A crosslinking method of UHMWPE irradiated by electron beam using TMPTMA as radiosensitizer

Trimethylolpropane trimethylacrylate/Ultra high molecular weight polyethylene (TMPTMA/UHMWPE) composite and pure UHMWPE plates were made by compression molding and electron beam (EB) irradiation crosslinking methods. Fourier transform infrared spectroscopy (FTIR), Soxhlet extractor, electromechanical tester, and wear tester were used for the characterization of the structure, mechanical properties, and tribological performance of the crosslinked UHMWPE. FTIR analyses show that trans‐vinylene (965 cm^?1) absorption increases with the increasing dose and the trans‐vinylene intensity of TMPTMA/UHMWPE is higher than that of UHMWPE at the same dose, and Soxhlet experiments reveal that gel fraction increases with the increasing dose, both proving that crosslinking took place in all the irradiated samples. The results of the tensile tests indicate a significant decrease in elongation at break, but the stress of UHMWPE increases to 47 MPa at 10 kGy and then decreases with the increasing dose. The stress of TMPTMA/UHMWPE composites keeps at about 39 MPa before 50 kGy and then decreases with the increasing dose because of plasticization effect. The stress changes indicate that crosslinking and degradation occurred at the same time. Wear rate of 100 kGy 1% TMPTMA/UHMWPE is 1.76 × 10^?7mg/Nm, only 23.5% of wear rate of 0 kGy UHMWPE and 44.2% of wear rate of 100 kGy UHMWPE. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Facile preparation of a crosslinked hydrophilic UHMWPE membrane

Ultra high molecular weight polyethylene (UHMWPE) filters are widely used in water treatment. In the present work, a facile crosslinking technique is first applied to a UHMWPE flat membrane as a model to realize long-lasting hydrophilicity and improved water treatment efficiency. In the presence of a crosslinker, N, N′-methylene bisacrylamide (MBA), 2-hydroxyethyl methacrylate (HEMA), a hydrophilic modifier, is soaked into the surface of UHMWPE particles by blending. Then, a crosslinking reaction occurs during the initial sintering stage. Finally, sintering is completed at high temperature and pressure. The FTIR and SEM results show that HEMA is successfully crosslinked on the UHMWPE particle surface. Compared to a pristine membrane, the crosslinked UHMWPE flat membrane presents a lower water contact angle and is more rapidly penetrated by water. As a result, the crosslinked membrane can realize pressureless filtration. Another meaningful result is that the water flux recovery rate (FRR) is extremely high both for BSA and sludge filtration tests. Also a parameter K of 1 was obtained to represent the efficiency of the membrane treatment of water under pressureless conditions. These findings demonstrate that the crosslinking strategy is an effective method for realizing long-lasting hydrophilicity and is very promising for UHMWPE filters and other engineering applications.     

Ultrahigh molecular weight polyethylene with improved crosslink density,oxidation stability,and microbial inhibition by chemical crosslinking and tea polyphenols for total joint replacements

Highly crosslinked ultrahigh molecular weight polyethylene (UHMWPE) stabilized by vitamin E (VE) is widely applied in artificial joints as the bearings. Despite the approval, there is a discord that VE lowers the crosslinking efficiency, limiting its use at high concentration. In this work, we aim to obtain highly crosslinked and oxidation resistant UHMWPE through the conjunction of tea polyphenol and chemical crosslinking. We hypothesized that highly incorporated tea polyphenol with multiple reactive sites can ameliorate crosslinking efficiency of chemical crosslinked UHMWPE in comparison to VE. Epigallocatechin gallate (EGCG) as representative tea polyphenol was incorporated into UHMWPE at high concentration (2–8 wt%), followed by chemical crosslinking with 2 wt% organic peroxide. Unlike VE/UHMWPE blends as the control, chemical crosslinking achieved an increasing trend in crosslink density of EGCG/UHMWPE blends with increasing antioxidant concentration. High concentration of EGCG also enhanced the oxidation stability of UHMWPE. Intriguingly, EGCG endowed UHMWPE with an excellent antimicrobial property, which was inefficient in VE/UHMWPE. Cell viability was hardly affected by the high loaded antioxidant and peroxide. The chemically crosslinked UHMWPE blended with EGCG is proved to be a reasonable, cost effective and realistic alternative for use in artificial joints.     

Preparation and characterization of ultrahigh molecular weight polyethylene and polyisoprene solvent-cast blend films

This study covers the preparation of noncrosslinked and crosslinked solvent-cast blend films of ultrahigh molecular weight polyethylene (UHMWPE) and polyisoprene rubber (PIR) and their mechanical, thermal, IR spectroscopic, and morphological characterizations. Solvent-cast films of polymer blends with 0, 10, 20, 35, 50, and 65% PIR composition were prepared by vigorous stirring from a hot decalin solution. The films were crosslinked chemically by using acetophenone as a crosslinking agent under UV radiation. The mechanical properties, measured as ultimate properties and tensile modulus, were found to decrease with PIR content but crosslinking was found to enhance the ultimate strength and tensile modulus. DSC results revealed that melting point of UHMWPE remains almost constant in blends. However, upon crosslinking, the melting point of UHMWPE is depressed almost 5°C. We observed a similar trend in the enthalpy change of the melting of UHMWPE and the variation of percent crystallinity in UHMWPE. Scanning electron microscopy (SEM) studies on the fractured surfaces of the blends showed that the fibrillar texture is present in both crosslinked and noncrosslinked blends. The crosslinking appeared to be through oxygen linkages, which are preferentially conjugated to double bonds, in addition to the possible carbon–carbon crosslinks. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:1619–1630, 1998     

Radiation crosslinking of polyethylene with electron beam at different temperatures

The effect of temperature over the range ?196 to 150°C on the crosslinking of polyethylenes irradiated by electron beam has been investigated on the basis of gel content determination and Fourier transform infra-red (FTIR) spectroscopy. The crosslinking efficiency increases significantly with increasing irradiation does and at elevated irradiation temperature. The crosslinking rates of high density polyethylene (HDPE) and low density polyethylene (LDPE) samples above the melting point (T_M) are much higher than those below T_m. The FTIR data give positive evidence: (i) that trans-vinylene double bonds in cross linked HDPE and LDPE samples increase with increasing irradiation dose temperature (ii) that vinyl double bonds in HDPE decrease rapidly with increasing irradiation dose and temperature, and (iii) vinylidene groups in LDPE decrease slowly with increasing temperature at the lower dose and are almost independent of the irradiation temperature at above room temperature and the higher dose of more than 100 kGy. Gas bubbles are observed in LDPE samples irradiated at 100 and 150°C with high dose (200 to 250 kGy). The size of the bubbles increases gradually at high temperatures.     

Properties of a poly(L‐lactic acid)/poly(D‐lactic acid) stereocomplex and the stereocomplex crosslinked with triallyl isocyanurate by irradiation

A poly(L ‐lactic acid) (PLLA)/poly(D ‐lactic acid) (PDLA) stereocomplex was prepared from an equimolar mixture of commercial‐grade PLLA and PDLA by melt processing for the first time. Crosslinked samples were obtained by the radiation‐induced crosslinking of the poly(lactic acid) (PLA) stereocomplex mixed with triallyl isocyanurate (TAIC). The PLA stereocomplex and its crosslinked samples were characterized by their gel behavior, thermal and mechanical measurements, and enzymatic degradation. The crosslinking density of the crosslinked stereocomplex was described as the gel fraction, which increased with the TAIC content and radiation dose. The maximum crosslinking density was obtained in crosslinked samples of PLA/3% TAIC and PLA/5% TAIC irradiated at doses higher than 30 kGy. The stable crosslinking networks that formed in the irradiated PLA/TAIC substantially suppressed the segmental mobility for the crystallization of single crystals as well as stereocomplex crystals. The crosslinking network also significantly improved the mechanical properties and inhibited the enzymatic degradation of crosslinked PLA/3% TAIC. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

Synthesis,characterization and crosslinking of functional star‐shaped poly(ε‐caprolactone)

Star‐shaped low molecular weight poly(ε‐caprolactone)s (PCLs) were synthesized and functionalized with crosslinkable terminal groups for subsequent crosslinking. The ε‐caprolactone (CL) prepolymers were polymerized by ring‐opening in the presence of polyglycerine (PGL) as an initiator (1, 3 and 5 mol%) and Sn(II)2‐ethylhexanoate as a catalyst. Characterization of the prepolymer by ¹³C/¹H nuclear magnetic resonance (NMR) spectroscopy, size exclusion chromatography (SEC), differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FTIR) revealed a six‐armed star‐shaped structure for the prepolymer with the molecular weight controlled by the ratio of PGL and CL. Functionalization of the hydroxyl‐terminated prepolymer was carried out with maleic or itaconic anhydride. In both cases, the characterization of the functionalized prepolymer showed that the hydroxyl groups were completely substituted. The functionalized PCLs were successfully crosslinked through the reaction of double bonds. The crosslinking was induced either thermally with organic peroxide or photochemically with a photosensitive initiator. Characterization of the crosslinked PCLs by Soxhlet extraction, DSC and FTIR showed that the itaconic double bond was much more reactive in thermal crosslinking than the maleic double bond. Thus, the crosslinked prepolymers that were functionalized with itaconic double bonds achieved a gel content of about 90%. A gel content of 100% was achieved with several compositions where crosslinking agents were employed. © 2002 Society of Chemical Industry     

Quantification of silane grafting efficacy,weak IR vibration bands and percentage crystallinity in post e-beam irradiated UHMWPE

Vinyl-tri-methoxy silane (VTMS) and vinyl-tri-ethoxy silane (VTES) were grafted onto ultra-high molecular weight polyethylene (UHMWPE) by irradiating the UHMWPE/silane hybrids with e-beam. The samples were irradiated under high moisture contents for total dose values of 30, 65 and 100 kGy, respectively. The synergistic effect of silane and irradiation on the grafting efficacy, concentration of weak bonds like trans-vinylene (–CH=CH–) and vinyl (–CH=CH₂) and percentage values of crystallinity were studied using FTIR spectroscopy. For the estimation of grafting reactions efficiency, absorption due to characteristic infrared absorption bands of –Si–CH– in the region ~800 cm^?1 was monitored and found that grafting efficacy of VTMS on UHMWPE was higher as compared to VTES and increased with irradiation. The relative amounts of grafting extension (R) for 100 kGy irradiated UHMWPE/VTMS and UHMWPE/VTES hybrids were found to increase 20 and 15 %, respectively. The concentration of trans-vinylene in UHMWPE was found to increase from 0.015 to 0.035 mmol/l due to synergistic effects of silane and irradiation. Moreover, crystallinity of UHWMPE was found to decrease from 65 to 55 % due to the abovementioned synergistic effects which was also confirmed with DSC tests. Furthermore, oxidation index values were measured to confirm the efficacy of silane as free radical quencher via silane grafting extension reactions.     

The sol/gel contribution to the behavior of γ-irradiated poly(vinylidene fluoride)

Poly(vinylidene fluoride) films were γ-irradiated in the dose range of 1–20 Mrad, resulting in up to 74% gel. The irradiated polymer undergoes both crosslinking and chain scission, about 5 : 3 events, respectively. Swelling measurements indicate an increasing crosslink density with the gel content, already at the lower doses. Thermal analysis of the gel fraction and the unextracted irradiated samples shows that although crosslinking affects the crystallization, degree of crystallinity, and the melting characteristics, the behavior of the crosslinked material is predominantly controlled by the extractable sol fraction which consists of the more mobile original chains, branched chains, and degraded ones. The crosslinks, already at low density, retard the development of ordinary crystalline polymer morphology.     

Radiation crosslinking of bisphenol-a polycarbonate in the presence of bisphenol-a dimethacrylate and triallyl cyanurate

Summary Radiation crosslinking of bisphenol-A polycarbonate (PC) was carried out by the γ-irradiation of the polymeric films containing 5 and 2 wt % of bisphenol-A dimethacrylate (BPDMA) or triallyl cyanurate, respectively, as well as by the BPDMA grafting from acetone solution onto PC preirradiated in air. The modified samples were analyzed for the sol/gel content, and the dependences of gel fraction yield of crosslinked polymer on monomers concentration and absorbed dose were found. The radiation-chemical yields of crosslinking and degradation as well as gelation doses were determined for the modified PC. Molecular weights of the starting and irradiated pure PC were detemined by the GPC method, and radiation-chemical yield of PC degradation was calculated. It has been found essential difference in efficiency of PC crosslinking depending on monomers and doses used as well as on methods of modification. Effects of crosslinking agents distribution in the PC matrix and simultaneous processes of crosslinking and degradation in the polymer-monomer compositions on efficiency of PC crosslinking have been discussed. Received: 22 March 2000/Revised version: 26 June 2000/Accepted: 26 June 2000     

Synthesis of 1-hexene/1,7-octadiene copolymers using coordination polymerization and postfunctionalization with triethoxysilane

Homo- and copolymerization of 1-hexene (H) and 1,7-octadiene (O) were done using two different catalysts 1,4-bis(2,6-diisopropylphenyl)acenaphthenediiminedibromo nickel (II) and rac-ethylenebis(indenyl)zirconium dichloride [rac-Et(Ind)₂ZrCl₂]. The metallocene catalyst showed higher activity than the nickel α-diimine catalyst in homo- and copolymerization. The ¹H NMR studies confirmed the formation of copolymers containing 8–47% of 1,7-octadiene. In the copolymerization of hexene and diene, as the amount of incorporated diene in the copolymers increased, their T _g increased. TGA results showed that thermal stability of the polymer increases with the increase of 1-hexene incorporation in the polymer chain. Finally 1-hexene/1,7-octadiene copolymers were functionalized by triethoxysilane in the presence of hexachloroplatinic acid. The ¹H NMR spectrum of the functionalized samples showed that the double bonds in the copolymer structure were completely eliminated. The DSC analysis showed higher T _gs for the functionalized copolymer. © 2020 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48934.     

Crystallization behavior and mechanical properties of crosslinked plasticized poly(L‐lactic acid)

Enhancing the stability of plasticized poly(L ‐lactic acid) (PLLA) with poly (ethylene glycol) (PEG) is necessary for its practical application. In this study, plasticized PLLA (PLLA/PEG 80/20 wt/wt) was crosslinked under γ‐ray (Co⁶⁰) in the presence of triallyl isocyanurate (TAIC) as crosslinking agent. FTIR analysis revealed that PLLA, PEG, and TAIC formed a cocrosslinking structure. Crystallization behavior and mechanical properties of the crosslinked plasticized PLLA were investigated by differential scanning calorimetry (DSC), wide‐angle X‐ray diffraction (WAXD), scanning electron microscopy (SEM), and tensile tests. Experimental results indicated that the crystallization behaviors of both PEG and PLLA in the blends were restrained after irradiation. The melting peak of PEG in the crystallized samples disappeared at a low irradiation doses about 10 kGy. Although PLLA still owned the behavior of crystallize, its cold crystallization temperature and glass transition temperature shifted to higher temperature. Mechanical properties of the plasticized PLLA were strengthened through crosslinking. Both yield strength and elastic modulus of the samples increased after crosslinking. Elongation at break of the crosslinked plasticized PLLA decreased with the increase of crosslinking density but remained a high value over 200%. SEM images of fracture surfaces confirmed that the ductile fracture behavior of plasticized PLLA was kept after suitable crosslinking. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Structure-property relationships of an electron beam cured model urethane prepolymer

A semicrystalline urethane prepolymer derived from polycaprolactone was crosslinked below and above the melt to different levels using electron beam radiation. Studies at room temperature on the systems crosslinked under ambient conditions, which is below the melting temperature, show that changes in mechanical properties which occur as the electron beam dose is increased are due principally to the increase in crosslink density and to the changes in the crosslinking mechanism. Specifically, crosslinking takes place mainly at the acrylate double bonds or may also occur along the polymer backbone. All systems, however, are semicrystalline and possess a spherulitic texture. Mechanical and rheo-optical testing above the melt on these same systems indicate that at extensions up to 125% classical rubber elasticity theory and photoelasticity theory is obeyed. Isothermal crystallization kinetics measurements show that the rate of crystallization decreases as the electron beam dose is raised. When the systems are crosslinked above the melt again a spherulitic texture results. Mechanical testing above the melting temperature on the prepolymer crosslinked up to 4 Mrad shows that at elongations up to 125% classical rubber elasticity theory is obeyed. At room temperature these latter crosslinked systems exhibited a lower modulus compared to the materials crosslinked below the melt. Polarizing optical microscopy carried out above the melting temperature strongly suggested that no order was present in these systems during crosslinking in contrast to those crosslinked below the melting temperature.     

Strahlenvernetzung von Polyäthylen in Gegenwart von polymerisierbaren Monomeren

The crosslinking of polyethylene by electron beams in the presence of acrylic esters of multifunctional alcohols is investigated. The analytical procedures for the characterization of the obtained crosslinked polyethylene are described. The actual amount of crosslinking agent after sample preparation prior to irradiation is obviously smaller than the amount originally added. The consumption of double bonds during irradiation has been determined by IR-spectroscopy. On the other hand, the crosslinked polyethylene has been determined again by IR-spectroscopy. The values obtained by the two methods are in good agreement. They show that during the crosslinking reaction by irradiation only a part of the double bonds of the monomer reacts with polyethylene.     

Preparation of crosslinked chitosan by electron beam irradiation in the presence of CCl4

In this article, we report the synthesis of crosslinked chitosan using 8 MeV electron beam (EB) irradiation in the presence of carbon tetrachloride. The crosslinked chitosan is characterized by dissolution, Fourier transform infrared spectroscopy (FTIR), X‐ray diffraction (XRD), scanning electron microscopy (SEM), differential scanning colorimetry (DSC), and nanoindentation studies. The insolubility of irradiated films in acetic acid indicates that chitosan has undergone crosslinking reaction. FTIR analysis also confirms the crosslinked structure of chitosan. Mechanical properties such as elastic modulus and hardness are calculated from the nanoindentation data. Modulus and hardness of chitosan increase with increase in the irradiation dose due to the increase in the crosslinking. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

辐照交联超高分子量聚乙烯的生物摩擦学性能研究

采用γ-射线对医用超高分子量聚乙烯(UHMWPE)进行辐照交联处理,研究了辐照交联对医用UHMWPE力学性能和生物摩擦学性能的影响。结果表明:辐照交联使UHMWPE的结晶度、硬度、弹性性能、抗划痕能力和摩擦磨损性能提高,但降低了UHMWPE的塑性性能。     

Crosslinking of poly(vinyl acetate) nanolatices by gamma and UV radiation

Poly(vinyl acetate) PVAc, in nanolatices with 10% polymer content, prepared by microemulsion polymerization was crosslinked by gamma and UV radiation. PVAc colloidal nanoparticles (average diameter, Dp = 58 nm) had M_w = 562,000 g/mol and about 95% conversions. PVAc nanolatices irradiated by gamma rays (1–13 kGy) at room temperature without crosslinking agent and by UV light (30–300 s exposure times) in the presence of divinylbenzene and allyl methacrylate showed crosslinking of up to 96% (high gel content), Dp < 100 nm and did not degrade as shown by FTIR spectroscopy. DSC and TGA characterization of irradiated PVAc samples indicated that T_g temperatures increased from 28°C for PVAc to 42°C and 39°C for UV and gamma rays crosslinked PVAc, respectively, whereas 10% weight losses occurred at 261°C for uncrosslinked PVAc and at 320 and 313°C for UV and gamma rays crosslinked PVAc. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Effects of nuclear radiations on structure and molecular motions in some crystalline stereoregular polymers

Young's modulus and the mechanical damping factor have been determined between ?180 and +280°C. (at a frequency of several kilocycles), in samples of isotactic polypropylene, isotactic polystyrene, and trans-1,4-polybutadiene, subjected to pile irradiation (γ-rays and neutrons) at γ-doses from 90 to 4000 Mrad. In isotactic polypropylene no important structural changes are produced by the irradiation, except for a partial destruction of crystallinity. The samples receiving high radiation doses exhibit a low temperature loss region, which is attributed to the formation of a certain number of branches. Isotactic polystyrene shows very slight modifications of the dynamic mechanical properties at room temperature. At low temperature an increase of intensity of the δ relaxation phenomenon (probably due to oscillations of phenyl rings) with increasing radiation dose is observed. Important structural modifications produced by the radiation, destruction of crystallinity accompanied by crosslinking, which transform the material into a crosslinked rubber, are observed in trans-1,4-polybutadiene. Unlike conventional (sulfur) vulcanization, crosslinking by radiation does not cause a marked shift of the glass transition point. A secondary low-temperature relaxation effect, not existing in the unirradiated material, appears in the mechanical loss curves of the irradiated samples; it is attributed to the formation of ? CH₂? sequences in the main chains through saturation of C?C bonds. The mechanical spectrum of irradiated polybutadiene is very similar to those shown by crosslinked ethylene–butadiene copolymers.     

Electron beam curing of aliphatic unsaturated polyesters. I. Mechanistic study on converting to pressure‐sensitive adhesives

Aliphatic unsaturated polyesters (UPEs) mixed with N, N‐diethylaminoethyl methacrylate (DEAEMA) were convertible by electron beam irradiation to soft solids of high peeling strength. Double bond conversions, gel contents, molecular weight distributions, and crosslinking densities of the irradiated mixtures were studied in comparison with those of UPE–vinyl acetate mixtures, which gave very low peel strength on irradiation. The latter system started gel formation even at earlier stages of irradiation and had higher cross‐linking densities as a result of copolymerization between polyester and monomer double bonds. In contrast, the UPE–DEAEMA system exhibited slow gel formation with predominant conversion of monomer double bonds, indicating formation of graft copolymers. This system also had lower crosslinking densities than the other system. Therefore, it was concluded that the pressure‐sensitive adhesive nature of the electron‐beam‐cured UPE–DEAEMA mixtures could be attributed to the formation of flexible graft polymers entangled in a loosely crosslinked network. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1854–1857, 2003     

Radiation Crosslinking of Poly(ethylene‐co‐octene) with Electron Beam Radiation

Films of ethylene‐co‐octene copolymer are irradiated in air after moulding between Mylar® films with electron beam at different doses. To correlate the change in structure with properties, the irradiated and unirradiated samples are characterised by FTIR spectroscopy, swelling and mechanical measurements. Obtained changes are dependant on the radiation dose of the incident electron beam. Irradiation induces trans‐vinylene double bonds detected by FTIR spectroscopy in transmission mode. No hydroxyl (OH) and carbonyl (C?O) groups were recorded by FTIR spectroscopy. More drastic changes are observed with swelling method and by mechanical properties showing the crosslinking effect. Based on the results obtained by analytical techniques used in this study, free radicals mechanism involving mainly the pendant chains of the PE‐co‐O is proposed.

Strain at break versus gel fraction.