Effect of γ-irradiation on the molecular-topological structure of the polyethylene matrix of glass-reinforced plastic

The molecular-topological structure of polyethylene (PE) and a PE matrix in a glass-reinforced plastic (GRP) after γ-irradiation of the plastic was studied by means of thermomechanical spectroscopy. The four-block topological structure of unirradiated PE (one amorphous block and three crystalline phases with different initial melting temperatures) is transformed into a three-block structure in the GRP already at a minimal radiation dose of 25 kGy. The intermediate crystalline phase disappears under these conditions, the molecular relaxation characteristics in all topological blocks alter, and chemical branching points appear in the pseudonetwork structure of the amorphous matrix block.     

Effect of γ-radiation on the molecular-topological structure of polytetrafluoroethylene

Four topological structures of polytetrafluoroethylene (PTFE): amorphous and three crystalline (high-melting, intermediate, and low-melting forms) blocks, were revealed by the technique of thermomechanical spectroscopy. The γ-irradiation of PTFE leaves both free volume and the molecular-mass characteristics in the pseudo-network structure of the amorphous block practically intact. In the crystalline phase, γ-irradiation decreases the molecular mass of crystallized chains of the low-temperature modification and leads to the disappearance of the intermediate and high-temperature crystalline phases as a result of their transformation into the amorphous phase.     

Molecular-topological structure of γ-irradiated ftorlon polytetrafluoroethylene

Six topological structures (an amorphous and five crystalline blocks) have been detected in a polytetrafluoroethylene film with a pseudo-network structure. During the Γ-irradiation of the polymer in air, the crystalline fractions degrade and gradually convert into amorphous and cluster states with the increasing radiation dose. After irradiation at a dose of 90 kGy, the polymer loses its capability for crystallization and forms a completely amorphous topological structure. However, regardless of dose in the range of 3–90 kGy, the topological structure of the polymer irradiated in a vacuum remains unchanged and consists of amorphous, cluster, and crystalline blocks.     

Radiothermoluminescence and thermomechanical spectrometry study of gamma-irradiated vinylidene fluoride–chlorotrifluoroethylene copolymer

Five topological units: low- and high-temperature amorphous blocks and three crystalline modifications that act as branching points in the networks of both amorphous blocks, have been detected for the first time in the pseudo-network structure of the unirradiated fluoroelastomer SKF-32 by means of thermomechanical spectrometry (TMS). When the rubber is γ-irradiated to a dose of 10 kGy, the structures of the intermediate and high-melting crystalline fractions degrade and their amorphized chains along with interjunction chains of both amorphous blocks assimilate into one amorphous block, and the latter is the block of the chemically crosslinked rubber already with a topologically diblock semicrystalline structure. A radiothermoluminescence (RTL) curve of the irradiated rubber shows four relaxation transitions (emissions peaks), with only the transition at–25°C almost coinciding with the glass transition temperature observed in thermomechanical analysis curve of the crosslinked rubber.     

Characterization of γ-irradiated polychlorotrifluoroethylene by thermomechanical spectrometry

Three topological blocks (low- and high-temperature amorphous and crystalline) have been detected for the first time in polychlorotrifluoroethylene with a pseudo-network structure. The molecular weight of the polymer decreases and the crystalline and high-temperature amorphous fractions degrade with an increase in γ-radiation dose. Thermal annealing at 493 K leads to amorphization of the polymer, as well as its radiolysis. However, slow recrystallization of the thermally annealed polymer has been observed during storage at 300 K.     

Molecular-topological structure of γ-irradiated polytetrafluoroethylene

The molecular-topological structure of polytetrafluoroethylene (PTFE) has been studied in the range of ?100 to +450°C by thermomechanical spectrometry. Revealed in this temperature range is a fourblock topological structure composed of one amorphous (T _g = 16°C) and three crystalline (low-melting (T _m = 315°C), intermediate (T _m ¹ = 355°C), and high-melting (T _m ² = 388°C)) polymorphs. At a dose of 1 kGy, the long-range orientation of chains in the intermediate and high-melting crystalline blocks of PTFE is replaced by short-range orientation of the cluster association structure. At doses of 100?C500 kGy, the latter structure transitions to the amorphous state and the irradiated samples acquire a semicrystalline structure of the two-block type. The molecular-mass distribution function of interjunction chains of the pseudo-network of the amorphous block is bimodal in character and its maxima are noticeable shifted toward lower masses with an increase in the radiation dose. As the dose increases, the crystallinity decreases and the molecular mobility of amorphized chains is enhanced. As a result, both the glass transition and the molecular flow onset temperatures of the polymer are reduced.     

Effect of γ-irradiation on the molecular–topological structure of a copolymer of tetrafluoroethylene and perfluoro(propyl vinyl ether)

The molecular–topological structure of a copolymer of tetrafluoroethylene and perfluoro(propyl vinyl ether) before and after γ-irradiation has been studied for the first time. The pseudo-network structure of the copolymer contains an amorphous block and the crystalline segments of macromolecules serve as branching points. After γ-irradiation to a dose of 15 to 2380 kGy, polyassociative cluster-type entities have appeared in the initial copolymer in place of the crystalline branching points with simultaneous structure amorphization and a decrease in the onset temperature of molecular flow.     

Effect of γ-irradiation and thermal annealing on the molecular–topological structure of a copolymer of tetrafluoroethylene and perfluoro(propyl vinyl ether)

The molecular–topological structure of a copolymer of tetrafluoroethylene and perfluoro(propyl vinyl ether) subjected to γ-irradiation and thermal annealing has been studied for the first time with the use of thermomechanical spectrometry. The pseudonetwork structure of the copolymer contains an amorphous block (interjunction chains) and crystalline segments (branching points). The diblock amorphous and crystalline structure with a crystal structure fraction of 0.21 transformed into an almost completely amorphous structure with a crystallite fraction of 0.06 after the irradiation of the copolymer at a dose of 600 kGy. Thermal annealing at 483 K formed a new structure: a high-temperature amorphous block.     

Influence of Gamma-Irradiation and Thermal Annealing on Molecular–Topological Structure of Tetrafluoroethylene–Ethylene Copolymer

The molecular–topological structure of a tetrafluoroethylene copolymer with ethylene after γ-irradiation and thermal annealing has been studied. The pseudo-network structure of the copolymer contains, in addition to the amorphous block, crystalline segments of macromolecules in the role of branching sites. Topologically, the diblock structure of the copolymer after thermal annealing at 538 K is transformed into a three-block structure with the appearance of a high-temperature amorphous block. Irradiation of the copolymer with γ-rays to a dose of 150 kGy does not lead to appreciable changes in its molecular–topological structure.     

Effect of γ-irradiation on the molecular-topological structure of Viton® fluoroelastomers

The molecular–topological structure of a terpolymer based on vinylidene fluoride, hexafluoropropylene, and tetrafluoroethylene has been studied for the first time with the use of thermomechanical spectrometry. A five-block topologically amorphous and crystalline pseudo-network structure with crystallites, which have different initial melting temperatures, as branching points has been detected in the terpolymer at temperatures from–100 to 250°C. When γ-irradiated at a dose of 30 kGy, the crystalline blocks of high-temperature modifications assimilated into one cluster block with the formation of a pseudo-network with a 1.5fold increase in the block-average molecular weight and a decreased initial molecular flow temperature.     

γ-辐照对PLLA分子量及结晶形态的影响

以左旋聚乳酸(PLLA)为研究对象,以多官能团单体三烯丙基异氰酸酯(TAIC)为交联剂,采用反应挤出技术制备了PLLA-TAIC体系,并利用60Co-γ射线源,在较低辐照剂量(Dose≤25kGy)范围内,对所制备的聚合物进行了γ-辐照。研究了γ-辐照剂量、交联剂含量对PLLA分子量和结晶形态的影响。结果表明,在0~25kGy辐照剂量范围内,PLLA-TAIC的粘均分子量(-Mη)随γ-辐照剂量的增加呈现出先升高后降低的变化趋势,辐照剂量为10kGy、TAIC含量为3份时,PLLA的-Mη提高的幅度最大;随着辐照剂量的增加,原料PLLA形成的球晶尺寸有所增大;对于γ-辐照的PLLA-TAIC体系,随着TAIC含量的增加,PLLA的结晶能力有所下降。     

Molecular-topological and thermal properties of gamma-irradiated alternating carbon monoxide-ethylene copolymer

Gamma-irradiation to a dose of up to 2000 kGy does not lead to substantial changes in the topological structure of a carbon monoxide copolymer with ethylene, thereby suggesting it high radiation resistance. The topological structure of unirradiated and irradiated copolymer samples is polyblock in nature having four crystalline phases as the branching “junctions” in the pseudo-network structure of its amorphous block. Copolymer molecular flow begins after completion of melting of its high-melting fraction and at an onset flow temperature of 484 ± 4 K regardless of the absorbed radiation dose. The irradiated and unirradiated copolymer releases the same gaseous products upon heating, and the irradiation itself does not affect the onset temperature of effective gas evolution.     

Study of Gamma-Irradiated Polyamide Using Thermomechanical Spectrometry and Radiothermoluminescence

The molecular–topological structure of polyamide before and after γ-irradiation has been first studied by thermomechanical spectrometry. The γ-irradiation with a dose up to 300 kGy does not change the topological structure of the polymer, the four-block pseudo-network structure of which contains crystalline segments of macromolecules and polyassociative entities of the cluster type in addition to low-and high-temperature amorphous blocks. During irradiation, only interblock mass transfer of the chain segments occurs, resulting in different dose-dependent values for the molecular weight of the chains, their weight fraction in each topological block, and the glass transition and molecular flow temperatures of the polymer. Radiothermoluminescence curves exhibit three maxima at 152, 200, and 330 K, of which the last one is detected in a temperature region close to the glass transition temperature of the high-temperature amorphous block on the thermomechanical analysis curve of the polymer.     

X-ray and NMR measurements on irradiated polytetrafluoroethylene and polychlorotrifluoroethylene

The effects of ⁶⁰Co γ-radiation on polytetrafluoroethylene (PTFE) and polychlorotri-fluoroethylene (PCTFE) have been studied for radiation doses up to 940 Mrad. The dependence of per cent crystallinity upon irradiation level has been determined from x-ray analysis. An initial increase in crystallinity in PTFE, attributable to chain scission in the amorphous phase of the material, was found, followed (above 300 Mrad) by a gradual decrease associated with a disordering of the crystallites. No initial increase was observed for annealed samples of PCTFE due to the large initial value of the per cent crystallinity. Above 200 Mrad the crystallinity was found to decrease with accumulated dose. Nuclear magnetic resonance measurements on PTFE have indicated a radiation-induced broadening of the amorphous component of the NMR line appearing to maximize above 700 Mrad. Similar measurements of PCTFE have shown a narrowing of the crystalline component of the NMR line and subsequent appearance of the amorphous component at approximately 200 Mrad. The data indicate that the radiation-induced behavior of PTFE and PCTFE is similar above 200 Mrad.     

Features of the molecular–topological structure of γ-irradiated powdered tetrafluoroethylene–perfluoro(propyl vinyl ether) copolymer

With the use of thermomechanical spectrometry in two modes, coaxial, when the load application vector is coplanar with the compacting pressure vector (semicrystalline copolymer) during the measurement of the deformation of a copolymer of tetrafluoroethylene with perfluoro(propyl vinyl ether), and mutually perpendicular (completely amorphous copolymer), it has been established that the axial compression of the copolymer brought its topological structure to an absolutely anisotropic state. After γ-irradiation, the semicrystalline structure of the copolymer was retained regardless of the radiation dose. The minimum values of the glass transition temperature of the amorphous block and the degree of crystallinity were observed in the copolymer irradiated to a dose of 150 kGy. The molecular weight distribution functions of interjunction chains in the networks of the amorphous blocks of the initial copolymer and its γ-irradiated analogs are bimodal.     

Thermo-stimulated luminescence of gamma-irradiated polytetrafluoroethylene

The thermo-stimulated luminescence of γ-irradiated commercial polytetrafluoroethylene (PTFE) was explored. There are up to four intense maxima in the luminescence curves of different formulations of PTFE. The position and number of maxima remain constant at doses up to 30 kGy. The differences of the glow curves in the different copolymers may be the result of impurities capable of reacting with ions or radicals formed under irradiation and by differences in the polymer’s topological structures.     

Molecular-topology of powder of the γ-irradiated tetrafluoroethylene/ethylene copolymer

The molecular-topological structure of γ-irradiated commercial copolymers of tetrafluoroethylene with ethylene (CTE) were explored in the coaxial mode, which has the vectors of CTE loading and compression pressure in the same plane, and in the perpendicular mode with the two vectors perpendicular to each other. Instead of the amorphous-crystal structure observed with the coaxial orientation of the vectors, the CTEs are completely amorphous in their perpendicular orientation. Radiolysis with a dose of 140 kGy leads to the formation of a crosslinked structure for the CTEs. On irradiation, the crystals are transformed to an amorphous state and CTE can form a fully amorphous structure after 600 kGy of irradiation.     

The effect of gamma-irradiation on the morphology of quenched isotactic polypropylene

Wide-angle X-ray diffraction, differential scanning calorimetry and gel-permeation chromatography measurements have been used to investigate the effect of low absorbed doses of γ-radiation, up to 100 kGy, on isotactic polypropylene (iPP). The bimodal endotherm for the sample quenched in iced water was attributed to the presence of both “smectic” and monoclinic crystalline phases. The changes in the morphology, molecular weight distribution, decrease of melting temperature and heat of fusion with absorbed dose are related to the radiation processes in pure iPP.     

Effect of bombardment with helium ions on the molecular-topological structure and elemental composition of the surface of polytetrafluoroethylene

Irradiation of a polytetrafluoroethylene (PTFE) film with accelerated (1–5 MeV) helium ions at a fluence of 10¹⁵ ion/cm² has been studied. The efficiency of carbonization, defined as a decrease in the fluorine content and an increase in the carbon content on the surface of the polymer, increases with the incident ion energy. A characteristic feature of the topological structure of PTFE is the presence of four high-meltingpoint crystalline modifications, the “branching points” of the pseudo-network of the amorphous matrix block, in addition to a low-melting-point modification with the melting onset temperature of 13°C. After bombardment with 3–5 MeV ions, only two crystalline blocks remain in the polymer and a cluster block, which was not present in the unirradiated polymer, appears. The overall mass fraction of the crystalline structure in the irradiated polymer (0.48) is below that in the initial polymer (0.66), indicating amorphization of its structure.     

Effect of Gamma-Radiation on the Molecular-Topological Structure of Polyethylene

The molecular-topological structure of powdered high-density polyethylene (PE) after its compression under an optimized pressure and γ-radiolysis was first analyzed. A semicrystalline structure composed of one amorphous block and three crystalline modifications was formed with different rates and different melting onset temperatures in unirradiated PE and in PE irradiated to a dose of 5.5 Mrad. This structure was retained to 242 Mrad; after such a dose, the amorphous block completely disappeared. The net crystallinity of PE at a dose of 5.5 Mrad reached a minimum value but was close to 100 wt % in the initial state or after irradiation to 242 Mrad.