Crystallization of poly(phenylenesulfide)/amorphous polyamide blends: DSC and microscopic studies

Poly(phenylenesulfide) (PPS) is a high-performance engineering thermoplastic with exceptional thermal and chemical resistance. The results of crystallization behavior of blends of PPS with amorphous polyamide (PA) are presented. The melting and crystallization behavior was studied using differential scanning calorimetry (DSC), and the crystalline morphology was studied using optical microscopy. The results of thermal analysis indicate that the blends exhibit composition-dependent melting point depression. Optical microscopy studies showed the uniform distribution of amorphous nylon in PPS spherulites. The presence of amorphous nylon enhanced the growth rate compared to that for the neat polymer. The observed changes in the equilibrium melting point crystallization behavior, and spherulitic growth rate are explained.     

Effect of gamma-ray irradiation on isothermal crystallization of biodegradable poly(ethylene succinate)

The effects of gamma-ray irradiation on the isothermal crystallization of biodegradable poly(ethylene succinate) (PESu) and the growth behavior of PESu spherulites have been studied by differential scanning calorimetry and polarized optical microscopy. The irradiation doses used in the study are 0, 200, 400, and 600 kGy. The kinetic parameters for the isothermal crystallization have been determined, using the Avrami relationship. The nucleation constants and activation energy for the growth of the PESu spherulites have been analyzed, using the Lauritzen-Hoffman growth theory. Triple melting points have been observed for all the irradiated PESu. The gamma irradiation has no observable effect on the Avrami exponent, and the composite rate constant increases first with the increase of the crystallization temperature, reaches maximum at the crystallization temperature of ~35 °C, and then decreases with the increase of the crystallization temperature for both the non-irradiated and irradiated PESu. There exists a transition of the growth of the PESu spherulites from regime II to regime III. Both the nucleation constants and activation energy increase with increasing the irradiation dose. The gamma irradiation increases the energy barrier for the migration of polymer chains.     

Thermal and optical properties of electron beam irradiated cellulose triacetate

Samples from Cellulose triacetate (CTA) sheets were irradiated with electron beam in the dose range 10–200 kGy. Non-isothermal studies were carried out using thermogravimetric analysis (TGA) to obtain the activation energy of thermal decomposition for CTA polymer. The CTA samples decompose in one main break down stage. The results indicate that the irradiation by electron beam in the dose range 80–200 kGy increases the thermal stability of the polymer samples. Also, the variation of melting temperatures with the electron dose has been determined using differential thermal analysis (DTA). The CTA polymer is characterized by the appearance of one endothermic peak due to melting. It is found that the irradiation in the dose range 10–80 kGy causes defects generation that splits the crystals depressing the melting temperature, while at higher doses (80–200 kGy), the thickness of crystalline structure (lamellae) is increased, thus the melting temperature increases. In addition, the transmission of these samples in the wavelength range 200–2500 nm, as well as any color changes, were studied. The color intensity ΔE* was greatly increased on increasing the electron beam dose, and accompanied by a significant increase in the blue color component.      

飞秒激光诱导Li2O-Nb2O5-SiO2玻璃析晶拉曼谱研究

通过使用波长 800nm、重复频率 250kHz的飞秒激光脉冲聚焦进Li2O-Nb2O5-SiO2组分的玻璃内部,空间选择性诱导出铌酸锂微晶.为了进一步地研究辐照区域晶体的生长机制,使用显微拉曼光谱仪分析了玻璃样品辐照区域不同位置的结构变化.研究表明,在飞秒激光辐照一段时间后的聚焦区域,由于非线性效应和热累积效应形成了一个高温辐射梯度场,在激光辐照中心区域超过玻璃的析晶温度而促使玻璃熔融析晶.     

Structure development in curing of poly(phenylene sulfide)

The structure development during melt curing of poly(phenylene sulfide) (PPS) is reported. The changes in the structure were monitored using various characterization techniques such as differential scanning calorimetry, thermogravimetric analysis, infrared spectroscopy, and optical microscopy. It was observed that the thermal parameters such as melting point and heat of fusion are very sensitive to the structural changes and can be effectively used to monitor the curing process. The effect of curing environment was also investigated, and it was found that the rate of change of structure is considerably higher in air than in nitrogen. The results are discussed on the basis of the different mechanisms for curing of PPS.     

Radiation effects on poly(vinylidene fluoride)

Melt-crystallized poly(vinylidene fluoride)s (PVF₂) with different crystallization histories were irradiated with γ-rays within the range of irradiation doses 0–83 Mrad. The effects on the crystalline structure and mechanical properties have been measured, compared, and discussed. The degree of crystallinity of the samples was found to increase with radiation dose. The differential scanning calorimeter scans of the quenched samples indicate that there are two melting peaks, and that the area of the lower temperature peak increases while the area of higher temperature peak decreases with increasing dose. Yield stress and breaking stress for all samples are not significantly affected by irradiation but elongation at break is.     

Effect of proton irradiation on the physical properties of PC/PBT blends

Samples from polycarbonate/poly (butylene terephthalate) (PC/PBT) blends film have been irradiated using different fluences (1?×?10¹⁵– 5?×?10¹⁷ H⁺/cm²) of 1?MeV protons at the University of Surrey Ion Beam Center, UK. The structural modi?cations in the proton irradiated samples have been studied as a function of fluence using different characterization techniques such as X-ray diffraction and UV spectroscopy. The results indicate that the proton irradiation reduces the optical energy gap that could be attributed to the increase in structural disorder of the irradiated samples due to crosslinking. Furthermore, the color intensity ΔE, which is the color difference between the non-irradiated sample and those irradiated with different proton fluences, increased with increasing the proton fluence up to 5?×?10¹⁷ H^+/cm², convoyed by an increase in the red and yellow color components. In addition, the resultant effect of proton irradiation on the thermal properties of the PC/PBT samples has been investigated using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). It is found that the PC/PBT decomposes in one weight loss stage. Also, the variation of transition temperatures with proton fluence has been determined using DSC. The PC/PBT thermograms were characterized by the appearance of two endothermic peaks due to the glass transition and melting temperatures. The melting temperature of the polymer, T_m, was investigated to probe the crystalline domains of the polymer, since the proton irradiation destroys the crystalline structure so reducing the melting temperature.     

Electron induced modification in poly(ethylene terephthalate)

Abstract

The effect of 100 kGy dose of 2 MeV electron irradiation on Poly(ethylene terepthalate) (PET) has been studied by different characterisation techniques such as the Fourier transformed IR spectroscopy, electron spin resonance spectroscopy, thermogravimetric analysis, differential scanning calorimetry and X-ray diffraction analysis. Oxidative degradation leading to amorphisation of the polymer has been observed from spectral analysis. The thermal stability of the polymer was found to decrease due to electron irradiation. The thermal decomposition temperature as well as the melting temperature in case of irradiated PET was found to be decreased due to electron bombardment. A decrease in crystallinity of the polymer has also been observed after irradiation.     

Effect of irradiation on interfacial interaction and structure formation in filled PTFE composites

The supramolecular structure and tribological properties of filled polytetrafluoroethylene composites irradiated above the melting point of the crystalline phase of the polymer component and the phase transitions in them are investigated. In unirradiated composites, phase separation is observed, that is, the separation of the filler from the polymer matrix. The supramolecular structure of the polymer component does not depend on the nature and concentration of the filler, and it is characterized by the formation of lamellae during sintering and subsequent crystallization. Radiation exposure leads to the disappearance of the phase separation and the formation of axiolites with the radial orientation of fibrils, in the center of which the filler particles are located. Changes in the structure are explained by an increase in interfacial interactions through the radiation grafting of macromolecules (and low-molecular-weight products) to the surface of the filler particles. The linear wear rate of irradiated composites is 50 times lower relative to the unirradiated samples because of the transition from the delamination to abrasive wear mechanism.     

Electron induced modification in polypropylene

The effect of 23 kGy dose of 2 MeV electron irradiation on polypropylene has been studied by different characterisation techniques, viz. Fourier transform IR spectroscopy, electron spin resonance spectroscopy, thermogravimetric analysis, differential scanning calorimetry and X-ray diffraction analysis. The thermal stability of the polymer was found to be increasing due to electron irradiation. The thermal decomposition temperature as well as the melting temperature in case of irradiated polypropylene was found to increase due to electron bombardment. The isotactic nature of the polymer was found to be unaffected by electron irradiation. An increase in crystallinity of the polymer has also been observed after irradiation.     

The mechanisms of recrystallization after melting in syndiotactic polypropylene and isotactic polystyrene

Several semicrystalline polymers show a recrystallization after melting during a heating scan. We have studied the mechanisms of such recrystallization processes for two different polymers, namely syndiotactic polypropylene (sPP) and isotactic polystyrene (iPS). This was done by monitoring the structure evolution during the recrystallization process and its changes during a subsequent heating scan via time- and temperature-dependent SAXS measurements, respectively. The results of this study showed that the sPP samples exhibited a recrystallization mechanism similar to the multi-stage route found upon initial crystallization of semicrystalline polymers from an entangled melt. Meanwhile, a different recrystallization mechanism was shown by the iPS samples. In this case, the recrystallization process proceeded as a direct growth into the melt in a one-step process. This is the first time we have observed such a mechanism which resembles the picture presented by the classical models for crystallization from an entangled polymer melt. The reason for such different mechanisms may be related to the initial melt state prior to crystallization. It seems as though, when crystallization sets in an entangled polymer melt, it follows the multi-stage route, whereas if the melt is locally disentangled, it proceeds by a direct growth mechanism. Received 23 July 2001 and Received in final form 4 October 2001     

聚丙烯/抗老化剂复合体系的γ-射线辐照降解研究

研究了聚丙烯(PP)及含有受阻酚类抗氧剂和受阻胺类光稳定剂复合体系的PP复合物经过γ-射线辐照后发生的结构变化及抗老化剂所起作用。实验利用红外光谱(FTIR)和示差扫描量热法(DSC)对PP的结构变化进行了系统表征。研究结果表明,当辐照剂量较小(50 kGy)时,纯PP及其复合物体系均未发生明显降解;当辐照剂量较大(≥50 kGy)时,PP及其复合物的羰基指数迅速提高,二者的结晶温度和熔融温度大幅度降低,说明PP发生了严重降解。在相同γ-射线辐照剂量条件下(≥50 kGy),PP复合物的羰基指数高于纯PP,而结晶温度以及熔融温度低于纯PP,表明高辐照剂量下抗老化剂复合物的存在不但没有阻止聚丙烯的降解,反而加快了降解的速率。     

The Role of Poly(phenylene sulfide) Microfibrils in Isothermal Crystallization of Isotactic Polypropylene under Shear

An optical polarizing microscope with a hot shear stage was used for an in‐situ investigation of the influences of poly(phenylene sulfide) (PPS) microfibrils on isothermal crystallization of isotactic polypropylene (iPP) under shear. As the nucleation sites on the PPS microfibril's surface are not able to induce a transcrystalline layer, there are only spherulites generated in a PPS/iPP in‐situ microfirbillar blend in quiescent condition. Applying shear during isothermal crystallization, the crystalline morphology greatly changes. There are fibrillar nuclei induced after steady shear with a shear rate of 5 and 10 s^–1, and these nuclei formed fibrillar crystals after crystallization completion. Two opposite effects coexist in PPS/iPP in‐situ microfibrillar blends during shear‐induced isothermal crystallization; one is the obstructive effect of PPS microfibrils on the iPP molecular chains orientation; the other is the positive effect provided by stress between fiber and matrix, generated by shear, which reduces the potential barrier of crystallization. The results of wide angle x‐ray diffraction (WAXD) show that there are β‐iPP crystals generated in neat iPP and PPS/iPP blends, but that PPS microfibrils have an inhibiting influence on the formation of β‐iPP.     

Erosion of polyimide modified by amorphous silica sol in the stream of oxygen plasma

Polymeric coatings derived from Kapton H polyimide, thermoplastic polyimide (PI), and a composite with amorphous silica sol (PI-SS) were irradiated in a magnetoplasma dynamic accelerator of oxygen plasma simulating the action of atomic oxygen (AO). The volumetric erosion coefficients of polymers were calculated, and the comparative analysis of the stability of coatings was performed. The changes in morphology of polymer surfaces before and after irradiation were studied by means of scanning electron microscopy. It was shown that the PI-SS composite has increased resistance to atomic oxygen. The composition of the PI-SS composite was found at which the particles of silica sol are uniformly dispersed over the polymer volume that explains a better resistance of PI-SS polymeric-inorganic compositions to the action of atomic oxygen. The lowest stability was registered for the coating based on Kapton H polyimide. The surfaces of all coatings after irradiation were found to possess a carpetlike morphology. Each polymer featured a number of distinctive peculiarities of the surface structure caused by the differences in the chemical structure of the polymides under investigation.     

Influence of a plasma jet on different types of tungsten

The influence of a plasma producing nonstationary thermal loads akin to edge-localized modes in a tokamak on different types of tungsten is investigated. Tungsten is irradiated by a jet of a hydrogen plasma generated in a plasma gun. The plasma density and velocity are on the order of 10²² m^?3 and 100–200 km/s, respectively, and the irradiation time is 10 μs. Two plasma flux densities, 0.70 and 0.25 MJ/m², are used. Structural modifications in irradiated single-crystal and hot-rolled tungsten samples, as well as in V-MP and ITER_D_2EDZJ4 tungsten powders, are examined. It is found that the plasma generates a regular crack network with a period of about 1 mm on the surface of the single-crystal, hot-rolled, and V-MP powder samples, while the surface of the ITER_D_2EDZJ4 powder is more cracking-resistant. The depth of the molten layer equals 1–3 μm, and the extension of intense thermal action is 15–20 μm. The material acquires a distinct regular structure with a typical grain size of less than 1 μm. X-ray diffraction analysis shows that irradiation changes the crystal lattice parameters because of the melting and crystallization of the surface layer. The examination of the V_MP tungsten powder after cyclic irradiation by a plasma with different energy densities shows that high-energy-density irradiation causes the most significant surface damage, whereas low-energy-density irradiation generates defects that are small in size even if the number of cycles is large.     

HT—6B等离子体对金属玻璃的辐照效应

金属玻璃是由熔态经急冷淬火形成的非晶态金属,具有很高的力学强度和良好的抗腐蚀、耐辐照性能。关于中子、质子、电子和He、Ar离子等分别对金属玻璃的辐照损伤效应已有一些研究报道。托卡马克装置中的等离子体辐照是一种十分复杂的过程,它包括有质子、电子、光子、氘核和少量杂质重离子与中性粒子的混合辐照。本工作研究了某些金属玻璃在托卡马克装置真空器壁处经等离子体辐照以后的结构变化,探索金属玻璃用于托卡马克核聚变装置真空器壁的可能性。     

Compaction of poly(dimethylsiloxane) (PDMS) due to proton beam irradiation

This work is about the detailed investigation of the changes of the surface topography, the degree of compaction/shrinkage and its relation to the irradiation fluence and the structure spacing in poly(dimethylsiloxane) (PDMS) patterned with 2 MeV proton microbeam. The irradiated periodic structures consisted of parallel lines with different widths and spacing. To achieve different degrees of compaction, each structure was irradiated with more different fluences. At the irradiated areas the surface topography, the adhesion, the wettability and the rigidity of the surface also changes due to the chemical/structural change of the basic poly(dimethylsiloxane) polymer. The surface topography, the phase modification of the surface, and the connection between them was revealed with using an atomic force microscope (AFM).     

Effect of gamma irradiation on high temperature hardness of low-density polyethylene

Gamma irradiation can cause the change of microstructure and molecular structure of polymer, resulting in the change of mechanical properties of polymers. Using the hardness measurement, the effect of gamma irradiation on the high temperature hardness of low-density polyethylene (LDPE) was investigated. The gamma irradiation caused the increase in the melting point, the enthalpy of fusion, and the portion of crystallinity of LDPE. The Vickers hardness of the irradiated LDPE increases with increasing the irradiation dose, annealing temperature, and annealing time. The activation energy for the rate process controlling the reaction between defects linearly decreases with the irradiation dose. The process controlling the hardness evolution in LDPE is endothermic because LDPE is semi-crystalline.     

Molecular dynamics simulation of structural changes in metals under irradiation with high-energy heavy ions

To study the processes of irradiating metals with high-energy heavy ions, a thermal spike model is often used, i.e., a system of electron-gas thermal conductivity equations and a lattice. Upon the irradiation of materials with high-energy heavy ions, more than 90% of the energy is consumed in the excitation of the electronic subsystem of the irradiated material. Further, this energy is transferred to the lattice subsystem and there is high heating of the lattice in a small volume, which can cause melting (evaporation), resulting in a structural change (amorphization, formation of high pressure areas, tracks, etc.) in the irradiated material. This work is devoted to studying structural changes in the surface of nickel by irradiation with high-energy ions of uranium. The thermal spike model is used for the initial distribution of temperature conditions in the irradiated nickel, which imitates the action of radiation on a molecular-dynamic system. The further evolution of the system is studied by molecular dynamics. As part of this approach, the processes of structural changes on the surface of the irradiated target can be investigated in more detail.     

Fabrication of optical devices in poly(dimethylsiloxane) by proton microbeam

Optical diffraction grating and micro Fresnel zone plate type structures were fabricated in relatively thin poly(dimethylsiloxane) (PDMS) layers using proton beam writing technique and the performance of these optical devices was tested. PDMS is a commonly used silicon-based organic polymer, optically clear, generally considered to be inert, non-toxic and biocompatible. PDMS has been used as a resist material for direct-write techniques only in very few cases. In this work, PDMS was used as a resist material; the structures were irradiated directly into the polymer. We were looking for a biocompatible, micropatternable polymer in which the chemical structure changes significantly due to proton beam exposure making the polymer capable of proton beam writing. We demonstrated that the change in the structure of the polymer is so significant that there is no need to perform any development processes. The proton irradiation causes refractive index change in the polymer, so diffraction gratings and other optical devices like Fresnel zone plates can be fabricated in this way. The observed high order diffraction patterns prove the high quality of the created optical devices.