Influence of chain extenders on the melt strength and thermal stability of polyglycolic acid

Biodegradable polyglycolic acid (PGA) has been attracting much attention recently. However, poor melt strength and thermal stability limit the processing of PGA by methods such as film blowing and injection molding. To improve melt strength and thermal stability, two reactive chain extenders, styrene–acrylonitrile-glycidyl methacrylate terpolymer (poly(St-AN-GMA)) and 4, 4′-methylenebis(phenyl isocyanate) (MDI), were incorporated respectively into PGA using twin-screw extrusion. MDI was found to be more effective in chain extension and enhancing thermal stability than poly(St-AN-GMA). The T_-5% (the temperature where the remaining weight percentage is 95%) of PGA modified with 3 wt% MDI increased to 334.5°C from 310.8°C for pure PGA. Melt flow rate for the same materials decreased from 47.2 g/10 min to 13 g/10 min. The activation energy of thermal degradations for MDI-modified PGA was twice that of the unmodified PGA as evaluated by the Flynn-Wall-Ozawa method.     

High strength retention and dimensional stability of silicone/alumina composite panel under fire

Compact silicone/alumina composite was obtained by highly filling aluminum oxides and hydroxides in silicone resin. The flexural strength and dimensional change of the silicone/alumina composite after being fired has have been studied. It presented a special fire resistance, which could well coordinate the contradiction between the mechanical strength retention and the dimensional stability of silicone‐based composite in case of catching fire. Thermogravimetric analysis, scanning electron microscopy, X‐ray diffraction, transmission electron microscopy, and electron dispersion spectroscopy were applied to systematically explore the process of the in‐suit organic‐to‐inorganic transformation. A possible mechanism was proposed to illustrate the phenomenon of the high strength retention and dimensional stability of silicone/alumina composite under fire. Copyright © 2011 John Wiley & Sons, Ltd.     

Research on high temperature thermal stability and safety of two types of composite inorganic phase change thermal storage materials

In this paper, nitrate (KNO₃, NaNO₃) and carbonate (Li₂CO₃, K₂CO₃, Na₂CO₃ and CaCO₃), which are composite inorganic phase change thermal storage materials suitable for industrial thermal storage, non-toxic and less corrosive, are used as phase change components, respectively. The thermal properties (melting point, latent heat) of 4 different ratios of nitrate phase change components and 6 different ratios of carbonate phase change components were studied, and a distribution ratio of molten salt phase change components was selected respectively. Using the principle of porous carrier adsorption, two types of composite molten salt thermal storage materials with the best ratio were prepared. The ease of decomposition of the thermal storage materials in different media atmospheres (Ar and air) was analyzed. TG-DSC-MS tested high temperature thermal decomposition products show that the composite nitrate thermal storage materials have stable physical and chemical properties and good safety when storing thermal at medium temperature (300℃), but they are easy to decompose NO and high temperature (500℃) or higher. NO₂ and air atmosphere are more likely to generate toxic gases, and composite carbonate thermal storage materials are more likely to generate CO in air than Ar, which affects the safety of the thermal storage process.     

两类复合无机相变储热材料高温热稳定性和安全性研究

以适合工业储热的复合无机相变储热材料硝酸盐（KNO₃、NaNO₃）和碳酸盐（Li₂CO₃、K₂CO₃、Na₂CO₃和CaCO₃）为相变组分,研究了4种不同配比硝酸盐相变组分和6种不同配比碳酸盐相变组分的热性能（熔点、潜热）差异,分别优选出一种熔融盐相变组分配比。利用多孔载体吸附原理,制备出两种最佳配比的复合熔融盐类储热材料,分析了储热材料在不同介质气氛中（Ar和air）分解难易程度,TG-DSC-MS联用测试的高温热分解产物表明,复合硝酸盐类储热材料在中温（300℃）储热时,物理化学性能稳定,安全性较好,但在高温（500℃以上）时易分解成NO和NO₂,且air气氛中更易生成有毒气体;而复合碳酸盐类储热材料在air中比在Ar中更易生成CO而影响储热过程中的安全性。     

Highly filled multilayer thermoplastic/graphene conducting composite structures with high strength and thermal stability for electromagnetic interference shielding applications

Polyvinyl chloride (PVC)/graphene and poly(methyl methacrylate) (PMMA)/graphene nanocomposites were made by solution casting technique with graphene weight fractions of 1, 5, 10, 15, and 20%. Multilayer structures of the composites were made by hot compression technique to study their electromagnetic interference shielding effectiveness (EMI SE). Tensile strength, hardness, and storage modulus of the nanocomposites were studied in relation with graphene weight fraction. There has been a substantial increase in the electrical conductivity and EMI SE of the composites with 15–20% filler loading. Differential thermal analysis of the composites shows improved thermal stability with an increase in graphene loading. PMMA/graphene composites have better thermal stability, whereas PVC/graphene composites have superior mechanical properties. About 2 mm thick multilayer structures of PMMA/graphene and PVC/graphene composites show a maximum EMI SE of 21 dB and 31 dB, respectively, in the X band at 20 wt % graphene loading. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47792.     

Continuous aluminum oxide-mullite-hafnium oxide composite ceramic fibers with high strength and thermal stability by melt-spinning from polymer precursor

Continuous aluminum oxide-mullite-hafnium oxide (AMH) composite ceramic fibers were obtained by melt-spinning and calcination from polymer precursor that synthesized by hydrolysis of the aluminum isopropoxide, dimethoxydimethylsilane and hafnium alkoxide. Due to the fine diameter of 8–9 µm, small grain size of less than 50 nm and the composite crystal texture, the highest tensile strength of AMH ceramic fibers was 2.01 GPa. And the AMH ceramic fibers presented good thermal stability. The tensile strength retention was 75.48% and 71.49% after heat treatment at 1100 °C and 1200 °C for 0.5 h respectively, and was 61.57% after heat treatment at 1100 °C for 5 h. And the grain size of AMH ceramic fibers after heat treatment was much smaller than that of commercial alumina fibers even when the heat treatment temperature was elevated to 1500 °C, benefited by the grain size inhibition of monoclinic-HfO₂ (m-HfO₂) grains distributed on the boundary of alumina and mullite grains.     

Flexible conductive graphene/poly(vinyl chloride) composite thin films with high mechanical strength and thermal stability

The fabrication and characterization of ultrathin composite films of surfactant-wrapped graphene nanoflakes and poly(vinyl chloride) is described. Free-standing composite thin films were prepared by a simple solution blending, drop casting and annealing route. A significant enhancement in the mechanical properties of pure poly(vinyl chloride) films was obtained with a 2 wt.% loading of graphene, such as a 58% increase in Young’s modulus and an almost 130% improvement of tensile strength. Thermal analysis of the composite films showed an increase in the glass transition temperature of the polymer, which confirms their enhanced thermal stability. The composite films had very low percolation threshold of 0.6 vol.% and showed a maximum electrical conductivity of 0.058 S/cm at 6.47 vol.% of the graphene loading.     

High temperature stability in fluorosilicone vulcanisates

Fluorosilicones are less heat stable than conventional methyl silicones because (a) they are more likely to revert to low molecular weight cyclic products, and (b) they are more susceptible to oxidation and free radical attack generally. Reversion is promoted by base catalyst residues from the polymerization process, but the effect can be minimized by a proper choice of compounding ingredients and vulcanizing reagents. Oxidation leads to crosslinking and in certain circumstances this can mask the effect of reversion.     

High temperature interfacial phase stability of a Mo/Ti3SiC2 laminated composite

A Mo/Ti₃SiC₂ laminated composite is prepared by spark plasma sintering at 1300 °C under a pressure of 50 MPa. Al powder is used as sintering aid to assist the formation of Ti₃SiC₂. The fabricated composites were annealed at 800, 1000 and 1150 °C under vacuum for 5, 10, 20 and 40 h to study the composite's interfacial phase stability at high temperature. Three interfacial layers, namely Mo₂C layer, AlMoSi layer and Ti₅Si₃ solid solution layer are formed during sintering. Experimental results show that the Mo/Ti₃SiC₂ layered composite prepared in this study has good interfacial phase stability up to at least 1000 °C and the growth of the interfacial layer does not show strong dependence on annealing time. However, after being exposed to 1150 °C for 10 h, cracks formed at the interface.     

The measurement of melt flow and melt stability

The melt flow of a plastic as measured by the standard method (ASTM D-1238) is at a high enough stress so that the flow is non-Newtonian. If the die in the plastometer is replaced by a nonstandard, tapered die of large orifice, a lower stress can be used and the flows are shown to be comparable to Newtonian viscosities measured in a cone and plate rheometer. Under these conditions the plastometer can be used as a sensitive measure of the melt stability of a plastic.     

复合增韧酚醛泡沫塑料及其热稳定性能的研究

采用异氰酸酯(MDI)和聚乙二醇(PEG)协同增韧酚醛树脂发泡材料,通过对酚醛泡沫塑料进行红外分析(IR spectra),拉伸强度测试和冲击强度测试,研究了异氰酸酯和聚乙二醇的结构和用量等因素对增韧效果的影响,同时分析增韧酚醛泡沫的热稳定性和阻燃性。结果表明,酚醛树脂100份,改性剂的总量15份,异氰酸酯和聚乙二醇的质量比为1∶3时,冲击强度最大,达到6.224 kJ/m2,拉伸强度为1.26 MPa,泡沫粉化率降低了5.11%。热稳定性和阻燃性有都所下降,平均燃烧时间增加了4 s。     

High temperature failure envelopes for thermosetting composite pipes in water

Abstract

This paper presents the results of an investigation of the biaxial stress–strain behaviour of filament wound glass fibre reinforced composite pipes exposed to high temperature water. Two matrix systems were investigated: cycloaliphatic amine cured epoxy resin; and siloxane modified phenolic alloy. Water absorption tests on pipe using the two systems at 95°C showed equilibrium moisture contents of 0.5 and 4.5%, respectively, saturation being achieved within seven days at this temperature in both cases. The axial moduli of the pipes were determined at temperatures up to 160°C, using a bending test. Reductions were observed in the T _g of both systems in the water saturated condition. Biaxial loading tests were carried out on the two pipe systems at temperatures from 20 to 160°. The results are presented in the form of failure envelopes and stress–strain relationships under load. At the highest temperatures (above its T _g ), significant weakening of the epoxy system was observed, especially in matrix dominated loading conditions. In contrast, the failure envelopes for the phenolic system showed remarkably little temperature influence.     

High temperature strength and fractography of sintered silicon nitride

Influences of the sintering liquid system, temperature, microstructure and post sintering heat treatment of high temperature (30–1250°C) strength, Young's modulus and fracture toughness of sintered silicon nitride (SSN) have been studied. Based on quantitative fractography, typical fracture origin statistics has been presented for SSN. The measured strength of the SSN is in good agreement with the fractographically predicted strength.     

新型丝素复合膜的微结构表征及热稳定性

基于丝素的高分子复合材料可以广泛地应用于组织工程、生物医药和半导体材料等领域。通过物理-共混技术制备了一种新型生物高分子丝素/聚乳酸复合膜。利用扫描电镜、傅里叶红外光谱、拉曼光谱、X射线衍射和热分析技术对其形貌、结构和相态组分以及热稳定性进行了表征,探究了不同比例复合膜的微结构、相互作用机理和热稳定性。结果表明：随着丝素含量的增加,复合膜中的β-折叠含量增多,α-螺旋和无规卷曲含量减少,玻璃化转变温度提高;由于丝素与聚乳酸间的相互作用,提高了复合膜的热稳定性。     

纤维级复合阻燃PA 6的制备及其热稳定性研究

以三聚氰胺氰尿酸盐(MCA)与硫化锌(ZnS)或类石墨相氮化碳(g-C₃N₄)或9,10-二氢-9-氧杂-10-磷杂菲-10-氧化物衍生物(ZDOPO)复配体系为阻燃剂,与聚己内酰胺(PA 6)切片共混、造粒、干燥、纺丝,制备阻燃PA 6纤维;通过常规升温热失重分析以及模拟纺丝过程恒温热失重分析,研究阻燃剂种类及含量对PA 6共混体系热稳定性的影响。结果表明:在阻燃剂总质量分数为6.0%条件下,添加MCA/ZDOPO复配体系对PA 6共混体系的热稳定性影响最小,制备的阻燃PA 6纤维具有良好的力学性能和阻燃性能;添加MCA质量分数3.0%、ZDOPO质量分数3.0%,PA 6/MCA/ZDOPO共混体系热失重5%时的热分解温度为393.8℃,热失重10%时的热分解温度为412.6℃,与纯PA 6的热学性能非常接近,制备的阻燃PA 6纤维的断裂强度为1.9 cN/dtex,断裂伸长率为75.8%,极限氧指数可达29.0%。     

高温熔盐的热物性测试及热稳定性分析

为满足太阳能高温传热、蓄热的要求,以价格便宜的氯化物为原料,通过静态熔融的方法配制出新型混合熔盐,并采用热重差热联用热分析仪及其他实验手段对熔盐的熔点、相变潜热及热稳定性进行了表征。实验结果表明:氯化物的混合熔盐具有较低的熔点,合适的潜热值及高温下良好的热稳定性的特点。氯化物熔盐的适宜使用温度在550~800℃。该实验研究为氯化物熔盐在太阳能高温利用中的使用提供了宝贵数据。     

发泡用高熔体强度聚丙烯的研究

以过氧化苯甲酰(BPO)为引发剂,在同向双螺杆挤出机上对聚丙烯(PP)进行硅烷交联,制备了高熔体强度聚丙烯(HMSPP),然后制得高发泡倍率的PP制品.实验对改性PP的熔体强度、力学性能、热性能和发泡性能进行了表征.结果表明:自制HMSPP的熔体强度是纯PP的5.01倍,力学性能和耐热性与纯PP相比均有较大提高,可用于成型高发泡倍率制品.     

High temperature morphology and stability of nanoporous Ag foams

Nanoporous silver foams (75 % porosity) synthesized by dealloying Ag₂₅Al₇₅ using two different electrolytes were heat treated in either argon or vacuum in order to induce changes in the morphology and ligament size. Several techniques including scanning electron microscopy, Raman spectroscopy, and X-ray powder diffraction are utilized to study the elevated temperature morphology and oxide formation. The ligament sizes increase with heat treating temperature, except for the sample heat treated in vacuum at 600 °C. Results show no significant silver oxide formation for any of the foams.