Advances in the applied chemistry of allylic...

Journal of Scientific & Industrial Research

Vol. 63, April 2004, pp 365-375

Advances in the applied chemistry of allylic polymers

C C Menon*

Devi Nivas, Edathil Road, Tellicherry 670 101

and

A Selvaraj

Hindustan Aeronautics Ltd, Bangalore

Received: 21 May 2003; revised received: 22 December 2003; accepted: 30 January 2004

Investigation of diallyl phthalate polymer (DAPP) based moulding powder with partial substitution of DAPP by

epoxidisied DAPP polymer (EDAPP) indicates improvement in mechanical properties without detriment to electrical

strength. Peak performance is manifested at 20 per cent substitution. EDAPP is also found to be an effective reactive diluent

for cold setting epoxy resin adhesives. Bond strength is observed to be unaffected by extension up to 40 per cent. Hardboard

(Fibre board) modified by DAPP as an impregnant results in a novel wood-polymer composite with tangible improvement

of density, electrical strength, modulus of rupture and reduced water absorption having varied applications.

Keywords: Diallyl phthalate polymer, Epoxy resin adhesive, Bond strength

IPC Code: Int. Cl.7: B 27 K 3/08, C 01 B1 13/18

Introduction

Allylic polymers constitute an obscure segment of the mammoth polymer industry. Though derived from C-3

building block with associated cost advantages the special features of allylic polymerisation erode the benefits

accruing from raw material. The industrial precursors to allylic polymers like, allyl alcohol, allyl acetate, and

allyl chloride are difficult to polymerise1. Further, unlike vinyl polymerization allylic compounds polymerise to

generate only dimers, trimers, tetramers, and other cyclised low molecular weight material2. Perforce conversion

has to be restricted to 25 per cent to avoid the danger of catastrophic gelation3. Improvement in the economics

of the process by recovery and recycling of unreacted monomer is hampered by constraints imposed by

considerations of safety and hazards. Notwithstanding all these inconvenient features allylic polymers have

etched a niche for themselves as a “speciality polymer” in electrical and electronic applications.

Allylic polymers are generally derived from diallyl or triallyl compounds. These multifunctional monomers

have enabled the development of sophisticated products like, UV - curable printing inks for high speed printing

operations, and products for inclusion in composites which require high energy electron beam activation to

penetrate bulky objects.

Diethylene glycol bis-(allyl) carbonate is used to cast ophthalmic lenses and is called optical monomer4.

Diallyl phthalate polymer based moulding powders have acquired importance in electrical and electronic

sectors.

Moulding powders obtained by blending DAP polymer with lubricant,pigment catalyst, fillers, and mould

release agents have acquired importance for making components with multiple metallic inserts made of gold,

silver, copper, and alloys . The moulded products are utilised in wide range of applications like, sockets, TV

tuners, connectors, AC switch gears, rotary switches, aviation and space control panels. Rapid production of

shapes of outstanding dimensional stability with retention of electrical properties is possible. Prolonged service

at high humidity and temperature without any deterioration is another characteristic of the product. Defence

applications encompass aircraft and guided missile parts, radomes, and submarine applications.

The main hurdle to the expansion of the market is the

high cost. It was therefore envisaged that the ——————

*Author for correspondence

J SCI IND RES VOL 63 APRIL 2004

366

development of an extender-cum-builder for the polymer may contribute to market expansion and cost

reduction. Investigation of the suitability of epoxidised DAP monomer and polymer was therefore undertaken.

It was also believed that the epoxidised derivatives may acquire a foothold in the sphere of large volume

plastics like, PVC as plasticiser-cum-stabilizer. Another prospective outlet envisioned was as reactive diluent

for epoxy resins having a large consumption in the adhesive sector. Based on these tenets a project was

conceived with the salient features5 described subsequently:

(i) Study of the variation of the properties of DAP moulding powder as a function of the concentration of

epoxidised additive and the identification of the optimal concentration of the candidate product for peak

performance.

(ii) Evaluation of the performance of epoxidised DAP derivatives as reactive diluent for epoxy resin

adhesives and the identification of optimal dilution level.

(iii) Investigation of the potential of DAP polymer as an impregnant to wood to develop novel wood-polymer

composites.

Materials and Methods

(a) Diallyl Phthalate Polymer (DAPP) as well as moulding powder derived (WIPON) were obtained from

Western India Plywoods Ltd., Kannur.

(b) All other ingredients involved in the formation of moulding powder like glass fibre, magnesium and

titanium oxides, blue pigment, calcium stearates and tertiary butyl per benzoate were obtained from the

production wing of Western India Plywoods Ltd, Kannur.

(c) Epoxidised DAP monomer and epoxidised polymer (EDAPP) were obtained from Sri Ram Institute for

Industrial Research, Delhi from their pilot plant where a project sponsored by Western India Plywoods was in

progress. Epoxidised products had the under mentioned quality parameters.

Product Oxirane oxygen

value

Iodine

value

Epoxidised DAP

monomer

5.5 97

Epoxidised DAP polymer 1 28

Moulding powder was made by blending the required ingredients. Moulding was done in compression

moulding machine supplied by Nuchem, Mumbai Mouldings were done at 1500

C, pressure 15 kg/cm2, and

cycles of 3-5 min.

Mechanical properties were determined using Universal Testing Machines 2 and 20 t capacity.

Bar mouldings weighing 20 g and disc moulding of 60 g were made. Impact strength was determined using

Charpy FIE-IT-042 Impact Tester as per MIL-1071 procedure. Rockwell hardness was determined using Brunel

FIE/74/180 tester as per MIL-108 procedure.

Electrical resistivity of disc samples was determined using AE High voltage (150 KV) Tester supplied by

Automatic Electrical Ltd., Mumbai according to MIL-4031 procedure.

The rheological properties of the moulding composition were evaluated using Haake Rheocord – 90,

Computerised Torque Rheometer providing information relating to fusion rates, curing, shear heat stability,

torque, melt temperature, melt flow, and rotor speed.

Molecular weight distributions of DAP polymer and EDAP polymer were obtained by using Gel permeation

chromatograph supplied by Waters Inc, USA.

Araldite resin AW106

Hardner HY 953U

MENON & SELVARAJ: ADVANCES IN APPLIED CHEMISTRY OF ALLYLIC POLYMERS

367

Manufactured and marketed by Hindustan Ciba – Geigy Ltd.

EDAPP polymer, 25 per cent, was allowed to swell in EDAP monomer (75 per cent) to obtain a

homogeneous viscous system. The viscous paste was used in different proportions with Araldite resin. The

variation of pot life and curing time of the composite adhesive at different concentrations were studied.

Different substrate configurations like, wood-wood, metal-metal, ceramic-ceramic, and ceramic-metal were

studied. Shear strength was determined by 2 t UTM machine.

The suitability of the composite adhesive for preparation of wood based laminate was studied. The face and

core veneers were Kalpine (Gurjan). Adhesive was spread on core veneer. The laminates were assembled and

configuration kept under pressure for 24 h. Glue shear strength was determined, using UTM as per IS 1708.

Pot life was determined by noting the time required for the composite adhesive to lose fluidity.

Cure time was indicated by the time required to reach the condition of the absence of tackiness on touching.

Standard hardboard having the following characteristics was used viz.

Density : 0.8 g/cc

Water absorption in 24 h : ≤ 40 per cent

Modulus of rupture : - 300 kg/cm2

DAP polymer of the

undermentioned quality was used

:

Softening range: 70 – 110o C

Acid value : 450

Iodine value : 55-65

Solubility in acetone : Good

Both the items were obtained from Western India Plywoods Ltd, Kannur. Acetone available commercially

was used.

Immersion of hardboard in a 10 per cent solution of DAP polymer in acetone containing 1per cent t-butyl

perbenzoate was the adopted procedure. Samples were taken to determine the progress of polymer absorption.

When the absorptions have reached the saturation level, the board was dried at 150oC for 3 min under 10kg/cm

2

pressure. Polymer uptake, density, modulus of rupture, and water absorption of samples were determined.

Results and Discussion

(i) The investigation provides strong evidence to the suitability and utilization of epoxidised diallyl phthalate

polymer as an additive to diallyl phthalate polymer based moulding composition. Data relating to mechanical

property improvements by substitution of DAPP polymer by EDAPP polymer have been found up to 20 per

cent. Above 20 per cent there is a declining trend which militates against the usage

(Tables 1-4). The electrical property is unaltered by substitution (Table 5).

Gel permeation chromotographic data of DAP polymer and EDAP polymer indicate absence of significant

reduction in molecular weight (Figure 1 and 2). Hence there is likelihood of parity in performance of the

derived moulding compositions. This view is further strengthened by rheological data of the moulding

compositions (Figure 3 and 4). The data presented together in a diagram exhibit virtual superimposition (Figure

5).

The thermogravimetry of the two compositions indicated the absence of any significant difference in thermal

resistance. DAP base moulding powder shows a weight loss of 42.7 per cent as a consequence of complete cycle

of heating upto 750oC. EDAP modified composition underwent 41.7 per cent weight loss. The absence of

change of decomposition point and near equality of percentage of weight loss confirm that partial substitution of

DAP polymer by EDAP polymer has no adverse impact on thermal stability (Figure 6 and 7).


368

A tentative view can be propounded relating to critical upper limit of 20 per cent and decline at

Table 1— Substitution of DAP polymer by EDAP polymer

Sl. No DAP polymer

content

per cent

EDAP

polymer

content

per cent

Modulus of

rupture

kg/cm2

1 100 619

2 80 20 725

3 60 40 541

4 40 60 668

5 20 80 393

6 0 100 299

Table 2—Compressive strength

100 per cent DAP 1400 kg/ cm2

80 per cent DAP + 20 per cent EDAP 1652 kg/ cm2

Table 3—Impact strength

100 per cent DAP 0.180

80 per cent DAP + 20 per cent EDAP 0.128

Table 4—Hardness

100 per cent DAP 115

80 per cent DAP + 20 per cent EDAP 124

Table 5 — Dielectric breakdown voltage and strength

Voltage Dielectric strength

kv kv/mm

100 per cent DAP 35 10

80 per cent DAP 35.6 10.86

+ 20 per cent EDAP


369

Figure 1 — Data relating to gel permeation chromatography of DAP powder


370

Figure 2 — Data relating to gel permeation chromotograph of EDAP polymer


371

Figure 3 — Rheological data of DAPP based moulding composition


372

Figure 4 — Rheological data of moulding composition using 80 per cent DAPP and 20 per cent EDAPP

higher levels. Up to 20 per cent epoxidised DAPP may function as a compatibiliser reducing interfacial tension

and improvement of mechanical properties6. The absence of any serious reduction in molecular weight by

epoxidation is shown by GPC data fulfilling the basic requirement of molecular size.

The catalyst used in moulding is an acid generator

which interacts with the oxirane ring of EDAPP,

thereby generating vic-glycol moiety. Above 20 per

cent EDAPP may become a contender to DAPP for free

radicals causing imperfect or incomplete cure. Further

above 20 per cent the vic-glycol group may be cleaved

by free radicals, thereby causing chain scission and

resultant dimunition of molecular size impairing

efficiency as compatibiliser, since the optimal

molecular size is an essential requirement for action as

a compatibiliser. It may cause decrease in the cohesion

of composition. Thus the symbiotic action of decrease

in compatibiliser efficiency and catalyst inadequacy

accounts for the observed declining performance at

higher levels of substitution.

But crucial to the expansion of market is likely the

performance of the product under severe and harsh

conditions of environmental deterioration for appli-

cations in avionics, aerospace, satellite technology, and

submarine sectors. An accurate appraisal of

performance under stringent conditions of environ-

mental stress is sine qua non for the verdict on the value of the innovation.

(ii) Epoxy resins have acquired almost unchallenged

Figure 5 — The data presented in Figure 3 and Figure 4 presented

together to highlight the near equivalence

Figure 6 — Data relating to thermogravimetry of DAPP based composition


373

supremacy for nearly a century in the case of adhesives with usage in electrical and electronic sectors, oil wells,

satellites, roads and bridges, and

buildings constructions and supersonic aircraft. For the cost reduction and enhancement of performance reactive

diluents are used. It has been found that epoxidised diallyl phthalate polymer is an effective reactive diluent to

epoxy resin adhesives with prospects of usage with reduced cost.

The results confirm that epoxy resin and EDAP polymer – EDAP monomer combination is an attractive

composite adhesive for wood. Peak performance is indicated at extension levels of 20-40 per cent (Tables 6-11).

Further the samples laminated by the composite adhesive were not affected by water. Hence the glue system is

suitable for wood joinery work.

Work was extended to examine the suitability for production of decorative laminates using decorative veneer.

The unexpected rise in the price of decorative wood has necessitated the use of extremely thin veneer due to

cost deletion. The composite adhesive developed has an advantage of facile spreading on glue surface and

generates a bond unaffected by cold water. Penetration to the surface was not found. Therefore the composition

developed is attractive for use in manufacture of decorative laminates.

(iii) Environmental compulsions have stimulated search for renewable raw materials. The wood based

Table 6 —Formulations investigated

Composition

of adhesive

Epoxy resin

AW106

Hardner

HV953U

Reactive diluent

25 per cent

solution of

EDAPP in EDAP

monomer

1 100 80 0

2 80 80 20

3 60 80 40

Figure 7 — Data pertaining to thermogravimetry of constituted 80 per cent DAPP and 20 per cent EDAPP


374

4 40 80 60

5 20 80 80

6 0 80 100

Table 7 — Tests results of plywood made with commercial

epoxy resin

Failing load Wood failure

in kg per cent

388 15

262 50

354 70

340 60

440 80

Table 8—Adhesive composition

Epoxy resin 100 per cent

Reactive diluent – EDAP mix at 20 per cent

Failing load, kg Wood

failure per cent

153 45

170 20

163 100

150 15

187 30

Table 9 — Adhesive composition

Epoxy resin 100

EDAP monomer

polymer mix 20

Failing load, kg Per cent

wood failure

205 80

185 80

195 100

162 15

150 50

industry is therefore engaged in the process of substitution of resources from natural forests by raw materials

from regenerative plantations. Wood polymer composites have therefore emerged as an attractive option in

materials. Both thermoplastic and thermosetting polymers have been used to produce composites. Earlier

investigations used phenolic resins and the composite was known as lignostone7. Acrylic and vinyl compounds

were later deployed and the reaction was induced by heat and / or catalyst8. The availability of γ-ray source

enlarged the scope

of action by the capability for radiation polymerization.


375

Wood polymer composites improved mechanical properties in conjunction with enhanced resistance to water

and resistance to fungal and insect attack9. Upgradation of the quality of wood by diverse chemical systems

acquired importance and several novel procedures have been developed10

. Chemical modification of hardboard

using DAP polymer was therefore undertaken for developing a versatile and durable fibreboard possessing

resistance to environmental degeneration.

Table 10—Adhesive composition

Epoxy resin 100

EDAPP + EDAP monomer 40

Failing load kg Per cent

wood failure

153 45

170 20

163 100

150 15

187 30

Table 11—Results for solid wood

Epoxy resin 100

EDAPP mix 20 per cent

Failing load kg Per cent

wood failure

150 0

222 0

300 0

The test samples were kept immersed in cold water for 8 h. No delamination was found to occur.

The processing has resulted in significant improvement of mechanical properties with reduction in water

absorption. The product parameters surpass IS standard requirements for superior quality hardboard namely,

tempered hardboard. Tempered hardboard is manufactured by treatment of hot hardboard from the press with

drying oil to give a retention of 8 per cent by weight. The drying oil undergoes oxidative polymerization with

concurrent side reactions like, cyclisation, copolymerisation with oxygen, branching, and even Diels-Alder

reaction. The complexity of these processes endows the resulting polymer with structural irregularities

vulnerable to the onset of degradation processes (Figure 8). Hardboard, modified by DAP polymer is less prone

to degradation because of the deficiency of defective sites (Tables 12-15).

It has been established that lignocellulose possesses ethylenic linkages. These linkages can undergo

crosslinking reaction with the double bonds in DAP polymer activated by the free radicals generated by the

decomposition of catalyst. The resultant product comprising two structurally different polymer chains


376

Figure 8 — Data showing the dependent uptake of DAPP from solution by hardboard

Table 12—Uptake of DAP polymer from solution by hardboard

Weight of sample (g) Per cent

polymer uptake

30.47 5.3

30.76 5.36

31.1 5.31

36.16 5.31

36.16 5.32

Table 13 – Properties of hardboard modified by DAP polymer

Density Modulus of Water absorption

g/cc rupture kg/cm2 per cent in 24 h

0.86 367 40.30

0.861 417 30.4

0.862 395 32.1

0.863 402 32.17

0.863 480 34

with cross-links resembles ladder polymer having chain-stiffening without segmental motion. Degradation of

such a macromolecule requires simultaneous rupture of several bonds with large energy requirements.

Hence, it may be mentioned that hardboard modified by DAPP surpasses tempered hardboard in durability

due to the advantages of the polymeric structure. This speculative view has to be buttressed by conclusion

from environmental impact studies.

Table 14 —Properties after thermal processing

Wt of Wt after Density MOR Water

sample absorption g/cc kg/cm2 absorption

(g) (g) in 24h

per cent


377

30.45 33.42 0.95 795 20.16

30.61 33.22 0.946 754 18.20

30.31 32.84 0.95 755 18.37

30.33 32.9 0.945 700 19.86

30.26 33 0.95 788 20.70

Equilibrium moisture content 5.6 per cent

IS Specification for tempered hardboard

MOR kg/cm2 ≥ 500

Water absorption in 24 h ≤ 20 per cent

Table 15 — Electrical properties

Thickness Break down Dielectric

voltage strength

2.95 mm 7.5 kv 2.54 kv/mm

3. mm 7.5 kv 2.5 kv/mm

2.95 mm 7.5 kv 2.54 kv/mm

3.1 mm 7.5 kv 2.54 kv/mm

Prospective applications of the product in building industry encompass cladding, box beams, ceilings,

roofing, partitions, etc. Housing for instrument in environmentally aggressive industrial locations, containers,

and luggage are some of the possible opportunities. Application in electrical industry as substitute for Compreg

in selected sectors may also emerge due to attractive properties (Tables 15).

References

1 Gewariker R, Viswanathan N V & Sreedhar J, Polymer science (Wiley-Eastern, New Delhi) 1986, p22.

2 Simpson W, Hot T & Zetie R J, Polym Sci, 10 (1953) 489.

3 Ravve A, Organic chemistry of macromolecules (Marcel-Dekker Inc, New York) 1967, p80.

4 Harry Szmant H, Organic building blocks of chemical industry (John Wiley and Sons, New York) 1989, p.255.

5 Selvaraj A, Investigation in the applied chemistry of diallyl phthalate polymer and its epoxidised derivative, MSc (Applied

Chemistry) Thesis, Bharathiar University, 1998, Coimbatore.

6 Oksman K, Wood Sci Technol, 30 (1996) 197.

7 Mayer J A & Skar C, Forest Prod J, 16(5) (1966) p426.

8 Mayer J A, Wood Sci, 14 (1981) 2.

9 Desch H E & Dinwoodie J M, Timber structure, properties, conversion and use (Macmillan Press Ltd, London) 1996, pp212.

10 Menon C C, J Sci Ind Res, 61 (2002) 444.

*Author for correspondence

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