Charlesby Pinner Equation Research Articles

Electron beam processing of rubbers and their composites

Abstract Electron beam (EB) processing of pristine and filled polymeric materials is considered as one of the most viable techniques in the development of three-dimensional (3D) network structures of polymeric or composite systems with improved physical and chemical properties. The grafting, or the crosslinking process induced by the merging of the macro free radicals generated during the electron beam modification without the aid of any chemical agent or heat, is responsible for the formation of the 3D networks in polymeric systems. Owing to its distinct advantages such as fast, clean and precise, electron beam (EB) radiation technology takes up a vital role in the crosslinking of polymeric compounds. However, during the course of electron beam treatment of polymers, two processes viz., crosslinking and chain scission take place simultaneously, depending on the level of radiation dose used for the processing. The present paper reviews the role of irradiation dose in the presence and absence of radiation sensitizer on the crosslinking and structure formation in a wide variety of soft matrices such as elastomers, latexes, thermoplastic elastomers and their respective filled systems. Notable improvements in mechanical and dynamic mechanical properties, thermal stability, processing characteristics, etc., of the EB processed elastomers and their composites are discussed elaborately in the paper. Specially, the property improvements observed in the EB processed pristine and filled rubbers in comparison to the conventional crosslinking technology are critically reviewed. The level of radiation dose inducing crosslinking in both pristine and filled rubbers, determined by calculating crosslink to scission ratio on the basis of Charlesby–Pinner equation is also discussed in the paper. Finally, the application aspects of electron beam curing technology with special emphasis to cable and sealing industries as developed by one of the authors are highlighted in the paper.

Preparation and property evaluation of biodegradable elastomeric PTMC/PLCL networks used as ureteral stents

Ureteral stents have a wide range of applications in urology. In this study, we aimed to prepare poly(1,3-trimethylene carbonate)/poly(L-lactide-co-ε-caprolactone) (PTMC/PLCL) networks with pentaerythritol triacrylate (PETA) as a crosslinking agent by gamma irradiation under vacuum to resist creep, improve shape stability and prevent the migration of stent tube. 1H and 13C NMR spectra showed that PTMC and PLCL were successfully synthesized. FTIR indicated that the PTMC/PLCL networks were successfully prepared. Both the PLCL content and the irradiation dose had an effect on the degree of crosslinking. The gel fraction of the networks increased first and then decreased. The optimized conditions for cross-linking were 20% PLCL and at a standard sterilization dose of 25 kGy. The PTMC/PLCL(80/20) network had a gel fraction of 92.5%, a tensile strength of 32.7 MPa, and a tensile set value as low as 5%. Meanwhile, the cross-linking behavior followed the Chen-Liu-Tang equation rather than the Charlesby-Pinner equation. Porcine pancreatic lipase effectively accelerated the degradation of the network in vitro. Cytotoxicity analysis showed that the PTMC/PLCL network containing PETA had no adverse effects on the growth and proliferation of cells. Therefore, the inherent biocompatibility and biodegradability, good flexibility and elasticity, and neither migration nor early fracture allowed the PTMC/PLCL network to be used as a ureteral stent.

Thermochemical compatibilization of reclaimed tire rubber/ poly(ethylene-co-vinyl acetate) blend using electron beam irradiation and amine-based chemical

Waste tire rubber is commonly recycled by blending with other polymers. However, the mechanical properties of these blends were poor due to lack of adhesion between the matrix and the waste tire rubber. In this research, the use of electron beam irradiation and (3-Aminopropyl)triethoxy silane (APTES) on enhancing the performance of 50 wt% reclaimed tire rubber (RTR) blend with 50 wt% poly(ethylene-co-vinyl acetate) (EVA) was investigated. Preparation of RTR/EVA blends were carried out in the internal mixer. The blends were then exposed to electron beam (EB) irradiation at doses ranging from 50 to 200 kGy. APTES loading was varied between 1 to 10 wt%. The processing, morphological, mechanical, and calorimetric properties of the blends were investigated. The stabilization torque and total mixing energy was higher in compatibilized blends. Mechanical properties of RTR/EVA blends were improved due to efficiency of APTES in further reclaiming the RTR and compatibilizing the blends. APTES improved the dispersion of embedded smaller RTR particles in EVA matrix and crosslinking efficiency of the blends. Calorimetric studies showed increased crystallinity in compatibilized blends which corresponds to improved mechanical properties. However, the ductility of the blend was decreased due to increased interaction between EVA and APTES. Presence of APTES increased the efficiency of electron beam irradiation induced crosslinking which was shown through gel content analysis and Charlesby-Pinner equation.

Biodegradable cross-linked poly(L-lactide-co-ε-caprolactone) networks for ureteral stent formed by gamma irradiation under vacuum

The poly(L-lactide-co-ε-caprolactone) (PLCL) ureteral stent creeps and loses shape stability, increasing the risk of stent tube dislocation. The rubbery biodegradable cross-linked PLCL networks were prepared through gamma irradiation under vacuum in the presence of trimethylolpropane triacrylate (TMPTA), pentaerythritol tetraacrylate (PET4A), and pentaerythritol triacrylate (PETA). At a standard sterilization dose of 25 kGy, the gel content and network density of PLCL networks increased with increasing crosslinking agent content (1, 3, 5, 7 wt%), and crosslinking efficiency decreased in the order of PETA > PET4A > TMPTA. The average molecular weight (Mc¯) between two crosslinks ranged from 2000 to 105 g/mol. To perform the beneficial semi-interpenetrated polymer network and characterized by the principle, the networks were processed in several doses (25, 50, 75, 100, and 125 kGy). In place of the Charlesby-Pinner equation, the irradiation cross-linking followed the Chen-Liu-Tang equation. The PLCL network with 7 wt% PETA had a gel fraction of 83%, tensile strength of 34.7 MPa, and tensile set value as low as 5%. Furthermore, degradation in vitro was slowed down. Thus, PLCL networks with appropriate elasticity and flexibility, inherent biodegradability, and excellent biocompatibility can provide a promising alternative method for soft tissue repair engineering, such as ureteral stents.

Biodegradable cross‐linked poly(1,3‐trimethylene carbonate) networks formed by gamma irradiation under vacuum

AbstractRubbery biodegradable cross‐linked poly (1,3‐trimethylene carbonate) (PTMC) networks were prepared by gamma irradiation under vacuum in the presence of trimethylolpropane triacrylate (TMPTA), pentaerythritol triacrylate (PETA), and pentaerythritol tetraacrylate (PET4A). The effect of crosslinking agent, crosslinking agent content (1, 3, 5, 7 wt%), and irradiation dose (25, 50, 75, 100, 125 kGy) on PTMC networks were evaluated. The crosslinking efficiency of PETA was better than that of TMPTA and PET4A at a standard sterilization dose of 25 kGy. The PTMC network with gel fractions up to 92% ± 1% and tensile strength up to 26.0 ± 2.2 MPa could be obtained by adding 7 wt% PETA. The increase in irradiation dose reduced the gel content and network density, and led to a decrease in mechanical properties. The PTMC network extracted by ethanol showed better flexibility and mechanical properties. The irradiation crosslinking of PTMC with 7 wt% PETA followed the Chen–Liu–Tang equation instead of the Charlesby–Pinner equation. The incorporation of crosslinking agents improved the creep resistance and thermal stability, resulting in low permanent set values (5.5%). Furthermore, the enzymatic erosion rates of the networks decreased. Therefore, these PTMC networks can be utilized in a broad range of soft tissue engineering.

New Materials Based on Ethylene Propylene DieneTerpolymerand Hemp Fibers Obtained by Green Reactive Processing.

The paper presents the obtaining of new green polymeric composites using a sustainable reactive processing method, namely electron beam irradiation. EPDM rubber mixtures were reinforced with different amounts of short hemp fibers, which were then irradiated at doses between 75 and 600 kGy. The samples were analyzed by determination of physical–mechanical properties, sol–gel analysis, crosslink density (using the well-known modified Flory–Rehner equation for tetra functional networks), determination of rubber–fiber interactions (using the Kraus equation), water uptake test and FTIR analysis. The obtained results indicate an improvement of the hardness, the tensile and tear strength as the quantity of hemp fibers increases. As the irradiation dose increases, there is an increase in the degree of crosslinking and the gel fraction. Analyzing the behavior of the irradiation samples using the Charlesby–Pinner equation, it is observed that all the samples tend to crosslink by irradiation, the share of degradation reactions being low. For these reasons, the new materials can be used in the food, pharmaceutical or medical field, because the obtained products are sterile and can be easily resterilized by irradiation. They have high elasticity values and can be used to make packaging, seals and other consumer goods.

Formation of 3D networks in polylactic acid by adjusting the cross-linking agent content with respect to processing variables: a simple approach

High-performance biodegradable polymers have attracted considerable attention over the years because of their eco-friendly nature. The effects of processing variables on the efficiency of crosslinking, and the rheological and thermal properties of cross-linked polylactic acid (XPLA) have not been comprehensively addressed yet. In this work, XPLA was prepared through solution casting followed by curing in an oven. Enhancements in properties could be quantified in terms of structural changes in 3D structure of XPLA by varying the amount of dicumyl peroxide (DCP) as a cross--linking agent and curing temperature and time. The XPLAs were characterized by differential scanning calorimetry, thermo-gravimetric analysis, swelling, and rheological techniques. The swelling data revealed an increase in gel fraction by 1.32% per 1 °C temperature rise in the range of 125–195 °C. The results were also indicative of an increase in gel faction by 0.32% per minute in the time range of 5–100 min. Maximum variation in gel fraction occurred at 195 °C with high peroxide content. At this temperature, the variation rate of gel content was about 14.99%. With gel formation evolution, especially at 85% completion stage, the melting point was vanished. Rheological measurements showed that the Newtonian plateau disappeared for the cross-linked samples, simultaneously with the onset of shear thinning and zero-shear viscosity, through which the molecular weight obtained by the Mark–Houwink equation shifted to lower frequencies. A mathematical model based on the Charlesby–Pinner equation was developed for predicting the gel content of the XPLA as a function of curing time and peroxide concentration. The Flory–Huggins parameter also changed during the cross-linking process as a function of cross-linking density. This study is focused on adjusting cross-linking density and processing factors, like temperature and time, to achieve an XPLA with desirable properties.

Chitosan-containing hydrogel wound dressings prepared by radiation technique

The aim of the study was to develop an antimicrobial hydrogel wound dressing by means of radiation-initiated crosslinking of hydrophilic polymers, i.e. by well-established technology comprising gel manufacturing and its sterilization in one process. The approach included admixture of chitosan of relatively low molecular weight dissolved in lactic acid (LA) into the initial regular components of the conventional hydrogel dressing based on poly(N-vinyl pyrrolidone) (PVP) and agar. Molecular weight of chitosan was regulated by radiation-initiated degradation in the range of 39–132kgmol−1. Optimum total concentration of LA in the resultant hydrogel dressing was evaluated as 0.05moldm−3, that is ca. 0.5%. Presence of LA in the system influenced essential radiation and technological parameters of hydrogel manufacturing. The setting temperature of the pre-hydrogel mixture, resulting from agar ability to congeal, was reduced with LA concentration, yet remained significantly above the room temperature. 0.5% of chitosan was effectively dissolved in aqueous solution of lactic acid due to its pH (lower than 5.5). Radiation parameters of PVP crosslinking in the presence of LA, as determined with generalized Charlesby–Pinner equation, were reflected in slight reduction of the maximum gel fraction and increase in gelation dose and in the factor comparing yields of scission to crosslinking. Nevertheless, essentially physical characteristics of the hydrogel was not affected, except for somewhat increased water uptake capacity, what in turn improves functionality of the dressing as extensive exudate for the wound can be efficiently absorbed. Preliminary microbiological studies showed antimicrobial character of the chitosan-containing hydrogel towards Gram-positive bacterial strain.

High-temperature study of radiation cross-linked ethylene–octene copolymers

Three ethylene–octene copolymers (EOC) with a wide range of octene content (17, 30, and 38 wt%) and with the same melt flow index of 1 g/10 min were cross-linked by e-beam radiation (in range 30–120 kGy). The testing methods comprised of rheology, a high-temperature creep test, an analysis of the gel content, and a dynamic mechanical analysis (DMA) test. It was discovered that copolymers with a high octene content attain a higher level of cross-linking density. Cross-linking influenced properties below T m only marginally as seen from the DMA results. However, the properties above T m were highly influenced as detected by high-temperature creep and rheology. Above T m, without the presence of crystals, only the chemical bonds holding the amorphous chains together manifested a gradually decreasing creep at 150 °C with an increasing irradiation level. The loss factor (tanδ at 0.1 Hz) at 150 °C revealed a decreasing trend (or higher cross-linking level) with an increasing octene content. High-temperature results were supported by an increasing gel content with increasing octene content. Samples irradiated to 30 kGy dissolved completely in xylene but showed significantly changed rheological characteristics indicating only an increase in the molecular weight and branching. Analysis according to the Charlesby–Pinner equation revealed increased cross-linking to the scission ratio G(X)/G(S) for EOCs with a higher octene content. While the q 0 value which relates to cross-linking changed only slightly, a significant decrease in the p 0 value which relates to chain scission was discovered.

Influence of Branching Density in Ethylene-Octene Copolymers on Electron Beam Crosslinkability

Two ethylene-octene copolymers (EOC) with the same melt flow index (MFI = 3 g/10 min) but different octene contents, being 20 and 35 wt % (EOC-20 and EOC-35), were compared with regard to sensitivity to electron beam crosslinking. Dynamic mechanical analysis (DMA) revealed a large influence of the octene content on the storage modulus and the glass transition temperature (Tg) but a smaller influence of irradiation on the properties below melting point (Tm). Rheology at 150 °C pointed out large differences in samples crosslinked in the 0–60 kGy range and at lower frequencies (0.1–1 Hz). The loss factor tanδ confirmed that before irradiation the two copolymers were very similar, while after irradiation to 120 kGy, the EOC-35 had considerably lower tanδ than EOC-20, which corresponds to a better elasticity (or a higher level of crosslinking). A high-temperature creep test showed a considerably lower creep for EOC with a higher octene content. An analysis of the insoluble gel content exhibited higher values for EOC-35 confirming a higher level of crosslinking. Analysis according to the Charlesby-Pinner equation revealed increased crosslinking-to-scission ratio, G(X)/G(S), for EOC-35. While the G(X) value changed only slightly, a significant decrease in the G(S) value was discovered.

A comparison between the effects of gamma radiation and sulfur cure system on the microstructure and crosslink network of (styrene butadiene rubber/ethylene propylene diene monomer) blends in presence of nanoclay

Abstract Rubber blends based on (styrene–butadiene rubber (SBR)/ethylene–propylene-diene monomer (EPDM)) with and without organoclay (OC) were prepared through a melt mixing process. The concentration ratio of the rubber phases (EPDM/SBR; 50/50 wt%) and the amount of the OC were kept constant. The samples were then vulcanized by means of gamma radiation using a Co-60 gamma source as well as sulfur cure system. The effect of absorbed dose on the formation of the crosslinks was confirmed by the Fourier transform infrared spectroscopy (FTIR). The effects of absorbed dose, sulfur cure system and OC on the gel content, and crosslink density were evaluated by the chemical tests. Applying the Charlesby–Pinner equation to estimate the radiation chemical yield, revealed that the use of OC in the blend caused 20% reduction in the degradation/crosslinking ratio. Employing the swelling test data, some thermodynamic parameters were determined. Using field emission scanning electron microscopy (FE-SEM) to investigate microstructure of the samples revealed a more homogeneous structure and also an increase in compatibility of the blend components in the sample cured by the irradiation in comparison to that cured by the sulfur curing system.

The use of gamma irradiation in preparation of polybutadiene rubber nanopowder; Its effect on particle size, morphology and crosslink structure of the powder

The aim of this work was the preparation and characterization of polybutadiene rubber (BR) powder by irradiating of rubber lattices using 60Co radiation and spray-drying of them at the appropriate condition. The influences of absorbed dose on the volume swelling ratio, molecular weight between crosslinks, gel fraction, and glass transition temperature of obtained powder were studied. Morphology, size and size distribution of rubber particles were examined by using scanning electron microscopy (SEM) and laser particle size analyzer (LPSA) technique, respectively. Results obtained by LPSA revealed that radiation has no effect on particle size of rubber latex but after drying, adherence properties of rubber particle causes increase in particle size of rubber powder, as shown in SEM photograph. Fourier transform infrared spectroscopy of rubber powders confirmed that with increasing the irradiation dose, characteristic peak corresponds to the >CC< double bands decreased. Also Charlesby–Pinner equation was used to evaluate radiation yield.

Radiochemical ageing of butyl rubbers for space applications

The effect of 60Co gamma irradiation in inert atmosphere at 25 °C and 70 °C on a butyl elastomer filled with carbon blacks has been investigated by SEM, 13C NMR, swelling measurements and mechanical tests.An increase of the tensile strength of the material was observed during ageing. This increase of the mechanical properties is due to a modification of the rubber network structure. This hypothesis was confirmed by swelling measurements done before and after ageing at various irradiation doses associated with an estimation of the crosslink density by the Flory–Rehner equation. Crosslinking and chains scission reactions occurred under irradiation and the contribution of both processes was estimated thanks to the Charlesby–Pinner equation. The high level of carbon blacks in the butyl rubber formulation plays also an important role in the degradation process. Correlations between mechanical properties and crosslink density are also presented. The modification of the rubber mechanical properties underlines that the degradation mechanism is strongly influenced by the temperature especially at high irradiation doses. At 25 °C, the chain crosslinking process predominates over the chain scission reactions whereas the two phenomena are in competition at the ageing temperature of 70 °C.

Study of dielectric relaxation behavior of electron beam-cured conductive carbon black-filled ethylene acrylic elastomer

Composites based on ethylene acrylic elastomer (AEM) filled with a special type of conductive carbon black (CCB) have been prepared by two-roll mixing mill. The compression-molded sheet of the prepared composites have been subjected to electron beam (EB) radiation dose up to 400 kGy to induce radiation crosslinked composites. The crosslinked density has been calculated according to Flory–Rehner equation and is found to increase with increasing EB dose and CCB loading. Chain scission-to-crosslink density has been calculated by Charlesby–Pinner equation, which shows decreasing trend with increasing radiation dose. The dielectric relaxation behaviors of different doses of EB-treated AEM/CCB composites have been extensively studied as a function of frequency of applied electric field (101–106 Hz), CCB loading [0–30 phr (parts per hundred)], temperature (25–120 °C), and EB dose (50–400 kGy). It is observed that the dielectric permittivity (e′) increases with CCB loading and temperature, but decreases with increasing EB dose. This can be explained on the basis of interfacial polarization. Based on dielectric loss tangent (tan δ) values, it is observed that the dielectric relaxation time decreases with increases in the filler loading and temperature. However, it increases with increase in the radiation doses. Both the real and imaginary parts of the impedance (Z′ and Z″) have been found to decrease with increase in conductive filler loading. The AC conductivity (σac) increases with increase in the CCB concentration, test temperature, and radiation doses, which is attributed to the more pronounced hopping and tunneling mechanism. The percolation threshold (φcrit) occurred in the range of 16 phr CCB loading. The dispersions of CCB phase in AEM matrix below and above percolation have been captured by the transmission electron microscope photomicrographs.

Gamma radiation on poly(ϵ‐caprolactone) in the presence of vinyltrimethoxysilane

AbstractThe performance and radiation‐induced cross‐linking of polycaprolactone (PCL) in the presence of vinyltrimethoxysilane (VTMS) have been investigated. Radiation‐induced cross‐linking of PCL in the presence of VTMS followed the Charlesby–Pinner equation, and VTMS promoted the radiation‐induced cross‐linking of PCL. As the concentration of VTMS increased, the gelation dose and the ratio of degradation to cross‐linking (p0/q0) decreased and the efficiency of radiation‐induced cross‐linking increased. Differential scanning calorimetry analyses showed differences between the first and second scans. Glass‐transition temperature (Tg) and mechanical properties of the polymers increased. Radiation‐induced cross‐linking of PCL in the presence of VTMS was found to retard hydrolytic degradation greatly. POLYM. ENG. SCI., 2011. © 2010 Society of Plastics Engineers

Properties of isotactic polypropylene irradiated in various atmospheres

In this paper, changes in structure and physical properties of stabilized isotactic polypropylene (iPP) were created by gamma irradiation, up to a dose of 700 kGy, in different media: air, deionized distilled (DD) water and acetylene. Two main effects occur when polyolefins, such as iPP, are subjected to ionizing radiation: crosslinking and scission of macromolecules. The domination of one or the other of these competitive processes is determined by both the structural peculiarities of the polymers and the experimental irradiation conditions. Gel and infrared (IR) spectroscopy measurements were used to determine the changes in the degree of network formation and oxidative degradation, respectively. Sol-gel analysis was studied in detail using the Charlesby-Pinner (C-P) equation. The radiation-induced changes in the structure and evolution of oxygen-containing species were also studied through dielectric loss (tan ?) analysis in a wide temperature and/or frequency range. Evolution of low temperature dielectric relaxations with gamma irradiation was investigated. The results showed that degradation was the major reaction in the initial step of irradiation, no matter what the atmosphere was. The C-P equation seemed applicable when stabilized iPP was irradiated within a certain dose range in various atmospheres. The iPP irradiated in acetylene/air had the lowest/highest values for oxidation level, dielectric losses, Dg and G(s)/G(x) values. The calculated Dg values are 1.5 and 5 times larger for the irradiation in DD water and air than for the acetylene. Furthermore, our data confirm that oxidation strongly affects the gel point but has a much lower effect on the G(S)/G(X) ratio. In the case of dielectric relaxation measurements, the connection between the oxidative degradation and dielectric properties is well established and is in good agreement with IR spectroscopy measurements. The amount of carbonyl, hydroperoxide and other polar groups is much higher for the irradiation in air than in other media, leading to higher dielectric losses. Disappearance of low temperature (? and ?) relaxations with gamma radiation confirmed great sensitivity of iPP structure to radiation-induced changes. Complete ?vanishing? of the ? relaxation in iPP samples irradiated in air is connected with a large radiation-induced oxidative degradation in this medium. Similar crosslinking, oxidation and dielectric behaviour was observed for the samples irradiated in water and acetylene, indicating DD water as a good crosslinking medium.

Effects of sensitizer length on radiation crosslinked shape–memory polymers

Shape–memory polymers (SMPs) are smart materials that can be designed to retain a metastable state and upon activation, recover a preprogrammed shape. In this study, poly(methyl acrylate) (PMA) is blended with poly(ethylene glycol) diacrylate (PEGDA) of various molecular weights in various concentrations and subsequently exposed to ionizing radiation. PEGDA sensitizes the radiation crosslinking of PMA, lowering the minimum absorbed dose for gelation and increasing the rubbery modulus, after crosslinking. Minimum dose for gelation, as determined by the Charlesby–Pinner equation, decreases from 25.57 kGy for unblended PMA to 2.06 kGy for PMA blended with 10.00 mole% PEGDA. Moreover, increase in the blend concentration of PEGDA increases the crosslinking density of the resulting networks. Sensitizer length, namely M n of PEGDA, also affects crosslinking and final mechanical properties. Increase in the length of the PEGDA molecule at a constant molar ratio increases the efficacy of the molecule as a radiation sensitizer as determined by the increase in gel fraction and rubbery modulus across doses. However, at a constant weight ratio of PEGDA to PMA, shorter PEGDA chains sensitize more crosslinking because they have more reactive ends per weight fraction. Sensitized samples of PMA with PEGDA were tested for shape–memory properties and showed shape fixity of greater than 99%. Samples had a glass transition temperature near 28 °C and recovered between 97% and 99% of the induced strain when strained to 50%.

Effect of γ‐radiation on the thermal and mechanical properties of a commercial poly(butylene adipate‐co‐terephthalate)

AbstractBACKGROUND: Poly(butylene adipate‐co‐terephthalate) (PBAT) has attracted wide interest as a biodegradable polymer. However, its use is restricted in certain applications due to its low melting point.RESULTS: PBAT was treated using γ‐radiation. The radiation features were analyzed using Soxhlet extraction, and the ratio of chain scission and crosslinking and gelation dose were determined using the classical Charlesby–Pinner equation. The results showed that PBAT is a radiation‐crosslinkable polymer. The degree of crosslinking increased with increasing radiation dose; the relation between sol fraction and dose followed the Charlesby–Pinner equation. Differential scanning calorimetry analyses showed that the melting temperature (Tm) and the heat of fusion (ΔHm) of PBAT exhibited almost no change in the first scan. The second scan, however, showed a decrease in Tm and ΔHm. The glass transition temperature of irradiated PBAT increased with increasing radiation dose. The weight loss of control and irradiated PBAT resulting from thermal degradation was a one‐step process. Moreover, the tensile strength and elongation at break decreased with an increase in radiation dose. However, the Young's modulus and stress at yield were not greatly affected by γ‐radiation.CONCLUSION: PBAT can be crosslinked using γ‐radiation. The crosslinking efficiency is relatively low. The thermal and mechanical properties of PBAT are affected by γ‐radiation. Copyright © 2009 Society of Chemical Industry

Effect of type of peroxide on cross-linking of poly( l-lactide)

Poly( l-lactide) (PLLA) was cross-linked with various types of peroxides under constant mole ratios of peroxide-derived radicals to PLLA during reactive extrusion. Peroxides were classified into three groups according to their decomposition rates (Group I: fast, Group II: moderate and Group III: slow) and comparisons were performed within each group. Cross-linking behavior was readily understood in terms of free radical efficiency and hydrogen abstraction ability of radicals. In the case of Groups II and III, the weight-average molecular weight ( M w) of cross-linked PLLA increased with overall hydrogen abstraction ability, because slow decomposition caused uniform cross-linking in molten PLLA. In Group I, M w and gel fraction were higher than other groups despite Group I's lower hydrogen abstraction ability, leading to the conclusion that peroxide decomposition localized in solid PLLA caused partial cross-linking because of rapid decomposition. Furthermore, the efficiency of peroxide-induced cross-linking was investigated using the Charlesby–Pinner equation.

Radiation effects on styrene–butadiene–styrene copolymer

Styrene–butadiene–styrene copolymer (SBS) of different configuration and block ratio were irradiated by 60Co γ-rays at 20 °C and 120 °C. The gel fraction and thermal properties before and after irradiation were discussed. The gel fraction increased with both absorbed doses and temperature. This means higher crosslinking efficiency was obtained at higher temperature. The radiation chemical yields were calculated according to the Charlesby–Pinner equation. The DSC analysis indicated that the crosslinking had taken place in the polybutadiene (PB) block while the chain scission of polystyrene (PS) block was dominant when irradiated at elevated temperature.