[en] 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

[en] The grafting of methyl methacrylate (MMA) onto polybutadiene rubber latex by the direct radiation method was carried out. The effects of monomer concentration, absorbed dose and dose rate of gamma rays on the grafting yield were investigated. The graft copolymers were characterized by transmission electron microscopy (TEM), FTIR spectroscopy, and differential scanning calorimetry. TEM photographs revealed that the core-shell structures of latex particles are formed at low MMA content, and with the increasing of MMA content, the semi-IPN-like structure with core-shell could be developed due to the high gel fraction of polybutadiene (PBD) seed particles. In addition, infrared analysis confirmed that MMA could be grafted onto PBD molecular chains effectively under appropriate irradiation conditions. The interfacial adhesion between PBD rubber (core) and PMMA (shell) phases could be enhanced with the increase of MMA concentration

[en] Two ethylene-octene copolymers (POE) were irradiated with ⁶⁰Co gamma radiation and influence of irradiation atmosphere, absorbed dose and heat treatment of samples on the crosslinking were studied. Thermal properties and crystalline morphology of non-irradiated and irradiated POE were determined by using differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXS), respectively. The Charlesby-Pinner equation was used to describe the relationship between absorbed dose and sol fraction. The gel fraction of irradiated POE was lower and decreased with the increase of octene content when irradiated in oxygen, compared to irradiation in nitrogen atmosphere. The gel fraction increased significantly with the increasing of absorbed dose for the two copolymers. Heat treatment of samples prohibited the crosslinking of irradiated POE. The DSC results indicated that a subtle change of thermal properties of POE was observed before and after gamma irradiation at low dose. No change was found from the WAXS spectra of non-irradiated and irradiated POE. For heat-treating samples, the Charlesby-Pinner equation can not fit perfectly with the relationship between the sol fraction and absorbed dose, but it fits well with the crosslinking reaction of POE pellets

[en] The relationship between radiation stability and isotacticity of polypropylene(PP), such as isotactic pentad ratio, was studied in this paper. It was found that the higher isotacticity, the better radiation stability. Compared with normal PP powder which has normal isotacticity, the special PP powder with higher isotacticity, such as, isotactic pentad ratio > 98%, can keep the Melting Index change less than normal PP after UV-light-oxygen aging or γ-irradiation in air. Furthermore, the special PP powder with higher isotacticity has lower intention of crosslinking or branching after 1KGy γ-irradiation in vacuum and has lower intention of degradation after 5KGy γ-irradiation in vacuum. The special PP powder with higher isotacticity also has lower content of carbonyl after 25KGy γ-irradiation in air. These demonstrated that the special PP with higher isotacticity made from 'special catalyst' is more suitable as the material for radiation sterilization than normal PP, because there are less 'week points' in PP with higher isotacticity than that in PP with lower isotacticity. The random copolymer with 2.7% ethylene units made from the 'special catalyst' mentioned above is even more stable in irradiation sterilization than homopolypropylene with higher isotacticity; therefore, it is reasonable that a random copolypropylene with about 4%wt ethylene made from the 'special catalyst' should be the much more suitable PP material than normal PP for irradiation sterilization. (author)

[en] The γ-radiation effect of polyropylene was investigated in the presence of three kinds of p-tert-butylcalix[n]arene (n=4,6,8) in air or in vacuum at ambient temperature. The influence of radiation dose and store time upon the mechanical properties of the irradiated PP sheets were measured. The results showed that the radiation stabilization was reduced with the increase of the ring size of calixarenes. Based on the mass spectra and the analysis of post-irradiated product, the mechanism of radiation degradation of p-tert-butylcalix[4]arene has been proposed. (author)

[en] The morphology of i-PP with different isotacticity under high absorbed dose were studied with the measurements of crystallinity, crystallite size, melting heat and melting point by x-ray diffraction and DSC methods respectively. The results indicate that the changes are not only related to the heat history but also related to the isotacticity of i-PP. In generally, the higher the isotacticity of i-PP, the less morphology changes, and the morphology of annealing samples change less than the virgin powder samples. It means that the annealed i-PP with higher isotacticity is more stable to radiation both in air and vacuum conditions. (author)

[en] The crosslinking behavior of carboxylated styrene-butadiene rubber latex (CSBRL) by using gamma radiation with 2-ethyl hexyl acrylate (2-EHA) as crosslinking sensitizer has been studied in detail. In addition, the variation of the particle size and distribution of latex, chemical structure and thermal property of CSBRL with absorbed dose have been discussed. Also the radiation vulcanization mechanism of CSBRL has been suggested. The experiments showed that, the dose rate has small effect on the cross-link behavior of CSBRL, and the swelling ratio decreased rapidly with the increase of absorbed dose. Increasing the dose, the average molecular weight per crosslinked units (Mc) decreased and crosslinking density increased. When the dose is below 25 kGy, no significant changes in the particle size and distribution of latex were observed. The micro-FTIR analysis and DSC curves confirmed the existence of grafting reaction accompanying the crosslinking reaction during the gamma irradiation with 2-EHA as sensitizer

[en] Poly (glycidyl methacrylate) grafted multi-wall carbon nanotubes (MWNTs-g-PGMA) was synthesized by simultaneous irradiation polymerization. MWNTs were dispersed in GMA-maleic acid (MA) aqueous solution by ultrasonication and the suspension was irradiated by ⁶⁰Co γ-rays. The remaining, MA was washed off by distilled water and MWNTs-g-PGMA was obtained. The product was blended with nylon 6 (PA6) by melt mixing method. Mechanical and thermal properties of the blend were investigated. Chemical structure of the MWNTs-g-PGMA was confirmed by FT-IR (Fig.1) and ¹H NMR. MA solution acted as a solvent for GMA and an inhibitor for homopolymerization of GMA. A graft yield of 17 wt % could be achieved, as was determined by thermal gravimetric analysis (TGA, Fig.2). Moreover, MWNTs-g-PGMA could be dispersed stably in water at a concentration of 1 g/L. Transmission electron microscope (TEM) image (Fig.3) showed that the diameter of grafted tubes increased and some entanglements were found. Compared with pure PA6, blend with only 0.2 wt % of MWNTs-g-PGMA had a remarkable increase in tensile strength, flexural strength, flexural modulus, heat distortion temperature, crystallization temperature and melting temperature. In addition, the notched impact strength of PA6/MWNTs-g-PGMA blend was improved compared with PA6/MWNTs blend. Polarizing microscopy (PLM) revealed that the crystal size of the blend was much smaller than that of pure PA6. Therefore, MWNTs-g-PGMA could act as a reinforcing agent as well as a nucleation agent for PA6. (authors)

[en] The three-phase structure model of crystal line polymer is used to calculate the one-dimensional electron density correlation function. The conclusion is that the definitions of lamellar thickness and invariant are not the same as those in the two-phase structure. Then utilizing this result to analyze some specimens, the authors found that the crystalline transition-layer thicknesses obtained by the correlation function method agree with those by the Ruland method, but the long periods obtained by correlation function are much different from the Bragg spacings. The reason is that the two methods to calculate crystalline transition-layer thicknesses are all based on the non-homogeneous area of the specimen electron density and have the same nature. However, the Bragg spacing and the correlation-function long period represent different regions of the non-homogeneous area

[en] A new kind of carbon hybrid material with a unique structure and outstanding mechanical and functional properties is reported in this article. Nitrogen-doped carbon nanotube (CNT) arrays with inside located Ni particles are in situ grown on the surface of phenolic carbon modified graphene fibers during their conversion from graphene oxide fibers. The carbon hybrid fibers exhibit not only high tensile strength and elongation at the break, but also excellent flexibility since the CNT arrays cover all the surface of the highly strong graphene fiber. This well-constructed carbon material would be suitable for catalysts, polymer composites, hydrogen storage, oxygen reduction reaction etc. (letter)