液固相法纤维素氨基甲酸酯的合成与表征

在高沸点非质子强极性溶剂N-甲基吡咯烷酮(NMP)的作用下,使碱化处理的纤维素与尿素反应合成纤维素氨基甲酸酯。采用傅里叶变换红外光谱、凯氏定氮仪、热重分析仪、扫描电镜、广角X射线衍射仪、13 C-NMR核磁共振仪对纤维素氨基甲酸酯产物进行表征。结果表明,采用高沸点非质子强极性溶剂NMP的液固相法能够使碱纤维素上的基团部分被氨基取代,制得纤维素氨基甲酸酯;纤维素氨基甲酸酯结晶度降低、热分解温度降低、结构疏松,预期有较好的溶解性。     

低热膨胀系数超支化共聚聚酰亚胺的构建及性能EI北大核心CSCD

以2,3,3',4'-联苯四甲酸二酐、3,3',4,4'-联苯四羧酸二酐、对二氨基二苯醚、对苯二胺和合成三胺单体为原料,合成了含有超支化链段的新型共聚聚酰亚胺。研究表明,与线型低热膨胀系数聚酰亚胺(HB-Co-PIS-0)相比,超支化链段引入后,其显著的优点是溶解性变好,引入超支化链段5%时,聚酰亚胺可在极性大的溶剂二甲基甲酰胺和甲基吡咯烷酮中溶解,在四氢呋喃等极性小的溶剂中回流微溶。另外,其聚酰亚胺酸黏度降低,热膨胀系数值维持较低的数值,无序结构增多,玻璃化温度和热分解温度降低,拉伸强度增大,断裂伸长率减小。并且,超支化链段引入,使原线型低热膨胀系数聚酰亚胺微突起的致密表面变为更多纳米突起的粗糙疏松表面,水接触角从原来72°增加到76°(3%超支化)和85°(5%超支化)。     

聚丙烯(PP)/纳米二氧化硅SiO2复合材料的制备及其性能研究

纳米材料因其独特的性能而广泛应用于聚丙烯(PP)等高分子材料的改性.本文用纳米二氧化硅与PP共混进行改性,利用双螺杆共混方法制备聚丙烯(PP)/纳米二氧化硅(SiO2)复合材料,研究了聚丙烯(PP)/纳米二氧化硅(SiO2)复合材料的力学性能,采用熔融流变仪、XRD、SEM对熔体流动速率、PP物相情况等进行了研究.实验结果表明,2%含量的纳米二氧化硅聚丙烯纳米复合材料综合性能最佳,提高了PP的综合力学性能.在本文中对纳米SiO2改性PP的机理进行了初步探讨,利用X射线衍射图谱分析,结果表明纳米SiO2的加入对PP中β晶型的产生有诱导作用.     

低热膨胀系数超支化共聚聚酰亚胺的构建及性能

以2,3,3',4'-联苯四甲酸二酐、3,3',4,4'-联苯四羧酸二酐、对二氨基二苯醚、对苯二胺和合成三胺单体为原料,合成了含有超支化链段的新型共聚聚酰亚胺。研究表明,与线型低热膨胀系数聚酰亚胺(HB-Co-PIS-0)相比,超支化链段引入后,其显著的优点是溶解性变好,引入超支化链段5%时,聚酰亚胺可在极性大的溶剂二甲基甲酰胺和甲基吡咯烷酮中溶解,在四氢呋喃等极性小的溶剂中回流微溶。另外,其聚酰亚胺酸黏度降低,热膨胀系数值维持较低的数值,无序结构增多,玻璃化温度和热分解温度降低,拉伸强度增大,断裂伸长率减小。并且,超支化链段引入,使原线型低热膨胀系数聚酰亚胺微突起的致密表面变为更多纳米突起的粗糙疏松表面,水接触角从原来72°增加到76°(3%超支化)和85°(5%超支化)。     

纳米云母对聚丙烯结晶形态和结晶性能的影响

采用热台偏光显微镜、差示扫描量热仪和X射线衍射仪研究了纳米云母(nano-Mica)对聚丙烯(PP)结晶形态和结晶性能的影响。结果表明,添加纳米云母使得聚丙烯的结晶速率提高,球晶尺寸变小,球晶数目增多,纳米云母起到了异相成核的作用;添加3%纳米云母后,聚丙烯的结晶温度从110.4℃提高到119.2℃,结晶度从33.1%提高到37.7%,熔点升高,过冷度降低;纳米云母的加入不改变聚丙烯的结晶晶型,但使得微晶尺寸和晶面间距都变小,这将产生更加致密的晶体结构,对复合材料的性能产生重要影响。     

可分散性纳米二氧化硅增强硅橡胶

采用表面经过硅烷偶联剂原位修饰的纳米二氧化硅增强硅橡胶。通过扫描电子显微镜和Payne 效应考察了纳米二氧化硅在硅橡胶中的分散特性; 用DSC 分析了复合体系的低温结晶行为; 考察了填料对硅橡胶力学性能的影响。结果表明, 由于修饰后纳米颗粒表面非极性有机基团的存在和表面能的降低, 无须加入分散剂, 纳米颗粒就能在硅橡胶中有较好的分散; 在各自最优添加量时, DNS-3 链状纳米二氧化硅增强的硅橡胶相对于气相法二氧化硅增强的硅橡胶在拉伸强度、撕裂强度及断裂伸长率上有显著提高; DNS-2 纳米二氧化硅增强性能与气相法二氧化硅的相当, 但前者混炼胶黏度较小, 有较好的加工性。      

介孔二氧化硅负载型有机磷酸盐成核剂对聚丙烯性能的影响

通过物理吸附的方法,将2,2-亚甲基-双(4,6-二叔丁苯氧基)磷酸钠(NA-11)负载于球形(16MSN)和棒状(18MSN)的纳米介孔二氧化硅上,研究了负载前后纳米介孔二氧化硅比表面积、孔径和总孔容的变化。采用差示扫描量热、偏光显微镜考察了纳米介孔二氧化硅、纳米介孔二氧化硅/NA-11复合成核剂对等规聚丙烯(iPP)结晶行为的影响,并对iPP样品的物理性能进行了研究。结果表明,纳米介孔二氧化硅和复合成核剂的加入,有效地提高了材料的结晶性和透明性等物理性能。当添加0.3%的16MSN/NA-11(16SNA)时,复合材料的结晶度达到了44.72%,雾度降到20.3%,弯曲强度相对于纯PP提高了26.8%,维卡软化温度提高了6.6℃,且其性能优于NA-11含量相同时的成核iPP。     

乳液聚合条件对聚苯胺性能的影响

以（NH4）2S2O8为催化剂,在非极性溶剂-功能质子酸-水三相体系中,采用乳液聚合方法合成聚苯胺。对乳液聚合与化学氧化溶液聚合合成的聚苯胺性能进行了比较,研究了掺杂酸、氧化剂、反应时间、温度等聚合条件对聚苯胺导电性、溶解性等性能的影响。结果表明,乳液聚合产率高于80%,聚苯胺电导率大于1S/cm,在有机溶剂中的溶解性与用化学氧化合成的聚苯胺比较有明显提高。     

可染聚丙烯合金纤维(英文)

采用聚丙烯/核壳纳米粒子共混物制备了可染聚丙烯合金纤维。染色实验结果表明:核壳纳米粒子的引入大幅度提高了聚丙烯纤维对于三种不同分散染料的染色性能,染色后的聚丙烯合金纤维颜色深且亮。力学实验结果表明:核壳粒子对聚丙烯合金纤维的机械性能影响很小。本文还对可染聚丙烯合金纤维的结晶度、取向度进行了研究,并推断了聚丙烯合金纤维染色深度提高的可能原因。     

药包塑料薄膜对印刷及胶粘常用溶剂的吸附性能

采用顶空气相色谱法,研究了聚酯(PET)、聚氯乙烯(PVC)、聚酰胺(PA-66)、聚丙烯(PP)和低密度聚乙烯(LDPE)等药品包装行业常用薄膜对印刷和复合薄膜制备中直接或间接接触到的异丙醇、乙酸丙酯、丁酮、乙酸乙酯和甲醇等溶剂吸附行为。研究结果表明:不同的薄膜对不同溶剂的吸附行为不一样,LDPE、PP等非极性聚烯烃薄膜对极性溶剂的吸附较少,而聚酰胺和聚氯乙烯等极性薄膜对极性溶剂的吸附量较大,其中PET和PA-66等容易吸附醇类溶剂。这些结果可为企业生产过程中的溶剂残留控制提供指导依据。     

Physical ageing of polypropylene in glassy state

Physical ageing behaviour of a semicrystalline polymer, polypropylene, has been studied at a pressure-temperature state (P=2.5 kbar,T=15° C) for which the amorphous region is in the glassy state. Polypropylene contains 57% crystallinity and its glass transition temperature at atmospheric condition is −20° C. The ageing behaviour was monitored by measuring the Young's modulus (E) from the stress-strain curves as a function of ageing time up to 200 h. The Young's modulus of the rapidly pressure quenched samples increased at 0.4% per ageing hour of the initial value for up to 30 h and tapered off thereafter. The glassy polypropylene also exhibited a memory behaviour when it was given a pressure perturbation.     

聚丙烯玻璃化转变温度的分子动力学模拟

对等规、间规、无规三种不同聚丙烯(PP)的玻璃化转变温度进行了分子动力学模拟。用分子动力学模拟来获得不同构型聚丙烯在不同温度下的特征体积,通过对模拟得到的体积-温度(V-T)作图,求得玻璃化转变温度,其模拟结果与实验值吻合得较好。同时分析了聚丙烯主链柔顺性、立构规整度和力场能量项对PP玻璃化转变温度的影响,模拟结果表明,二面角扭转能和非键能在玻璃化转变温度附近出现拐点,这是高分子出现玻璃化转变的主要根源。     

扩链增韧环氧树脂水分散乳液的制备及性能

采用聚丙二醇对高相对分子量环氧树脂E-20进行扩链增韧,即而丙烯酸类极性单体进行自由基接枝共聚合,制备了增韧改性的环氧树脂水分散乳液。利用ZETA电位分析仪、差示扫描量热法和热重分析等对其乳液的粒径与分布、稀释行为,改性树脂的玻璃化转变温度、耐热性能及力学性能进行了测定与分析。结果表明,水分散乳液粒径随着改性树脂中羧基中和程度的增加而减小,其稀释行为与溶剂分散体系明显不同;当作为固化涂膜材料时,比较改性环氧树脂与未改性树脂,其柔韧性和耐热性能均有显著提高。     

THE NUCLEATION OF MICROCELLULAR FOAMS IN SEMI CRYSTALLINE THERMOPLASTICS*

The nucleation of microcellular foams in amorphous thermoplastics has been performed by supersaturation with gas at an elevated temperature. Pressure and temperature are then carefully reduced in the vicinity of the glass transition temperature of the material. The result is a foam structure with cells on the order of 10 microns. This material exhibits greatly increased impact strength, as well as thermal and electrical insulation properties as compared to conventional foams. A new process has been developed to produce microcellular foams in semi-crystalline polymers. The process operates in the vicinity of the polymer's melting point, as opposed to the glass transition point. This is due the low solubility of the gases in and the rigidity of the crystalline phase. Microcellular foams have been produced successfully in polypropylene. The effects of various additives have been investigated experimentally. The theory developed for the amorphous materials has been compared to these new experimental results and again qualitatively agrees.     

Fracture behaviours of epoxy nanocomposites with nano-silica at low and elevated temperatures

An investigation was conducted to characterize fracture behaviours of nano-silica modified epoxies at low and elevated temperatures. A nano-silica dispersed epoxy (Nanopox XP 22/0516, Hanse-Chemie, Germany) with 40 wt% silica nano-particles was used as modifier to toughen an epoxy resin, Araldite F (Bisphenol A based, Ciba-Geigy). Fracture toughness and other mechanical properties were measured using standard compact tension (CT), tensile and flexural specimens to elaborate the effects of nano-silica particles on fracture behaviours of epoxy nanocomposites at different temperatures, −50, 0, 23, 50 and 70 °C. Dynamic mechanical analysis (DMA) was utilized to define the glass transition temperature (T _g) upon the addition of different amounts of nano-silica particles. Fracture toughness of the nano-silica modified epoxies was clearly increased at 23 °C and 50 °C, but the role of nano-silica particles in enhancing the fracture toughness became less pronounced at 0 °C and −50 °C and disappeared at 70 °C.     

Failure behaviour of self-reinforced polypropylene at and below room temperature

Self-reinforced polypropylene is a very tough material. It is even thought that its impact resistance increases with decreasing temperature. This was investigated by examining the constituent tapes and matrix. Tensile tests on both drawn polypropylene tapes and self-reinforced polypropylene were similar: the stiffness increased and the failure strain slightly decreased at low temperatures. The matrix, however, embrittled below room temperature due to the glass transition. In contrast with literature data on Izod impact resistance, the penetration impact resistance did not increase at low temperatures. At lower temperatures, the damaged area after non-penetration impact was significantly reduced. This was caused by a change in the damage mode from tape–matrix debonding to matrix cracking, as the matrix went through its glass transition. These conclusions provide the first understanding of the failure behaviour of self-reinforced polypropylene below room temperature, and can be exploited to further optimise the excellent impact resistance of self-reinforced polymers.     

自动铺放成型热塑性复合材料的非等温结晶动力学研究

利用差示扫描量热仪结合Avrami方程研究玻璃纤维增强聚丙烯复合材料自动铺放成型过程非等温结晶动力学,推导非等温结晶动力学模型,并通过构建冷压辊下方铺层的冷却模型,将结晶动力学模型和传热模型相结合,设定自动铺放成型过程中的冷却条件,探讨冷却速率及冷却时间对基体材料结晶行为的影响,求解出不同冷却速率下的最大铺放速率。研究结果表明:铺层树脂基体的结晶度随冷却速率的增大而依次减小;随着冷却速率的提高,树脂结晶起始温度和结晶完成温度均向低温方向移动,且树脂相对结晶度随温度变化规律接近反S形曲线;自动铺放成型实验件的压缩强度及层间剪切强度随着铺层结晶度的增大基本呈增大趋势,而冲击强度与铺层结晶度的变化趋势完全相反,随着结晶度的增大,材料韧性越差。     

Oxygen and water vapor barrier properties of MMT nanocomposites from low density polyethylene or EPM with grafted succinic groups

LDPE, EPM and their derivatives containing a moderate amount (0.08-1.8 by mol) of diethylsuccinate or succinic anhydryde groups were used as matrices in blending with different amount of organophilic montmorillonites and the resulting composite morphology and structure (by XRD, SEM, TEM microscopy, DSC analysis and selective solvent extraction) were studied with reference to the polar groups/MMT ratio. Exfoliated, intercalated and mixed morphologies were achieved. High concentrations of polar groups grafted to the polyolefin and montmorillonite loading not larger than 5% wt were favourable for obtaining high exfoliation degree. Particularly in the exfoliated MMT composite LDPE had lower crystallinity degree, while EPM showed increased glass transition temperature and reduced solubility in hot toluene. Moreover, oxygen and water vapor barrier property improvement was observed in films where MMT exhibits either exfoliated or intercalated morphologies. Strong interactions with the montmorillonite particle surface through the polar groups grafted to the polyolefin seems to be the basic effect responsible for the morphology and peculiar properties. A model based on the reduced mobility of the polymer located near the particle surface or inside the MMT gallery (confined phase) was proposed to explain the observed oxygen permeability reduction, the T(g) increase and solubility of poly(ethylene-ran-propylene)/MMT nanocomposites.     

Effect of fiber surface modification on the lifetime of glass fiber reinforced polymerized cyclic butylene terephthalate composites in hygrothermal conditions

Mechanical performances of polymerized cyclic butylene terephthalate (pCBT) matrix, glass fiber reinforced pCBT (GF/pCBT), and nano-silica modified glass fiber/pCBT composites (nano-GF/pCBT) in hygrothermal condition were investigated. All the materials were aged in hygrothermal environments for up to three months, and then their mechanical strength degeneration ratio (SDR) was calculated. To study the aging effect of temperature, specimens with and without nano-silica modification were tested in temperatures ranging from 298 to 500 K. Differential scanning calorimeter (DSC) test, dynamic mechanical analysis (DMA), and fiber pull-out test were adopted to complement the experimental results. It is found that all the SDR-time curves follow the linear relationship in hygrothermal environment, while SDR-temperature curves follow a bilinear relationship due to the effect of glass transition temperature (T_g) of the matrix. Fibers modified by coating nano-silica on the surface could decrease SDR of the composites. This is due to the fact that the fillers on the fiber surface could resist the movement of pCBT molecular chain and diffusion of water molecules in aging conditions. The fiber pull-out test verifies that the interface strength between fiber and matrix is enhanced by the modification.     

增塑剂对聚合物电解质性能的影响

对PVB＋LiClO4 PC组成的聚合物电解质体系,探讨了增塑剂PC对聚合物电解质性能的影响。随着增塑剂浓度的增加,聚合物电解质的玻璃化转变温度下降,加快了高分子的链段运动,使聚合物的电导率增加;同时,PC也起到了溶剂化的作用,使LiClO4的溶解度增大。但PC浓度的增加,使聚合物电解质为力学性能下降。