Characterization of Electron Beam Irradiated Ethylene Methyl Acrylate

Ind. Eng. Chem. Res. 2010, 49, 7113–7120

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Characterization of Electron Beam Irradiated Ethylene Methyl Acrylate Copolymer Nilambar Mongal,† Debabrata Chakraborty,‡ Rupa Bhattacharyya,*,§ Tapan Kumar Chaki,| and Pinaki Bhattacharya⊥ Nicco Corporation Ltd, Cable DiVision, Athpur, Shyamnagar, West Bengal, India, Department of Polymer Science & Technology, UniVersity of Calcutta, 92, A.P.C Road, Kolkata -700092, West Bengal, India, Department of Chemistry, Narula Institute of Technology, 81, Nilgunj Road, Kolkata -700109, Rubber Technology Centre, Indian Institute of Technology, Kharagpur, India, and Department of Chemical Engineering, JadaVpur UniVersity, 188, Raja S. C Mallik Road, Kolkata -700032. Kolkata, India

The effect of electron beam dose on the mechanical, thermal, and electrical properties over ethylene methylacrylate (EMA) copolymer was investigated. The copolymer (Elvaloy 1224) was subjected to electron beam radiation at different doses for cross-linking, with the incorporation of the sensitizer trimethylolpropane trimethacrylate (TMPTMA) at various levels. It was observed that the mechanical properties reached an optimum level around 60 kGy radiation dose and 1 phr sensitizer. Beyond that, an increase in irradiation dose or sensitizer level contributed little to modify the properties further. These observations were supported from spectral studies. Improved thermal behavior was observed from the thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) thermograms. The electrical properties were affected very little by irradiation. Introduction The electron beam irradiation method of producing crosslinked polymers is often an easier method to employ and control than conventional chemical methods. This technique has gained commercial importance, especially in the cross-linking of heatshrinkable materials, wire and cable, surgical goods, and in many other applications. One of the investigations on the influence of additives including acids, inorganic salts, organic inclusion compounds like urea, multifunctional acrylates, and methacrylates on radiation curing has been reported by Dworjanyn et al.1 Datta et al.2 have reported the effect of electron beam radiation at various dosages on blends of trimethylolpropane trimethacrylate (TMPTMA) and ethylene vinyl acetate (EVA). Their IR study showed some residual unsaturation retained in irradiated pure TMPTMA, whereas in blends, all unsaturation was used up at a very early stage of irradiation. Bafsar3 reported the flame retardancy of radiation cross-linked poly (vinyl chloride), used as an insulating material for wires and cables. Studies on the incorporation of TMPTMA and TAC (triallyl cyanurate) on ethylene vinyl acetate have been elaborately studied by Chaki et al.4 However, it is thought that there is enough scope to investigate electron beam-initiated cross-linking of ethylene methyl acrylate (EMA) to understand the effect of process variables on the cross-linking. It is also felt that studies on the incorporation of various concentration levels of TMPTMA sensitizer will also be an interesting area from a process engineering point of view. This is expected to modify the compound nature and process variation, which is widely applicable in the case of wire and cable industries. A literature survey shows several significant important properties of modified ethylene methyl acrylate copolymer in * To whom correspondence should be addressed. E-mail: [email protected]. † Nicco Corporation Ltd. ‡ University of Calcutta. § Narula Institute of Technology. | Indian Institute of Technology. ⊥ Jadavpur University.

the field of process engineering, which have been identified by various investigators.5,6 Fan et.al7 have shown experimentally that an ethylene methyl acrylate copolymer produced from a tubular reactor is effective in toughening polypropylene (PP), even at low concentration. In fact, they have used EMA as a modifier of PP. In the present investigation, a thorough and programmed study has been carried out on the curing of ethylene methyl acrylate copolymer by TMPTMA sensitizer using the electron beam technique and characterizing the modified polymers by their mechanical, electrical, and thermal properties. Because in any polymer industry the selection of the optimum level of operating variables for the manufacturing process is of the utmost importance, in the present investigation an attempt has been made to optimize the concentration level of TMPTMA sensitizer and irradiation dosage to achieve a modified EMA copolymer having the best possible physicomechanical properties. Elvaloy 1224 was selected as the base polymer in this study, with a methyl acrylate content of 24 and a melt flow index (MFI) of 2. It was subjected to various dosages of irradiation at different sensitizer levels. TMPTMA is a polyfunctional unsaturated monomer, which is very efficient in producing high yields of radicals during irradiation. A large number of radicals help in achieving better grafting and enhance the degree of cross-linking.8,9 Experimental Section Materials. Elvaloy 1224 was supplied by M/s DuPont Specialty Elastomers, Belgium. An antioxidant, Irganox 1010 (hindered phenol type) was supplied by Ciba Specialty Chemicals and TMPTMA was supplied from Sartomer Chemicals. Preparation of Samples. One hundred parts by weight of Elvaloy 1224 was mixed with 3 parts by weight of Irganox 1010 and a proportionate quantity of TMPTMA in a Haake Rheocord (Model Haake Rheocord system 40) at a temperature of 100 °C. Elvaloy was first allowed to melt in the mixer, the complete melting being followed by the addition of antioxidant and TMPTMA. The mix so obtained was sheeted out through an open mill with a 2 mm nip gap.

10.1021/ie901966s  2010 American Chemical Society Published on Web 07/13/2010

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Ind. Eng. Chem. Res., Vol. 49, No. 16, 2010

Table 1. Formulation of Samples Elvaloy 1224 (parts by weight)

TMPTMA (parts by weight) (phr)

radiation dose (kGy)

100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100

0 0 0 0 0 0 1 1 1 1 1 1 2 2 2 2 2 2 3 3 3 3 3 3 4 4 4 4 4 4

0 30 60 90 120 150 0 30 60 90 120 150 0 30 60 90 120 150 0 30 60 90 120 150 0 30 60 90 120 150

sample code C000 C003 C006 C009 C012 C015 C100 C103 C106 C109 C112 C115 C200 C203 C206 C209 C212 C215 C300 C303 C306 C309 C312 C315 C400 C403 C406 C409 C412 C415

Table 2. Specification of the Electron Beam Accelerator energy range

1 to 3 MeV

beam power beam energy spread average current accelerating voltage frequency duration pulse current (max) pulse current (min) power supply voltage power supply voltage frequency consumption of power manufacturer model no.

0.5 to 150 kW 50% to 99.9% 0.5 to 50 mA 100 kHz to 0.1 MHz any number of passes 50 mA 0.5 mA 440 V 50 Hz 0.5 to 150 kW RDI, USA 369/3 MeV/50 mA/220 mm Dynamitron Oscillator Model 375

The sheets were then compression molded between aluminum foils at 110 °C at a pressure of 14 × 106 N/m2 in an electrically heated press. Aluminum foils were used to reduce the shrink marks on the molded surface. The moldings were cooled under compression to maintain the overall dimensional stability of the samples. The thickness of the films obtained was around 1.5 mm. Radiation. The molded Elvaloy samples in the form of rectangular sheets were irradiated by an electron beam accelera-

Figure 1. Variation of tensile strength with electron beam dose.

Figure 2. Variation of elongation at the break electron beam dose.

Figure 3. Variation of modulus at 100% elongation with electron beam dose.

tor at Nicco Corporation Ltd., Cable Division, Shyamnagar. The beam energy of the accelerator is 1-3 MeV and the beam power is 0.5 to 150 kW. Irradiation doses of 30, 60, 90, 120, and 150 kGy were used. The formulations of the samples are given in Table 1 and the specification of the accelerator is given in Table 2. Characterization. Physico-mechanical Properties. Tensile strength, percent elongation at the break, and modulus at 100% elongation were measured on dumbbell specimens according to ASTM D412 in a Zwick-1445 Universal Testing Machine at a strain rate of 50 mm/min at 27 ( 2 °C. The average was Scheme 1. Self Cross-Linking of Ethylene Methyl Acrylate and Network Formation

Ind. Eng. Chem. Res., Vol. 49, No. 16, 2010 Scheme 2. Cross-Linking by TMPTMA

Figure 4. IR spectra of unsensitized and sensitized samples.

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Scheme 3. Oxidation by Aerial Oxygen

Figure 5. Variation of gel content with electron beam dose.

Scheme 4. Termination Reaction by Combination and Disproportionation

taken on four samples and the experimental error was (5%. The tear strength was measured on a trouser-shaped specimen following ASTM D412 in a Universal Testing machine model no. ZMGI-25. Hardness of the prepared samples was measured by a Durometer on a Shore A scale. Gel Content. The gel content of the samples were measured in a Soxhlate apparatus by extraction using ethyl acetate as a solvent. Absolutely dry samples were subjected to fractionation for 72 h at 65 °C and dried in an air oven at 80 °C until a constant weight is obtained. The initial weight of the sample is taken as W1 and the final weight as W2. The cross-link density is then given as W2/ W1*100. Infrared (IR) spectra. IR spectra were taken on sample sheets using a PerkinElmer (model Paragon 1000 PC) spectrophotometer using the attenuated total reflectance (ATR) mode. Thermal Properties. Thermogravimetric Analysis. The thermogravimetric measurements were carried out in a thermogravimetric analyzer, model no. TGA Q50 V6.1 within the temperature range of 27 to 600 °C and at a heating rate of 10 °C/min in an inert atmosphere of nitrogen. Differential Scanning Calorimetry. The differential scanning calorimetric measurements were carried out on a DSC apparatus, model DSC Q100 V8.1, within a temperature range of -200 °C to +150 °C. The rate of heating was maintained at 10 °C/min. Electrical Properties. Volume Resistivity. The volume resistivity of the samples was measured on a volume resistivity testing machine model no. 4339B. The manufacturer was Agilent Technology Japan Ltd. Circular samples of area 19.64 cm2 were used after cutting from the molded sheets. Dielectric Constant. The dielectric constant of the samples was measured in a dielectric constant meter from Sivananda Electric, India, with an operating frequency of 1 MHz.

Breakdown Strength. Breakdown strength was measured in a BDV tester with a voltage application rate of 100 to 500 V/sec. Results and Discussion Mechanical Properties. Figure 1 shows a plot of tensile strength versus irradiation dose at different TMPTMA levels. It is observed that with an increase in irradiation dose, the tensile strength increases for all of the samples, reaches a maximum, and then decreases. In the case of samples with 1 and 2 phr TMPTMA, the reduction in tensile strength is observed at 60 kGy irradiation dose. It is also observed that for a sample with 1 phr TMPTMA (C1) the tensile strength is at a maximum compared to all other samples. It is interesting to note that the sample with no sensitizer (C0) shows maximum tensile strength having a magnitude almost the same as that with C1 at an appreciably higher irradiation dose (100 kGy). Although samples C1 and C2 achieved the maximum tensile strength at almost the same irradiation dose (60 kGy), it is evident that the

Figure 6. Variation of tear strength with electron beam dose.


Figure 7. Variation of hardness with electron beam dose.

Figure 8. TGA curves at 1 phr TMPTMA incorporation.

maximum tensile strength of C2 is less than that of C1. For samples C3 and C4, the maximum tensile strength is attained at a much lower level of radiation dose (30 kGy) compared to that of C2 and C1. From the behavior shown in Figure 1, it may be concluded beyond a doubt that the influence of the sensitizer is quite insignificant above 2 phr level irrespective of the irradiation dose. Elongation at the break against irradiation dose (Figure 2) clearly indicates that elongation monotonically decreases with an increase in the irradiation dose for all of the samples. Figure 3 shows a plot of the modulus at 100% elongation against the irradiation dose. It is observed that for all of the cases the modulus at 100% elongation increases marginally with an increase in radiation dose. The high-energy electron beam causes ionizing radiation by knocking off electrons and creating ions or free radicals.10 These free radicals generated within the base polymer, undergo chemical reactions and subsequently increase the cross-link density of the system. The electron beam radiation may cause combination or coupling of two macroradicals or of a macroradical with TMPTMA as per schemes 1 and 2 as shown below. The unsaturation present in TMPTMA serves as centers of crosslinking the macroradicals. The trifunctional TMPTMA enhances gel formation because the monomer end-capped macroradicals have greater reactivity. The tensile strength and modulus at a given elongation is proportional to the number of cross-links formed. The tensile strength, which is assumed to be a function of cross-link density, energy dissipation, chain scission, hindrance to crystallization, and modification of the main chains, increases with an increase in TMPTMA levels up to a level of 1 and 2 phr and 60 kGy

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dose (C106 and C206). The increase in tensile strength at the initial stages can be attributed to the increasing gel content and hence the cross-link density of the polymer.11 The sensitizer TMPTMA being trifunctional in nature reacts with the system to attain a saturation level of cross-link density. This optimum level is attained faster in the case of samples sensitized with 3 and 4 phr (C303 and C403) compared to the 1 and 2 phr sensitized ones (C106 and C206), owing to the presence of a greater amount of TMPTMA in the former. As a result, the compounds with 3 and 4 phr sensitizer optimize in tensile values at a lower irradiation dosage compared to the 1 and 2 phr ones, where the optimization is reached at a higher level. Thus, at a similar maximum value of cross-link density, C306 and C406 over cures, whereas C106 and C206 remain unabated and exhibit a maximum value of tensile strength. IR Study. Figure 4 shows the normalized ATR spectra of C000 to C115 in the region of 2000 to 600 cm-1. A range of 0 to 150 kGy irradiation has been considered for investigation. The ATR spectra of pure ethylene methyl acrylate (C000) shows a peak at 1735 cm-1 due to carbonyl stretching (>CdO) for the ester group, 1585 cm-1 due to >CdCCdC< conjugated with >CdO of the methacrylate group in TMPTMA. As the irradiation dose increases, it is distinctly noticed that from 30 to 60 kGy, there is a distinct diminution of this peak. Again from 90 to 150 kGy, the peak starts developing and shows a peak intensity at the 150 kGy dose, which is almost similar to that obtained with that of the 30 kGy dose. In the first instance, the diminution of the 1585 cm-1 peak might be due to the consumption of the trans vinylene group of TMPTMA, either through a grafting or cross-linking reaction. At the 60 kGy dosage, the almost flattening of the peak at 1585 cm-1 signifies full utilization of the vinylene group in the above process. Nethsinghe and Gilbert13 also reported that there was no such peak corresponding to unsaturation at 1640 cm-1 when PVC was modified by TMPTMA. However, reappearance of the peak beyond 90 kGy (i.e., at 90, 120, and 150) is a significant observation, which may be explained as follows. The reappearance of the said peak may possibly be attributed to the random chain scission of either the ethylene methacrylate polymer chains or the random cleavage of the TMPTMA-induced cross-links. The high energy associated with the emission of the electron beam (more than 60 kGy) helps to augment the process of such cleavage. The formation of ether linkage is indicative of some oxidation reaction taking place due to aerial oxygen, producing a peroxyradical. The peroxyradical being unstable breaks down as shown in the reaction of Scheme 3. The peak observed at 1017 cm-1 may be attributed to the formation of the ether linkage connecting two polymer chains. The percent elongation at the break exhibits a gradual decreasing tendency over the entire range of irradiation dosage irrespective of the presence or absence of sensitizer at any level. The gradual formation of the more and more stiff, hard crosslinks within the polymer matrix reduces the possibility of chain

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Figure 9. (a) DSC heating curve at 1 phr TMPTMA incorporation, (b) DSC cooling curve at 1 phr TMPTMA incorporation. Table 3. Onset Temperature of Degradation and Maximum Temperature from Thermogravimetric Analysis code

Tonset (°C)

Tmax (°C)

C000 C103 C106 C109 C112 C115

365 380 390 390 376 376

449 451 464 459 453 451

slippage and consequently the percent elongation at the break. At higher doses of irradiation when cross-link density is high, decoiling of the polymer chains are prevented even upon application of more load, resulting in a brittle fracture, which is depicted by the continuous fall in elongation over the entire range of radiation. This observation is supported by the continuous rise in gel content as shown in Figure 5. The moduli increase steadily with increasing proportion of the sensitizer and irradiation dose. The initial rise in modulus for both the sensitized and nonsensitized samples may be attributed to the formation of a network structure when the electron beam is incident over them. The stress-induced orientation of the molecular chains in the direction of the applied force results in

the rise in moduli values. Thus, it has been observed that the rise in gel content directly influences the changes in mechanical properties. However, C106 must be considered to be the optimized condition instead of C206 as the former reaches a higher tensile strength at a lower sensitizer level. Beyond this optimum level, chain scission predominates over cross-linking and influences the mechanical properties.14 The changes in tensile strength and gel content in nonsensitized samples reaches an optimum at around 90 kGy dosage of irradiation. The termination of the cross-linking reaction either by recombination of the end free radicals or by disproportionation of the molecules after chain scission by electron beam irradiation have been depicted in Scheme 4. The tear strength values (Figure 6) bear a direct proportionality to that of the elongation at the break. The steady decrease in tear strength with increasing irradiation dose is a measure of increasing brittleness with rise in cross-link density. The indentation hardness, a surface phenomenon, which reflects the resistance to local deformation is a complex property related to modulus, tensile strength, elasticity, and plasticity. The hardness increases marginally (Figure 7) in all levels of TMPTMA and over the entire range of radiation studied.


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Table 4. Glass Transition, Crystallization and Melting Temperature from DSC Thermograms code

Tg

Tc

Tm

C000 C103 C106 C109 C112 C115

-83 -77 -73 -72 -72 -70

64 57 54 53 54 55

80 82 83 83 84 85

Thermal Properties. The thermogravimetric plots of Elvaloy 1224 and its series with 1 phr TMPTMA at different doses of irradiation have been shown in Figure 8. It is quite interesting to note that the degradation temperature (i.e., the onset of degradation) of the samples under investigation rises consecutively as the dose of the electron beam increases as shown in Table 2. This also bears a direct proportionality with a rise in gel content. The rise in gel content is indicative of the rise in cross-link density. As the cross-link density of the samples increases with the increase in electron beam doses, the ability to withstand thermal degradation also increases due to the crosslinked network structure.15 The differential scanning calorimetric studies (Figure 9) based on constant 1 phr TMPTMA exhibit a gradual rise in glass transition temperature with rise in irradiation dose. The shift in Tg from -83 to -70 °C for C000 to C115 may account for the increased cross-linking, resulting in a more restricted movement of molecular chains. However, from the cooling curve, the observed crystallization temperature exhibits a gradual decrease with rising irradiation dose. The shift in Tc is found to be from 64 to 55 °C for C000 to C115 (Table 3). This may be attributed to the fact that higher cross-linked structures have lesser tendency to crystallize when cooled from the temperature higher than the crystalline melting point (Tm). It has also been observed that C000 exhibits a sharp crystalline melting point but the irradiated samples undergo a broad transition over the melting temperature range. As C000 is thermoplastic in nature, it shows a sharp and comparatively narrow crystalline melting point but, with the commencement of cross-linking, the peak broadens on account of the development of their insoluble and infusible characteristics. Electrical Properties. Volume resistivity, dielectric constant, and breakdown voltage of ethylene methyl acrylate were measured at constant TMPTMA with variation of electron beam dosage as explicit in Figures 10, 11, and 12, respectively. The volume resistivity of the various samples of ethylene methyl acrylate remains almost invariant with changes in irradiation doses or TMPTMA levels. With an increase in cross-link density, the polar copolymer inhibits the movement of the dipoles by increasing the viscosity of the system. The dielectric constant or permittivity gives us the ratio of capacitance of an electric capacitor filled with the polymeric

Figure 10. Variation of volume resistivity with electron beam dose.

Figure 11. Variation of dielectric constant with electron beam dose.

Figure 12. Variation of breakdown voltage with electron beam dose.

substance under study to that of the same capacitor in vacuum at a definite field frequency. The dielectric constant in this case reduces marginally with the increasing irradiation doses under study. The dielectric constant of a polymer arises from the various molecular phenomena that come into play when the polymer is subjected to an electric field. In the case of ethylene methyl acrylate copolymers, the orientation polarization contributes a major part of the total polarization. It arises due to the presence of dipoles associated with the chains, either due to chemical construction of the material or other effects such as oxidation or diffusion of polar molecules from the environment. The dipolar polarization of such molecules depends upon the segmental mobility. As there are several types of motion in the polymer molecules, including the main chain and the side groups, it is to be expected that the polymer molecules have relaxation temperatures depending on the motion of different parts of the molecule. The higher the viscosity of the medium (polymer matrix), the greater will be the hindrance to free dipolar orientation polarization from the neighboring molecules and the lower will be the dielectric constant. With the increase in irradiation dose in the present case, the increasing cross-link density raises the viscosity of the polymer matrix such that it reduces the possibility of dipolar orientation from the adjacent molecules. Moreover, the transition temperatures as depicted by the DSC curves display marginal differences, which are indicative of the restricted mobility of the chains, thus contributing little to cause variation in the dielectric constant.16 The breakdown of polymer dielectrics is closely related to the interfacial polymerization within the polymer matrix.17 In the present case, the presence of a single polymeric phase eliminates the possibility of space charge build-up across the

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microscopic interfaces thus giving almost invariant values of breakdown strength along with the rise in irradiation doses. Conclusions The effect of electron beam irradiation on ethylene methyl acrylate copolymer in the presence of different concentration levels of TMPTMA sensitizer has been investigated. It is observed that ethylene methyl acrylate copolymer with 1 phr TMPTMA at 60 kGy gives the maximum tensile strength having acceptable other mechanical properties like elongation, modulus, tear strength, and hardness. Four different schemes have been proposed to explain the structural modification behavior. TGA and DSC study of the modified polymer clearly indicate that the thermal properties have been effectively improved in all of the cases. But the electrical properties as observed from the volume resistivity, dielectric constant, and breakdown voltage study are not satisfactorily improved compared to the unmodified ethylene methyl acrylate copolymer. On the basis of the overall study, it may be finally concluded that ethylene methyl acrylate copolymer with 1 phr TMPTMA at 60 kGy irradiation dose is the optimum system within the range studied in the present investigation. Acknowledgment The authors acknowledge Nicco Corporation Ltd. for providing the electron beam facility and research support. The authors are thankful to M/s Du Pont Speciality Elastomers, Ciba Speciality Chemicals, and Sartomer Chemicals for providing the raw materials. Literature Cited (1) Dworjanyn, P. A.; Garnett, J. L.; Mulearap, A. K.; Maojin, X.; Meng, P. Q.; Nho, Y. C. Novel additives for accelerating radiation grafting and curing reactions. Radiat. Phys. Chem. 1993, 42, 31. (2) Datta, S. K.; Bhowmick, A. K.; Tripathy, D. K.; Chaki, T. K. Effect of electron beam radiation on structural changes of trimethylolpropane trimethacrylate, ethylene vinyl acetate and their blends. J. Appl. Polym. Sci. 1998, 60, 1329.

(3) Bafsar, A. A. Flame retardancy of radiation cross linked poly(vinyl chloride) used as an insulating material for wire and cable. Polym. Degrad. Stab. 2002, 77, 221. (4) Chaki, T. K.; Roy, S.; Despande, R. S.; Majali, A. B.; Tikku, V. K.; Bhowmick, A. K. Electron beam initiated grafing of triallyl cyanurate onto polyethylene: Structure and properties. J. Appl. Polym. Sci. 1994, 53, 141. (5) Bayram, G.; Yilmazer, U.; Xanthos, M. Viscoelastic properties of reactive and non-reactive blends of ethylene methyl acrylate copolymers with styrene maleic anhydride copolymer. Polym. Eng. Sci. 2001, 41, 262. (6) Kramer, R. H.; Blonqvist, P.; Hees, P. V.; Gedde, U. W. On the intumescence of ethylene-acrylate copolymers blended with chalk and silicone. Polym. Degrad. Stab. 2007, 92, 1899. (7) Fan, X. S. Mechanical properties of (ethylene acrylate copolymer)modified polypropylene-TiO2 blends. J. Vinyl AddtV. Technol. 2007, 13, 65. (8) Aoshima, M.; Jinoo, T.; Sassa, T. Electron beam cross linking of ethylene-propylene rubber. Kautschuk Gummi Kunststoffe. 1992, 45, 644. (9) Harnischfiger, P.; Kinzel, P. K.; Jungnickel, B. J. Die Angew. Makromol. Chem. 1990, 175, 157. (10) Kumar, R. N.; Mehnert, R. Electron beam curing of the system cycloaliphatic- epopxidized natural rubber-glycidyl methacrylate in presence of cationic initiators. Macromol. Mater. Eng. 2001, 286, 449. (11) Lappan, U.; Geibler, U.; Uhlmann, S. Pre-irradiation grafting of styrene into modified fluoroelastomers. Macromol. Symp. 2007, 254, 254. (12) Socrates, G. Infrared Characteristic Group Frequencies; John Wiley and Sons: New York, 1980. (13) Nethsinghe, L. P.; Gilbert, M. Structure-property relationship of irradiation cross linked flexible PVC. II Properties. Polymer. 1989, 30, 35. (14) Burger, W.; Lunkwitz, K.; Pompe, G.; Peter, A.; Jehnichen, D. Radiation degradation of fluoropolymers: Carboxylated fluoropolymers from radiation degradation in presence of air. J. Appl. Polym. Sci. 1992, 48, 1973. (15) Sengupta, R.; Sabharwal, S.; Bhowmick, A. K.; Chaki, T. K. Thermogravimetric studies on polyamide-6,6 modified by electron beam irradiation by nanofillers. Polym. Degrad. Stab. 2006, 91, 1311. (16) Mateev, M.; Karagcargier, S. The effect of electron beam irradiation and content of EVA upon the gel forming processes in LDPE-EVA films. Radiat. Phys. Chem. 1998, 51, 205. (17) Chattopadhyay, S.; Chaki, T. K.; Khastagir, D.; Bhowmick, A. K. Electrical properties of electron beam modified films of thermoplastic elastomeric LDPE and EVA blends. Polymer and Polymer Composites. 2000, 8, 345.

ReceiVed for reView December 11, 2009 ReVised manuscript receiVed April 19, 2010 Accepted June 6, 2010 IE901966S

Characterization of Electron Beam Irradiated Ethylene Methyl Acrylate

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