SiO_2粒子对PMMA/SAN共混体系相分离行为的影响

采用小角激光光散射(SALLS)并结合动态流变学方法,考察了气相法二氧化硅(SiO2)粒子的加入对聚甲基丙烯酸甲酯/苯乙烯-丙烯腈无规共聚物(PMMA/SAN)共混体系相行为的影响,得到了添加SiO2粒子前后的相图,发现SiO2粒子对基体相行为的影响与基体的组成有关.对PMMA/SAN(60/40)体系,加入SiO2粒子后相分离温度上升,但并未改变相分离机理,仍为亚稳单相分解过程(spinodal decomposition,SD);而对于PMMA/SAN(30/70)体系,加入SiO2粒子后却降低了体系的相分离温度.该现象可能是SiO2粒子和基体组分界面间组成与PMMA/SAN共混物基体组成的差异造成的.     

聚丙烯合金PP-c的晶相结构及形态

用偏光显微镜和广角X射线衍射研究了聚丙烯合金PP c的结晶形态.发现PP -c的晶相结构中不仅存在α-晶型聚丙烯(α- PP ) ,也存在着β-晶型聚丙烯(β-PP) .计算了不同乙烯含量PP c的结晶度和β- PP含量.表明随着乙烯含量的增加,β- PP的含量增加,而PP- c的结晶度下降.通过与同等熔融结晶条件下等规聚丙烯(iPP)的结晶形态相比较,发现乙烯组分含量的增加,改变了球晶的生长状况,降低了PP- c晶相的晶体完整性.     

Effect of oscillatory shear on the mechanical properties and crystalline morphology of linear low density polyethylene

In this study,effects of oscillatory shear with different frequencies(0-2.5 Hz) and amplitudes(0-20 mm) on the mechanical properties and crystalline morphology of linear low density polyethylene(LLDPE) were investigated.It was found that the mechanical properties of LLDPE are improved because of the more perfect crystalline structure when LLDPE crystallizes under low-frequency and small-amplitude(0.2 Hz/4 mm) oscillatory shear.The mechanical properties can be further improved by increasing either the frequency or the amplitude of oscillatory shear.The Young's modulus and tensile strength of LLDPE are improved by 27% and 20%,respectively,when the frequency is increased to 2.5 Hz and the amplitude is maintained at 4 mm; while the Young's modulus and tensile strength are improved by 49% and 47%,respectively,when the amplitude is increased to 20 mm and the frequency is remained as 0.2 Hz.The crystallinity and microstructure of LLDPE under different oscillatory shear conditions were investigated by using differential scanning calorimetry,wide angle X-ray diffraction and scanning electron microscopy to shed light on the mechanism for the improvement of mechanical properties.     

聚丙烯催化合金的结晶行为研究

近 1 0年来 ,Montell公司发展的聚丙烯催化合金 (Polypropylene catalloy,PP-c)技术受到广泛关注 .该技术采用具有特定结构的催化剂粒子 ,在适当的聚合条件下 ,得到具有一定大小、形状及内部形貌的聚合物粒子 .由 PP-c技术获得的材料性能可以在非常宽的范围内进行调节 ,其呈现出的高强度可以与工程塑料相比拟 ,柔性可以与聚乙烯相媲美 [1] .结晶性聚合物的结晶度、球晶尺寸等因素对其机械性能 ,尤其是冲击韧性具有重要的影响[2 ,3] .改性聚丙烯的结晶行为及其与物理机械性能之间的关系一直备受关注 .对于纯聚丙烯、聚丙烯与橡胶的共混物…     

Flame-retardant Coating by Alternate Assembly of Poly（vinylphosphonic acid） and Polyethylenimine for Ramie Fabrics

A novel intumescent flame retardant coating,consisting of poly(vinylphosphonic acid)(PVPA) as the acid source and branched polyethylenimine(BPEI) as the blowing agent,was constructed on the surface of ramie fabrics by alternate assembly to remarkably improve the flame retardancy of ramie.The PVPA/BPEI coating on the surface of individual fibers of ramie fabric pyrolyzes to form protective char layer upon heating/burning and improves the flame retardancy of ramie.Thermogravimetric analysis reveals that the PVPA/BPEI-coated ramie fabrics left as much as 25.8 wt% residue at 600 °C,while the control(uncoated) fabric left less than 1.4 wt% residue.Vertical flame test shows that all PVPA/BPEI-coated fabrics have shorter after-flame time,and the residues well preserved the original weave structure and fiber morphology,whereas,the uncoated fabric left only ashes.Microscale combustion calorimetry shows that the PVPA/BPEI coatings greatly reduce the total heat release by as much as 66% and the heat release capacity by 76%,relative to those of the uncoated fabric.     

动态流变法在聚合物/聚合物界面分子链扩散研究中的应用

聚合物/聚合物界面的分子链扩散问题在塑料注塑、焊接、共混等领域普遍存在.动态流变法是研究聚合物/聚合物界面分子链扩散的一种有力手段,这种方法对于界面间分子链扩散的监测非常灵敏.本文简述了用动态流变法研究聚合物/聚合物界面扩散的原理、实验方法以及优点,着重讨论了采用该方法研究初始界面分子链末端分布对扩散机理的影响、对称聚合物/聚合物界面分子链扩散的量化,非对称聚合物/聚合物界面的相互扩散,分子量多分散性对聚合物/聚合物界面扩散的影响,聚合物/聚合物界面间的流动和扩散耦合以及近年来动态流变法在化学反应型聚合物/聚合物界面的应用进展.     

Effect of surface modification of montmorillonite on the properties of rigid polyurethane foam composites

<正>This study investigated the influence of various organically modified montmorillonites(organoclays) on the structure and properties of rigid polyurethane foam(RPUF) nanocomposites.The organoclays were modified with cetyltrimethyl ammonium bromide(CTAB),methyl tallow bis(2-hydroxyethyl) quaternary ammonium chloride (MT2ETOH) and tris(hydroxymethyl)aminomethane(THMA) and denoted as CMMT,Cloisite 30B and OMMT, respectively.MT2ETOH and THMA contain hydroxyl groups,while THMA does not have long aliphatic tail in its molecule. X-ray diffraction and transmission electron microscopy show that OMMT and Cloisite 30B can be partially exfoliated in the RPUF nanocomposites because their intercalating agents MT2ETOH and THMA can react with isocyanate.However, CMMT modified with nonreactive CTAB is mainly intercalated in the RPUF matrices.At a relatively low filler content,the RPUF/CMMT composite foam has a higher specific compressive strength(the ratio of compressive strength against the apparent density of the foams),while at relatively high filler contents,RPUF/Cloisite 30B and RPUF/OMMT composites have higher specific compressive strengths,higher modulus and more uniform pore size than the RPUF/CMMT composite.     

聚丙烯催化合金(PP-c)的晶体结构及其影响因素

用差示扫描量热法(DSC)和广角X射线衍射(WAXD)研究了两种乙烯含量不同的聚丙烯反应合金(PP-c)等温结晶下的晶体结构及PPβ晶含量的影响因素.结果表明,在通常的等温结晶条件下,乙烯含量较高的试样(PEP40)的熔融曲线出现双熔融峰.WAXD分析证明,其熔融双峰分别代表均聚聚丙烯(PP)的α晶和β晶.计算结果表明,PEP40中β晶含量与结晶温度有关,124℃结晶时β晶含量最高.在220℃对PP-c熔体进行热处理可显著提高PEP40中β晶的含量;在相同温度下热处理后,较低乙烯含量的试样(PEP20)也出现晶型异构.比较200℃与220℃下热处理对PEP20等温结晶的结晶形态的影响,发现后者使微晶尺寸明显变小,并呈现较完善的β球晶形态.