Radiation-resistant polypropylene improved by a compatibilizer

A compatibilizer is normally added to enhance the compatibility during blending of two polymers. Polypropylene (PP) has two degradations, during irradiation and also during storage after irradiation in radiation sterilization. A compatibilizer was added to PP to reduce these degradations. Compatibilizers, such as hydrogenated styrene (10 mol%)/butadiene rubber (CPB-2) and ethylene/propylene rubber grafted with maleic anhydride, were found to retard remarkably the above-mentioned degradations of PP. The compatibilizer concentration required for enhancing the radiation resistance of PP depends on the radiation resistance before addition of the compatibilizer. Poor radiation-resistant PP of a lower molecular weight (Melt flow index, 10) required a higher concentration, above 10% of CPB-2 to impart radiation resistance, but high-molecular-weight PP (Melt flow index, 1.0) and copolypropylene (CPP) with an ethylene content of 2.5% required CPB-2 of 5% and 10% to induce sufficient radiation resistance. Furthermore, CPB-2 was effective for improvement of transparency besides its contribution to radiation resistance of PP. The CPB-2 lead to lower crystallinity to retard the crystallization of PP and CPP and also may result in a mixed monoclinic and smectic structure giving radiation resistance.     

Effects of electron beam irradiation on poly(butylene adipate)diol

Effects of electron beam (EB) irradiation on poly(butylene adipate)diol (PBAD) were studied by means of GPC, DSC, and X-ray diffractometry. Below 5 Mrad, chain scission predominantly occurs, while above 10 Mrad, crosslinking and chain scission take place in parallel. Structure of EB-irradiated PBAD is mainly characterized by the main reactions, degradation and crosslinking. Crystallinity of PBAD increased by EB irradiation. This phenomenon was explained by reorganization due to high molecular mobility of EB-irradiated PBAD. But, increment of crystallinity decreased with increasing dose because of formation of crosslinking, excessive degradation and thermal effect of EB. As the result, the crystallinity of EB-irradiated PBAD with a high dose becomes lower than that of original PBAD by thermal treatment.     

Inhibition of radiation degradation of polyolefins by hydroaromatics

Heavy hydroaromatics from petroleum (HHAP) which has evident inhibiting ability toward deterioration of hydrocarbon oils was added to high density polyethylene (PE) and isotactic polypropylene (PP), and the additive effects were examined. After the confirmation of the prominent effects to thermal oxidation of PE and PP, the additive effects to radiation degradation were tested by γ-ray and electron beam irradiations in air. The addition of HHAP was obviously effective in radiation degradation, and the crosslinking of PE was distinctly suppressed by HHAP.     

The effect of nucleating agent on radiation stability of polypropylene

The radiation stability of polypropylene (PP) with and without nucleating agent (NA) is compared in relation to radiation sterilization of medical devices. In both cases high-and-low-molecular weight PP, the addition of NA increased the transparency and peak crystallization temperature of the PP. On the other hand, in poly(propylene-co-6%ethylene) copolymer, the addition of NA did not improve the transparency but crystallization occurred at higher temperature. Thus, adding NA to PP and copolymer give the advantage of shorter moulding time in the production of medical devices. It is found that both PP and copolymer with NA are less stable during irradiation and during storage after irradiation than without NA, this being the case especially for the lower molecular weight PP. The higher transparency and peak crystallization temperature in the PP and CP with NA were found to be due to smaller spherulites. As the effect of irradiation on polymer, addition of NA induce reduction of radiation stability of polymer owing to the change in morphology.     

Effects of electron beam irradiation on chemical composition,antinutritional factors,ruminal degradation and in vitro protein digestibility of canola meal

The aim of the present study was to determine the impact of electron beam (EB) irradiation at doses of 15, 30 and 45 kGy on the nutritional value of canola meal. The phytic acid and total glucosinolate content of EB-irradiated canola meal decreased as irradiation doses increased (P<0.01). From in situ results, irradiation of canola meal at doses of 45 kGy decreased (P<0.05) the effective degradibility of crude protein (CP) by 14%, compared with an untreated sample. In vitro CP digestibility of EB-irradiated canola meal at doses of 15 and 30 kGy was improved (P<0.05). Electrophoresis results showed that napin and cruciferin sub-units of 30 and 45 kGy EB-irradiated canola meal were more resistant to degradation, compared with an untreated sample. Electron beam irradiation was effective in protecting CP from ruminal degradation and reducing antinutritional factors of irradiated canola meal.     

γ-irradiation of polypropylene in vacuum and in air

Polypropylene films were irradiated with ⁶⁰Co γ-rays in vacuum or in air and stored in air. Just after irradiation, the concentration of carbonyl group of the sample irradiated in air only increased with dose. The concentrations of both samples increased with storage time. The more the absorbed doses, the higher the increasing rates. The increasing rate of the concentration of carbonyl group during irradiation in air was higher than those during storage in air. Just after irradiation, the tensile strengths and the elongations of the both samples somewhat increased with dose at the doses less than 5 Mrad, but decreased at doses more than 13 Mrad. The tensile strength and the elongation of the sample irradiated in air decreased with storage time. Those of the sample irradiated in vacuum also decreased with storage time but the decreasing rates were much smaller than those in the sample irradiated in air. The gel fractions of the samples irradiated in vacuum and annealed in vacuum were somewhat higher than those irradiated in vacuum and not annealed. To elucidate high oxidation rate in the sample irradiated in air during and after irradiation, reaction mechanisms were discussed. To clarify the difference of mechanical properties between the samples irradiated in vacuum and in air, the effect of crosslink was considered, together with the oxidation.     

Radiation degradation of blends polypropylene/poly(ethylene-co-vinyl acetate)

Physicochemical and mechanical characteristics of irradiated electron beam polypropylene/ethylene-vinyl acetate (PP/EVA) blends and individual components were investigated. Although oxidation of alkyl radicals in the blends proceeds slower than in PP, the total oxidation effect monitored by content of oxygen-containing groups shows opposite tendency. Blending with EVA does not affect degree of PP crystallinity. The enthalpy of melting and crystallization of the blends reveal phase separation between dispersed copolymer and PP matrix. In all studied blends, degradation prevails over tendency of EVA to cross-linking.     

等规聚丙烯在γ射线辐照下的链结构和结晶行为

利用凝胶渗透色谱(GPC)、傅里叶变换红外光谱(FTIR)和示差扫描量热(DSC)等手段对不同剂量γ射线辐照后等规聚丙烯(iPP)的分子链结构及结晶行为的变化进行了研究.结果表明,γ射线辐照使iPP的分子量下降,并在其分子链中产生羟基和羰基等极性基团,从而影响其结晶行为.在非等温结晶过程中,当辐照剂量≤50 kGy时,iPP的热结晶温度略有升高;增大辐照剂量,iPP的热结晶温度明显降低.iPP的熔融温度则随辐照剂量的增大而降低,且分裂成双峰.利用Avrami方程研究了辐照前后iPP的等温结晶动力学,发现辐照前后样品的Avrami指数n都在3左右,表明iPP的结晶遵循异相成核机理,且不受辐照剂量和等温结晶温度的影响,但总结晶速率随等温结晶温度和辐照剂量的升高而逐渐减小.探讨了iPP经过γ射线辐照后,分子链断裂、链结构变化和结晶速率之间的关系.     

Effect of γ-ray irradiation on the germinating characteristics of wheat seed

Few researches have been reported on the long-term germination characteristics and the effect of high gamma radiation dose on cereal seeds. In this paper, to observe the effects of gamma irradiation (0-3 kGy) on the germination of wheat seed in long-term (within 20 months), wheat seed was dried after irradiation and the germination experiment during storage time was conducted. It was found that the lengths of buds of irradiated wheat seeds diminished, the roots of irradiated wheat seeds disappeared, and no germinations in irradiated wheat seed was found. The influence of γ-ray irradiation on roots was more significant than that on buds. After long-term storage, the germination of irradiated wheat seeds increased.     

Outdoor and accelerated weathering tests for polypropylene and polypropylene/talc composites: A comparative study of their weathering behavior

In this study, the comparisons of degradation behavior of polypropylene(PP) and PP/talc composites were carried out with one outdoor weathering test and three accelerated weathering (xenon, metal halide and carbon arc lamps) tests, respectively. The outdoor exposure vigorously advanced these degradations with the lowest amount of UV exposure energy. It was found that the degradation rates were affected by the visible light intensity in the light sources. In the case of the existence of talc compound, the degradation was synergistically accelerated by the exposures of the sunshine, the xenon and the metal halide lamps having higher visible light intensities. In addition, the degradations of the PP and the PP/talc composites were found to be synergistically accelerated by sunlight exposure and the acid rain, too.     

Research on radiation stability of polypropylene

The effect of isotacticity of polypropylene(PP) on its radiation stability has been investigated in the present work. It was found that (1) The G value of H₂ and CH₄ is smaller if isotacticity of PP is higher; (2) It is easier to be crosslinked by radiation for the PP with higher isotacticity; (3) The shape of DSC peak changes smaller after irradiation for PP with higher isotacticity. These results have been explained by the measurement of ¹³C-NMR and small angle X-ray scattering.     

Temperature dependent oxidative-induction time (TOIT) of irradiated and non-irradiated polypropylene—a new method

OIT's oxidation condition is very harsh for pure and irradiated polymers, particularly PP. PP undergoes pronounced molecular weight degradation in the course of processing and is prone to very fast oxidation and consequently very fast degradation, especially on samples submitted to previous aging and irradiation.

We developed a more useful method applicable by a much broader set of resins. Our group has recently introduced a new procedure to determine OIT, in non-stabilized and stabilized, irradiated and non-irradiated polypropylene. The new procedure was based on two main features: (1) starting the oxidation on melted samples at temperatures as low as possible; (2) oxidation under slow heating conditions. So each sample has a set of two values of time and temperature, as the new method is not isothermal any longer, so we better call it “Temperature dependent oxidative induction-time”. The new method showed itself as reproducible, sensitive to small changes in additive compositions and simple and inexpensive.     

Radiation resistant polypropylene blended with mobilizer,: antioxidants and nucleating agent

Post-irradiation storage of medical disposables prepared from isotactic polypropylene renders them brittle due to degradation. To avoid this, isotactic polypropylene [(is)PP] was blended with a mobilizer, dioctyl pthallate (DOP), three antioxidants (hindered amines and a secondary antioxidant) and benzoic acid to obtain radiation-resistant, thermally-stable and transparent material. Different formulations prepared were subjected to gamma radiation to doses of 25 and 50 kGy. Tests of breakage on bending after ageing in an oven at 70°C up to 12 months have shown that the addition of DOP and the antioxidants imparts improved radiation and thermal stability as compared to (is)PP alone or its blend with DOP. All the formulations irradiated or otherwise demonstrated excellent colour stability even after accelerated ageing at 70°C for prolonged periods.     

Thermal and photo induced reactions in blends of polypropylene and poly(methyl methacrylate)

Thermal Volatilization Analysis (TVA) demonstrates that poly(methyl methacrylate) (PMMA) is stabilized by blending with polypropylene (PP). Although well-defined radical reactions occur in both polymers under 2537 Å radiation, there is no evidence of the formation of block or graft copolymers when blends of the two are irradiated. Preirradiation suppresses the amount of monomeric methyl methacrylate formed on subsequent thermal degradation. The missing methyl methacrylate units appear in the chain fragment fraction. The characteristics of the thermal degradation of blends of unirradiated PP with preirradiated PMMA are similar to those of unirradiated rather than pre-irradiated blends, thus emphasizing the importance of the PP component in determining the thermal stability of blends after irradiation. These observations are discussed mechanistically.     

Effect of isotacticity on radiation stability of polypropylene under lower dose irradiation

Relationship between radiation stability and isotacticity of polypropylene was studied. It was found that the higher the isotacticity, the better the radiation stability under lower dose irradiation. Special PP power with higher isotacticity can keep the melting index change less after γ-irradiation in air. Furthermore, the special PP powder with higher isotacticity has lower intention of branching after 1 kGy γ-irradiation in vacuum and has lower intention of degradation after 5 kGy γ-irradiation in vacuum.     

Thermal characterization of the oxo-degradation of polypropylene containing a pro-oxidant/pro-degradant additive

The oxo-degradation process of polypropylene (PP) samples containing different concentrations (4% and 10% w/w) of pro-oxidant/pro-degradant additive Envirocare™ AG1000C was investigated under accelerated test conditions. Samples were initially exposed to UV radiation for 300 h. The tendency to biodegradation in soil medium of these UV-aged samples was then indirectly assessed by an indirect method for a period of 6 months. The entire degradation process of these materials was first examined by monitoring changes in their morphological properties (melting temperature, maximum lamellar thickness and crystallinity) with the ageing time, by Differential Scanning Calorimetry (DSC). Then, changes in the thermal properties (onset temperature and maximum decomposition temperature) of these materials with the ageing time were analysed by Thermogravimetric Analysis (TGA). Furthermore, the kinetics of the thermal decomposition of these PP samples with pro-oxidant/pro-degradant was also studied during the oxo-degradation process, by means of the Chang differential method. During exposure to UV radiation, the more significant changes in the morphological and thermal properties that were detected in PP samples containing pro-oxidant/pro-degradant additive compared to pure PP, clearly suggest a higher level of oxidation in these samples, confirming the effectiveness of this pro-oxidant/pro-degradant additive in promoting the abiotic oxidation of polypropylene during UV-irradiation. Moreover, the level of oxidation observed in UV-aged samples seems to be dependent on the additive load.     

The effect of adding virgin material or extra stabilizer on the recyclability of polypropylene as studied by multi-cell imaging chemiluminescence and microcalorimetry

The effect of adding virgin material or new stabilizers on the recyclability of polypropylene (PP) was determined. Stabilized PP was subjected to oven ageing at 130 °C for 100, 250 or 500 h before and after upgrading with virgin material (0, 20, 50, 80 or 100%) or additional stabilizer during reprocessing. The effect of upgrading recycled PP with extra stabilizer or virgin material was determined by measuring the elongation at break, yellowness change, oxidation induction time (OIT) or total luminous intensity (TLI) by chemiluminescence (CL) techniques. Selected specimens were analysed by microcalorimetry (MC).It has been shown that upgrading recycled PP with virgin material was not effective. Adding 80% virgin material did not increase the lifetime more than adding 20% virgin material. This indicates that a small amount of recycled material can induce degradation by contamination. Adding extra stabilizers instead of virgin material was much more effective. Of all techniques used the OIT as determined with CL showed a clear difference in residual stability of differently treated materials and seems to be the most valuable analytical method to determine the recyclability of PP. A comparison between CL and MC shows that MC is sensitive enough for measuring the solid-state oxidation of stabilized PP. Slightly lower OITs were detected by MC probably associated with the static atmosphere used during the measurements. The TLI method is not suitable to determine the degradation state of to be recycled material.     

Approaches for Making High Performance Polymer Materials from Commodity Polymers

A brief surrey of ongoing research work done for improving and enhancing the properties of commodity polymers by the author and author’s colleagues is given in this paper. A series of high performance polymers and polymer nanomaterials were successfully prepared through irradiation and stress-induced reactions of polymers and hydrogen bonding. The methods proposed are viable, easy in operation, clean and efficient. 1. The effect of irradiation source (UV light, electron beam, γ-ray and micr…     

Effect of dose rate on inactivation of microorganisms in spices by electron-beams and gamma-rays irradiation

Total aerobic bacteria in spices used in this study were determined to be 1 × 10⁶ to 6 × 10⁷ per gram. A study on the inactivation of microorganisms in spices showed that doses of 6–9kGy of EB (electron-beams) or γ-irradiation were required to reduce the total aerobic bacteria in many However, a little increase of resistance was observed on the inactivation of total aerobic bacteria in many spices in case of EB irradiation. These difference of radiation sensitivities between EB and γ-rays was explained by dose rate effect on oxidation damage to microorganisms from the results of radiation sensitivities of Bacillus pumilus and B. megaterium spores at dry conditions. On the other hand, these high dose rate of EB irradiation suppressed the increase of peroxide values in spices at high dose irradiation up to 80 kGy. However, components of essential oils in spices were not changed even irradiated up to 50 kGy with EB and γ-rays.     

Post-irradiation oxidation of different polyethylenes

The radiation-induced oxidative degradation of polyethylenes (PEs) with different degrees of crystallinity was characterized after electron-beam irradiation and during storage at room temperature.UHMWPE, HDPE, LDPE, LLDPE and an ethylene-octene copolymer (Engage) were e-beam irradiated to 30 or 60 kGy in vacuum or in air and stored at room temperature in air. EPR spectroscopy was used to investigate macro-radicals produced during irradiation and their post-irradiation changes. FTIR spectroscopy was used to monitor changes in the polymer structure, induced by irradiation, and to follow post-irradiation oxidation.We found that the crystallinity and the size of the crystalline lamellae, in particular, play a major role on the post-irradiation effects. The low-crystallinity polyethylenes showed no oxidation or oxidation only to a small extent, even when irradiated and stored in air. On the contrary, development of post-irradiation oxidation was observed in HDPE and UHMWPE. We attribute these results to a different reactivity of the macro-alkyl radicals formed upon irradiation in the amorphous or in the crystalline phase. While the radicals formed in the amorphous phase decay in short time, the migration time of the radicals trapped in the crystalline phase to the amorphous one is a key factor, governing the oxidation process.