THE EFFECT OF MATRIX TOUGHNESS ON THE BRITTLE-DUCTILE TRANSITION OF HDPE/CaCO_3 BLENDS

The effects of HDPE matrix toughness on the brittle-ductile transition of HDPE/CaCO_3blends are investigated. Not all HDPE can be toughened by CaCO_3 particles. The ability of thematrix to yield plays a fundamental role in determing whether HDPE can be toughened or not.There exists a critical matrix toughness (I_(sc)≈45J/m) below which HDPE can not be toughenedobservably by CaCO_3 particle at given average size, and above which the critical matrix ligamentthickness (τ_?) is proportional to matrix impact strength.

Effect of Grain Size of β-Si_3N_4 and Glassy Phase on Strength and Fracture Toughness of In-Situ Toughened Si_3N_4

An in-situ toughened Si_3N_4 ceramic is obtained by hot-pressing.Its flexural strength and fracture toughness are 960MPa,12.74MPa·m^(1/2)at room temperature and 720MPa,23.94 MPa·m~_(1/2)at 1350℃,respectively.The relation between grain size of β-Si_3N_4 and mechanical properties is investigated.The glassy phase containing Y and La plays an important role in increasing high-temperature mechanical properties because of its high viscosity and softening temperature.Crack deflection,crack branching and pullout of rodlike β-Si_3N_4 grains are ob- served in this material by SEM,and the toughening mechanisms are discussed.

Effects of two modification methods on the mechanical properties of wood flour/recycled plastic blends composites: addition of thermoplastic elastomer SEBS-g-MAH and in-situ grafting MAH

The effect of maleic anhydride grafted styrene-ethylene- buty-lene-styrene block copolymer （SEBS-g-MAH） and in-situ grafting MAH on mechanical, dynamic mechanical properties of wood flour/recycled plastic blends composites was investigated. Recycled plastic polypro-pylene （PP）, high-density polyethylene （HDPE） and polystyrene （PS）, were mixed with wood flour in a high speed blender and then extruded by a twin/single screw tandem extruder system to form wood flour/recycled plastic blends composites. Results show that the impact properties of the composites were improved more significantly by using SEBS-g-MAH compatibilizer than by using the mixtures of MAH and DCP via reactive blending in situ. However, contrary results were ob-served on the tensile and flexural properties of the corresponding com-posites. In General, the mechanical properties of composites made from recycled plastic blends were inferior to those made from virgin plastic blends, especially in elongation break. The morphological study verified that the interfacial adhesion or the compatibility of plastic blends with wood flour was improved by adding SEBS-g-MAH or in-situ grafting MAH. A better interfacial bonding between PP, HDPE, PS and wood flour was obtained by in-situ grafting MAH than the addition of SEBS-g-MAH. In-situ grafting MAH can be considered as a potential way of increasing the interfacial compatibility between plastic blends and wood flour. The storage modulus and damping factor of composites were also characterized through dynamic mechanical analysis （DMA）.

Crystalline Morphology and Crystallization Characteristics of In-situ Blends of Anionic Polyamide 6 with Noncrystallizable Semiaromatic Polyamide Copolymer

A noncrystallizable semiaromatic polyamide copolymer（NSAP） was dissolved in molten caprolactam, and PA6/ NSAP blends were produced in-situ via the anionic ring-opening polymerization of caprolactam. The presence of a single loss tangent（tanS） peak measured by means of dynamic mechanical analysis（DMA） proves the miscibility between PA6 and NSAP in the blends. It was found that there existed drastic changes in the crystallographic form and crystallization kinetics for the in-situ blends, e.g. , when 20% NSAP was added, nearly all crystallites existed in the ,y form and the crystallization could hardly occur upon cooling even at a rate of 2.5 ℃/min. Moreover, cold crystallization appears during the subsequent heating, and its melting point is 40 ℃ lower than that of the virgin system. On the other hand, the size of the spherulites only decreases modestly. It is suggested that the introduction of irregular stiff segments originated from NSAP into PA6 macromolecule chain, which resulted from transamidation during the polymerization play a dominant role in the drastic change of crystallization kinetics and the resultant morphology of the in-situ blends.

TerminalBlend废胶粉-纳米SiO_2改性沥青粘温关系及低温韧性

为评价废胶粉-纳米复合改性沥青的高温抗变形性、流变特性及低温韧性,制备了湿法Terminal Blend胶粉-纳米SiO_2复合改性沥青,并借助旋转粘度、针入度、软化点、5℃和15℃延度试验进行了性能表征,还基于实测表观粘度拟合了复合改性沥青粘度-温度关系。结果表明:掺加纳米SiO_2后,复合改性沥青针入度减小,软化点升高,高温抗变形性能得到改善,且纳米SiO_2掺量越大,改善越显著;纳米SiO_2掺量4%时5℃延度比未掺前提高约37.5%。此外,复合改性沥青高温粘度较基质沥青和未纳米改性时有所增加,但135℃粘度不超过1500cP,施工和易性良好;粘度数据拟合还表明在135~200℃温度域内,复合改性沥青粘温关系符合较好的指数关系。

Investigation on Thermal and Dimensional Stability of Epoxy Resin In-Situ Modified by Cyanate Ester Resin and Polydimethylsiloxane

The thermal and dimensional stability of epoxy resin(EP)in-situ modified by cyanate ester(CE)and polydimethylsiloxane(PDMS)are investigated by means of experiments and numerical simulation.Thermal gravimetric analysis(TGA)and differential scanning calorimeter(DSC)are used to analyze the heat resistance of the modified EP.The dimensional stability is characterized by the volume shrinkage of the series PDMS/CE/EP obtained by the density method.The chemical structure of the PDMS/CE/EP is analyzed by Fourier transform infrared spectroscopy(FTIR).The results of TGA and DSC indicate that the thermal stability of PDMS/CE/EP decreases firstly and then increases with the increase in the amount of CE.The addition of PDMS shows a slight effect on the thermal stability.The 40%CE makes the blending system exhibit the lowest initial decomposition temperature,which reduces by 15.5%and 40.8%compared with pure EP and CE,respectively.The FTIR results suggested that the influence of CE on the thermal stability of the modified EP is mainly ascribed to the generation of oxazolidinone ring with low thermal stability and the increase in the triazine ring with high thermal stability.The volume shrinkage measurement results show that the introduction of CE and PDMS are both beneficial to the improvement of the dimensional stability of the blending systems.The in-situ addition of 80%CE shows the lowest volume shrinkage of6.11%.The thermal stress distribution of PDMS/CE/EP generated during the solidification process is simulated by the finite element analysis.The results suggested that the introduction of 80%CE into EP results in the lowest thermal stress in the blending system,which indicates that the system has the lowest volume shrinkage,which agrees well with the experimental results.

生物可降解PPC/P34HB共混物制备与性能

采用熔融共混的方法制备了不同质量比的聚碳酸亚丙酯/聚(3-羟基丁酸酯-co-4-羟基丁酸酯)共混物(PPC/P34HB),分析了P34HB添加量对共混物性能的影响。结果表明,PPC共混物的韧性随着P34HB的加入逐渐增大,当其添加量为30%时,冲击强度提升了271.4%。由复合材料流变性能测试可知,P34HB由于含有侧甲基,将其引入体系中提高了共混物的储能模量和损耗模量,降低了其复数黏度,改善了材料的加工性能。热失重结果表明,P34HB的引入,提高了共混物的初始分解温度。由其微观形貌可知,断面表面从光滑表面最后转变为“海岛”结构,证明材料韧性得到了改善。

Toughening of Polycarbonate through Reactive Melt Blending: Effect of Hydroxyl Content and Viscosity of Hydroxyl-terminated Polydimethysiloxane

In this study, four hydroxyl-terminated polydimethylsiloxanes （PDMSOH） with different viscosities and hydroxyl contents were used to improve the toughness of polycarbonate （PC） through reactive melt blending. A largely improved toughness of PC has been achieved, and the low temperature toughness of PC/PDMSOH blends could overtake that of PC homopolymer in much higher temperatures （e.g. -10 ~C versus 23 ~C）. Moreover, it was found that the more the hydroxyl content, the less the PDMSOH was needed to reach the highest toughness, suggesting that equivalent molar ratio between the carbonyl group content of PC and the hydroxyl group content of PDMSOH was required for the toughening of PC. Ultraviolet spectrophotometry was used to analyze the possible reaction between PC and PDMSOH. Contact angle was measured to assess the change of interfacial interaction between PC and PDMSOH as change of viscosity and hydroxyl content. The formation of PC-co-PDMSOH copolymer was believed to be the key for the toughening effect. This work gives a profound recommendation of the optimum kind and dosage of PDMSOH which should be used to improve the toughness of PC and will find immediate industrial applications.

Preparation and Characterization of DGEBA/EPN Epoxy Blends with Improved Fracture Toughness

The physical and mechanical properties of blends composed of two kinds of epoxy resins of different numbers of functional groups and chemical structure were studied. One of the resins was a bifunctional epoxy resin based on diglycidyl ether of bisphenol A and the other resin was a multifunctional epoxy novolac resin. Attempt was made to establish a correlation between the structure and the final properties of cured epoxy samples. The blend samples containing high fraction of multifunctional epoxy resin showed higher solvent resistance and lower flexural modulus compared with the blends containing high fraction of bifunctional epoxy resin. The epoxy blends showed significantly higher ductility under bending test than the neat epoxy samples. The compressive modulus and strength increased with increasing of multifunctional epoxy in the samples, probably due to enhanced cross-link density and molecular weight. Morphological analysis revealed the presence of inhomogeneous sub-micrometer structures in all samples. The epoxy blends exhibited significantly higher fracture toughness（by 23% at most） compared with the neat samples. The improvement of the fracture toughness was attributed to the stick-slip mechanism for crack growth and activation of shear yielding and plastic deformation around the crack growth trajectories for samples with higher content of bifunctional epoxy resin as evidenced by fractography study.

不同增容剂对POE增韧聚乳酸性能的影响

用双螺杆挤出机制备了聚乳酸(PLA)、聚烯烃弹性体(POE)和4种不同增容剂(马来酸酐接枝POE、马来酸酐、丙烯酸酯双官能化POE、丙烯酸酯与缩水甘油酯双官能化的POE、甲基丙烯酸缩水甘油酯接枝POE)的共混物,考察了不同增容剂对共混物力学性能和断面形貌的影响,分析了退火前后共混物力学性能的变化。结果表明,在使用自制的甲基丙烯酸缩水甘油酯接枝POE(POE-g-GMA)作为增容剂,三元体系PLA/POE/POE-g-GMA的质量比为80/15/5时,复合材料力学性能达到最佳,此时缺口冲击强度为12.3 kJ/m2,是纯PLA的3.7倍,拉伸强度为47.5 MPa。

纳米SiO_2增强增韧聚丙烯的研究

通过熔融共混法制备了SiO2 分散很好的聚丙烯 /纳米SiO2 复合材料。力学性能测试结果表明 ,当使用 2份纳米SiO2 时 ,聚丙烯 /纳米SiO2 复合材料的力学性能最优 :与纯PP相比 ,V形缺口冲击强度提高了 90 %,弯曲强度提高了 2 3%,拉伸强度提高了 5 %;成型收缩率增大 ,这是由于大量分散于PP中的超细SiO2 使PP晶体变小引起的。

增韧环氧树脂相结构

用SEM分别对不同配比的热塑/热固(TP/TS)原位共混增韧体系和“离位”增韧体系的浇注体固化后的相形貌进行了观察。结果显示:对于共混增韧体系,当热塑性树脂含量为16.7%-20.0%时体系发生相反转。通过对发生相反转体系的热固性颗粒尺寸的统计分析可知,随着TP含量的增加,热固性颗粒的粒子直径越来越小,且粒子直径的分散性也越来越小;在统计分析结果的基础上由数学分析给出了粒子直径与TP含量的经验关系式,由该经验式可知,热固性粒子直径的上下限分别是1.838μm和0.925μm,对应的质量分数分别约为16.0%和39.0%。对“离位”增韧的相形貌进行了分析,“离位”增韧体系形成了增韧层过渡层本体层的复合结构。TP含量在增韧层保持较高水平,在过渡层中迅速降低,在本体层中几乎不存在;同时为达到较好的增韧效果,过渡层厚度不应超过增韧层厚度。

高韧性聚乙烯合金的制备与性能

采用氢化苯乙烯-丁二烯-苯乙烯共聚物(SEBS)、二元乙丙橡胶(EPR)、三元乙丙橡胶(EPDM)及乙烯-辛烯共聚物(POE),分别与高密度聚乙烯(HDPE)以不同比例在双螺杆挤出机中熔融共混,制备高韧性聚乙烯合金。冲击测试表明,在四种共混物中,HDPE/POE具有较佳的力学性能;Vu-Khanh方程表明,Gi与冲击性能有很好的对应关系;扫描电镜表明,弹性体在HDPE中有很好的分散,橡胶粒径较小,分散均匀;形变区观察显示,纯HDPE为脆性断裂,而HDPE/弹性体断裂表面发生塑性形变,发生剪切屈服,呈明显的韧性断裂。

透明PVC/MBS合金的研究

本文对不同型号的ＰＶＣ与ＭＢＳ进行共混改性，通过冲击、应力应变试验、动态力学分析（ＤＭＡ）、扫描电镜（ＳＥＭ）和紫外可见光谱研究了ＰＶＣ／ＭＢＳ共混体系的性能与形态结构之间的关系。结果表明，用ＭＢＳ改性ＰＶＣ既能有效地提高共混物的韧性，又能保证其具有良好的透光率。

壳-核结构增韧剂超高增韧非晶共聚酯的形貌和形态

研究了马来酸酐接枝的壳核结构增韧剂 (TPEg)对非晶热塑共聚酯 (PETG)的增韧和增强效果 ,并与马来酸酐接枝的纯橡胶类增韧剂 (POEg)作了对比 .TPEg对PETG具有显著的增韧效果 ,当TPEg含量由 5%增加到 1 0 %时 ,共混物就可以发生由脆性到超高韧性的快速转变 .而POEg虽然也可以使PETG发生由脆性到韧性的快速转变 ,但转变是在较高的增韧剂含量下发生的 ,这意味着共混物的抗张强度和模量损失更多 .利用扫描电镜观察、分析了随增韧剂含量的增加 ,共混物的形貌、形态的演化过程 .共混物的缺口冲击韧性与其形貌、形态之间存在很好的对应关系 .

PS/SBS/CaCO_3共混物体系脆韧转变

研究了不同组成的聚苯乙烯 (PS)基三元共混物体系的缺口冲击性能、拉伸性能和断面形貌以及相形态 .实验结果表明 ,微米级碳酸钙的增韧改性效果稍好于纳米级碳酸钙 ,但增强效果却相反 .随着分散相含量的增加 ,3种共混物韧性皆明显提高 ,拉伸曲线向右下方移动 ,应变软化减弱 ,应变硬化增强 .研究发现了随分散相含量的增加 ,PS共混物出现了脆韧转变 ,而且脆韧转变以不同的形式表现了出来 ,即冲击强度。

聚丙烯/玻璃纤维复合材料增强与增韧改性研究

研究了不同含量的马来酸酐接枝聚丙烯(PP-g-MAH)相容剂对玻璃纤维增强聚丙烯/聚乙烯蜡(GFRPP/PW)复合材料体系力学性能和结构的影响。结果表明,少量的PP-g-MAH可以改善"浮纤"现象,促进GFRPP/PW/PP-g-MAH复合材料的相容性和PP基体中γ晶的产生;与原体系相比,加入少量相容剂后冲击强度提高了37.9%,屈服强度提高了3.2%,热变形温度增加了3.9℃。

茂金属聚苯弹性体增韧改性聚苯乙烯的研究

本文主要研究了聚苯弹性体 (PSE)通过与聚苯乙烯 (PS)共混对PS力学性能的影响。结果表明 ,PSE树脂与PS可以相容 ,且这种相容性随树脂中苯乙烯质量分数的提高而增大。PSE与PS共混可以获得力学性能优异的韧性材料。当PSE在共混合金中的质量分数较低时 ,PSE树脂以小于微米的尺寸呈微区分散于PS中。PSE添加量达到 40 %时 ,PSE与PS形成了两相连续分布的共混合金 ,这种合金既具有强度又具有韧性。PSE的增韧效果随其苯乙烯质量分数的提高而增大 ,在苯乙烯质量分数为 72

PP/EPDM共混物断裂性能的研究

采用三元乙丙橡胶(EPDM)对共聚聚丙烯(PP)增韧改性。研究了共混物的力学性能和断裂性能,着重采用基本断裂功方法探讨了材料组成对共混体系断裂性能的影响。研究发现:随EPDM用量的增加,共混物的拉伸强度逐渐下降,冲击强度均较纯PP有一定程度的提高。不同组成的PP/EPDM共混物的we均高于纯PP,we值随EPDM用量的增加呈先增大后减小的趋势,且we主要受we,n变化的影响,同样βwp的变化主要受βnwp,n变化的影响。

PP/OBC共混材料的性能

以均聚聚丙烯(PP)为原料,乙烯-辛烯嵌段共聚物(OBC)为增韧材料,采用双螺杆挤出和注塑成型方法制备PP/OBC共混材料,用SEM、DSC分析OBC对PP断面相结构和结晶性能的影响,测试共混材料的力学性能。结果表明:OBC在PP基体中分散较均匀,形成了以PP为连续相,OBC为分散相的"海-岛"结构;含20%OBC的PP/OBC共混材料,与纯PP材料相比,熔融峰温度和熔点分别下降了4.47和4.81℃,熔融结晶温度上升2.3℃,缺口冲击强度和断裂伸长率分别提高了142.43%和2.77倍,柔韧性大幅度提高。