HDPE等温结晶中液-固转变的流变特性

摘要研究了高密度聚乙烯(HDPE)等温结晶过程中液-固转变的流变行为. 发现在等温结晶过程中, 旋转流变仪的平行板上会产生法向拉应力; 在结晶初期, 此应力会快速松弛; 一定时间后, 呈现出积聚并迅速增加的现象. 针对此现象提出了一种新的静态测试方法, 即利用由结晶导致的体积收缩测量法向拉力. 对动态测试和静态测试方法下的流变行为进行比较发现, 动态测试适用于结晶速率较慢的体系, 而静态测试则适用于结晶速率较快的体系. 相对于前者而言, 后者具有不干扰被测试样结晶行为的优点.     

等规聚丙烯/炭黑等温结晶过程中流变与导电行为的关联与同步测试

采用流变-导电行为同步测试方法,研究了等规聚丙烯(iPP)/炭黑(CB)复合体系的等温结晶行为,发现当CB体积含量φCB远高于渗流转变上限时,其体系的流变行为与导电性能均在某一特征时间处发生突变,电阻突变的特征时间短于动态储能模量(G′)或法向应力(FN)突变的特征时间,表明结晶诱导期存在CB粒子运动,促使CB粒子在晶粒尺寸增长期形成渗流网络;另一方面,与静态方法相比较,动态方法所测特征时间较短,表明动态方法对体系结晶结构变化的响应较静态方法更为灵敏.     

Effect of crystallization on tensile mechanical properties of PET foam: Experiment and model prediction

Currently Polyethylene terephthalate (PET) foam is the most promising structural core materials, and the tensile mechanical properties are one of its important application indicators. Herein, environmental-friendly supercritical CO₂ (ScCO₂) extrusion foaming was adopted to prepare PET foam. Aiming at investigating the influence of crystals on the mechanical properties, isothermal treatment in the post-process was used to improve the crystallization process of PET foams. Due to the crystal perfection proceeds via migration and rejection of the structural defects at the crystallites induced by slow crystallization, the crystallinity increased rapidly with the rise of isothermal temperature, especially above the glass transition temperature (T_g). Qualitatively, it can be concluded that the crystalline phase contents have an intimate positive correlation with the tensile modulus, meanwhile, the shape ratio of the crystal have no significant effects on the tensile modulus. In addition, a coupling scheme of aggregate two-layered composite inclusion model and Simone-Gibson equation was first proposed to quantify the mathematical relationship between crystallization and tensile modulus of PET foam, which realized basic agreement.     

剪切作用下马来酸酐接枝乙烯-辛烯共聚物和乙烯-丙烯酸丁酯-甲基丙烯酸缩水甘油酯共聚物对PA1010/PP共混物的增容作用比较

采用熔体共混的方法制备了两种增容剂增容的聚酰胺1010/聚丙烯(PA1010/PP)共混物,通过扫描电镜(SEM)、力学性能和差示扫描量热(DSC)测试,对动态保压注射成型(动态)和普通注射成型(静态)中增容剂POE-g-MAH(马来酸酐接枝乙烯-辛烯共聚物)和PTW(乙烯-丙烯酸丁酯-甲基丙烯酸缩水甘油酯共聚物)对PA1010/PP共混物的增容作用进行了比较研究.研究结果表明,普通注射成型中,PTW增容体系具有更小的分散相粒子,在DSC测试中出现两个结晶峰,即出现异相成核结晶和均相成核结晶,具有更好的拉伸和冲击性能,增容作用更佳.动态保压注射成型中施加剪切可以提高所有共混物的拉伸强度、拉伸模量和缺口冲击强度,PTW和POE-g-MAH两种增容剂增容体系冲击性能相近,但POE-g-MAH增容体系的分散相相区尺寸减小明显、分布均匀性显著增加,材料冲击强度增加幅度更大,表明剪切更有利于POE-g-MAH增容作用的进行.两种增容剂增容作用的不同源于它们化学组成的不同引起的材料形态差别.     

Influence of film preparation procedures on the crystallinity, morphology and mechanical properties of LLDPE films

Influence of various film preparation procedures on the crystallinity, morphology and mechanical properties of pure linear low-density polyethylene and its calcite filled composite films has been studied using differential scanning calorimeter (DSC), wide-angle X-ray diffractometer (WAXRD), atomic force microscope (AFM) and ultimate tensile testing machine (UTM). The film preparation procedures include variation in cooling rates such as quenching, force (fan) and natural cooling and in techniques such as extrusion followed by melt squeezing and compression molding. The heat of fusion (from DSC), the degree of crystallinity (from WAXRD) and the crystallite size (from WAXRD and AFM) are found to be the highest for naturally cooled specimen, followed by fan cooled and quenched ones. The AFM images of surface topology exhibit stacked lamellar morphology for forcefully cooled (fan cooled and quenching) samples and spherulitic ‘lozenges’ for naturally cooled ones. The Young’s modulus and yield stress (from UTM) are the highest for naturally cooled samples, followed by fan cooled and quenched ones. Amongst the calcite filled composites, the ‘base film’, which is prepared by extrusion followed by melt squeezing and natural cooling, exhibits the lowest heat of fusion, degree of crystallinity and Young’s modulus, but the highest yield stress, elongation at break and tensile strength compared to the compression molded ones.     

Effect of TiO2 nanoparticles on structure and properties of high density polyethylene membranes prepared by thermally induced phase separation method

Polyethylene/TiO₂ membranes were fabricated via thermally induced phase separation (TIPS) method. A set of characterization tests including FE‐SEM, EDX, XRD, DSC, TGA, DMA, mechanical test and relative pure water flux for characterization of membranes were carried out to investigate the effect of TiO₂ nanoparticles on membrane properties. The results of EDX, XRD and TGA analyses confirmed the presence of TiO₂ nanoparticles in the polymer matrix. The results of DSC analysis revealed that the melting point as well as the crystallinity of the membranes increased slightly with increasing TiO₂ content. However, the glass transition temperature of the membranes was not affected by the presence of particles. Addition of nanoparticles also increased storage modulus, loss modulus and tensile strength at break of the membranes due to the stiffness improvement effect of inorganic TiO₂. Finally, it was observed that incorporation of the nanoparticles improved pure water flux of the membranes. Copyright © 2015 John Wiley & Sons, Ltd.     

不同分子量聚丙烯β晶相的形成

结晶速率;晶相转变;不同分子量聚丙烯β晶相的形成     

The crystalline and mechanical properties of PLA/layered silicate degradable composites

The poly(lactic acid) (PLA)/montmorillonite (MMT) composites were prepared by melt blending in an internal mixer. The effect of MMT and organically modified MMT (OMMT) addition on crystallization and mechanical preferences has been studied. The DSC results show that the crystallization ability of PLA is improved by MMT or OMMT. The addition of MMT and OMMT increase the crystallinity of PLA from 27.3 to 32.8%, and the cold crystallization temperature (T_CC) of PLA decreases from 93.1 to 88.9°C with the MMT. However, the nucleating effect of MMT is better than that of OMMT due to the velvety surface resulted from the organic modification. The average size of the spherulites in PLA/MMT is smaller than that in PLA/OMMT. The addition of MMT or OMMT increases the tensile strength of PLA from 29.6 to 34.7 MPa and decrease the elongation at break of PLA. The modulus of PLA composites is enhanced rapidly from 338 to 660 MPa by the addition of MMT.     

CHANGES OF STRUCTURE AND PROPERTIES OF POLY (ETHYLENE TEREPHTHALATE) CAUSED BY IN-SITU POLYMERIZATION OF PYRROLE

Conductive polymer composites based on crystalline polymer matrix have been prepared by using an in-situ polymerization process of pyrrole in amorphous poly (ethylene terephthalate) (PET) film. The DSC and WAXD measurement and SEM observation show that liquid-induced crystallization of PET matrix has occurred during the preparation of composite films. Depending upon the equilibrium degree of swelling and crystallinity, the limited depth of penetration of pyrrole molecules results in a skin-core structure of the composite film. The skin layer containing charge transfer intercalated polypyrrole has a surface resistance of 3.5×10~4 Ω. Rigid and heat-resistant polypyrrole molecules formed in PET film increase the tensile modulus and, especially, the rigidity of PET at elevated temperatures. However, they decrease the tensile strength and elongation at break, and impair the thermal ductility of PET.     

MISCIBILITY, CRYSTALLIZATION AND MECHANICAL PROPERTIES OF PPC/PBS BLENDS

In this paper,melt blends of poly(propylene carbonate)(PPC)with poly(butylene succinate)(PBS)were characterized by dynamic mechanical analysis(DMA),differential scanning calorimetry(DSC),tensile testing,wide-angle X-ray diffraction(WAXD),polarized optical microscopy and thermogravimetric analysis(TGA).The results indicated that the glass transition temperature of PPC in the 90/10 PPC/PBS blend was decreased by about 11K comparing with that of pure PPC.The presence of 10% PBS was partially miscible with PPC.The 90/10 PPC/PBS blend had better impact ==========and tensile strength than those of the other PPC/PBS blends.The glass transition temperature of PPC in the 80/20,70/30,and 60/40 PPC/PBS blends was improved by about 4.9 K,4.2 K,and 13 K comparing with that of pure PPC,respectively;which indicated the immiscibility between PPC and PBS.The DSC results indicated that the crystallization of PBS became more difficult when the PPC content increased.The matrix of PPC hindered the crystallization process of PBS.While the content of PBS was above 20%,significant crystallization-induced phase separation was observed by polarized optical microscopy. It was found from the WAXD analysis that the crystal structure of PBS did not change,and the degree of crystallinity increased with increasing PBS content in the PPC/PBS blends.     

1,2-丁二醇共聚对聚对苯二甲酸乙二醇酯结晶行为及力学性能的影响

为了探索生物基乙二醇中的1,2-丁二醇(1,2-BDO)作为共聚单体对生物基聚对苯二甲酸乙二醇酯(PET)的结晶行为和力学性能的影响。 本文合成了生物基PET均聚物和不同1,2-BDO共聚单元摩尔分数的系列生物基PET共聚物(共聚单体摩尔分数分别为2.0%、2.7%和5.6%),并采用傅里叶变换红外光谱仪(FTIR)、差示扫描量热仪(DSC)和力学测试等技术手段研究了其结晶行为和力学性能。 结果表明,随着1,2-BDO共聚单元摩尔分数的增加,PET共聚物的熔融温度、结晶速率及结晶度均明显降低,表明1,2-BDO共聚单体的引入破坏了PET分子链的规整性,阻碍了PET链段的结晶。 PET材料的拉伸强度随着1,2-BDO共聚单元摩尔分数的增加而降低,而弯曲强度和弯曲模量略有升高。     

STRUCTURE AND THERMAL MECHANICAL PROPERTIES OF ORIENTED POLYIMIDE (PEI-E)

The strain induced crystallization behaviour in polyimide from 1,4-bis (3', 4'- dicarboxyphenoxy)benzene and 4,4'-oxydianiline (PEI-E)has been investigated by WAXD, DSC and FTIR. The results obtained show that crystallization in PEI-E did take place just after tensile yielding. Meanwhile, the effect of strain induced crystallization on the thermomechanical properties was studied by DMA and TMA, the results of which indicate that the crystallization and hot stretching have a certain influence on the dynamic mechanical properties, such as weakening the βrelaxation and decreasing the glass transition temperature. The TMA results confirm the shifting of glass transition temperature to lower temperature region after hot stretching. This phenomenon could be well explained by the effect of residual stress according to Eyring's theory.     

Use of thermal analysis techniques for examining blow-molded pet bottle specimens

Eight samples from different areas of stretch-blow-molded poly(ethylene terephthalate) [PET] bottles, including a PET resin control, were tested by differential scanning calorimetry (DSC) and thermomechanical analysis (TMA). The glass transition temperature (T _g) was found to linearly decrease about 6C from zero to 45 percent initial crystallinity. Measurements ofT _c (crystallization temperature, DSC) and film tension modulus (TMA) were related to crystallization rate during stretch-blow-molding. The TMA linear coefficients of thermal expansion and shrinkage were shown to be important for blow-molding temperature control.     

Thermal properties and applications of low molecular weight polyhydroxybutyrate

The properties of the low molecular weight polyhydroxybutyrate (LMWPHB) and LMWPHB plasticized polyhydroxybutyrate (PHB) are studied using differential scanning calorimetry (DSC), thermogravimetric analysis, wide-angle X-ray diffraction (WAXD), polarized optical microscope (POM), mechanical, and biodegradation tests. The results of DSC, WAXD, and POM indicate that LMWPHB has a lower glass transition temperature (T _g), crystallinity, crystallization rate, melting temperature (T _m), and crystal size than PHB due to its much smaller molecular weight. The tensile strength, T _g, T _m, crystallinity, crystallization rate, and thermal stability of LMWPHB plasticized PHB decrease, while the flexibility and biodegradation rate increase with the increasing content of the added LMWPHB. It is confirmed that LMWPHB can be used to improve the brittleness and control the biodegradation rate of PHB.     

Effects of stereo-defect distribution on the crystalline morphology and tensile behavior of isotactic polypropylene prepared by compression molding process

In this study, the aggregation morphology, tensile behavior, and morphology evolution during the tensile test of two isotactic polypropylene (iPP) samples with similar molecular weight and average isotacticity but different uniformities of stereo-defect distribution are investigated by differential scanning calorimetry (DSC), two-dimensional wide angle X-ray diffraction (2D-WAXD), and scanning electronic microscopy (SEM). The results revealed that the uniformity of stereo-defect distribution of iPP determines the crystalline structure and aggregation morphology, and further influences the tensile behavior and morphology evolution during the tensile test. For PP-A with less uniform stereo-defect distribution, its ability of crystallization is stronger compared with PP-B, resulting in smaller spherulite sizes, higher melting point and degree of crystallinity, and narrower distribution of lamellar thickness of the compression molding specimens. During the tensile test, mainly the inter-spherulite deformation takes place at the early stage for deformation, which further results in drastic deformation of lamellar and high degree of reorientation at the strain increases, exhibiting higher yield strength and elastic modulus, and lower elongation at break compared with PP-B; for PP-B with more uniform stereo-defect distribution, larger spherulite sizes, lower melting point and degree of crystallinity in its compression molding sample are observed. During the tensile test, intra-spherulite deformation mainly takes place, which can disperse the tensile stress more uniformly. As the strain increases, lower degree of crystalline destruction and reorientation of the crystallites take place. The yield strength and elastic modulus of PP-B is lower than PP-A, and its elongation at break is higher.     

聚丁二酸丁二酯/纳米二氧化硅共混体系的结晶和动态力学性能研究

用溶液共混法制备了聚丁二酸丁二酯(PBS)/纳米二氧化硅(nano-SiO2)复合材料,并通过DSC、XRD、TEM和DMTA对其结晶、微观结构和动态力学性能进行了研究.DSC与XRD结果表明,在PBS中加入纳米SiO2,提高了PBS的结晶温度,并随着nano-SiO2含量的增加呈正相相关性,从纯PBS的67.7℃提高到含5%nano-SiO2时的73.3℃;在空气淬火条件下,提高了复合材料中PBS的结晶度,在nano-SiO2含量为2%时达到42.4%;TEM照片表明SiO2与基体PBS的界面模糊,表明二者之间具有一定的相互作用;这种相互作用和复合材料结晶性能的变化使PBS/nano-SiO2复合材料的储能模量和损耗因子均高于纯PBS.上述结果表明在PBS中添加适量的nano-SiO2,能显著提高PBS的结晶和动态力学性能.     

聚对苯二甲酰对苯二胺纤维在热处理时的二次结晶

用X-射线衍射、TEM、FTIR、DSC、PPM等方法,研究了热处理前后PPTA纤维的一系列结构参数,发现该纤维聚集态结构参数随温度变化曲线在380℃左右出现拐点,晶粒尺寸长大,结晶度提高,晶区取向度增加同时晶格畸变增大。通过DSC谱图进一步确认了该纤维在热处理过程中的二次结晶,并表明它是热处理后PPTA纤维模量大幅度提高的主要原因。     

Intercalated poly(vinylidene fluoride)/clay nanocomposites: Structure and properties

The preparation and characterization of melt‐intercalated poly(vinylidene fluoride) (PVDF)/clay nanocomposites are reported. Organophilic clay (clay treated with dimethyl dihydrogenated tallow quaternary ammonium chloride) was used for the nanocomposite preparation. The composites were characterized with X‐ray diffraction (XRD), differential scanning calorimetry (DSC), and dynamic mechanical analysis (DMA). XRD results indicated the intercalation of the polymer in the interlayer spacing. The incorporation of clay in PVDF resulted in the β form of PVDF. DSC nonisothermal curves showed an increase in the melting and crystallization temperatures along with a decrease in crystallinity. Isothermal crystallization studies show an enhanced rate of crystallization with the addition of clay. DMA indicated significant improvements in the storage modulus over a temperature range of ?100 to 150 °C. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 31–38, 2003     

Structure–property relationships in polyamide 6/multi‐walled carbon nanotubes nanocomposites

Polyamide 6 (PA6)/multi‐walled carbon nanotubes (MWCNT) nanocomposites were produced by diluting a masterbach containing 20 wt % nanotubes using melt mixing. The influence of the addition of well dispersed MWCNT (as indicated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM)) on the thermal transitions, and crystallization behavior of the PA6 matrix is investigated. Differential scanning calorimetry (DSC) results show a reduction in heat capacity jump at the glass transition which is interpreted by an immobilized interfacial layer near the nanotubes. Furthermore, both DSC and X‐ray diffraction (XRD) measurements indicate that nanotubes favor the formation of the α crystalline form of PA6. These findings are correlated with the observed improvement of the storage modulus as revealed by dynamic mechanical thermal analysis (DMTA). Additionally, a new crystallization peak appears when MWCNT are added, and is attributed to the formation of a different morphology of the same type crystallite around the nanotubes walls (trans‐crystallinity). Finally, water sorption measurements show an increase of water content, normalized to the amorphous polymer fraction, in the nanocomposites. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 764–774, 2009     

Reactively compatibilized and dynamically vulcanized thermoplastic elastomers based on high-density polyethylene and reclaimed rubber

Melt blending was employed to prepare thermoplastic elastomer (TPE) of reclaimed rubber (RR) and high density polyethylene (HDPE). Mechanical properties of TPE samples were improved in different methods including dynamic vulcanization and reactive blending (reactive compatibilization) during melt mixing in an internal Haake mixer. The physical and mechanical properties of the TPE blends were investigated by the dynamic mechanical analysis (DMA) and tensile tests. The thermal behavior was characterized by differential scanning calorimeter (DSC) and thermogravimetric analysis (TGA). The phase morphology of the blends was studied by scanning electron microscopy (SEM). Experimental results showed that, both static and dynamic mechanical properties of reactively-compatibilized and dynamically-vulcanized samples improved significantly compared with the virgin samples. The effect of dynamic-vulcanization and reactivecompatibilization on the mechanical properties revealed that the Young’s modulus and storage modulus increased with both improvement methods. SEM results showed that, dynamic-vulcanization and reactivecompatibilization methods improved the distribution of RR particles in HDPE matrix. Although both methods improved the thermal and mechanical properties of the HDPE/RR blends, dynamic-vulcanization was more effective and promising approach due to the higher properties of HDPE/RR blends prepared by this method.