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Anal. Chern. 1985, 57, 187R-191 R (532) Mliis, T.; Price, W. N.; Price, P. T.; Roberson, J. D. “Instrumental Data for Drug Analysis, Volume I”; Elsevier: New York, 1982. (533) Mills, T.; Price, W. N.; Price, P. T.; Roberson, J. C. “Instrumental Data for Drug Analysis, Volume 11”; Elsevier: New York, 1984. (534) Ardrey, R. E.; Brown, C.; Allan, A. R.: Bal, T. S.; Moffat, A. C. “An Eight Peak Index of Mass Spectra of Compounds of Forensic Interest”; The Forenslc Society: Harrogate, England, 1983. (535) Qaensslen, R. E. “Sourcebook In Forensic Serology, Immunology, and Biochemistry”; US. Government Prlnting Office: Washington, DC, 1983. (536) “Proceedings of the Internatlonal Symposium of the Analysis and De- tectlon of Exploslves”; US. Government Printing Office: Washington, DC, 1984. Rubber Anoop Krishen Chemical Research & Development, The Goodyear Tire & Rubber Company,’ Akron, Ohio 44316 This review covers methods for identification, characteri- zation, and determination of rubber and materials in rubber. Literature which became available to the author between November 1982, the end of the period covered by the last review in the series (47), and November 1984 is reviewed. Abbreviations recommended in ASTM Designation D1418-18 have been used (3). There are listed in Table I. GENERAL INFORMATION The American Society for Testing and Materials published the 1983 annual edition of test methods for rubber (3). Some of the new standards issued by International Or- ganization for Standardization (ISO) are 1. International Standard 6101/1-1982. Rubber- Determination of Metal Content-Flame Atomic Absorption Spectrometric Method-Part 1: Determination of Zinc Content. 2. International Standard 6235-1982. Rubber, Raw-De- termination of Block Polystyrene Content-Ozonolysis Me- thod. The third edition of the book “Analysis of Rubber and Rubber-like Polymers” was published (97). This book presents a balanced picture of the current technology in the rubber and rubberlike polymers. Chapters are given on sampling and sample preparation, extractions, analysis of extracts, chemical analysis for polymer type, quantitative elemental analysis, solution methods, instrumental polymer analysis, polymer characterization, inorganic fillers and trace metal analysis, carbon black, formulation derivation and calculation, blooms and visually similar phenomena, and finally validity of results. The review on analysis of high polymers (88) presented important references which have bearing on the subject of this review as well. An account of the approach and methods used in an industrial laboratory for analysis of rubber compounds was presented (57). Chemical analysis of plastics and elas- tomers was the subject of a book published recently (46). One chapter in a recent publication delineates the various isom- erization and cyclization reactions which occur with rubber under pyrolytic and nonpyrolytic conditions (33). Various aspects of polymer characterization are detailed in the recent publication edited by J. J. Dawkins (21). MICROSCOPY Some of the techniques used by microscopists to isolate and identify contaminants in rubber by light and electron mi- croscopy were discussed (72). Techniques for isolation use forceps, needles, replicas, selective dissolution, thin sectioning, and direct transfer. Identification by using polarized light microscopy, morphology, and IR analysis was detailed. Phase contrast produced in electron microscopy by defocus techniques was used to obtain the first unstained images of styrene-isoprene and styrene-butadiene diblock and triblock copolymers (36). Theoretical image calculations based on square-wave and circular cross sectional one-dimensional ‘Contribution No. 654 from The Goodyear Tire & Rubber Co., Research Laboratory, Akron, OH 44316. Table I. Abbreviations Recommended by ASTM (3) BR butadiene rubber CR chloroprene rubber EPDM terpolymer of ethylene, propylene, and a diene with residual unsaturated portion of the diene in the side chain IR isoprene synthetic rubber NBR nitrile-butadiene rubber NR natural rubber models were used to demonstrate the effects of mean inner potential difference, interface width, and microscope optics on resultant images. Experimental phase contrast images of microtomed block copolymers with ordered lamellar, cylin- drical, and disordered spherical morphologies were in good agreement with theory and experimental scatterlng contrast images (osmium tetraoxide stain). The phase contrast tech- nique was sufficient to visualize the phase-separated regions of polymers of similar atomic composition and for density. Transmission electron microscopy studies with ultrathin sections of cords embedded in rubber were shown to provide valuable information about resorcinol-formaldehyde-latex and predip locations which could not be obtained by standard optical methods (31). A scanning electron microscopy study was made of the tear structure of SBR cross-linked with either a sulfur-curing system or a peroxide-curingsystem (83). The effect of the addition of ISAF carbon black and the influence of cross-link density in the case of the sulfur-cured vulcanizates were examined. The particle size distribution of BR latex was studied using a transmission electron microscope coupled to a computer- controlled image analyzer by means of a fixed focus television camera and a fiber optic fluorescent screen (34). By a special agglomeration program, it was possible to distinguish highly agglomerated particles as single particles, approximating their shape to a spherical one. A description of the principles of Nomarski double beam interface contrast microscopy was given and the use of this technique in the study of polymeric materials was illustrated (74). Scanning electron microscopy was used to study the ozone resistance of NR and NR/EPDM blends (61). Advances in SEM of polymers was the subject of a recent review by White (99). NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY (NMR) The use of NMR for studying complex molecular structures of diene polymers and copolymers was reviewed (37). Poly- mers examined were BR, BR copolymers, IR, IR copolymers, polypentadiene, pentadiene copolymers, CR, CR copolymers, and other modified diene polymers. A model was established to illustrate the magnetic relaxation properties of proton pairs linked to strongly entangled chains (1). This model was compared with NMR spectra of real chains like cis-1,4-BD. This indicated that the splitting of the chain relaxation spectrum into two well-defined dispersions may be perceived 0003-2700/85/0357-187R$01.50/0 0 1985 American Chemical Society 187 R
Transcript
Page 1: Rubber

Anal. Chern. 1985, 57, 187R-191 R

(532) Mliis, T.; Price, W. N.; Price, P. T.; Roberson, J. D. “Instrumental Data for Drug Analysis, Volume I”; Elsevier: New York, 1982.

(533) Mills, T.; Price, W. N.; Price, P. T.; Roberson, J. C. “Instrumental Data for Drug Analysis, Volume 11”; Elsevier: New York, 1984.

(534) Ardrey, R. E.; Brown, C.; Allan, A. R.: Bal, T. S.; Moffat, A. C. “An Eight Peak Index of Mass Spectra of Compounds of Forensic Interest”;

The Forenslc Society: Harrogate, England, 1983. (535) Qaensslen, R. E. “Sourcebook In Forensic Serology, Immunology, and

Biochemistry”; US. Government Prlnting Office: Washington, DC, 1983. (536) “Proceedings of the Internatlonal Symposium of the Analysis and De-

tectlon of Exploslves”; US. Government Printing Office: Washington, DC, 1984.

Rubber

Anoop Krishen

Chemical Research & Development, The Goodyear Tire & Rubber Company,’ Akron, Ohio 44316

This review covers methods for identification, characteri- zation, and determination of rubber and materials in rubber.

Literature which became available to the author between November 1982, the end of the period covered by the last review in the series (47), and November 1984 is reviewed.

Abbreviations recommended in ASTM Designation D1418-18 have been used (3). There are listed in Table I.

GENERAL INFORMATION The American Society for Testing and Materials published

the 1983 annual edition of test methods for rubber (3). Some of the new standards issued by International Or-

ganization for Standardization (ISO) are 1. International Standard 6101/1-1982. Rubber-

Determination of Metal Content-Flame Atomic Absorption Spectrometric Method-Part 1: Determination of Zinc Content.

2. International Standard 6235-1982. Rubber, Raw-De- termination of Block Polystyrene Content-Ozonolysis Me- thod.

The third edition of the book “Analysis of Rubber and Rubber-like Polymers” was published (97). This book presents a balanced picture of the current technology in the rubber and rubberlike polymers. Chapters are given on sampling and sample preparation, extractions, analysis of extracts, chemical analysis for polymer type, quantitative elemental analysis, solution methods, instrumental polymer analysis, polymer characterization, inorganic fillers and trace metal analysis, carbon black, formulation derivation and calculation, blooms and visually similar phenomena, and finally validity of results.

The review on analysis of high polymers (88) presented important references which have bearing on the subject of this review as well. An account of the approach and methods used in an industrial laboratory for analysis of rubber compounds was presented (57). Chemical analysis of plastics and elas- tomers was the subject of a book published recently (46). One chapter in a recent publication delineates the various isom- erization and cyclization reactions which occur with rubber under pyrolytic and nonpyrolytic conditions (33).

Various aspects of polymer characterization are detailed in the recent publication edited by J. J. Dawkins (21).

MICROSCOPY Some of the techniques used by microscopists to isolate and

identify contaminants in rubber by light and electron mi- croscopy were discussed (72). Techniques for isolation use forceps, needles, replicas, selective dissolution, thin sectioning, and direct transfer. Identification by using polarized light microscopy, morphology, and IR analysis was detailed.

Phase contrast produced in electron microscopy by defocus techniques was used to obtain the first unstained images of styrene-isoprene and styrene-butadiene diblock and triblock copolymers (36). Theoretical image calculations based on square-wave and circular cross sectional one-dimensional

‘Contribution No. 654 from The Goodyear Tire & Rubber Co., Research Laboratory, Akron, OH 44316.

Table I. Abbreviations Recommended by ASTM (3)

BR butadiene rubber CR chloroprene rubber EPDM terpolymer of ethylene, propylene, and a diene with

residual unsaturated portion of the diene in the side chain

IR isoprene synthetic rubber NBR nitrile-butadiene rubber NR natural rubber

models were used to demonstrate the effects of mean inner potential difference, interface width, and microscope optics on resultant images. Experimental phase contrast images of microtomed block copolymers with ordered lamellar, cylin- drical, and disordered spherical morphologies were in good agreement with theory and experimental scatterlng contrast images (osmium tetraoxide stain). The phase contrast tech- nique was sufficient to visualize the phase-separated regions of polymers of similar atomic composition and for density.

Transmission electron microscopy studies with ultrathin sections of cords embedded in rubber were shown to provide valuable information about resorcinol-formaldehyde-latex and predip locations which could not be obtained by standard optical methods (31). A scanning electron microscopy study was made of the tear structure of SBR cross-linked with either a sulfur-curing system or a peroxide-curing system (83). The effect of the addition of ISAF carbon black and the influence of cross-link density in the case of the sulfur-cured vulcanizates were examined.

The particle size distribution of BR latex was studied using a transmission electron microscope coupled to a computer- controlled image analyzer by means of a fixed focus television camera and a fiber optic fluorescent screen (34). By a special agglomeration program, it was possible to distinguish highly agglomerated particles as single particles, approximating their shape to a spherical one.

A description of the principles of Nomarski double beam interface contrast microscopy was given and the use of this technique in the study of polymeric materials was illustrated (74). Scanning electron microscopy was used to study the ozone resistance of NR and NR/EPDM blends (61). Advances in SEM of polymers was the subject of a recent review by White (99).

NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY (NMR)

The use of NMR for studying complex molecular structures of diene polymers and copolymers was reviewed (37). Poly- mers examined were BR, BR copolymers, IR, IR copolymers, polypentadiene, pentadiene copolymers, CR, CR copolymers, and other modified diene polymers. A model was established to illustrate the magnetic relaxation properties of proton pairs linked to strongly entangled chains (1). This model was compared with NMR spectra of real chains like cis-1,4-BD. This indicated that the splitting of the chain relaxation spectrum into two well-defined dispersions may be perceived

0003-2700/85/0357-187R$01.50/0 0 1985 American Chemical Society 187 R

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RUBBER

from NMR. Distribution of double bonds in thermallv de- graded polyisobutylene was quantitated using pulsed" FT- proton NMR (51).

The use of pulsed NMR techniques for the study of polymer DroDerties like molecular size. mobilitv. and arraneement was Eedewed (14). The chemical'structuie of natural6 occurring cis-polyisoprene from olden rod (Solidago altissima) was determined by 13C NMk (93). The alignment of the isoprene units in the polymer was estimated to be in the order: di- methyl allyl terminal unit, three trans units, about 1000-2000 internal cis units, and a cis allyl alcohol terminal unit.

The applications of high-resolution NMR to the analysis of the microstructures of synthetic organic polymers were reviewed (26). Four selected samples of tires were pyrolyzed in nitrogen at 673-733 K. The pyrolysis products were dis- solved in CDC13. lH and 13C NMR spectra of the solutions were used to identify and quantitate all the types of rubber (82). NMR was utilized as a fast and efficient means of monitoring the incorporation and dispersion of carbon black in a reinforced rubber compound (98). Tests could be carried out at all stages of processing, including masterbatch stock. The fraction of polymer bonded to the surface of the filler particles was determined and correlated with the degree of filler dispersion determined optically.

Microstructure determinations of NBR and SBR using 13C NMR were made without involving "empirical factors" (96). Experimental parameters were devised to overcome difficulties due to long spin-lattice relaxation times and due to different nuclear Overhauser effects.

Copolymerization of butadiene with styrene and diad analysis of the copolymers were studied by 13C NMR to obtain information on the penultimate unit effect on the micros- tructure of the butadiene unit (44). Effects of magic-angle spinning (MAS), high ower decouplin , and resonance fre- quency on the 13C NMk line widths of Eulk polyisobutylene and bulk trans-BD were examined (45). 13C line widths in- creased with resonance frequency, were unaffected by high power decoupling and were reduced by varying amounts by MAS. A study was made of NR and cis-BR, cross-linked with dicumyl peroxide, using solid-state 13C NMR and FT-TR. Cis-trans conversion in the main chain backbone by allylic shift of the double bond was observed as well as quaternary carbon formation for NR. All resonance line widths were found to increase with degree of cure, the increase being attributed to C-H dipolar interaction.

Microstructtlre of cyclized NR and IR was examined by 13C NMR and 'H NMR analysis (67). Configurational sequencing analysis of 1,2-BR was conducted with 13C NMR (49). Sol- id-state 13C NMR was employed to determine the nature of the fold surface of solution-grown 1,4-trans-BR single crystals as well as the fraction of crystallinity and chain conformation (78). Crystal content was estimated to be 74% and spin- lattice relaxation was shown to be almost entirely dipolar using scalar decoupling techniques. Magic angle spinning dipo- lar-decoupled measurements showed that crystal chain folds have essentially the Bame average conformation as the trans-1,4 sequences in amorphous bulk polybutadiene, despite constraints imposed by the requirements of adjacent reentry.

THERMAL METHODS Differential thermal analysis (DTA) and thermogravimetric

analysis (TGA) techniques were used to study the effectiveness of some of the common stabilizers in BR (32).

Two melting points were observed in the melting of cis- 1,4-polyisoprene which had been crystallized under prede- termined temperature-deformation conditions (50). This was considered an indication of topomorphism in this rubber,

Volatiles produced on pyrolysis were examined by pyroly- sis-GC and TGA (59). The rate of volatilization provided information on polymer degradation which differed from the data obtained by measuring weight loss specially for those polymers which do not degrade to nionomers. Changes in the degradation products were observed when heating rate was changed and approached the heating rate found in burning polymers.

The use of TGA in combination with other analytical techniques-IR, MS, chromatography-was found to provide additional information regarding thermal stability of polymers (22). Thermal stability, evolution of organic material in nonoxidizing atmospheres, and the kinetics of polymer deg-

188R ANALYTICAL CHEMISTRY, VOL. 57, NO. 5, APRIL 1985

radation were examined by TGA. Thermal decomposition of polyisobutene was studied by

differential scanning calorimetry (DSC) (60). Under iso- thermal conditions, weight loss was found to be independent of the molecular wei ht. Activation energy for decomposition was determined to f e 184 kJ mol and the glass transition

composed polymer was 200 f 3 K. Thermal analysis techniques-TGA, evolved gas analysis,

DTA, DSC, TMA, and dynamic thermomechanical analysis-as ap lied to various polymers were discussed and

Derivative thermograms obtained by TGA were charac- teristic of IR, SBR, and BR but were not suitable for iden- tifying mixtures of these polymers (9). Burfield and Lim (10) presented the results of an investigation to determine Tg for natural and synthetic cis- and trans-1,4-polyisoprenes using DSC. A review was presented on characterization of polymer blends by thermal analysis (27). This included an assessment of blend morphology in terms of transition temperatures and quantitative thermal analysis of both compatible and phase separated blends, limitations of thermal analysis, and the utility of thermal methods vs. other techniques used to characterize polymer blends.

A discussion of some of the advantages and limitations of thermoanalytical measurements for examining combustion of polymers was presented (18).

The equilibrium melting temperature of cis-polyisoprene was determined to be 35.5 "C at atmospheric pressure (20). Unpolarized light was used in the optical turbidimetric technique for obtaining the melting data.

TGA was used to determine carbon black type in CR and SBR (101). Vulcanizates containing these polymers were decomposed by heating in concentrated HNOs at 95 "C for 2 h. The carbon black recovered by this process was examined by TGA to obtain "T15", the temperature at which the carbon black lost 15% weight. T15 was found to decrease with in- creasing specific surface area of carbon black.

A TGA/DTA technique was applied to the characterization of different types of carbon black in NR vulcanhates (63). This method allowed the determination of the overall carbon black content, but it was not possible to determine the pro- portion of each type when a combination of different blacks was present. This study revealed a relationship between the specific surface of the black and TGA.

TGA was described as being suitable for quality control of rubber vulcanizates with reproducibility claimed to be f0.4% (86). Weight loss up to 300 "C can be related to oils, plas- ticizers, and other additives; up to 550 "C represents polymers; up to 650 "C in air represents carbon black; up to 800 "C represents CaC03. The residue in the absence of inorganic fillers is ZnO. NR, BR, and SBR can be determined with a precision of f2% in the absence of bitumen. The ratio of NR to SBR or BR can be determined. Quantitation of graphite is possible only in the absence of CaC03 since graphite burns at temperatures where C02 is evolved from CaC03.

SBR was identified by TGA-atmospheric pressure chemical ionization mass spectrometry (25). The molecular ion of 54 for butadiene and 104 for styrene increased in intensity as the pyrolysis of SBR took place. The system was sensitive to conformational changes in the polymer system as demon- strated by observed difference between the mass intensity ratio of cis- and cis,trans-polybutadiene.

A review of thermoanalytical methods (79) covered in- strumentation, qualitative applications of TGA, DTA, DSC, and thermal volatilization, kinetic aspects of polymer degra- dation for nonisothermal conditions, solid-gas reactions, isothermal polymer degradation, differential and integral methods, thermoanalysis, quantitative applications, recent trends, and conclusions. Limitations of the methods and conclusions drawn from the results in studying polymer degradation kinetics and mechanisms are also emphasized.

The use of combined thermogravimetry and pyrolysis-gas chromatography was presented for the rapid determination of the level and type of polymer and blend ratios as well as the levels of oil, carbon black, and inorganic components in small samples of vulcanized rubber (81). Pyrograms for NR, SBR, butyl rubber, BR, EPDM, neoprene, butyl/EPDM blends, SBR/BR blends, and NR/BR blends and DTG curves of compounded NR and IR and calibration curves for

temperature (Tg) for the un 1 ecomposed and partially de-

compared by Ip ay (38).

Page 3: Rubber

RUBBER

SEC of polymem of ul h mol& weighta WBS resented (30). A comparison of 9 SE and field-flow fraction &FF) was ressntad to show that most of the complexities of SEC could 1 ' e avoided by using the FFF system. Relationships were derived between the spreading factor

and the slopes of actual and effective linear calibrations in SEC (48). On the basis of these data, a new calibration procedure was developed for determining the dependence of molecular weight and the spreading factor on the elution volume of polydisperse polymer samples. Hardware and software for collecting and storing GPC data from equipment fitted with UV absorbance and differential refractive index detectors for printing and plotting them on the screen and for data reduction were developed for a GPC system interfaced with an Apple I1 Plus microcomputer (62). The advantages of this system over manual calculations were emphasized.

A theoretical study was made of problems of interpreting results of GPC using a continuous laser nephelometer or a continuous viscometer which recorded the pressure drop in a calibration capillary as an added detector (91). The in- strumental widening effect on the material eluted was cal- culated and the possibility of using continuous absolute de- tectors for determining MWD of branched polymers was ex- plored. Phenol-formaldehyde resols were dissolved in tri- chloroacetic acid and their MWD was determined on Styragel columns using THF as eluant (6).

PYROLYSIS-GAS CHROMATOGRAPHY-MASS SPECTROSCOPY (PY-GC-MS)

Use of Py-GC was described for determining the mixing efficieney of master hatches containing NR. BR, and SBR (90). Three major peaks in the pyrograms were used for this pur-

Retention times in Py-GC were standardized by using a polyethylene standard pyrogram (35). Variations in nor- malized retention times due to minor fluctuations in exper- imental conditions were studied, and i t was found that the relative standard deviation was leas than 1% over a 1-month period. Sulfur bridges in carbon black ffled NR vulcanizatea were

studied with Py-GC using a flame photometric detector (4). It was found that the main products were carbon disulfide and thiophenes but their yields depended on the cure systemaulfur/N-cyclohexyl-Z-he~othi~olesulfenamide or sulfur/tetramethylthiuram disulfideand the degree of cure.

Py-GC was utilized for investigating the composition and structure of polymers and to distinguish between random copolymers and mixtures of homopolymers (24). Regression analpis was employed to optimize the selection of peaks. The concept of direct compound analysis using Py-MS was out- lined (69) for the analysis of three typea of materials. Uncured rubber blends were examined to demonstrate that polymer mixtures could he differentiated. Cured rubber compounds were analyzed to determine polymers and some of the addi- tives. Chlorinated PVCs were examined to obtain structural information. An automated Curie point Py-GC system was described for obtaining qualitative and quantitative infor- mation on NR, IR, SBR, BR, EPDM, and other polymers- both individually and as mixtures (80).

The use of positive and negative chemieal ionization Py-MS was described for the identification of various polymers (2).

Characterization of resols was obtained by GC-MS (5). The resols were etherified with methanol under acidic conditions, converted to trimethylsilyl derivatives, and then separated by capillary GC. Structure assignments were made from MS data.

CHROMATOGRAPHIC TECHNIQUES Methods of extraction and thin-layer chromatography

(TLC) were applied to isolate accelerators from rubber (66). Quantitation was achieved by UV spectroscopy. About 1748% of the original amount of accelerators was recovered after vulcanization.

Tu: and LC (liquid ehromatagraphy) were used to estimate the content of thiobisphenolic antioxidants (76). Styrene oligomers were separated using a nitrile-bonded LC column (52). The nitrile column was shown to act as a SEC column in polar solvents like dichloromethane. W and fluorescence detectors were used.

ANALYTICAL CHEMISTRY. VOL. 57. NO. 5, APRIL 1985 0 189R

pose.

SBR/BR blends, NR/SBR blends, and butyl/EPDM blends are presented.

Direct determination of Tg was obtained by DSC of NR later (11). This Tg was identical with that of dried rubber. The dry rubber content of the latex wan shown to be closely related to heat capacity change and enthalpy of fusion values determined for the Tg and serum melting proeeas, respectively.

INFRARED AND ULTRAVIOLET SPECTROSCOPY (1% UV)

Attenuated total reflection (ATR) IR WBS proposed for uantitative study of polymer films with an absorption gra- !. lent (89). Advantages and limitations of the method were

presented. The use of differential IR (computer-assisted IR and

Fourier-transform IR) in the analysis of polymer blends and compounds was discussed (39). The crystallinity of the mm- ponenta in blends was lower than it would he in unblended wmponenta probably due to interpenetration of nonrrystalline portions of different polymers. Highly filled materials are claimed to he identified reliably if the filler or reinforrement is monodisperse. Materials highly filled with organic fillers could be identified by differential IR if the absorption of the binder did not coinride with strong bands for the filler. Ar- tifacts which falsify differential spectra were discussed. IR analysis was shown to he useful to differentiate between various environmental causes of polymer degradation (43). Various changes were examined by IR fnr NR. BR. CR. and NR latex when these materials were subjected to oxygen, UV radiation. heat and ozone.

Interaction of tetramethylthiuram disulfide with 2- merraptobenzothiazole with and without zinc oxide was studied by derivative L'V and IR (88). A mechanism for the reaction was suggested which leads m a n increase in the in- duction period fur vulcanization.

Model reactions involving phenol and aminotriazine de- rivative were used to study the synthesis of phenol-mel- mineformaldehyde copolymer resins by polycondensation (8) . Analysis of the product8 by chromatn aphy and IR showed that methylene bridges were formed 6 the reaction of melamine and p-methyphenols under slightly acidic con- ditions while under strongly acidic and alkaline conditions only homocondensation rnduct8 were formed.

A review was presentelon the application of FT-IR spec- troscop to the study of synthetic polymers (40). The theo- retical gackground and the advantages of FT-IR were d e scribed along with a desrription of FTIH-photoacoustic spectroscopy.

GEL PERMEATION AND SIZE EXCLUSION CHROMATOGRAPHY (CPC-SEC)

A survey of Soviet literature covering molecular weight distribution (MWD) by GPC was published (84).

Corrections for axial correction in GPC were described (64). Differential CPC-where one polymer was a standard and

a solution of this polymer was used as the eluant-was de- &bed (77). The chromatograms ohtained were both negative and positive with respect to the base line. This technique was suggested as a quality control rwedure where the positive portion9 represent an excess antnepative portions s defiriency as compared to the standard.

Correlation of efficiency in CPC as a function of flow rate was described (16). Analpis of fundamental obstacles tn the

Page 4: Rubber

RUBBER

A study was made of the migration of sulfur and thiuram, thiazole, and sulfenamide accelerator in EPDM/NR and EPDM/SBR using HPLC and computerized analytical techniques (75). Computer modeling revealed that the dis- tribution of sulfur and N-cyclohexyl-2-benzothiazyl di- sulfenamide was nonuniform. Sulfur was shown to move toward the unsaturated phase while thiurams and thiazoles did not migrate. The reasons for selecting TLC for the identification of compounding ingredients were outlined and results obtained by using two different absorbents-silica gel and C18 reverse phase-were presented (29). A TLC method was proposed for determining the molecular wei ht of poly- mers (56). This method is based on a universal fiependence of the length of the chromatographic zones on the intrinsic viscosity.

Determination of -phenylenediamine type of antiozonants was achieved on a 8DS-2 column using 75/25 acetonitrile/ 0.06% tetrameth lammonium bromide as eluant (73). The extraction from 8 R was achieved with acetonitrile and the UV detector was at a wavelength of 300 nm.

ANALYSIS RELATED TO SAFETY AND HEALTH

Toxicity of mix ingredients which can migrate from the rubber was found to be affected by the composition of the mix (85). Thus, the effect of tetramethylthiuram disulfide was different when diphenyl guanidine, N-phenyl-P-naphthyamine, or zinc chloride was present.

The condensed aromatic hydrocarbon content of carbon blacks was determined by capillary GC of carbon disulfide extracts (65).

Volatile organics from vulcanization areas were collected on activated charcoal, desorbed with trichlorofluoromethane, and analyzed by GC-MS (17). About 100 different compounds were identified and quantitated.

Identification and quanitation of rubber fumes by GC-MS using a gas transfer mold were described (100).

Burning mechanism and fire retarding methods as appli- cable to compounding for fire resistance were given (19). The areas discussed include, input of heat, elevation of tempera- ture, emission of gaseous decomposition products, mixing with oxygen to form a combustible mixture, ignition, flaming, flame spread, and after glow and solid phase combustion.

Methods for the measurement of oxygen index of polymers were considered, together with the application of these techniques to the assessment of polymer flammability and the effectiveness of flame retardants (12).

MISCELLANEOUS The de ree of unsaturation in isoprene rubber was mea-

sured by fissolvin the rubber in CC1, or CC14, treating with

trichloroacetic acid at 50-60 “C for 5-6 h, and titrating excess I2 with sodium thiosulfate (54).

Dry rubber content of fresh Hevea latex was calculated from microwave attenuated power (42). The calculation was based on a model of water suspension by Weiner and showed that the dry rubber content of the latex could be determined from microwave attenuation, latex density, and thickness of the latex layer.

Four methods were used to study the progress of carbon black dispersion in rubber during mixing-small angle X-ray scattering, dynamic mechanical moduli, scanning electron microscopy, and electrical resistance (23).

Isothermal degradation of high cis-1,4-polyisoprenes with different cross-link structures was studied by weight loss, IR, NMR, GPC, and GC (92). Various methods used for deter- mining the dispersion of carbon black-electrical resistivity, optical microsco y, surface analysis method of Hess-were compared for HWF blacks in SBR (13).

Ultrasonic propagation for the characterization of homo- and heterophase polymers was reviewed (70, 71). Techniques and theories for the measurement of sound propagation in solid polymers were summarized. The use of IR and Raman spectroscopy in polymer characterization was reviewed (58). Influence of zinc oxide on the properties of vulcanizates was studied by electron microscopy, scanning electron microscopy, UV fluorescence microscopy, and microprobe and X-ray fluorescence (95).

190 R ANALYTICAL CHEMISTRY, VOL. 57, NO. 5, APRIL 1985

a solution of Iz in E C14 in the presence of mercury acetate and

Molecular weight averages used in polymer characterization were defined and a survey was made of the principal tech- niques for molecular weight measurement (28). The tech- niques considered were membrane osmometry, light scattering, intrinsic viscosity, and GPC. The influence of molecular weight determination on polymer properties such as glass transition temperature, tensile strength, elongation at break, impact resistance, crack propagation, and melt viscosity was also discussed.

An improved method for determining natural higher fatty acid soaps in freshly prepared NR latex concentrates was presented (15). This method uses cold extraction of the soaps.

A rapid gravimetric procedure for determining the resin and rubber content of Guayule was described (7). This technique uses a two-step solvent extraction procedure in which the ground shrub is further treated in a high-speed homogeniz- er-grinder to render the rubber accessible to the solvent.

The origin of the small angle X-ray diffraction peak ob- tained from vulcanized NR and changes in the peak caused by swelling, stretch relaxation, heat or extraction were in- vestigated (94). The influence of compounding ingredients on small an le X-ray diffraction was also studied. The results

stearate and was not directly related to sulfur cross-links. An X-ray procedure was descibed which involved both

diffraction and X-ray spectrometry to obtain information on rubber compounds and their ash (53). A good approximation for the composition of the ash and the identity of the crys- talline compounds in the rubber and ash was obtained and used for reconstruction of the inorganic portion of the rubber compound. Determination of SBR and NR in vulcanized rubber by pyrolysis-IR spectroscopy was described (45). IR calibration curves were obtained from a series of SBR/NR standards. The calculation curves were based on the ratio of absorbances a t 7001 1380, 700/890, 700/1480, and 890/910 cm-l. This eliminated the effect of film thickness.

The application of gas chromatography to the study of solid polymers was described (55). By use of inverse gas chroma- tography, Tgs, percent crystallinities, and surface areas were determined. Solution studies used the polymer as the con- centrated “solventn and small amounts of organic vapor were the solute or probe. The data obtained were utilized to calculate diffusion constants, solubility for the probe in the polymer, activity coefficients, heats of solution, FIory-Huggins interaction parameters, and infinite dilution polymer solubility parameters.

suggested t a at the peak resulted from the formation of zinc

ACKNOWLEDGMENT

The permission of The Goodyear Tire & Rubber Company to prepare and publish this review is greatly appreciated.

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This is the 17th review in a series which began in this journal in January 1953 (1A) and which has appeared in April of odd numbered years since then (2A-16A). It covers papers abstracted in Chemical Abstracts, Analytical Abstracts (London), and the American Petroleum Institute Refining

Literature Abstracts during the period July 1982 through June 1984.

J. D. Beardsley has written a section for each of these reviews since 1965. Her retirement makes this year’s con- tribution the last in that series, and her services will be missed.

0003-2700/85/0357-19IR$O6.50/0 0 1985 American Chemical Society 191 R


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