observed, β = heating rate, θ = thermal condition and tf

= time to condition at temperature θ Because of the simplicity and reliability, this approach is generally

preferred for determining thermal rating where thermal degradation is the

result of simple chemical reaction.

Figure 4.3. Representative TGA Curves

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In the filler concentration range studied, both, the 5% and 10% loss

temperatures, somewhat increase with the filler concentration. The activation

energy for decomposition of the compound decreases in presence of

cenospheres, the magnitude of this decrease being maximum at 6 phr of filler

and becoming progressively less pronounced at higher filler concentrations.

A similar trend is noted for thermal rating values as well.

4.2.3. Glass transition temperature (Tg) studies

At a relatively simple-minded practical and operational (and thus

theoretically non-rigorous) level of treatment, glass transition temperature

may be defined as the temperature at which the forces holding the distinct

components of an amorphous solid together are overcome by thermally

induced motions within the time-scale of the experiment, so that these

components become able to undergo large-scale molecular motions on this

time-scale, limited mainly by the inherent resistance of each component to

such flow. The practical effects of the glass transition on the processing and

performance characteristics of polymers are implicit in this definition. The

standard Tg value for PVC from literature is 75 - 82 oC.

For the three compositions PM25, PM26 and PM28, the Tg values

were measured using the thermo mechanical analyzer (TA Instruments: TMA

Q400 Model). The curves are shown in the figures 4.3., 4.4. and 4.5. and

readings are given in table 4.9. The Tg value decreases in presence of

cenospheres, again the decrease being maximum at the lowest concentration

studied. Lower Tg would mean increased polymer flexibility.

Glass transition temperatures

Sample Tg ( o C) PM 25 82.13PM 26 66.55

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PM 28 77.63

A careful consideration of the consolidated data obtained so far led to

the following three formulations, PM30, PM31 and PM32. Their mechanical

properties were measured and are given in table 4.20 of this chapter.

Figure 4.4. TMA curve for the composition PM25


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Table 4.10. Compositions of the PVC systems PM30, PM31 and PM32

Sample Code

Components (in phr units)a b c d e f g h i j k l

PM30 100 30 8 14 30 3 1 10 0.2 0.2 14 0.6PM31 100 30 8 14 30 3 1 10 0.2 0.2 15 0.6PM32 100 30 8 12 30 3 1 10 0.2 0.2 15 0.6

(a). PVC, (b).DOP, (c). TCP, (d). CaCO3, (e). martinal (f). Mg(OH)2, (g). zinc borate, (h). Ca/Zn stabilizer, (i). calcium stearate, (j). stearic acid, (k). glass, (l). bisphenol A

To understand the effect of drying on properties, the components

PVC, CaCO3, martinal and glass were dried at 105 oC for one hour and five

compositions were prepared, choosing the composition PM31 as basis.

These were designated as PM31.1 (30 minutes blending), PM31.2 (25

minutes blending), PM31.3 (20 minutes blending), PM31.4 (15 minutes

blending) and PM31.5 (10 minutes blending), respectively. As an additional

confirmatory measure, four more compositions were prepared (the

components are as taken for PM31), two, using components without drying

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and two, using components with drying. Blending times were also different.

They were designated as PM31 (R1), PM31 (R2), PM31 (R1-D) and PM31

(R2-D), ‘D’ indicating that dried components were used.

Their electrical and mechanical properties for all the nine cases were

evaluated and the values are given in tables 4.23. and 4.24.

Further considerations led to the following 3 formulations.

Table 4.11. Compositions of the PVC systems PM33, PM34 and PM35

Sample Code

Components (in phr units)(a) (b) (c) (d) (e) (f) (g) (h) (i) (j) (k) (l)

PM33 100 30 10 12 30 3 1 10 0.2 0.2 15 0.6PM34 100 30 9 12 30 3 1 10 0.2 0.2 14 0.6PM35 100 30 10 14 30 3 1 10 0.2 0.2 15 0.6

(a). PVC, (b).DOP, (c). TCP, (d). CaCO3, (e). martinal (f). Mg(OH)2, (g). zinc borate, (h). Ca/Zn stabilizer, (i). calcium stearate, (j). stearic acid, (k). glass, (l). bisphenol A

On considering the entire evaluation data, the composition PM34 was

selected as the preferred choice and repeat trials (nine times) conducted.

Three of them (the relevant data for them are shown in later pages) are

designated as PM34.1, PM34.2 and PM34.3.

4.2.4. DTG studies

DTG curves were recorded for some compositions in order to

supplement the thermal decomposition data obtained using TGA. The

representative curves are shown in the figures 4.7. to 4.10.

154

Figure 4.7DTG curve for a PVC composition at 2oC heating rate



155


The curves give accurate values for the decomposition temperature at

each heating rate and also show that the decomposition temperature shifts to

lower values with reduced heating rate.

4.3. Study of electrical propertiesSurface resistivity, volume resistivity, capacitance and tan δ: these

properties together characterize dielectric properties of electrical insulation

materials (conductive materials are those having a surface resistivity < 1x105

Ω/sq (or Ω) or volume resistivity < 1x104 Ω-cm).

The higher the values for surface and volume resistivities, the better it

is for an insulation material.

Capacitance is the measure of a capacitor's ability to store an electric

charge on its plates. Thus, for an insulation material, the lower the

capacitance value, the better.

The greater the ‘phase defect angle’, δ, the greater is the tan δ value

and the worse is the cable.

The insulating material is prone to stresses like thermal stress,

electrical stress, mechanicals stress, and environment stress etc. The normal

practice is that capacitance and tan δ values are obtained on new insulation

are treated as benchmark readings. By measuring and comparing the

periodical readings of the capacitance and tan δ of the insulating material

156

with the benchmark readings, one can know the rate of deterioration of the

health of the insulation.

The electrical properties recorded for different compositions are

tabulated in tables 4.12. to 4.17.

Table 4.12. Electrical properties for compositions PM01 to PM05

Sample Code Electrical propertiesCapacitance (30 o C) (pF) tan δ (30 o C)

PM01 - -PM02 22.259 0.0644PM03 24.095 0.0600PM04 34.16 0.06989PM05 26.15 0.0596

From table 4.12., it is observed that at 30 o C, maximum value for

both capacitance and tan δ is shown by the composition PM04, whereas

minimum value for capacitance and tan δ is shown by the compositions

PM02 and PM05, respectively.


Sample Code Electrical propertiesCapacitance (30 o C) (pF) tan δ (30 o C)

PM13 47.323337 0.1375767PM14 47.63434 0.1315667PM15 49.788033 0.1384933PM16 48.79841 0.1418267PM17 47.259007 0.1395333PM18 47.473043 0.1312933PM19 43.772187 0.1166433PM20 49.975113 0.1471333PM21 46.58698 0.130900

The electrical properties recorded at 30oC for the next batch of nine

compositions are tabulated in table 4.13. It is observed that the minimum

value for both capacitance and tan δ is shown by the composition PM19.

157


Sample Code

Electrical propertiesSurface

resistivity

Volume

resistivity

Capacitance (pF)

(30 o C)tan δ

(30 o C)

PM22 21.44E13 6.0241E12 39.7236 0.1031133PM23 19.05E13 3.6533E12 40.0366 0.1083233PM24 14.104E13 2.3130E12 35.9868 0.11658

The three compositions listed in table 4.14. above showed much

better (lower) values for capacitance and tan δ. The lowest value for

capacitance tan δ is shown by PM24. The surface resistivity and volume

resistivity values are also good; the highest for both these values is shown by

the composition PM22. The anti-oxidant BPA, present in the three

compositions, makes a strong positive contribution to volume resistivity.


Sample CodeElectrical properties

Surface resistivity

Volume resistivity

Capacitance (pF)(30 o C)

tan δ(30 o C)

PM25 94.91E13 5.95E13 34.82 0.07619PM26 73.66E13 5.747E13 30.902 0.07769PM27 70.69E13 4.546E13 30.490 0.07654PM28 72.30E13 6.86E13 30.401 0.07592PM29 83.37E13 1.569E13 30.051 0.07500

The next batch of five compositions prepared using cenospheres as

fillers showed further improvement in electrical characteristics. From table

4.15., it can be noticed that the capacitance and tan δ values are still lower

compared to the values for the compositions listed in the tables so far. The

lowest value for capacitance and tan δ is shown by the composition PM29,

158

containing maximum filler concentration of 24 phr, possibly implying the

ability of this filler to improve electrical characteristics. It is also clear that

the volume resistivity and surface resistivity values are quite good, though,

the highest values for these properties are shown by the composition not

containing cenospheres.

Effect of temperature on tan δ and capacitance was studied for a few cases.

Table 4.16. Effect of temperature on capacitance and tan δ for compositions PM22, PM23 and PM24

Temperature Sample CodePM22 PM23 PM24

30 o C Capacitance (pF) 39.7236 40.0366 35.9868

tan δ 0.1031133 0.1083233 0.11658

60 o C Capacitance (pF) 58.3899 59.5654 58.4614

tan δ 0.3761167 0.4137867 0.5678367

90 o C Capacitance (pF) 109.9661 101.8278 -tan δ 2.066 2.2930 -

As can be expected, the capacitance and tan δ values show a regular

increase with increase in temperature from 30 o C to 90 o C, in case of the

three compositions studied.

Table 4.17. Effect of temperature on capacitance and tan δ for compositions PM25 through PM29

Temperature Sample CodePM25 PM26 PM27 PM28 PM29

30 o C Capacitance (pF)

34.817 30.902 30.490 30.401 30.051

tan δ 0.07619 0.0776 0.07592 0.0759 30.051

159

9 2


50.417 44.697 47.231 44.744 42.734

tan δ 0.05901 0.06060

0.06159 0.06143

0.06260


55.956 45.111 50.271 45.609 45.132

tan δ 0.06869 0.06850

0.08395 0.07967

0.08491

The temperature effects on the five compositions listed in the table

4.17. show that the capacitance values register a regular increase with

increase in temperature from 30 oC to 90 oC for each of the five

compositions, though the increase in the tan δ values is not regular in the

temperature range studied.

4.4. Study of mechanical properties

Tensile strength (T.S.) and % elongation at break: these are the main

mechanical properties of interest in the present context. These properties are

measured in relevant cases and the data tabulated below. Target values are:

Min: 12.5N/mm2 and Min: 150 %.

Table 4.18. Tensile strength and elongation at break for the three compositions PM22, PM23 and PM24

Composition Tensile Strength, (N/mm2) % Elongation at break

trials average Trials averagePM22

Specimen 1 14.0914.49

125142Specimen 2 15.39 160

Specimen 3 13.99 140PM23

Specimen 1 13.9114.66

130143Specimen 2 14.95 135

Specimen 3 15.12 165

160

PM24Specimen 1 13.16

12.65170

153Specimen 2 12.81 165Specimen 3 11.97 125

Mechanical properties were studied for the compositions PM22,

PM23 and PM24, that showed good electrical properties, and the data are

given in table 4.18. As can be seen, for these compositions, mechanical

properties are not in the fully acceptable range.

Table 4.19. Mechanical properties for compositions PM25 through PM29

Sample Code

Mechanical propertiesT.S. (MPa) Elongation at break, %

PM25 19.0 127.7PM26 16.8 139.6PM27 16.9 71PM28 15.0 58.5PM29 12.8 53.3

The compositions PM25 to PM29, that showed promise in terms of

thermal and electrical properties, were studied. Their mechanical properties,

given in table 4.19., show that the more desirable values are showed by the

composition PM26, containing cenospheres concentration at 6 phr level (but,

lowest capacitance and tan δ values were shown at cenospheres

concentration of 24 phr).

Table 4.20. Tensile strength , elongation & thermal stability for the three compositions PM30, PM31and PM32

Composition Tensile Strength, (N/mm2)

% Elongation at break

Thermal Stability,(minutes)

trials average trials averagePM30 Specimen 1 15.78 100

161

15.69 120 95 – 100Specimen 2 14.62 110Specimen 3 16.21 115Specimen 4 16.14 155

PM31

Specimen 1 15.2514.92

165164 75 – 80Specimen 2 14.00 175

Specimen 3 14.86 145Specimen 4 15.56 170

PM32

Specimen 1 15.6015.60

95135 95 – 100Specimen 2 15.34 155


The set of three compositions PM30, PM31 and PM32 were studied.

Their mechanical properties and also thermal stability time are given in table

4.20. The more desirable values are shown by the composition PM31.

However, the thermal stability value for this composition needs

improvement.

Table 4.21. Mechanical properties and thermal stability-time for the three compositions PM33, PM34 and PM35



Thermal Stability,(minutes)trials average trials average

PM33

Specimen 1 14.9714.93

9086 85 – 90Specimen 2 14.81 65


PM34

Specimen 1 18.1217.52

95100 95 – 100Specimen 2 16.91 105


PM35

Specimen 1 14.7415.54

85106 90 – 95Specimen 2 16.51 120


162

From table 4.21., it is observed that maximum tensile strength value is

shown by the composition PM34. The thermal stability time also meets the

requirement better than the other two compositions.

The data in tables 4.20. and 4.21. illustrate that small variations in

concentrations of plasticizer, filler and flame-retardant additives can together

bring about significant differences in tensile properties. The synergistic effect

is probably better at 9 phr TCP, 12 phr CaCO3 and 14 phr glass.

Table 4.22. Mechanical properties and thermal stability-time for the composition PM34 to verify repeatability

CompositionTensile Strength,

(N/mm2)% Elongation at

breakThermal Stability,(minutes)trials average trials average

PM34.1

Specimen 1 14.2314.49

95149 85 – 90Specimen 2 14.32 165


PM34.2

Specimen 1 14.0515.06

100139 85 – 90Specimen 2 16.82 170


PM34.3

Specimen 1 14.9614.91

135153 80 – 85Specimen 2 14.27 135


In order to verify the repeatability of the performance characteristics

by the composition PM34, three more samples were prepared and their

mechanical properties and thermal stability studied. The data are given in

table 4.22. It is clear that the variation in properties is within acceptable

range. The composition is being considered for scale-up studies and

extrusion trials.

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Table 4.23. Mechanical properties and thermal stability-time for the composition PM31with varying blending times and drying of components



Thermal Stability,(minutes)trials average trials average

PM31.1 (30 min. blending)Specimen 1 15.64

16.19175

158 95 - 100Specimen 2 16.75 130Specimen 3 16.72 195Specimen 4 15.64 130

PM31.2 (25 min. blending)Specimen 1 15.40

15.67185

170 95 – 100Specimen 2 16.29 160Specimen 3 15.85 165Specimen 4 15.12 170

PM31.3 (20 minutes blending)Specimen 1 13.18

14.48155



15.30195

184 90 – 95Specimen 2 15.89 190Specimen 3 15.07 175Specimen 4 14.82 175


14.23170


The above compositions are five times repetitions of PM31 [Drying PVC, CaCO3, martinal and glass at 1050C for 1.0 hour].

164

Table 4.24. Mechanical properties and thermal stability-time for the composition PM31with different blending times and drying of components (cross-verification)



Thermal Stability (minutes)

trials average trials average trail 1 trail 2PM31(R1) Specimen 1 14.21

13.74

135

159 75 – 80 75 - 80

Specimen 2 14.46 185Specimen 3 13.64 185Specimen 4 12.38 140Specimen 5 14.09 150

PM31(R2)Specimen 1 15.27

14.11

180

182 85 – 90 85 – 90


PM31(R1-D)Specimen 1 13.70

13.99

165

173 85 – 90 90 - 95


PM31(R2-D)Specimen 1 14.67

14.02

220

188 85 – 90 85 – 90


R1 = 10 minutes blending; R2 = 15 minutes blending; (R1-D) =10 minutes blending [Drying PVC, CaCO3, martinal and glass at 1050C for 1 hour] and (R2-D) =15minutes blending [Drying PVC, CaCO3, martinal & glass at 1050C for 1 hour]

As PM31 showed good mechanical properties though somewhat less

than required thermal stability time, it was considered appropriate to study

165

the effect of drying the major ingredients that go into the resin matrix on

these properties. Drying components before blending seems to have an

effect in that the mechanical properties apparently improve while there is an

almost definite increase in the thermal stability time. The improvement in

mechanical properties appears better at higher blending times upto a limit.

The data seem to suggest that here the optimum blending time is fifteen

minutes.

To reaffirm the observations just made, another batch of four samples

with the same composition as that of PM31, but with dried ingredients were

prepared. As can be seen from table 4.24., it turns out that somewhat better

properties are actually obtainable at fifteen minutes blending time.

4.4.1. Study of specific gravity

The specific gravity (S.G.) measurements (ASTM D792-00) for

PM22 to PM29 are given in table 4.25.

Table 4.25. Specific gravity data

Sample Code PM22 PM23 PM24S.G. 1.5079 1.5152 1.5458

Sample Code PM25 PM26 PM27 PM28 PM29S.G. 1.5032 1.4485 1.4282 1.3701 1.3792

(Temperature of testing: 25.8 o C; ρ (H2O) at 25.8 o C is 0.996836)

Among the three compositions, PM22, PM23 and PM24, there is a

regular increase in the specific gravity value, as the concentration of the

additive increases from 10 phr to 30 phr in going from PM22 to PM24. This

is expected as glass is a somewhat dense additive. In the case of the

compositions PM25 to PM29, there is a gradual decrease in the specific

gravity value as the concentration of cenospheres increases; again, this is

expected as cenospheres are lightweight filler additives.

166

4.4.2. Study of surface hardness

Shore A: Shore A is used for hardness testing of softer plastics such as

rubbers and fluoropolymers found in products such as tires, wiper bladers,

gasket seals, and much more. Shore A is used when Shore D results are less

than 20.

Shore D: Shore D is used to characterize harder plastics such as

polyester, PVC, and acrylics. Shore D is used when Shore A results are over

90. Surface hardness was measured for various compositions, using Shore D

Durometer. The values lie in the range 55 to 60 for all the compositions.

4.5. Study of FRLS properties

Limiting Oxygen Index and Smoke Density Rating: these two

constitute FRLS properties. These properties are measured in required cases

and the data tabulated below. The higher the LOI, the better. The lower the

SDR, the better. Target values are: LOI>30 and SDR < 60.

Table 4.26. FRLS properties for compositions PM22, PM23 and PM24

Samplecode

Limiting Oxygen Index (%) Smoke Density Rating (%)Trials Average Trials Average

PM22 31.4 31.2 54.45 55.9731.2 60.5531.0 52.92

PM23 31.2 31.0 51.62 52.3031.0 57.6330.8 47.65

PM24 31.0 31.5 53.69 51.3031.8 51.2231.2 48.99

All the three compositions, PM22, PM23 and PM24, shown in table

4.26., show acceptable FRLS properties. TCP, one of the plasticizers present

in them is an effective flame-retardant, but generates high smoke under fire

conditions. Martinal is an additive that performs the dual role of a flame-

167

retardant and a filler. Zinc borate present in these compositions is a smoke-

suppressant. The LOI and SDR values reflect the net outcome of the rivaling

effects of the various additives present.

Table 4.27. FRLS properties of compositions PM25 through PM29

Sample Code FRLS propertiesLOI (%) SDR (%)

PM25 32.6 55.6PM26 34.4 68.8PM27 33.9 70.6PM28 33.5 56.3PM29 32.9 56.8

It was discussed earlier that more acceptable thermal, electrical and

mechanical properties are shown by these compositions containing

cenospheres as filler additives, but not all at the same concentration of

cenospheres. It is seen from the FRLS data in table 4.27. that such behavior

continues in the case of FRLS properties as well. Better FRLS performance

is shown by PM28 and PM29, containing 18 phr and 24 phr of cenospheres.

For the compositions listed in table 4.28., it appears that though

flammability is acceptable, consistently the SDR values are rather high. Also,

the blending time and SDR values show no perceivable trend.

Table 4.28. FRLS properties of composition PM31 repeated with different blending times and drying of components

Sample Code FRLS propertiesLOI (%) SDR (%)

PM31.1 31.2 62.03PM31.2 31.6 57.02

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PM31.3 31.7 67.94PM31.4 32.0 62.35PM31.5 - 69.96

Table 4.29. FRLS properties of PM31(R1), PM(R2), PM(R1-D) and PM(R2-D)

Sample Code FRLS properties

LOI (%) SDR (%)

PM31(R1) 31.3 69.55PM31(R2) 31.5 70.36PM31(R1-D) 30.7 70.99PM31(R2-D) 30.0 71.95

The FRLS properties for the ‘repeat’ compositions are given in table

4.29. The values for PM31(R1-D) and PM31.5 are similar. For PM31(R2-D)

and PM31.4., LOI values correlate better than the SDR values.

4.6. Calculation steps

An illustrative example for detailed calculation of kinetic parameters

using Ozawa’s method from TGA data at various heating rates is given for

the composition PM02 below.

Sample: PM02, temp. range: 30-700 oC, atmosphere: N2, weight: 8-10 mg

Sl No. β (o C . min –1 ) T5% T10%

1 2 206 2312 4 214 2433 8 234 2554 12 236 261

4.6.1. Calculation of E valueA. Calculations for 5% weight loss

Sl No.

β(o C . min –1 )

log β T5%

(oC)Tp

(t o C + 273) K1/Tp*10

001 2 0.3010 206 479 2.08772 4 0.6021 214 487 2.0534

169

3 8 0.9031 234 507 1.97244 12 1.0792 236 509 1.9646

Slope: - 5.52The related equation is:- log β – 0.457 E/R ( 1/Tp ) = constant or

- log β = constant + (– 0.457 E/R) (1 / 10 3 ). ( 1/Tp *10 3 ). Thus, slope (m) = (– 0.457 E/R) (1 / 10 3 ) = - 5.52Therefore, E = 5.52 x R x 10 3 / 0.457 = 24 Kcal. K–1. mol–1

B. Calculations for 10% weight loss

Sl No.

β(o C . min –1 )

log β T10%

(o C )Tp (t o C + 273)

K1/Tp*1000

1 2 0.3010 231 504 1.98412 4 0.6021 243 516 1.93803 8 0.9031 255 528 1.89394 12 1.0792 261 534 1.8727

Slope: - 6.92Thus: E = 6.92 x R x 10 3 / 0.457 = 30.09 Kcal. K–1. mol–1

The activation energy values for the 5% decomposition step and 10%

decomposition step are 24 Kcal. K–1. mol–1 and 30.09 Kcal. K–1. mol–1,

repectively. This is as expected.

4.6.2. Calculation of Arrhenius factor (5% weight loss data considered)

A= (βE/R Tp 2) . exp E/R Tp

Sl. No. β (o C . min –1 )

Tp (K) A (min –1 )(x 10 10 )

1 2 479 0.942 4 487 1.203 8 507 0.84

170

4 12 509 1.13

A average = 1.03 x 10 10 min –1

The Arrehenius factor, A, also called frequency actor is a measure of

inter-molecular collisions occurring per unit time in the reaction phase.

4.6.3. Calculation of rate constant, k (5% weight loss data considered)

Sl. No. Tp (K) A (min –1 )(x 10 9 )

k (min –1 )(x 10 –1 )

1 479 0.94 0.11532 487 1.20 0.17443 507 0.84 0.46394 509 1.13 0.5094

k = A. exp -E/R Tp

k average = 0.3158 min –1

The rate constant shows that thermal decomposition of the polymer

compounds under investigation can be treated as a first order reaction.

4.7. Conclusion

A number of polymer compounds of varying compositions were

prepared and their various properties studied. The properties studied include

thermal properties, electrical properties, mechanical properties and FRLS

properties. Compositions holding out promise for scale-up studies were

arrived at.

In relevant cases, thermogravimetric data were obtained using TGA,

and kinetic parameters and thermal rating values calculated. DTG curves

were recorded for a representative sample.

171

172

Chapter 5 STUDIES ON

EPDM COMPOSITIONS

5.1 Introduction5.2 Relevance of the present investigation5.3 Materials used5.4 Compounding of the resin systems5.5 Results and Discussion5.6 Conclusion

173

5.1. Introduction

EPDM rubber (ethylene propylene diene monomer (M-class) rubber

[114,115], a type of synthetic rubber, is an elastomer which is used for a

wide range of applications. The E refers to ethylene, P to propylene, D to

diene and M refers to its classification in ASTM standard D-1418. The M

class includes rubbers having a saturated chain of the polymethylene type.

Dienes currently used in the manufacture of EPDM rubbers are

dicyclopentadiene (DCPD), ethylidene norbornene (ENB), and vinyl

norbornene (VNB). EPDM rubber is closely related to ethylene propylene

rubber (ethylene propylene rubber is a copolymer of ethylene and propylene

whereas EPDM rubber is a terpolymer of ethylene, propylene and a diene

component).

In EPDM rubbers, the ethylene content is around 45% to 80%. The

higher the ethylene content, the higher the loading possibilities of the

polymer, better the mixing and the extrusion. Peroxide curing of these

polymers gives a higher crosslink density compared to their amorphous

counterpart. The amorphous polymers are also excellent in processing, which

is strongly influenced by their molecular structure. The dienes, typically

comprising from 2.5% to 12% by weight of the composition, serve as

crosslinks when curing with sulphur and resin, with peroxide cures the diene

(or third monomer) functions as a co-agent, which provides resistance to

unwanted tackiness, creep or flow during end use.

5.1.1. General Chemistry of EPDM

Ethylene-propylene rubbers use the same chemical building blocks or

monomers as polyethylene (PE) and polypropylene (PP) thermoplastic

polymers. These ethylene (C2) and propylene (C3) monomers are combined

in a random manner to produce rubbery and stable polymers. A wide family

174

of ethylene-propylene elastomers can be produced ranging from amorphous,

non-crystalline to semi-crystalline structures depending on polymer

composition and how the monomers are combined [116].

To appreciate long-term performance of EPDM rubbers in various

applications, one needs to examine the chemical structure of the parent

EPDM polymer, which is synthesized from three building block monomers-

ethylene, propylene, and a diene [117]. The ethylene and propylene

monomers combine to form a chemically saturated, stable polymer

backbone. The third, a non-conjugated diene monomer can be

terpolymerized in a controlled manner to maintain the saturated backbone

and place the reactive unsaturation in a side chain, making it available for

vulcanization or polymer modification chemistry. Thus, since the

unsaturation is protected, EPDM is inherently ozone-resistant as compared to

other rubber materials. It is also resistant to acid and base attack, and

possesses excellent weathering properties. [118].

The two most widely used diene termonomers are primarily

ethylidene norbornene (ENB) followed by dicyclopentadiene (DCPD). An

EPDM polymer structure is illustrated in figure 5.1. The ethylene-propylene

copolymers are called EPM.

Figure 5.1. Structure of EPDM containing ENB.

As mentioned above, the diene is the reactive part of the EPDM

molecule - cross linking agents react with the diene to 'tie' the polymer

175

molecules together, increasing physical and mechanical properties, such as

heat and solvent resistance, tensile and tearing strength. Most importantly,

cross-linking increases the material’s service-life [119].

5.2 Relevance of the present investigation

In the wire and cable industry, for some years now, interest in

elastomers has been increasing. Spurred by legislative changes and customer

demands [120], particularly in the developed world where the PVC claims

more than 50% market share, the work for cleaner technologies using

halogen-free resins and lead-free stabilizers has acquired high priority. In the

wake of rising environmental, health and safety concerns, the recent research

has been directed towards low-smoke emission, low corrosivity, low toxicity,

low heat release, flame-retardant, and zero-halogen polymeric compositions

to substitute halogen-based systems. This is reflected in the growing

requirement for low-smoke zero-halogen (LSZH) materials manufactured in

a wide variety of compositions. Some of the materials that have held out

promise include silicone, nylon, polypropylene, acrylic, and thermoplastic

elastomers such as EPDM.

The main advantageous properties of EPDM are its great heat, ozone

and weather resistance; its resistance to polar substances and steam is also

good. It has very good electrical insulating properties. It does not contain any

halogen. Hence, it is almost toxicity and corrosion free. The pure resin has an

LOI of about 21%, somewhat close to the threshold value of 30%, the

minimum required for a flam-retardant composition. In addition, it is already

being used as a material for the outer casing on wires in electrical appliances

for outdoor installation, or in those exposed to UV light. In particular, in

cost, it is more or less comparable to PVC. For all these reasons, EPDM was

considered a suitable resin for present investigations.

176

These polymers respond well to high filler and plasticizer loading,

providing economical compounds. They can develop high tensile and tear

properties, excellent abrasion resistance, as well as improved oil swell

resistance and flame-retardance. A general summary of properties is shown

in table 5.1.

Table 5.1. Properties of Ethylene-Propylene Elastomers

Polymer Properties

Mooney Viscosity, ML 1+4 @ 125°C

5 – 200+

Ethylene Content, wt. % 45 to 80 wt%Diene Content, wt. % 0 to 15 wt%

Specific Gravity, gm/ml 0.855 – 0.88#

Vulcanizate Properties*

Hardness, Shore A Durometer 30A to 95ATensile Strength, MPa 7 to 21

Elongation, % 100 to 600Useful temperature range, °C -50° to +160°

Tear Resistance Fair to GoodAbrasion Resistance Good to

ExcellentElectrical Properties Excellent

# Depending on polymer composition, * Range can be extended by proper

compounding. Not all of these properties can be obtained in one compound.

5.3 Materials used

HERLENE 512 grade EPDM, with Ethylene/Propylene weight ratio

68 / 32 and Mooney viscosity of 55 value (ML 1+4) at 125 0C, has been used

as such. The locally available additives have been used. The DOP has been

used as primary plasticizer, paraffin wax, as an external lubricant, sulphur, as

vulcanizing agent, and Dibenzothiazole disulphide (MBTS, molecular

formula: C14H8N2S4) and Tetramethyl thiuram disulphide (TMTD, molecular

formula: C6H12N2S4), as accelerators. The accelerator activators used in this

study are zinc oxide and stearic acid. Stearic acid also acts as an internal

177

lubricant, thereby improving processability. Clay has been used as filler,

litharge (PbO), as an acid scavenger and bisphenol-A, as an anti-oxidant.

Flame-retardant additives, antimony trioxide and trihydrated alumina, were

procured locally and used as such. The modified transition metal sulphate

glass, prepared in the laboratory [121], was ground to fine powder and used

in the EPDM system.

5.4. Compounding of the resin systems

The compositions were prepared using the Brabender Plasticordor

(PLE 331) and cured using a compression molding machine. Test specimens

as per various test requirements were cut from the cured sheets.

5.4.1. Toxicity index measurement studies

In toxicity index measurement studies, the specimen holder is a non-

combustible device and holds the specimen at its top over the burner without

masking the specimen from the flame by more than 5% of its surface area.

Fourteen gases can be detected using the apparatus. A maximum of one gram

of the sample (EPDM-E) is burnt for a maximum of three minutes. ‘Gas

reaction tubes’ are used to determine the quantity of a gas evolved. The

sample is placed on the glass wool to prevent char particles, formed if any,

from falling into the Bunsen burner below, inside the Test Chamber.

5.5. Results and Discussion

An outline of the compositions prepared: EPDM: 100, ZnO: 5-10,

stearic acid: 1-5, clay: 40-80, DOP: 2-10, bisphenol-A: 1-5, red lead: 2-5,

paraffin wax: 1-5, Sb2O3: 5-15, trihydrated alumina; 50-100, sulfur: 1-2,

TMTD: 0.1-0.5, MBTS; 0.5-2.0 and sulfate glass: 5-30 (all in phr). The

compositions of the samples taken for analysis are given in table 5.2, the

178

variant being the mixture (M1) of the flame-retardant additives Sb2O3 and

trihydrated alumina combined in a specified ratio.

Table 5.2. The EPDM-based compositions

Sample code M1 (in phr)EPDM-A 20EPDM-B 40EPDM-C 60EPDM-D 80EPDM-E 100

EPDM-based compositions using the ingredients in the ranges

outlined above were prepared and their electrical, mechanical and FRLS

properties evaluated [122]. The addition of trihydrated alumina along with

antimony trioxide to EPDM composition enhances the flame-retardancy by

improving the oxygen index values from a minimum of 21 % to a level of

32%.

The addition of antimony oxide increases the oxygen index, but the

flame-retardant efficiency starts to decrease when the antimony oxide

concentration exceeds about 5%. Addition of 20-30% of aluminum

trihydroxide to these formulations raises the oxygen index above the values

obtained using antimony oxide alone. The magnitude of increase depends on

the amount of plasticizer and antimony oxide used in the formulation. The

increase is more pronounced at low to moderate plasticizer concentrations.

Formulations containing higher levels of antimony oxide also benefit by the

addition of ATH or other inorganic hydroxides. However, proper formulation

can achieve flame-retardant systems without incorporation of antimony

oxide. These systems produce less smoke than those containing antimony

oxides. The particle size of the ATH used also has a definite effect on the

179

flame-retardant performance of flexible PVC. The use of 1 -µm precipitated

ATH gives a two or three oxygen index unit increase over coarser products.

The thermal data for the five compositions are given in tables 5.3a

and 5.3b. TG curves at different heating rates and DTG curve for EPDM-E

are given in figures 5.2. and 5.3.

Table 5.3a. Temperature of 5% weight loss of EPDM-based compositions at different heating rates (obtained from thermogravimetric data).

β (o C. min–1 )

EPDM-A

EPDM-B EPDM -C

EPDM-D EPDM-E

2 234 232 225 251 2104 247 240 244 264 2266 258 244 253 272 --8 -- 255 -- -- 23110 274 -- 254 254 --12 -- 271 -- -- 248

Table 5.3b. Temperature of 10% weight loss of EPDM-based compositions at different heating rates (obtained from thermogravimetric data).

β (o C. min–1 )

EPDM-A

EPDM-B EPDM -C

EPDM-D EPDM-E

2 266 264 267 282 2484 283 275 287 297 2646 293 277 294 309 --8 -- 289 -- -- 27310 313 -- 295 295 --12 -- 308 -- -- 290

180

Figure 5.2. TGA curves of the EPDM-E composition at different heating rates

Figure 5.3. DTG curve of the EPDM-E composition

From the tables and the figures, it is clear that the compositions are

thermally stable upto 200 0C. This is the temperature at which the EPDM, in

its pure form is flammable. This implies that the additives have not had any

undesirable influence on the thermal stability of the compositions. It is also

observed that for each composition, the temperatures at which 5% and 10%

181

weight losses are shifted to lower values with reduced scan rate. It may

further be seen that for lower heating rates the maximum values for

temperatures at 5% and 10% weight losses are observed in the case of

EPDM-D, which contains 80 phr of the flame-retardant mixture. For higher

heating rates, EPDM-A shows higher thermal stability. In all cases, the

thermal degradation occurs at nearly 500 o C.

5.5.1. Calculation of activation energy for thermal decomposition, E

Ozawa’s method [123], based on variable heating rate, has been

normally used to derive kinetic parameters for many industrial materials. A

relationship connecting peak temperature, Tp and heating rate, β, has been

derived:

- log β – 0.457 E/R (1/Tp ) = constant (5.1)

The kinetic parameters, ‘E’, ‘A’ and ‘k’ are calculated for all samples

using equation (5.1) [123,124-126].

- log β – 0.457 E/R (1/Tp ) = constant or

- log β = constant + (– 0.457 E/R) (1 / 10 3). (1/Tp *10 3).

Slope = (– 0.457 E/R) (1 / 10 3) = -5.7

E = 5.7 x R x 10 3 / 0.457 = 24.78 Kcal. K–1. mol–1

As a representative case, the details of calculations for EPDM-A

along with relevant data are given in tables 5.4. and 5.5.

Table 5.4. Calculations for 5% weight loss

Sl No.

β(o C. min –1 )

log β Temp of 5% wt loss (oC )

T (t o C + 273) K

1/Tp*1000

1 2 0.3010 234 507 1.972 4 0.6021 247 520 1.923 6 0.7782 258 531 1.884 10 1.0000 274 547 1.83

(Sample: EPDM-A, temperature range: 40 o C – 600 o C, atmosphere: N2)

182

Table 5.5. Calculations for 10% weight loss

Sl No.

β(oC . min –1 )

log βTemp of 10% wt loss (oC )

T (t o C + 273) K

1/Tp*1000

1 2 0.3010 266 539 1.862 4 0.6021 283 556 1.803 6 0.7782 293 566 1.784 10 1.0000 313 586 1.71

E = 3.23 x R x 10 3 / 0.457 = 14.04 Kcal. K–1. mol–1

The activation energy E value is 24.78 Kcal. K–1.mol–1 and 14.04

Kcal.K–1.mol–1 for 5% weight loss step and the 10% weight loss step,

respectively.

5.5.2 . Calculation of Arrhenius factor, A

The Arrhenius factor, a measure of the frequency of molecular

collisions during a reaction, is calculated as per the following formula [124]:

A= (βE/R Tp 2). exp E/R Tp (5.2)

Taking β = 2 o C. min –1, A= 4.6 x 10 9 min –1



A average = 4.03 x 10 9 min –1

5.5.3. Calculation of rate constant, k

Knowing the ‘A’ value, the rate constant is calculated using the

familiar Arrhenius equation.

k = A. exp -E/R Tp (5.3)

= 4.03 x 10 9 min –1. exp -24.78 x 1000/1.987 x 520

= 4.03 x 10 9 x (3.8 x 10 -11)

= 1.53 x 10 -1 min –1

It can be seen that the decomposition follows first-order kinetics.

5.5.4. Evaluation of thermal condition, θ

183

The mathematical expression to evaluate θ is given by Toop

(discussed earlier in the thesis) [125-127]:

log tf = E/2.303 Rθ + log E p (xf)/ βR (5.4)

where log p (xf) = -2.315 – 0.457 E/R Tf , E = energy of activation,

R = gas constant, Tf = temperature at which specific change is

observed, β = heating rate, θ = thermal condition and tf = time to

condition at temperature θ.

Because of the simplicity and reliability, this approach is generally

preferred for determining thermal rating where thermal degradation is the

result of simple chemical reaction [128, 129].

5.5.4.1. Thermal condition for EPDM-based compositions

As representative cases, for the samples EPDM-C and EPDM-D, the

details of calculation of thermal rating values are given in tables 5.6 and 5.7.

The ‘E’ and the corresponding ‘θ’ values for all the five compositions are

summarized in table 5.8.

Table 5.6. Thermal index values for EPDM-C

Sl. No. β (oC. min –1) Tf (K) E/R Tf p(xf) (x10 –13) θ (o C )1 2 498 23.90 0.67593 104.342 4 517 23.02 1.7518 107.463 6 526 22.63 2.6733 107.674 10 527 22.59 2.7923 102.07

(5% wt loss data used; E= 23.65 Kcal. K–1 mol–1; tf = 20000 hrs; R= 1.987 Cal. K–1. mol–1)

Table 5.7. Thermal index values for EPDM-D

184

Sl. No. β (oC. min –1 ) Tf (K) E/R Tf p(xf) (x10 –17) θ (o C )1 2 524 31.73 1.5526 147.022 4 537 30.97 3.4798 149.173 6 545 30.51 5.6752 149.134 10 549 30.29 7.1717 146.18

(5% wt loss data used; E= 33.04 Kcal. K–1.mol–1; tf = 20000 hrs; R= 1.987 Cal. K–1. mol–1)

Table 5.8. Thermal Rating Summary

Sl. No

Sample name

Kinetic parameter θ(o C )E (Kcal. K–1.

mol–1)*A

(min–1)k

(min–1)

1 EPDM-A 24.78 4.03 x 10 9 1.53 x 10 -1 1152 EPDM-B 23.04 1.07 x 10 9 1.15 x 10 -1 103.63 EPDM-C 23.65 2.14 x 10 9 1.77 x 10 -1 105.394 EPDM-D 33.04 7.768 x 1012 3.58 x 10 -1 147.95 EPDM-E 27.57 - - 108.1

*calculated at 5% wt loss

From thermal rating summary, it is observed that for all the

compositions, the activation energy for decomposition lies in the range 23 to

33 Kcal. K–1. mol–1. Also, the thermal rating, that is, the maximum and/or

minimum temperature at which a material will perform its function without

undue degradation, lies within the acceptable range.

5.5.5. Toxicity Index (T. I.) test

The TI is a measure of the amount of toxic gases a composion would

evolve on burning. The products of combustion in the test chamber, the

following gases, are quantitatively measured and the T.I. value is calculated

using the formula given below:

T. I. C = (5.5)

185

where, Cf = concentration of the gas considered fatal to man for a 30 minute exposure time (ppm), C = concentration of gas detected (ppm), m= fire test mass (g) and v = volume of test chamber (m³).Here, v = 0.7 m³

m = 0.9622 g

Now, C w.r.t. CO2 = (0.4 x 104 x 0.7x 100)/ 0.9622/105 = 2.91

C w.r.t. H2CO = (0.5 x 0.7x 100)/ 0.9622/500 = 0.073

Total T. I. for the sample = 2.91 + 0.073 = 2.983 (i.e. < 3)

Table 5.9. The T. I. test data

Sl. No.

Gas Initial reading

Final Reading

Quantity of gas evolved

Cf values for gases (ppm)

1 CO2 0.5% 0.9% 4000 ppm 1000002 CO 5 5 Nil 40003 NOx 2 2 Nil 2504 H2CO 0.5 1.0 0.5 5005 CH2CHCN 1 1 Nil 4006 HCl 0 0 Nil 4007 H2S 0 0 Nil 7508 NH3

Not measured as EPDM has none of N,S,Ph,or Br/F

5509 SO2 40010 PhOH 25011 HCN 15012 HBr 15013 HF 10014 COCl2 25

Sample description on burning: not burnt fully; only slightly charred.

It is evident from the table that no HCl is released during the combustion of

the EPDM sample.

5.6. Conclusion

In the range investigated, for the EPDM-based compositions, the

thermal rating values are acceptable and have toxicity index less than three.

186

They do not release any toxic or corrosive gases on burning. The FRLS,

mechanical and electrical properties are also within range. In line with the

current trend of zero-halogen polymeric compositions substituting halogen-

based systems, they hold out promise as commercially viable compositions

for electrical cable sheathing applications.

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