多臂星形聚乙二醇-聚乳酸嵌段共聚物的降解特性EI北大核心CSCD

采用直接法合成了线型和多臂星形聚乙二醇-聚L-乳酸嵌段共聚物((PLLA-b-PEG-b-PLLA和sPEG-b-PLLA)。研究了3种嵌段共聚物在37℃、pH=7.2的磷酸盐缓冲液中的降解机理。结果表明,共聚物降解后失重明显,亲水性降低;降解一定时间后共聚物的相对分子质量分布呈双峰分布,随着降解的进行,较低相对分子质量组分的相对分子质量并没有发生明显的变化。XRD数据表明,降解前后的主要组成为结晶PLLA嵌段;1H-NMR分析证实,共聚物的降解过程中PEG嵌段和PLLA嵌段内部的降解程度很小。说明sPEG-b-PLLA在中性水性体系中的降解主要发生在连接PLLA和PEG的酯键上,而PLLA嵌段则由于处于结晶态,降解程度很低。     

NMR研究聚乙二醇的热氧降解

采用1H，13C和2D－NMR技术研究了聚乙二醇（PEG）的热氧降解，对产物的结构作了详细分析和表征，并定量讨论了抗氧剂2，6－二叔丁基－4－甲基酚（BHT）对其热氧解降解的影响，PEG的氧化降解发生在醚键氧碳上，遵循自由基氧化机理，最后形成大量的甲酸酯等酯类以及甲基，亚甲二氧基和醇，抗氧剂BHT不仅降低了PEG的氧化降解程度，而且改变了降解产物的结构分布，显著抑制了碳酸酯和亚甲二氧基结构的生成，相对增加了端羟基和端甲基结构。     

热氧老化对阻燃型长玻纤增强尼龙6静动态力学及降解动力学的影响

研究了160℃不同热氧老化时间对阻燃型长玻纤增强尼龙6(FR/PA6/LGF)复合材料的静、动态力学性能及降解行为的影响。热与氧对FR/PA6/LGF复合材料的影响通过差示量热分析、动态力学性能分析、扫描电镜及力学性能表征。结果表明,虽然由动态力学性能分析可知热氧老化使得树脂基体分子链的刚性增加,但最终基体分子链断裂、降解导致老化试样表面出现的凹坑、微裂纹和脱粘在老化进程中占据了主导地位。利用Ozawa法求出了不同老化时间处理后FR/PA6/LGF热氧降解反应的活化能,结果表明热氧老化降低了阻燃材料的热稳定性,影响了其在不同燃烧区的阻燃效率。     

阻燃型玻纤增强尼龙10T复合材料的热氧老化行为及热降解动力学

研究了不同热氧老化温度(160℃、200℃和240℃)和时间(0~50d)对溴化环氧树脂/Sb2O3协效阻燃短玻纤增强尼龙10T复合材料(PA10T/GF/FR)的热氧老化行为以及热降解动力学的影响。采用力学性能测试、SEM、DMA和TGA分析对老化前后复合材料的动静态力学、微观形貌以及热降解行为进行研究,并使用Kissinger和Flynn-Wall-Ozawa两种方法计算了复合材料的热降解活化能。结果表明:老化过程中基体树脂降解分子量降低,纤维与基体界面性能恶化,复合材料力学性能下降;160℃老化过程部分PA10T分子链发生交联反应,储能模量和玻璃化转变温度(Tg)增加,200℃和240℃下Tg先上升后下降,老化后期树脂分子链以降解为主;活化能计算表明160℃老化50d后复合材料热稳定性提升,200℃老化50d以及240℃老化30d后,复合材料结构破坏严重,热降解行为变化显著。此外,阻燃剂的添加能够提升老化试样的热稳定性。     

95 ℃热水老化后聚碳酸酯的热稳定性

目的研究聚碳酸酯(PC)在95℃热水老化后的热稳定性。方法通过体视显微镜进行表观形貌分析;氮气下进行热重分析,用Freeman-Carroll法和Coats-Redfern法进行热降解动力学分析;利用凝胶渗透色谱进行分析。结果 PC经过热水老化后内部会产生缺陷,随着老化时间的延长,缺陷数量增多,尺寸变大;热稳定性随热水老化时间的延长总体呈下降趋势,残炭量增多,相对分子质量降低,大分子链降解。结论 95℃热水老化后PC的热稳定性降低。     

不同聚乙二醇相对分子质量的聚碳酸酯聚氨酯的防水透湿性

采用不同相对分子质量的聚乙二醇(PEG)分别与聚碳酸酯二元醇(PCDL)、二苯基甲烷二异氰酸酯(MDI)反应,合成了一系列聚碳酸酯聚氨酯(PU)。通过差示扫描量热分析、红外光谱分析、原子力显微镜分析等研究了不同相对分子质量的PEG对聚碳酸酯聚氨酯的形态结构和防水透湿性的影响。研究结果表明,分子链中引入PEG后,PU软段的Tg逐渐下降,且PU软硬段均不结晶。随着PEG相对分子质量的提高,PU微相分离程度先减小后增大,PU的亲水性提高,透气性先减小后增大。     

三种添加物对聚乳酸复合膜性能影响

目的 研究聚乳酸复合膜的降解性能,加快聚乳酸材料降解速率。方法 选取淀粉、羧甲基纤维素钠（CMC）、聚乙二醇（PEG）等3种材料,与聚乳酸混合制备4种不同的复合膜。测定复合膜的透光率、力学性能、热性能等指标,使用红外光谱仪对复合膜的基团组成进行表征,使用磷酸盐缓冲液浸泡,测试其降解性能。结果 红外光谱结果显示PLA膜与PLA复合膜的吸收峰没有明显的差别,这证明改性材料与聚乳酸没有发生化学反应。复合膜的DSC曲线显示,添加改性剂后,熔融温度变化不大,无明显影响。降解性能方面,按PLA与复合物的质量比9∶1,8∶2,7∶3,6∶4,5∶5制备多种复合膜,其中质量比9∶1,7∶3,5∶5的PLA/淀粉复合膜在第70天降解率分别为24.11%,24.8%,35.6%;PLA/CMC复合膜的3种质量比降解率为27.64%,30.37%,45.2%。按照PLA与PEG质量比为99∶1,98∶2,97∶3,96∶4,95∶5制备了PLA/PEG复合膜,其中质量比为99∶1,97∶3,95∶5的PLA/PEG复合膜在第70天的降解率分别为25.45%,38.83%,45.83%。PLA/淀粉/PEG复合膜是在PLA/淀粉复合膜的基础上添加PEG制备的,复合膜成分与PEG的质量比为99∶1,98∶2,97∶3,96∶4,95∶5,其中99∶1,97∶3,95∶5这3种复合膜的降解率为40.52%,49.54%,55.67%。各种复合膜的降解率均远优于PLA膜2.5%的降解率。结论 复合材料的添加改变了聚乳酸薄膜的透光性能,增强了薄膜的拉伸强度和断裂伸长率。改性材料的添加能够在不影响聚乳酸本身结构的情况下,显著增强聚乳酸的降解率。     

不同分子量聚乙二醇/二氧化硅定型相变材料的性能

以聚乙二醇为相变材料、二氧化硅为基体材料,采用温度促凝法制备出不同相对分子质量的聚乙二醇/二氧化硅定型相变材料(PEG/SiO2ss-PCMs)。运用综合热分析、红外光谱及偏光显微镜分析不同相对分子质量的PEG对PEG/SiO2性能的影响。结果表明,ss-PCMs中PEG与SiO2凝胶相互之间是靠氢键进行简单的物理吸附的,SiO2未影响PEG的相变行为,ss-PCMs中的PEG仍具有良好的结晶性能。ss-PCMs的相变温度、相变焓随相对分子质量的增加而增长,在多次温度循环下相变焓为85.3 J/g~108.1 J/g。     

改性聚乙烯醇/聚乙二醇共混复合材料的制备与性能

通过溶液共混法制备了改性聚乙烯醇(VE-PVA)与不同类型聚乙二醇(PEG)的共混复合材料,分别研究了相对分子质量、含量、不同端基类别的聚乙二醇对VE-PVA/PEG复合材料性能的影响。通过差示扫描量热分析、动态力学分析、拉伸测试、动态流变测试等考察VE-PVA/PEG复合材料的热性能、力学性能及流变性能。结果表明,PEG和VEPVA是相分离体系,各自形成独立的晶相。PEG在一定程度上会阻碍VE-PVA结晶,降低其结晶温度和结晶度。PEG对VE-PVA有明显的增塑和润滑作用,能降低熔体黏度,改善体系加工性能。而且PEG中端羟基含量越大,增塑作用越强。当PEG质量分数小于10%时,能提高复合材料的断裂伸长率。     

极性化SBS的热氧老化——(I)微观结构变化

利用动态力学分析、红外光谱分析以及光电子能谱(XPS)分析方法,研究了不同老化条件下极性化SBS(SBSVP)的热氧老化行为。试验结果表明,不含防老剂的SBSVP在高温下会发生老化,在SBSVP的热氧老化过程中,先以交联反应为主,而后降解反应占优势,聚合物交联密度的变化导致模量和玻璃化转变温度发生相应的变化。老化后,SBSVP中C=C键的含量逐渐降低,生成C=O键。随着SBSVP老化温度的升高和老化时间的延长,聚合物表面氧元素的相对含量会发生相应的变化。对于SBSVP的热氧老化来说,温度的影响要大于时间的影响。     

AGING CHARACTERISTICS OF TERNARY BLENDS OF POLYETHYLENES. I

Degradation of a low-density polyethylene (LDPE)/linear low-density polyethylene (LLDPE)/high-density polyethylene (HDPE) blend having different weight ratios of LLDPE (10-35 wt%) and HDPE (40-65 wt%) with fixed percentage of LDPE (25 wt%) was studied by aging the film samples at 55, 70, 85, and 100°C in air. Reactions involved in changing the molecular structure and formation of oxygenated and unsaturated groups during thermo-oxidative degradation are discussed. The molecular weight (M_v) showed very little change in the initial hours of aging at different temperatures. Tensile strength was found to increase initially and then decrease with aging time. The increase in tensile strength suggests molecular enlargement, mainly by recombination of alkyl and alkoxy radicals, which produces nonradical products. The thermal stability decreases with increase in aging time and temperature.     

热氧老化对纬编双轴向多层衬纱织物增强复合材料力学性能的影响

通过改变预制体结构衬纱取向的方法制备了几种含不同剪切角的纬编双轴向多层衬纱(Multilayered biaxial weft knitted,MBWK)织物增强复合材料。基于Arrhenius模型和Ozawa法设计了热氧老化试验,采用力学性能测试、DSC、FTIR和DMA测试对老化前后的试样热-物理性能进行了表征。实验结果表明：预制体的纱线剪切角不同,其复合材料受热氧老化后力学性能的保留率也显著不同,由于乙烯基酯树脂在热氧老化环境中会发生后固化现象,因此复合材料的弯曲模量在老化过程中呈现先增加后下降的趋势,而拉伸性能则受到增强体结构的影响,纤维/基体界面的结合力退化使拉伸模量在老化过程中持续下降;随着老化时间的延长,树脂的固化度逐渐增加,玻璃化转变温度T_g逐渐升高,储能模量峰值在老化初期由于分子链交联上升,老化后期分子链断裂占据主导作用致使峰值逐渐下降。     

Accelerated thermo-oxidative aging for carbon fiber reinforced polycyanate under high pressure atmosphere

The aim of this study is to accelerate thermo-oxidative aging in carbon fiber reinforced plastics (CFRP) submitted to high temperature atmospheric pressure. In this study, long-term thermo-oxidative aging test was conducted to examine the effect of high pressure atmospheric environment on the weight and mechanical properties of CFRP to accelerate the rate of thermo-oxidative degradation. The effect of thermo-oxidative environment under high atmospheric pressure on the change in weight, strength, and shrinkage behavior of a CFRP with polycyanate (FSD-M-08178) was investigated. The aging test was conducted at 180 °C up to 8,000 h under atmospheric pressure and the test result was used as a reference data. Other aging tests were also conducted under elevated pressure conditions (0.3 and 0.5 MPa) at the same exposure temperature up to 2,000 h and the test results were treated as the accelerated aging test data. Unidirectional laminates [0]₈ and [90]₈ for tensile specimens and angle ply laminates [±45]_2S for off-axis tensile specimens were aged in oven, and then mechanical tests were carried out on them. The results indicated that elevated pressure would cause faster and larger weight gain in earlier aging period. The outcomes of these experiments were changes in weight, strength, and local shrinkage deformation were changed quickly under elevated atmospheric pressure environment. Same micro damage onset and extension irrespective of pressure during thermo-oxidative aging and subsequent loading test were observed. The test results indicate that the change in weight, strength, and local shrinkage deformation could be accelerated by elevated pressure without change in thermo-oxidative degradation mechanism. Therefore, the elevated pressure testing would be a better method to accelerate thermo-oxidative degradation. On the other hand, the change in strength under elevated pressure conditions is faster than local shrinkage deformation. Equivalent acceleration rate of degradation could not be obtained.     

结晶度对高密度聚乙烯热氧老化特性的影响

研究了结晶度对高密度聚乙烯(HDPE)在110℃人工热氧老化条件下老化特性的影响,分别采用力学实验、衰减全反射红外光谱技术、凝胶渗透色谱、扫描电子显微镜和X射线衍射技术比较了不同结晶度HDPE的热氧老化特性,研究了结晶度对聚乙烯力学性能、化学结构、相对分子质量、表面微观结构和晶体结构的影响规律。结果表明,结晶度越高,HDPE拉伸强度、拉伸模量和弯曲模量下降越快,抗冲击性能提高;不饱和度增长越剧烈,支化作用和断链作用更明显,羟基指数增长更快,且区别主要集中于老化后期;相对分子质量分布下降越快;表面微观形貌老化程度越严重;主要晶面衍射角和晶胞参数变化越显著。结晶度越高,HDPE缺陷也就越多,在热氧环境中越容易发生氧化,老化现象更严重。     

双酚A缩水甘油醚/乙二胺环氧树脂的热分解行为

采用傅里叶红外光谱法研究了双酚A缩水甘油醚/乙二胺环氧树脂(DGEBA/EDA)在不同温度时分解残留物的红外吸收光谱;利用热分析技术考察了DGEBA/EDA从室温到600℃之间的热解反应。结果表明,DGEBA/EDA环氧树脂在氮气中分解时存在一个热解阶段,最低热解活化能为195.74 kJ/mol。色谱-质谱联用(GC/MS)分析DGEBA/EDA环氧树脂热解残留物,表明在热解过程中主要生成苯酚、对异丙基苯酚和双酚A。讨论了DGEBA/EDA环氧树脂热解的机理。经热解后的残留环氧树脂的热稳定性降低明显,环氧树脂发生了明显的化学裂解。     

Anisotropic oxidation and weight loss in PMR-15 composites

Durability and degradation mechanisms in composites are fundamentally influenced by the fiber, matrix, and interphase regions that constitute the composite domain. The thermo-oxidative behavior of the composite is significantly different from that of the fiber and matrix constituents as the composite microstructure, including the fiber–matrix interphases/interfaces, introduces anisotropy in the diffusion behavior. In this work, unidirectional G30-500/PMR-15 composite specimens were aged at elevated temperatures in air resulting in oxidation propagation parallel and perpendicular to the fibers. Four different specimen geometries were chosen such that different surface area ratios (i.e., ratios of surface area perpendicular to the fibers to surface area parallel to the fibers) were obtained. Weight loss and volumetric changes were monitored as a function of aging time to study the high-temperature anisotropic oxidation process. Optical micrographs were taken on polished internal sections and viewed in the dark-field mode to measure the degree, depth and distribution of thermal oxidation development from surfaces perpendicular and parallel to the fibers. An empirically based weight loss model is investigated and used to predict weight loss in unidirectional and woven composites.     

聚乙二醇辅助光化学制备SnO2及其光催化性能

采用硫酸亚锡作为锡源,加入4种不同分子量的聚乙二醇(PEG),于低功率紫外光辐照下制备二氧化锡。通过X射线衍射(XRD)、扫描电镜(SEM)、傅里叶变换红外光谱(FT-IR)和比表面测试对其结构与形貌进行表征。考察聚乙二醇分子量变化对产物结构和光催化性能的影响。所制备SnO2的形貌尺寸、比表面积以及其光催化性能与使用PEG的分子量密切相关,分子量越大,所制备SnO2粉体尺寸越小,分布越均匀。以甲基橙为目标降解物进行光催化实验,结果表明,分子量为6000的聚乙二醇诱导制备的二氧化锡在模拟可见光和紫外光照下均显示了较高的催化活性。     

等离子体表面接枝改性聚对苯二甲酸乙二醇酯的血液相容性研究

利用等离子体表面接枝改性方法在聚对苯二甲酸乙二醇酯(polyethylene terephthalate，PET)材料表面接枝不同分子量的聚乙二醇(PEG)，体外血液相容性实验表明．接枝了PEG的PET材料的血液相容性与PEG的分子量有关；当接枝的PEG分子量达到6000时，材料的血液相容性最好。     

Effect of long-term thermo-oxidative aging on weight and fracture toughness of polycyanate neat resin

This study focuses on the effect of long-term thermo-oxidative aging on weight and fracture toughness (K_IC) of polycyanate ester (PCy) neat resin (FSD-M-08178). Thermo-oxidative aging was conducted at 180 °C up to 8000 h under atmospheric pressure in order to investigate susceptibility to thermo-oxidative environment in the PCy. Weight and K_IC changes were investigated with chemical structure changes due to thermo-oxidative degradation. The chemical structure changes were analyzed by means of Fourier transformed infrared spectroscopy with attenuated total reflection system. To investigate degree of degradation, carbonyl index (CI) was analyzed with triazine ring peak which is characteristic peak of the cured polycyanate resin. Single-edge-notch bending test was conducted for each aged (non-aged, 100, 197, 500, 1000, 2000, 4000, and 8000 h) condition to investigate K_IC change and evaluated with CI. The result indicated that the weight increased first 500 h. Then, the weight decreased. The result also indicated that the K_IC sharply dropped first 100 h. After 100 h, the K_IC was almost same up to 8000 h. The result suggested the K_IC depend on the CI which was chemical structure changes of the specimen surface due to thermo-oxidation degradation.