聚丙烯/累托石纳米复合材料的非等温结晶动力学研究

在双螺杆挤出机上熔融共混制备了聚丙烯 (PP) 有机累托石 (OREC)纳米复合材料 ,采用广角X 射线衍射 (WAXD)定性地分析了PP OREC纳米复合材料及纯PP的结晶形态 ,由半峰宽定性地判断了对应晶面法向的晶粒的大小 .结果表明有机累托石没有改变聚丙烯的结晶晶型 (纳米复合材料主要还是α晶型 ) ,但是细化了晶粒的尺寸 .采用差示扫描量热法 (DSC)定量地研究了复合材料的非等温熔融结晶动力学 ,对所得数据分别用Jeziorny法的Mo法进行了处理 ,表明非等温结晶动力学参数Zc 及Avrami指数n随冷却速率的增加而增加 ,复合材料的Avrami指数n大于纯PP的n ;对相同配比的纳米复合材料 ,随着结晶度的增加 ,单位结晶时间里达到一定结晶度所需要的降温速率F(T)增大 ,对同一个设定的结晶度 ,纳米复合材料的F(T)比纯PP的小 ,说明需要的降温速率减小 .所有这些均说明有机累托石可作为聚丙烯的结晶成核剂 .     

辐照法制备的醋酸乙烯酯/蒙脱土纳米复合材料与HDPE和PA6共混物的研究

利用γ射线辐射引发醋酸乙烯酯(VAc)在蒙脱土(MMT)中的原位插层聚合,X射线衍射测试与透射电子显微镜观察结果表明,PVAc/MMT复合材料为纳米复合材料.其与HDPE和PA6的共混物的扫描电镜测试结果表明,PVAc-MMT纳米复合物以微胶囊的形式存在于PVAc-MMT/HDPE/PA6共混物中,均匀分散的PVAc-MMT纳米复合物改变了复合材料的相结构.热失重测试结果显示,PVAc-MMT/HDPE/PA6的起始分解温度明显高于PVAc/HDPE/PA6,热失重过程差异较大,MMT纳米粒子的存在改变了材料的结构,使材料热性能得到了改善.在PVAc-MMT/HDPE/PA6共混物中,PVAc-MMT具有增强与增韧作用.     

聚碳酸亚丙酯对聚(β-羟基丁酸酯-β-羟基戊酸酯)结晶行为的影响

用FTIR和DSC研究了PHBV及其与聚碳酸亚丙酯(PPC)熔融共混样的熔融结晶行为和等温结晶动力学.结果表明,PHBV与PPC熔融共混过程中发生了酯交换反应,两组分间存在一定的相互作用.PPC虽然能降低PHBV结晶折迭链的表面自由能,但同时也能够降低PHBV的结晶度、球晶径向生长速率、平衡熔点和结晶能力.     

不同分子量的高密度聚乙烯与茂金属线型低密度聚乙烯的相容性

采用动态流变学测试和结晶动力学的方法研究了两种分子量的高密度聚乙烯(HDPE)与茂金属线型低密度聚乙烯(m-LLDPE)共混体系的相容性.流变学研究表明,HDPE/m-LLDPE共混物在低ω区域lgG′-lgω关系曲线偏离线性规律,在熔融态为非均相体系.DSC分析发现HDPE/m-LLDPE共混物体系中HDPE的熔点随着m-LLDPE含量的增多而逐渐下降,说明HDPE与m-LLDPE二者具有机械相容性.当HDPE在m-LLDPE的熔体中等温结晶,分子量较高的HDPE结晶速率与纯HDPE相近,m-LLDPE的含量变化对Avrami指数n的影响不大;分子量较低的HDPE指数n和半结晶时间t1/2随m-LLDPE含量的增加逐渐增大,结晶速率随着m-LLDPE含量的增加逐渐下降,表明熔融态的m-LLDPE和HDPE存在着较强的分子间相互作用,二者具有一定的相容性.     

HDPE／LDPE共混体系的晶性研究

用DSC和WAXD方法考察了高密度聚乙烯和低密度聚乙烯共混体系(HDPE/LDPE)的结晶性能。结果表明,在共混物中HDPE含量大于50%时,共混物只出现HDPE的熔融峰,且熔融温度随HDPE含量减小而降低;LDPE含量大于50%时,DSC图上只出现熔点介于HDPE和LDPE之间的新熔融峰。DSC和WAXD法所测结晶度均偏离共混物的线性加和值,而晶胞参数则随共混物组成变化出现最小值,表明HDPE和LDPE可以形成共晶相容体系。Raman光谱测得介晶相αb值的膨胀,支持这一观点。     

聚醚醚酮/聚醚醚酮酮共混体系的熔融和等温结晶行为

采用熔融共混方法制备了聚醚醚酮和聚醚醚酮酮的共混物,用DSC对共混物的熔融行为和等温结晶行为进行了研究.结果表明,共混物熔点随聚醚醚酮含量增加而降低,但与聚醚醚酮酮有相同的平衡熔点,二者共混没有改变其结晶的成核与生长机制.     

聚丙烯/蒙脱土纳米复合材料的等温结晶研究

采用差示扫描量热法 (DSC)对插层聚合法制备的聚丙烯 /蒙脱土纳米复合材料 (PP MMT)的等温结晶过程进行了研究 .引入蒙脱土 (MMT)后 ,PP MMT的结晶速率大幅度提高 ,相对结晶度略有下降 .采用Avrami方程对结晶动力学进行研究 ,Avrami指数n≈ 3 .0 ,半结晶时间t1 2 大幅度降低 .采用Hoffman理论计算了PP MMT的球晶生长的单位面积表面自由能σe,结果表明σe 随MMT含量的增加逐渐降低     

聚丙烯/插层改性水滑石纳米复合材料结构与性能研究

采用离子交换法制备了十二烷基磺酸钠和衣康酸共同改性水滑石(LDHs2),FTIR、XRD分析表明,十二烷基磺酸钠和衣康酸能够同时进入水滑石片层之间,层间距有很大提高。利用改性水滑石,通过马来酸酐-苯乙烯共接枝改性聚丙烯相容剂的熔融共混和聚丙烯与水滑石溶液共混制备母粒,然后与聚丙烯分别熔融共混两种方法制备聚丙烯/水滑石纳米复合材料。TEM分析表明,马来酸酐-苯乙烯共接枝改性聚丙烯作相容剂可以使水滑石在聚丙烯基体中达到更好分散。DSC、XRD分析表明,水滑石、相容剂以及短链共聚聚丙烯对聚丙烯晶型没有影响,但对其结晶速率、结晶度以及晶粒大小有所改变,复合材料中聚丙烯的起始结晶温度、结晶峰温度、结晶速率、结晶度均比纯聚丙烯高,晶粒粒径分布也更均匀。     

紫外光交联聚乙烯的结晶行为

采用熔融共混法制备了高密度聚乙烯(HDPE)/光引发剂(BDK)/交联剂 (TAIC) 共混物,在高压汞灯辐照下制备了一系列不同交联程度的样品. 通过广角X射线衍射(XRD)与差示扫描量热法(DSC)等测试技术研究了紫外光交联对HDPE的晶体结构及非等温结晶动力学行为的影响. 结果表明,紫外光交联不改变HDPE晶型. 随着光交联时间的增加,结晶峰的强度下降,晶粒尺寸变小. 随着降温速率的增加,HDPE与交联HDPE(XLPE)的结晶峰变宽,结晶温度(Tp)向低温方向移动,结晶速率变快,结晶度(Xc)下降. 相比较而言,XLPE的Tp较低,F(T)较大,Xc较小,结晶活化能(ΔE)较高,表明紫外光交联抑制了HDPE的结晶.     

尼龙6与半芳香性非晶尼龙原位共混物的结构与性能

一种半芳香的非晶尼龙共聚物溶解于熔融的己内酰胺中,引发后者负离子开环聚合原位制备尼龙6与非晶尼龙的共混物.与纯尼龙6相比较,此原位共混物的强度与模量显著提高.非晶区呈现单一的玻璃化转变,表明共混物为均相体系,其组分的相容性源于负离子聚合过程中链交换反应引起的共聚.与纯尼龙6相比较,此共混物的熔点与结晶度显著降低.此外,与纯尼龙6只存在α晶不同,共混物中伴生有大量的γ晶.当非晶尼龙含量为20 wt%时,绝大部分晶体为γ晶.然而,共混物中球晶仅有一定程度细化.共混物强度和模量的提高被认为主要源于非晶区分子活动能力降低以及γ晶相对含量的提高.     

γ-辐射对聚丙烯及聚丙烯/聚乙烯共混物结晶熔融行为的影响

<正> 近年人们对于聚丙烯(PP)辐射效应的研究与日俱增,主要目的在于寻求增强PP辐射稳定性的有效途径。迄今为止文献报道的方法有:添加小分子游动剂(mobilizing addi-tives)、抗氧剂、多官能团单体等,笔者曾研究过不同晶型和含少量聚乙烯(PE)链     

TRANSAMIDATION IN THE in situ BLENDING OF POLYAMIDE 1212 WITH POLYAMIDE 6 THROUGH ANIONIC POLYMERIZATION OF CAPROLACTAM

20 wt% polyamide 12(PA1212)pellets were dissolved in molten caprolactam.The caprolactam was then catalyzed at 180℃and polymerized by means of anionic ring-opening polymerization to produce in situ blends of the resultant polyamide 6(PA6)and PA1212.Mechanical blends with same ingredient were prepared through melt blending on a twin-screw extruder.Scanning electron microscopy(SEM)observation revealed that contrary to the mechanical blends with small spherulites embedded in the matrix,no phase-separation existed in the in situ blends.The results of thermal analysis by differential scanning calorimetry(DSC)showed that single melting peak and crystallization peak existed for the in situ blends,while two melting and crystallization peaks appeared for the mechanical blends.The in situ blend film and the mixed blend film,both cast from a dilute formic acid solution with a concentration of 0.5 g/L,remained similar crystallization and melting behavior as above.It is proved by solution ~(13)C-NMR analysis that transamidation took place during the in situ blending,and it is suggested that the combination of temperature increasing and the basic surrounding derived from NaOH during polymerization resulted in the occurrence of transamidation.Furthermore,it is proposed that the interchange reaction between PA1212 and PA6 also resulted from the degradative reaction during the anionic polymerization.     

On the crystallization of syndiotactic polypropylene (sPP)/high density polyethylene (HDPE) blends

 The crystallization kinetics of syndiotactic polypropylene (sPP)/high-density polyethylene (HDPE) blends were investigated by thermal and microscopical methods. Isothermal crystallization obtained by differential scanning calorimetry (DSC) was used to study the nucleation ability of HDPE on sPP crystallization. Morphological studies with polarized light microscopy (PLM) of solution cast films resulted in a transcrystalline-like overgrowth of the sPP on HDPE spherulites. The arrangement of the HDPE lamellar crystals in the blend were observed in transmission electron microscopy (TEM). But from these results, no straightforward conclusion about the transcrystalline nature of the sPP crystals can be given. Received: 24 November 1997 Accepted: 23 February 1998     

Multiple melting and crystallization of nylon‐66/montmorillonite nanocomposites

Nylon‐66 nanocomposites were prepared by melt‐compounding nylon‐66 with organically modified montmorillonite (MMT). The organic MMT layers were exfoliated in a nylon‐66 matrix as confirmed by wide‐angle X‐ray diffraction (WAXD) and transmission electron microscopy. The presence of MMT layers increased the crystallization temperature of nylon‐66 because of the heterogeneous nucleation of MMT. Multiple melting behavior was observed in the nylon‐66/MMT nanocomposites, and the MMT layers induced the formation of form II spherulites of nylon‐66. The crystallite sizes L₁₀₀ and L₀₁₀ of nylon‐66, determined by WAXD, decreased with an increasing MMT content. High‐temperature WAXD was performed to determine the Brill transition in the nylon‐66/MMT nanocomposites. Polarized optical microscopy demonstrated that the dimension of nylon‐66 spherulites decreased because of the effect of the MMT layers. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2861–2869, 2003     

Various crystalline morphology of poly(butylene succinate-co-butylene adipate) in its miscible blends with poly(vinylidene fluoride)

Poly(vinylidene fluoride) (PVDF) and poly(butylene succinate-co-butylene adipate) (PBSA) are crystalline/crystalline polymer blends with PVDF being the high-T(m) component and PBSA being the low-T(m) component, respectively. PVDF/PBSA blends are miscible as shown by the decrease of crystallization peak temperature and melting point temperature of each component with increasing the other component content and the homogeneous melt. The low-T(m) component PBSA presents various confined crystalline morphologies due to the presence of the high-T(m) component PVDF crystals by changing blend composition and crystallization conditions in the blends. There are mainly three different types of crystalline morphologies for PBSA in its miscible blends with PVDF. First, crystallization of PBSA commenced in the interspherulitic regions of the PVDF spherulites and continued to develop inside them in the case of PVDF-rich blends under two-step crystallization conditions. Second, PBSA spherulites appeared first in the left space after the complete crystallization of PVDF, contacted and penetrated the PVDF spherulites by forming interpenetrated spherulites in the case of PVDF-poor blends under two-step crystallization condition. Third, PBSA spherulites nucleated and continued to grow inside the PVDF spherulites that had already filled the whole space during the quenching process in the case of PBSA-rich blends under one-step crystallization condition. The conditions of forming the various crystalline morphologies were discussed.     

Solid-state relaxations in linear low-density (1-octene comonomer), low-density,and high-density polyethylene blends

Extensive thermal and relaxational behavior in the blends of linear low-density polyethylene (LLDPE) (1-octene comonomer) with low-density polyethylene (LDPE) and high-density polyethylene (HDPE) have been investigated to elucidate miscibility and molecular relaxations in the crystalline and amorphous phases by using a differential scanning calorimeter (DSC) and a dynamic mechanical thermal analyzer (DMTA). In the LLDPE/LDPE blends, two distinct endotherms during melting and crystallization by DSC were observed supporting the belief that LLDPE and LDPE exclude one another during crystallization. However, the dynamic mechanical β and γ relaxations of the blends indicate that the two constituents are miscible in the amorphous phase, while LLDPE dominates α relaxation. In the LLDPE/HDPE system, there was a single composition-dependent peak during melting and crystallization, and the heat of fusion varied linearly with composition supporting the incorporation of HDPE into the LLDPE crystals. The dynamic mechanical α, β, and γ relaxations of the blends display an intermediate behavior that indicates miscibility in both the crystalline and amorphous phases. In the LDPE/HDPE blend, the melting or crystallization peaks of LDPE were strongly influenced by HDPE. The behavior of the α relaxation was dominated by HDPE, while those of β and γ relaxations were intermediate of the constituents, which were similar to those of the LLDPE/HDPE blends. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 : 1633–1642, 1997     

聚L-乳酸/聚(天冬氨酸-co-乳酸)共混物的制备及其相容性研究

采用氯仿/乙醇共沸溶液浇铸法制备了混合均匀的聚L-乳酸/聚(天冬氨酸-co-乳酸)共混物(PLLA/PAL)体系.研究了PLLA/PAL共混体系的热性能、结晶行为、形态结构和力学性能,评价了PLLA和PAL之间的相容性.结果表明,PAL对PLLA的结晶行为和热性能产生了较大的影响,共混物的结晶度较低,共混体系中部分PAL会进入PLLA球晶的片晶而导致PLLA球晶结构不完善,熔点降低.PAL的含量小于20%的PLLA/PAL共混物的拉伸强度和断裂延伸率均高于纯PLLA.PLLA和PAL分子链相互缠结,产生的氢键使分子链间存在较强的相互作用,具有较好的相容性.     

Characterization and properties of polyethylene blends II. Linear low-density with conventional low-density polyethylene

Melting and crystallization phenomena in blends of a linear low-density polyethylene (LLDPE) (ethylene butene-1 copolymer) with a conventional low-density (branched) polyethylene (LDPE) are explored with emphasis on composition by differential scanning calorimetry (DSC) and light scattering (LS). Two endotherms are evident in the DSC studies of the blends, which suggests the formation of separate crystals. Light-scattering studies indicate that the blend system is predominantly volume filled by the LLDPE component whereby the LDPE component crystallizes as a secondary process within the domain of the LLDPE spherulites. In contrast to those of the LLDPE/HDPE blends, the mechanical and optical relaxation behavior of the LLDPE/LDPE blends are dominated by the LLDPE component in the vicinities of γ and β regions, whereas the trend reverses at high temperature α regions. This observation is accounted for on the basis of the relative restrictions imposed by the deformation of spherulites (which are primarily made up of the LLDPE component) at different time scales.     

Isothermal crystallization behavior of exfoliated‐PP/IMMT nanocomposites via in situ polymerization

Highly exfoliated isotactic‐polypropylene/alkyl‐imidazolium modified montmorillonite (PP/IMMT) nanocomposites have been prepared via in situ intercalative polymerization. TEM and XRD results indicated that the obtained composites were highly exfoliated PP/IMMT nanocomposites and the average thickness of IMMT in PP matrix was less than 10 nm, and the distance between adjacent IMMT particles was in the range of 20–200 nm. The isothermal crystallization kinetics of highly exfoliated PP/IMMT nanocomposites were investigated by using differential scanning calorimeter(DSC) and polarized optical microscope (POM). The crystallization half‐time t_1/2, crystallization peak time t_max, and the Avrami crystallization rate constant K_n showed that the nanosilicate layers accelerate the overall crystallization rate greatly due to the nucleation effect, and the crystallization rate was increased with the increase in MMT content. Meanwhile, the crystallinity of PP in nanocomposites decreased with the increase in clay content which indicated the PP chains were confined by the nanosilicate layers during the crystallization process. Although the well‐dispersed silicate layers did not have much influence on spherulites growth rate, the nucleation rate and the nuclei density increased significantly. Accordingly, the spherulite size decreased with the increase in MMT content. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 2215–2225, 2009