γ-ray-induced degradation in ethylene–propylene copolymer

The stabilization of polypropylene-disposable medical syringes against the γ-ray-induced degradation has been the subject of active research during the last decade due to the large-scale use of γ-irradiation for sterilization purposes. Ethylene–propylene (EP) copolymers have been suggested as suitable alternatives to polypropylene for these purposes. In this article, we investigated the effect of irradiation dose and postirradiation time on the melt index and mechanical properties of an EP copolymer. We also determined the chemical changes occurring during irradiation and storage using IR spectroscopy and have made an attempt to co-relate the changes in chemical structure to the changes in mechanical properties and melt index measurements. © 1996 John Wiley & Sons, Inc.     

Gamma-sterilization effects and influence of the molecular weight distribution on the postirradiation resistance of polypropylene for medical devices

In the present study, the dose-rate effects of γ-irradiation in air on two isotactic polypropylene grades of different molecular weight distribution, used for medical devices, were investigated. The thermal, mechanical, rheological, and photometric properties of these materials were examined using DSC, stress–strain measurements, MFI, and a yellow index. At low dose rates (0.12 Mrad/h), the oxygen diffusion parameter prevailed. At high dose rates (2.84 Mrad/h), the thermal degradation became dominant. However, at high dose rates, an increase in sample temperature was monitored. This temperature rise is thought to increase the oxygen diffusion rate, peroxide decomposition, and radical migration. As a result, intermediate dose rates (in the region of 0.72 Mrad/h) gave the lowest changes in physical properties in both samples. Furthermore, it was found that the polypropylene grade of broader molecular weight distribution and lower M_n had a higher γ-irradiation and postirradiation resistance. © 1994 John Wiley & Sons, Inc.     

Comparison of the effect of ethylene oxide and γ-irradiation on selected tyrosine-derived polycarbonates and poly(L-lactic acid)

Tyrosine-derived polycarbonates are a new class of degradable polymers that have possible biomedical applications. In this study, the effect of the two most common sterilization techniques, ethylene oxide and γ-irradiation (0.3, 1.1, 3.9, 6.4, 10.6 Mrad), was evaluated for a family of four structurally related tyrosine-derived polycarbonates and for poly(L-lactic acid) (PLLA). The four polycarbonates were poly(DTE carbonate), poly(DTB carbonate), poly(DTH carbonate), and poly(DTO carbonate) and differed only in the length of the pendent chain. Ethylene oxide exposure had little effect on molecular weight, surface composition, mechanical properties, or degradation rate of all test polymers except for poly(DTO carbonate). Poly(DTO carbonate) was unique since following ethylene oxide exposure it degraded faster than did the nonsterilized control. γ-Irradiated tyrosine-derived polycarbonates retained over 81% of their initial molecular weight when exposed to a clinically relevant dose of 3.9 Mrad and retained still 58% of the initial molecular weight when exposed to the highest test dose of 10.6 Mrad. No changes in surface composition and only slight changes in yield strength and the Young's modulus were detected for any of the tyrosine-derived polycarbonates following γ-irradiation. In vitro, irradiated films of poly(DTE carbonate), poly(DTB carbonate), and poly(DTH carbonate) degraded at approximately the same rate as did the nonsterilized films regardless of irradiation dose. Only poly(DTO carbonate), irradiated at high doses, degraded faster than did the control. Medical-grade PLLA was tested under identical conditions. Ethylene oxide exposure of PLLA did not affect the molecular weight, surface composition, mechanical properties, or in vitro degradation rate. However, upon irradiation at 10.6 Mrad, PLLA retained only 29% of its initial molecular weight; a dose of 3.9 Mrad resulted in retention of 49% of the initial molecular weight. In correspondence with earlier publications, irradiation of PLLA induced significant losses in the Young's modulus, % strain at break, and changes in the postirradiation rate of degradation in some specimens. Compared to PLLA, tyrosine-derived polycarbonates are significantly more stable to γ-irradiation and can be sterilized by conventional γ-sterilization techniques. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 1499–1510, 1997     

Specific characteristics of infrared spectra of irradiated γ-polypropylene

Nonvolatile products have been identified that arise through γ-irradiation in isotactic polypropylene by Fourier transform infrared (FTIR) analysis. The γ-irradiation was performed in the air with doses varying between 20 and 1200 kGy, for a dose rate of 800 Gy/h. The contour lines of FTIR absorption bands of carbonyl groups at different region of the cross section of an irradiated sample have been determined. The carbonyl groups arise from the concentration of esters or ketones, carboxylic acids, and γ-lactones, but their structure is different for different doses. We have also investigated the degradation of irradiated polypropylene by using FTIR mappings. Dust particles of irradiated brittle polypropylene have also been studied. The gel fraction has been determined for different doses of irradiation, and the relation between the moment of the appearance of the gel and disappearance of the carbonyl groups has been made evident. © 1996 John Wiley & Sons, Inc.     

Effects of the γ-irradiation strength and basalt additive content on the mechanical performance and dielectric response of polypropylene films

In this study, we investigated the effects of high-dose γ-ray irradiation on the mechanical and dielectric properties of polypropylene (PP)–basalt thick films. PP–basalt thick-film composites with various basalt contents from 0.5 to 10.0% were prepared by a hot-press method. The samples were exposed to γ radiation at different doses in the range 3–25 kGy. The mechanical properties of the samples, such as the Young's modulus, tensile strength, percentage strain at break, and energy at break, were examined in the context of the γ-irradiation process. Although the maximum elasticity was obtained for the unirradiated 0.5% basalt-added composite, the 6 kGy γ-irradiated PP–1.0% basalt sample exhibited the highest elasticity properties among all of the composites. The best mechanical properties, including the ultimate tensile strength and energy at break values, were achieved for the 12 kGy γ-irradiated neat PP. The dielectric properties of the PP–basalt composites were also investigated in the 100 Hz to 15 MHz frequency region at room temperature. According to the analysis of the dielectric properties, the 3 kGy γ-irradiated neat PP may have potential for microelectronic device applications that require low dielectric constant and dielectric loss materials. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47414.     

Study of the effect of γ-dose rate on the oxidation of polypropylene

Polypropylene PP (high and low crystallinity) was λ-oxidized, in the presence of air, using different dose rates (from 2 to 100 rad/s). Oxidation outcomes were identified and quantified by FTIR spectroscopy coupled with derivatization reactions (NO and SF₄). The difficulty to separate secondary and tertiary hydroperoxides from FTIR measurements after NO treatment was addressed. Polymer physical degradation was also monitored during the λ-irradiation process. GPC was used to follow molecular weight changes and tensile tests for elongation at break modifications. Comparison of the extent of oxidation product for-mation over λ-irradiation allowed us to investigate the importance of λ-dose rate on chemical and physical changes of PP. From this, different mechanisms of ketone and ester formation were examined; relationship between the molecular weight changes and the elongation at break modifications was also investigated. © 1996 John Wiley & Sons, Inc.     

Structure and mechanical properties of isotactic polypropylene and iPP/talc blends functionalized by electron beam irradiation

The structure and mechanical properties of isotactic polypropylene (iPP) functionalized by electron beam irradiation are investigated by differential scanning calorimetry, wide‐angle X‐ray diffraction, thermogravimetry, thermomechanical analysis, melt index and mechanical measurements. The experimental results show that the degree of crystallinity, the thermal degradation temperature and the dimensional stability increase with dose in the range 0–5 kGy. At 5 kGy, the initial and final degradation temperatures of the irradiated iPP are raised by 66 °C and 124 °C, respectively. The melt index increases with increasing dose. The mechanical measurements show that the stiffness of iPP is greatly enhanced by electron beam irradiation. A small dose of irradiation (0.75 kGy) can increase the Young's modulus to 1284 MPa compared with 1112 MPa for unirradiated iPP. Adding 10 % by weight of irradiated iPP powder into iPP/talc (70/20 % by weight) blends, changes the processing parameters significantly and makes the Young's modulus rise substantially. At a dose of 40 kGy the Young's modulus of iPP/talc blend jumps to 3611 MPa against the original 2201 MPa. © 2000 Society of Chemical Industry     

Hydrolytic degradation of melt-extruded fibers from poly(β-propiolactone)

β-Propiolactone was polymerized in bulk at 5°C using pyridine as initiator. The melt spun fibers were drawn at 50°C and subjected to degradation, which was monitored by mechanical, thermal, and molecular weight measurements. The hydrolytic degradation of poly(β-propiolactone) fibers has been investigated in a buffered salt solution (pH 7.2) maintained at 37°C. The degradation was found to be very rapid during the first 90 days of immersion, with respect to mechanical properties and the weight average molecular weight. Between 90 and 180 days there were no significant changes in the mechanical properties which, however, rapidly decreased thereafter and finally reached zero at 240 days. The crystallinity seemed to increase in a linear fashion, during the same period, from about 55 to 70%.     

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 weight changes in irradiated polypropylene

We have shown by two separate measurements that polypropylene when melted after irradiation undergoes crosslinking from the inception of irradiation. The first proof was an immediate increase in the solution viscosity of a narrow molecular weight fraction of polypropylene. The second proof was the marked change in melt-flow properties on irradiation of a broad molecular weight distribution polypropylene. These findings tend to support one of the two currently held views on the action of radiation on polypropylene. In addition we have confirmed previous reports that melting after irradiation contributes to the overall crosslinking reaction.     

Low dose γ-irradiation of some fluoropolymers: Effect of polymer chemical structure

The effect of low dose (1–20 Mrad) γ-irradiation on five fluoropolymers (PVF, PVDF, ETFE, FEP, PFA), differing in fluorine content and chain structure, was studied. The radiation effect, reflected by changes in thermal and mechanical properties, as well as NaOH etched surface morphology, was investigated. The main chain structure was found to predominate the irradiated polymers' behavior. The tensile strength of PVF and its resistance to etching increased with radiation dose, while its degree of crystallinity and melting temperature decreased. These changes were correlated with network formation by irradiation and by the incorporation of crosslinked segments into the crystalline phase during recrystallization. Solvent extraction of PVDF (no solvents were found for the other fluoropolymers) revealed increased gel formation with increasing dose. The degree of crystallinity and the tensile strength dependence on radiation dose for PVDF and ETFE reflected the competition between crosslinking and chain scission events. FEP and PFA undergo predominantly chain scission accompanied by reduction of their mechanical properties. PFA even exhibited an increase in both its melting temperature and degree of crystallinity, stemming from a massive degradation process forming shorter chains. Chemical mechanisms are discussed in an attempt to correlate the irradiation effects with the polymers' chain structure.     

聚碳酸亚丙酯/聚乳酸共混物光照条件下的降解行为研究

研究了聚碳酸亚丙酯（PPC）/聚乳酸（PLA）共混物在光照条件下的降解性能,通过力学实验、质量变化、扫描电子显微镜（SEM）、衰减全反射红外光谱技术（ATR-FTIR）、高温凝胶渗透色谱（GPC）和热重分析（TG）分别研究了共混物力学性能、质量损失、表面微观形貌、化学结构、相对分子质量和热稳定性的变化规律。结果表明,100/0、70/30、50/50、30/70、0/100（质量比,下同）的PPC/PLA共混物光照56d时质量损失率为34.89%、40.50%、39.38%、29.6%和6.24%,共混物在14d时几乎损失所有的力学性能;光照56d后PPC和50/50的PPC/PLA共混物表面有明显的裂纹和孔洞,而PLA表面没有变化,光照时间越长,共混物表面越粗糙,降解程度越大;共混物的羟基指数（HI）和羰基指数（CI）在前21d不断增大,其中前14d比较明显;共混物在光照56d后相对分子质量降低,多分散性指数减小,分子量分布变窄;共混物失重5%的热分解温度（T-5%）和最大速率失重温度（TP）提高,而PPC的TP却降低。     

Radiolysis of Ribonuclease in Controlled Environments

The separate contributions of the primary aqueous radicals to the changes in activity, molecular configuration and amino acid composition of RNase, produced by γ-irradiation of dilute solutions, have been identified. The most effective radical for inactivation is the H atom. Additional molecular products are formed on irradiation of the enzyme. Amino acid analyses of the irradiation products show significant damage only to the aromatic and sulfur-containing residues.     

Evolution of the peroxide‐induced degradation of polypropylene along a twin‐screw extruder: Experimental data and theoretical predictions

This article reports an experimental and theoretical study of the peroxide‐induced degradation of polypropylene in a corotating twin‐screw extruder. Experiments were performed with different peroxide concentrations and different operating conditions. The evolution of the chemical reaction along the extruder was monitored with specific sampling devices. Material changes were characterized by rheological measurements and via the determination of the molecular weights of samples collected at the same locations. The theoretical results were obtained with a model that coupled the interactions between flow conditions encountered in the extruder, the kinetics of the reaction, and the changes in the viscosity induced by changes in the molecular weight. The experimental results evidenced the relationships between the process conditions (peroxide concentration and processing parameters) and material properties (rheological properties and molecular structure of the modified polypropylene). Good agreement between the theoretical and experimental results was obtained. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci, 2006     

Effects of the ionizing irradiation of γ-rays,X-rays,and UV-rays on the optical properties of Ag-contained/Ag-free photo-thermo-refractive glass

To simulate the effects of ionizing irradiation on photo-thermo-refractive (PTR) glass in a cosmic environment, the optical properties changes under ionizing irradiation (γ-, X- and UV-ray) were investigated on PTR-glass with and without Ag doped (named as PTR-S and PTR-F, respectively) samples. Thermoluminescence (TL), transmission electron microscopy (TEM) measurements, UV-VIS absorption spectroscopy analysis, Gaussian peak fitting, and continuous wave electron paramagnetic resonance (CW-EPR) were used to determine the species of the irradiation-induced color centers. The radiation resistance properties of the Ag-species on the PTR-S glass were evaluated by comparing the defect center concentrations in the irradiated PTR-S and PTR-F glasses. The results showed that absorption in PTR-F and PTR-S glass increased significantly with increasing γ-irradiation dose, which was related to HC₁, HC₂, E′, L, ETC defect centers and Ag-species, and the formation of HC₁, HC₂, E’, and L-centers was reduced by the doping of Ag into the PTR-S glass matrix. Compared with the γ-irradiation, X-irradiation showed a similar effect. In comparison, UV-irradiation induced fewer defect centers and smaller Ag (NPs). This discrepancy could be caused by variations in photon energies.     

可控流变聚丙烯的制备及性能研究

聚丙烯双螺杆挤出过程中加入降解剂进行化学降解,以此方法制备可控流变性能聚丙烯(CRPP)材料.研究降解剂对聚丙烯流动特性、力学性能、综合热性能、分子量及其分布的影响.结果表明,过氧化二叔丁基(DTBP)添加0.47％时,聚丙烯树脂熔体质量流动速率(MFR)达到1 910 g/10min,熔体流动活化能降低到33.71 ...     

Die Bestimmung einiger Kennzahlen von freien Fettsäuren natürlicher Fette nach γ-Bestrahlung

Some Characteristic Values of Free Acids of Natural Fats after Irradiation with γ-Rays The alteration of some characteristic values of palmitic, stearic, linoleic and oleic acids after irradiation with γ-rays at 25, 40, 60 and 90 Mrad was investigated. With increasing dose of irradiation the acid value indicated a falling tendency in all cases, whereas the iodine value after γ-irradiation showed varying values. Benzidine value which could be measured at 25 Mrad only, showed a slight increase. At the highest dose of irradiation, peroxide value of saturated and unsaturated fatty acids behaved in different manner; compared to the value obtained at 40 Mrad, a relatively strong increase was observed with saturated fatty acids and a rather considerable decrease was found with unsaturated fatty acids. The refractive index of oleic and linoleic acids increased steadily, corresponding to the dose of irradiation on individual fatty acids.     

Mechanical behavior,microstructure and thermooxidation properties of sequentially crosslinked ultrahigh molecular weight polyethylenes

The aim of this study was to explore the impact of the sequential irradiation and annealing process on the microstructure, thermooxidation behavior and mechanical properties of GUR 1050 ultrahigh molecular weight polyethylene (UHMWPE) with respect to the postirradiation annealed material. For this purpose, the effects of a variety of irradiation and annealing conditions on microstructure and mechanical properties were investigated. Differential scanning calorimetry was performed to characterize melting temperature, crystalline content and crystal thickness, whereas transmission electron microscopy provided additional insights into crystal morphology. Thermogravimetric experiments in air served to assess thermooxidation resistance and changes associated to radiation‐induced crosslinking. Fatigue properties were studied from three different approaches, namely short‐term cyclic stress–strain tests, long‐term fatigue experiments and crack propagation behavior. Likewise, three experimental techniques (uniaxial tensile test, impact experiments, and load to fracture of compact tension specimens) allowed evaluation of the fracture resistance. The present findings confirm sequentially crosslinked UHMWPE exhibited improved thermooxidation resistance and thermal stability compared to post‐irradiation annealed UHMWPE. Also, the mechanical behavior, including the fatigue and fracture resistance, of these materials was generally comparable regardless of the annealing strategy. Therefore, the sequential irradiation and annealing process might provide higher oxidation resistance, but not a significant improvement in mechanical properties compared to the single radiation dose and subsequent annealing procedure. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

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.     

γ-射线辐照对聚丙烯纤维及非织造布性能的影响

研究了在室温下、空气中γ射线辐照对聚丙烯纤维及非织造布性能的影响。发现辐照对聚丙烯非织造布力学性能的影响很大,但在辐照剂量低于9 kGy 时,其力学性能下降不大;辐照聚丙烯纤维的FTIR 的结果表明有过氧化物形成;W AXD,DSC分析了辐照前后聚丙烯纤维晶体结构的变化