Effect of high-energy radiation on the uniaxial tensile creep behaviour of ultra-high molecular weight linear polyethylene

The tensile creep (and other tensile) properties of ultra-high molecular weight polyethylene (UHMW PE) have been determined before and after electron beam irradiation and compared with similar results on normal molecular weight high-density polyethylene (NMW PE). In both polymers, irradiation increases the tensile modulus and the yield stress whilst reducing creep. The major effects occur over the first 20 MRad irradiation dose, though creep strain continues to diminish with dose in UHMW PE up to 64 MRad. Most of the effects can be attributed to crosslinking in the amorphous phase, though the rise in yield stress seems to require crosslinking in the crystalline phase, and the initial rise in modulus in UHMW PE seems to reflect a rise in crystallinity. Comparison with other polymers shows that the creep behaviour of UHMW PE remains relatively poor, even after irradiation. The improvements obtained may, however, be significant in applications where creep resistance is of secondary importance compared with, say, impact and wear resistance, in which UHMW PE excels.     

A novel,efficient route for the crosslinking and creep improvement of high modulus and high strength polyethylene fibres

A new route is presented for the chemical crosslinking of solution‐spun, ultra‐drawn Ultra‐High‐Molecular‐Weight Polyethylene (UHMW‐PE) fibres. UHMW‐PE fibres with a range of draw ratio's, Young's moduli and tensile strengths were impregnated with a radical initiator using supercritical carbon dioxide as a carrier. After impregnation, the drawn fibres were crosslinked with ultra‐violet light and fibres with a high gel content (> 90%) were obtained. It was found that the chemical crosslinking strongly reduces the plateau creep rate of the fibres and that the threshold stress for irreversible creep is enhanced. Simultaneously, the high Young's modulus and the high tensile strength of the drawn fibres are preserved which illustrates that the long term properties of the fibres (i. e. creep) are improved without a large sacrifice short term mechanical properties such as Young's modulus.     

Permeation of gases through modified polymer films. V. Permeation and diffusion of helium,nitrogen, methane,ethane, and propane through γ-ray crosslinked polyethylene

The permeation and diffusion of helium, nitrogen, methane, ethane, and propane through γ-irradiated polyethylene films were investigated. These studies were carried out with two objectives in mind: (1) to determine the effect of crosslinking by γ irradiation on permeability and diffusivity using the gas molecules as molecular probes; and (2) to study the plasticizing effects of the low hydrocarbons on the polyethylene film. The γ-ray-induced crosslinking efficiency of polyethylene was investigated in the following irradiation atmospheres: vacuum, acetylene, and nitrogen–acetylene mixtures. Results showed that irradiation in acetylene decreased the crosslinking efficiency while an acetylene–nitrogen atmosphere increased the efficiency compared to irradiation in vacuum. Both the permeation constants and the diffusion coefficients were found to decrease with increasing irradiation dose while the activation energies increased. The permeation constants of the organic gases through polyethylene increased with molecular diameter while the diffusion coefficients decreased. This increase in permeability was attributed to an increase in the solubility due to solubilization of the membrane by the penetrant. For example, the molecular diameter of propane is 4.397 Å compared with 2.807 Å for methane; however, propane permeated the polyethylene film at a rate twice that of methane. Nitrogen and methane have approximately the same molecular diameters—2.7085 and 2.807 Å, respectively—but owing to the plasticizing effect of methane, it permeated the film at a rate three times greater than that of nitrogen. It is interesting to note that the stronger the plasticizing ability of the penetrant, the greater the effect of the irradiation dose. The permeability of propane decreased by 40.7%, while the permeability of helium decreased by 6.4% after an irradiation dose of 50 Mrad.     

Improvement of the mechanical properties of an ultrahigh molecular weight polyethylene fiber/epoxy composite by corona‐discharge treatment

The interfacial shear strength of an ultrahigh molecular weight (UHMW) polyethylene (PE) fiber/epoxy‐resin system was greatly improved by the corona‐discharge treatment of the fiber. The UHMW PE‐fiber/epoxy‐resin composite was prepared with corona‐discharge‐treated UHMW PE fiber. The mechanical properties of the composite sheet were determined by tensile testing. The tensile strength of the composite was also very much improved. However, the tensile strength of the composite was about one‐half of the theoretical strength. This result was due to the molecular degradation of the PE‐fiber surface caused by surface modification. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1162–1168, 2001     

Mechanical properties of polyethylene mixtures crystallized under high pressure

The mechanical properties of a medium molecular weight polyethylene (MMW‐PE) and an ultrahigh molecular weight PE (UHMW‐PE) binary mixture with different weight fractions crystallized from the melt at 0.1 and 450 MPa were studied. The tensile modulus, yield stress, and strain were obtained as a function of the weight fractions in the PE mixtures at 25 and 85°C. The tensile modulus in the sample crystallized at 0.1 MPa decreased from 1.5 GPa of pure MMW‐PE to about 0.4 GPa of pure UHMW‐PE with the UHMW‐PE content but it did not decrease with the UHMW‐PE in the sample crystallized at 450 MPa in testing at 25°C. A decreasing rate of the storage modulus E′ of UHMW‐PE in a dynamic measurement for the sample crystallized at 0.1 MPa with the temperature is larger than that of the sample crystallized at 450 MPa. These experimental facts are interpreted in relation to the molecular motion and crystallinity of the sample. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1962–1968, 2003     

Effects of gamma irradiation,gas environments,and postirradiation aging on ultrahigh molecular weight polyethylene

The effects of low-dose (1 to 5 Mrad) gamma irradiation in different gas environments on thermal and tensile properties, and mass of melt-crystallized ultrahigh molecular weight polyethylene (UHMW-PE) have been investigated. The gamma irradiation was conducted under four different environments, air, nitrogen, acetylene, and vacuum. Thermal parameters were investigated using differential scanning calorimetry. The results showed that both irradiation dose and environments affected the thermal and tensile properties. Gamma irradiation significantly increased the melting temperature of UHMW-PE in all cases. However, the oxidation temperatures of irradiated polyethylene was lowered in all cases except those associated with acetylene environment. The crystallinity of the polymer was increased upon irradiation. Tensile yield strength and modulus of irradiated UHMW-PE increased for all cases except those treated at 1.25 and 2.5 Mrad, and in nitrogen environment that showed a decrease in the modulus. Gamma irradiation caused a weight gain of UHMW-PE in all conditions. To further the study, the postirradiation aging effect on the irradiated polymer was examined during a period of 1 year, and the results showed that the thermal and tensile properties of UHMW-PE were, indeed, affected. The data suggests that irradiation in acetylene affects mainly the crosslinking of the polymer. © 1995 John Wiley & Sons, Inc.     

超倍热拉伸PE–UHMW干法纤维的结构与性能

以黏均分子量为600万的超高分子量聚乙烯(PE–UHMW)树脂为原料,通过干法路线纺丝制备出了具有较高拉伸性能的PE–UHMW纤维。测试研究了纤维在热拉伸过程中的力学性能变化,发现纤维在拉伸40倍时断裂强力出现最大值。利用动态扫描量热、X射线衍射、扫描电子显微镜表征了PE–UHMW纤维在拉伸过程中结构变化,分析了结构变化对力学性能的影响,发现过高的拉伸倍数反而会破坏纤维的结晶结构从而导致断裂强力的下降。最后对热拉伸中纤维微观结构变化机理进行了推导。     

干法工艺制备PE–UHMW纤维

采用干法纺丝工艺,以超高分子量聚乙烯(PE–UHMW)纤维专用树脂为原料,制备高性能PE–UHMW纤维,通过电子拉力机、扫描电子显微镜、差示扫描量热仪对不同后拉伸倍率的纤维进行力学性能和微观结构分析。结果表明,随着拉伸倍率的增加,纤维初生丝结晶度由49.57%逐渐提高至72.17%,拉伸倍率50倍以后,结晶度逐渐趋于平稳;随着拉伸倍率的增加,纤维的力学性能逐渐增强,在拉伸倍率达到83.3倍时,纤维的力学性能达到最佳,纤维断裂强度为31.53 c N/dtex,断裂伸长率为2.69%,断裂模量为1 054.78 c N/dtex;纤维微观表面结构也发生有规律的变化。     

Accelerated electron effects on EVA based compound

The major effects induced by accelerated electron irradiation on EVA based polymeric compound were evaluated for various doses up to 240 kGy. Some main characteristics (gel fraction, density, elongation at break, and tensile strength) were investigated. Oxygen uptake and thermal analysis methods (TG, DTG, and DTA) were applied for determination of oxidation resistance of radiation processed EVA samples. It was established that a 30 kGy exposure dose promotes maximum crosslinking. At this dose the density and tensile strength reach maximum values, which are maintained for higher doses up to 240 kGy. On the other hand, the thermooxidative stability exhibits a sharp decrease as the absorbed dose rises from 0 to 30 kGy and has a constant value for the absorbed dose range 30–240 kGy. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 613–617, 2005     

熔纺PE⁃UHMW/PE⁃HD共混纤维的力学性能和晶体结构研究

通过熔融纺丝工艺制备了拉伸强度为1.13 GPa的超高分子量聚乙烯（PE?UHMW）/高密度聚乙烯（PE?HD）共混纤维。采用差示扫描量热仪（DSC）、扫描电子显微镜（SEM）、X射线衍射仪（XRD）、声速取向测试、纤维强度测试等方法研究了初生丝和纤维的晶体结构及力学性能。结果表明,将PE?UHMW与低熔体流动速率（MFR）的PE?HD共混后,提高了共混纤维的分子链取向度、结晶度及力学性能;由高度取向的分子链形成的晶粒可以在轴向上被有效拉伸,形成更规则和致密的晶体结构,从而提高了纤维的力学性能。     

Effects of gamma irradiation,irradiation environment,and postirradiation aging on thermal and tensile properties of ultrahigh molecular weight polyethylene fibers

The effects of gamma irradiation in four types of irradiation environment on the thermal and tensile properties of gel-spun, ultrahigh molecular weight polyethylene fibers (Spectra™ 1000) have been investigated. The gamma irradiation was conducted at 2.5 Mrad and in air, nitrogen, acetylene, and vacuum to study the effects of irradiation media on the aforementioned properties. Thermal and tensile properties of virgin and irradiated fiber samples were examined using differential scanning calorimetry and an Instron tensile tester, respectively. The results indicate that both gamma irradiation and irradiation environment affected the properties of the polyethylene fibers, and substantial changes were observed for the oxygen-containing environment. The tensile-fractured surfaces of the fibers were examined by scanning electron microscopy. The properties of irradiated fibers were further evaluated at 160 days postirradiation and found to be affected, substantially. The postirradiation aging significantly decreased the tensile strength and elongation of the irradiated fibers, indicating that polyethylene fibers should not be exposed to gamma irradiation. © 1996 John Wiley & Sons, Inc.     

Molecular structure and physical properties of E‐beam crosslinked low‐density polyethylene for wire and cable insulation applications

Crosslinking of homemade low‐density polyethylene (LDPE) was performed by electron‐beam (EB) irradiation. The gel content of the EB‐exposed LDPE was determined by the solvent‐extraction method. The degree of crosslinking was also evaluated by a hot set measuring test. The results obtained from both the gel–sol and the hot set methods showed that the degree of crosslinking was dependent on the deposited energy in LDPE samples. Increasing the absorbed dose increased the degree of network formation. The LDPE with higher molecular weight yielded higher efficiency of crosslinking at the same irradiation dose. The effect of irradiation dose on the molecular weight between crosslinks (M_c), glass‐transition temperature, and free volume were calculated. Mechanical test results showed that the tensile strength of the samples increased with increase in the irradiation dose up to 150 kGy and then slightly decreased with further increasing the deposited energy. The elongation at break decreased with increasing the absorbed dose. The results obtained from differential scanning calorimetry exhibited a small reduction in the melting point and the degree of crystallinity of the EB‐exposed LDPE samples compared to those of the untreated samples. The effect of crosslinking on the electrical properties of the irradiated samples was insignificant. The dielectric constant of the treated samples remained nearly constant within the irradiation dose range, although the dissipation factor increased slightly with increasing the absorbed dose. The results obtained from characterizing the EB‐induced crosslinking of homemade polyethylene, including LH0030 and LH0075, showed the higher molecular weight polyethylene (LH0030) as a preferred option for wire and cable insulation. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1959–1969, 2002     

Structure and properties of closed‐cell foam prepared from irradiation crosslinked silicone rubber

Silicone rubber foam was prepared through crosslinking with electron beam irradiation and foaming by the decomposing of blowing agent azobisformamide (AC) in hot air. The crosslinking and foaming of silicone rubber was carried out separately, which was different from the conventional method of chemical crosslinking and foaming. After foaming, the silicone rubber foam was irradiated again to stabilize the foam structure and further improve its mechanical properties. The effects of irradiation dose before and after foaming, and the amount of blowing agents on the structure and properties of silicone rubber foam were studied. The experimental results show that with the increase of AC content, the average cell diameter of silicone rubber foam increases a little, the foam density decreases to a minimum value when AC content is 10 phr. With the increase of irradiation dose before foaming from 10 to 17.5 kGy, the cell nucleation density of silicone rubber foam increases, the average cell diameter decreases, and the foam density increases. With the increase of irradiation before foaming, the tensile strength, tensile modulus, and the elongation at break of the silicone rubber foam increase. Through irradiation crosslinking again after foaming, the foam density is decreased and the mechanical properties of silicone foam are further improved. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

PE⁃UHMW/海泡石纤维复合材料的力学性能与摩擦学性能研究

采用硅烷偶联剂KH550对海泡石纤维（Sep）进行了改性,采用平板硫化机通过热压成型法制备了超高分子量聚乙烯（PE?UHMW）/Sep和PE?UHMW/改性海泡石纤维（O?Sep）复合材料,并通过红外光谱仪（FTIR）、电子万能试验机、扫描电子显微镜（SEM）等对Sep 及O?Sep的表面结构和复合材料的力学性能、摩擦学性能及磨痕形貌进行了表征和测试。结果表明,O?Sep表面存在KH550分子,其在复合材料中分布比Sep更为均匀;当O?Sep含量达到6 %（质量分数,下同）时,复合材料力学性能和摩擦学性能表现最佳,其拉伸强度、弯曲强度、弯曲模量和冲击强度分别为32.1 MPa,171.2 MPa、138.3 GPa和17.62 kJ/mm²,比纯PE?UHMW分别提高了41.4 %、40.0 %、95.6 %和36.9 %;其摩擦因数和磨损量分别为0.124和 0.1 mg,比纯PE?UHMW分别提高了77.1 %和80 %。     

Application of radiation curing in the preparation of polycarbosilane-derived SiC fibers

Polycarbosilane fibers were irradiated by gamma-rays under vacuum and by electron beam in He gas flow or under vacuum at room temperature. Free radicals on Si and C atoms were produced. Most radicals reacted with each other, causing cross-links between polycarbosilane molecules. Some radicals, which did not contribute to cross-linking, were fairly stable under vacuum or in inert gas at room temperature but oxidized on exposure to air. The number of stable radicals under vacuum could be decreased by annealing. The remaining radical concentration was about 1% after annealing at 513 K. By a combination of radiation curing and annealing, SiC fibers with smaller quantities of oxygen were prepared. The mechanical properties of the SiC fibers showed a high tensile strength of 2.5 GPa after heat treatment at 1773 K. On the other hand, polycarbosilane fibers could be cured by radiation oxidation at room temperature, that is, gamma-ray or electron irradiation in oxygen, and the oxygen content could be well controlled by irradiation dose and dose rate. The SiC fibers obtained by the radiation oxidation had an oxygen gradient from the surface to the center which was dependent on the radiation oxidation conditions.     

Gamma radiation effect of polymethylvinylphenylsiloxane rubbers under different temperatures

The gamma radiation effect on polymethylvinylphenylsiloxane (PMVPS) rubbers is investigated by irradiation exposure of PMVPS rubbers to a maximum dose of 200 kGy in the temperature range 28–110 °C. Compared with unirradiated PMVPS rubber, the elongation at break of irradiated PMVPS rubber decreases while its elastic modulus increases with the increase of absorbed dose or radiation temperature. DSC, ATR‐FTIR, XPS, and ¹H‐NMR indicate that slight degradation and oxidation reaction occur during the irradiation of PMVPS. Solvent swelling and gel fraction study confirms that the crosslinking density of PMVPS rubbers increases gradually with increasing absorbed dose or radiation temperature. Therefore, radiation‐induced crosslinking of PMVPS is dominant reactions for the chosen dose or temperature range. Furthermore, synergistic effect exists in the high‐temperature radiation process for PMVPS rubbers. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45404.     

Polymer electrolyte membranes prepared by EB‐crosslinking of sulfonated poly(ether ether ketone) with 1,4‐butanediol

Crosslinked sulfonated poly(ether ether ketone) (SPEEK) membranes were prepared through the electron beam (EB)‐irradiation crosslinking of SPEEK/1,4‐butanediol under various irradiation conditions and used as a proton exchange membrane (PEM) for fuel cell applications. The crosslinked membranes were characterized by gel fraction, a universal testing machine (UTM), dynamic mechanical analysis (DMA), and small‐angle X‐ray scattering (SAXS). The gel fraction of the crosslinked membranes was used to estimate the degree of crosslinking, and the gel fraction was found to be increased with an increase of the crosslinker content and EB‐absorbed dose. The UTM results indicate that a brittle EB‐crosslinked membrane becomes more flexible with an increase in the crosslinker content. The DMA results show that the EB‐crosslinked membranes have well‐developed ionic aggregation regions and the cluster T_g of membranes decrease with an increase in the 1,4‐butanediol crosslinker content. The SAXS results show that the Bragg and persistence distance of crosslinked membranes increase with an increase in the crosslinker content. The proton conductivities of the EB‐crosslinked membranes were more than 9 × 10^?2 S/cm. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41760.     

Electron beam irradiation of ethylene‐propylene terpolymer: Evaluation of trimethylol propane trimethacrylate as a crosslink promoter

The effect of electron beam irradiation on ethylene‐propylene terpolymer (EPDM) was investigated. A 50‐part oil‐extended EPDM with high termonomer (ENB) content (iodine number of base polymer) 19, was selected for this study. An increase in irradiation dose from 0 to 200 kGy resulted in increased crosslinking, measured by an increase in gel contents and better swelling resistance. The effect of the multifunctional monomer trimethylol propane trimethacrylate (TMPTMA) as a crosslink promoter was studied using IR spectroscopy. The IR studies revealed enhanced peak absorbances at 1725, 1257, and 1023 cm^?1 as a result of the increased concentration of C = O and C‐O‐C groups and reduced absorbance at 1630 cm^?1 due decreased concentration of C = C groups with TMPTMA level in the irradiated samples. The presence of TMPTMA increased the level of crosslinking at a given irradiation dose, which was manifested by improvement in tensile properties. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 968–975, 2005     

Controlled degradation and crosslinking of polypropylene induced by gamma radiation and acetylene

Isotactic polypropylene (iPP) undergoes crosslinking and extensive main chain scissions when submitted to irradiation. The simultaneous irradiation of PP and acetylene is able to control chain scission and produce grafting. The grafted PP further reacts with PP radicals resulting in branching and crosslinking. In this work, commercial polypropylenes (iPP) of different molecular weights were irradiated with a ⁶⁰Co source at dose of 12.5 kGy in the presence of acetylene in order to promote the crosslinking. The mechanical and rheological tests showed a significant increase in melt strength and drawability of the modified samples obtained from resins with high melt flow index. The characterization of the molecular modifications induced by gamma irradiation of isotactic polypropylenes under acetylene atmosphere proved the existence of branching, crosslinking and chain scission in a qualitative way. The G′ and G″ indicated the presence of LCB in all samples. Therefore, PP irradiation under acetylene was proved to be an effective approach to achieve high melt strength polypropylene (HMSPP).     

Free radical activity in gamma‐irradiated polyethylene film,drawn tape and ultra‐high‐modulus fibres determined by grafting performance

Grafting rates of gaseous butadiene to a range of morphological forms of gamma‐irradiated polyethylene, including ultra‐high‐modulus fibres (UHMPE), have been measured in order to determine the availability of active free radicals over time at various temperatures. Blank experiments on unirradiated samples showed that monomer diffusion is not rate‐controlling with film and natural draw ratio tapes, but is likely to be a major factor in the control of grafting rates in UHMPE fibres. Grafting rates from monomer loss/time experiments with irradiated samples indicate that grafting is always in competition with free radical self‐annihilation, the extent being influenced by temperature, dose and morphology, including prior sample annealing. At lower temperatures, graft‐active radicals are produced over long periods of time, eg close to linear grafting rates were monitored over 20 hours for PE tape at 0 °C (50 kGy) and for gel‐spun UHMPE at 40 °C (100 kGy). At higher temperatures, grafting rates steadily decrease with time. Grafting rates are almost independent of irradiation dose in the early stages, however, the dose has an increasing positive influence as the reaction proceeds. At any given temperature and irradiation dose, the rates decrease in the series undrawn film; natural draw ratio tape; high draw ratio gel‐spun fibre; high draw ratio melt‐spun fibre. An analogy is drawn between these results and the optimum conditions required for improving the creep properties of PE tape and UHMPE fibres by acetylene‐sensitized irradiation crosslinking. Copyright © 2005 Society of Chemical Industry