New aspects of the microstructure of glassy PET/PEN blends as revealed by microhardness

The microhardness of films of poly(ethylene terephthalate) (PET) and poly(ethylene naphthalene-2,6-dicarboxylate) (PEN) blends prepared by co-precipitation from solution followed by melt-pressing and quenching was determined. The miscibility, transesterification and crystallization properties of these blended films were reported previously [1]. The PET/PEN compositions chosen were 10/90, 30/70, 44/56, 60/40, 70/30 and 90/10. The microhardness of films was notably affected by the composition. It is shown that the deviation of microhardness from the additivity law of the single components depends on the time for which the blend was melt-pressed before quenching in ice water. The results are discussed in light of changes occurring from the initial two-phase structure of the single components through the one-phase structure up to the PET-co-PEN obtained by transesterification of the two components. This revised version was published online in November 2006 with corrections to the Cover Date.     

PP/EPDM反应挤出共混制备高熔体黏度PP的研究

采用反应型双螺杆挤出机,用过氧化物(BPO)为交联剂、不饱和烯烃为交联助剂,对PP/EPDM体系进行反应增容,一步实现聚丙烯(PP)与少量EPDM的共混、接枝与交联,制备出了具有高熔体黏度的发泡用聚丙烯.对改性材料熔体流动性能、力学性能和发泡性能研究结果表明:当交联剂、交联助剂的质量比约为0.78 :1时,可以获得最佳的改性效果,改性后体系的熔体流动速率(MFR)下降92.9%;改性PP的多项力学性能都有显著改善,其中拉伸强度提高12.9%,缺口冲击强度提高93%;改性使材料的发泡性能得到显著提高,采用反应共混改性PP可获得泡孔大小约100μm,泡沫密度在0.44g/cm3左右,且分布均匀,闭孔率高的发泡材料.     

Cold crystallization studies on PET/PEN blends as revealed by microhardness

The cold crystallization of amorphous films of poly(ethylene terephthalate) (PET) and poly(ethylene naphthalene-2,6-dicarboxylate) (PEN) blends, with different composition, prepared by co-precipitation from solution followed by melt-pressing for 2 min at 280°C and quenching in ice-water, was followed by measuring the microhardness, H, in real time as a function of crystallization temperature and time. An analytical model was derived, relating properties of the individual components to the blend microhardness based on an Avrami-type equation to account for the crystallization of the components upon heating. Fitting of the model to the experimental results revealed a two-step hardening process of the blends. The degree of transesterification of the blends, can be estimated with this model. Finally, a removal of the physical ageing, inducing a decrease in H of PET in the blend, was observed upon heating above its glass transition temperature. This revised version was published online in November 2006 with corrections to the Cover Date.     

Microstructural changes in polyethylene-polypropylene blends as revealed by microhardness

Microhardness is used to examine the microstructural changes of a series of polyethylene (PE) /polypropylene (PP) blends in a wide composition range. This study complements previous hardness results obtained on high-density/low-density polyethylene systems. The use of isotactic polypropylene, as a blend component allows investigation of a material in which the hardness of the amorphous phase, contrary to PE, differs from zero. The influence of treatments such as crystallization of the PP-phase in the presence of molten PE, within the blend, or annealing the PE phase, while leaving the PP component unmodified, are discussed with reference to the additivity hardness values of the single componentsH _PE andH _PP. It is shown that the coexistence of the PP and PE phases inhibits the crystallization capability of one phase and modifies the annealing behaviour of the other phase leading, as a result, to depressedH _PP andH _PE values. The observed deviations ofH _blend, throughout the composition range, from the additivity law of single components are quantitatively justified in the light of crystallinity changes of the PP phase and in terms of the population of modified lamellae of the PE component.     

Structure development in PET/PA6 microfibrillar-reinforced composites as revealed by revealed by microhardness

Homopolymer poly(ethylene terephthalate) (PET) and nylon-6 (PA6) and a blend (1 : 1 by weight) of these polymers, were extruded as strips and ultraquenched from the melt. After zone drawing and additional annealing at temperatures, T _a, of 220 or 240 °C for 5 or 25 h in vacuum, the samples were studied by scanning electron microscopy (SEM), wide-angle X-ray scattering, solubility and microhardness, H, tests. In conformity with previous studies of the same system, the present SEM observations show that mechanical drawing results in the formation of a highly oriented fibrillar structure of PET which is preserved even after annealing above the melting point of PA6. Furthermore, raising of both annealing temperature and duration up to 240 °C and 25 h, respectively, results in a strong decrease of the solubility of the PA6 fraction in formic acid (five-fold). This is attributed to intensive chemical interactions between components, drastically improving the adhesion between matrix and reinforcing microfibrils. From the dependence of H on degree of crystallinity, w _c, the hardness values for completely amorphous, H _a, and fully crystalline, H _c, neat homopolymers were extrapolated (H _a ^PET = 128 MPa, H _c ^PET = 294 MPa, H _a ^PA = 52 MPa and H _c ^PA = 283 MPa). Using these values and applying the additive law, the H-value of the microfibrils is derived. The high value obtained for PET fibrils (360 MPa) is explained by the peculiarity in the structure formation of these microfibrils. The effect of crystal size on the formation of H is also discussed. The H-value of infinite large PA6 crystals is derived to be H = 460 MPa. It is shown that the type and extent of the mutual dispersion of the components, as well as the adhesion between them, are important factors for the proper applicability of the additive law.     

电子束熔炼制备块体钨的组织与显微硬度研究

钨材料具有极高的熔点,传统上采用粉末冶金方法制备,获得的钨材料具有晶粒细小、微观组织均匀等优点, 但致密性不足。为进一步提升钨材料的性能,本研究将98.3%的钨粉和1.7%的碳粉均匀混合,在1 800 ℃、26 MPa条件下热压成型,而后采用电子束熔炼技术对成型后的钨块进行熔炼,利用金相显微镜、SEM、显微硬度计等对其显微组织、致密度和显微硬度进行评价,并与传统粉末冶金法制备的块体钨的性能进行了对比。结果表明:电子束熔炼制备的钨锭冶金质量好,致密度可达99.8%;试样的显微硬度达到9.16 GPa,显著高于粉末冶金法制备的块体钨材料,突破了热压烧结工艺制备块体钨的致密度-显微硬度的关系;经1 300 ℃、6 h退火热处理后,显微硬度略有下降,但仍达到8.86 GPa,显示出电子束熔炼技术在制备块体钨硬度性能方面的优势。     

Influence of reactive compatibilizers on the rheometrical and mechanical properties of PA6/LDPE and PA6/HDPE blends

In this work, the influence of reactive compatibilizers on the rheometrical and mechanical properties of polyamide 6/low density polyethylene (PA6/LDPE) and polyamide 6/high density polyethylene (PA6/HDPE) blends was investigated. Polyethylene grafted with maleic anhydride (PEgMA), polyethylene grafted with acrylic acid (PEgAA), and ethylene-methyl acrylate-glycidyl methacrylate (EMA-GMA) were used as compatibilizers. The blends were characterized by torque rheometry, mechanical properties, and morphology. Rheometrical properties results show that PEgMA and PEgAA compatibilizers are more reactive with PA6 than EMA-GMA. Mechanical properties and scanning electron microscopy analysis results show that EMA-GMA compatibilizer is as effective as PEgMA and PEgAA for PA6/LDPE blend. For PA6/HDPE blend, PEgAA and EMA-GMA compatibilizers proved to be as effective as PEgMA. For PA6/HDPE blend compatibilized with PEgAA, an intriguing “web” or “bridge” like structure was observed.     

Fracture toughness and failure mechanisms in unreinforced and long-glass-fibre-reinforced PA66/PP blends

In this paper unreinforced and long-glass-fibre-reinforced PA66/PP blends with different glass-fibre sizing were studied with respect to their fracture toughness determined by the typical K_c method. The fracture surfaces of these blends were studied by scanning electron microscopy in order to characterize the failure mechanisms. For the unreinforced blends a decrease in fracture toughness was observed when 25 wt% of polyamide (PA) was added to the polypropylene (PP) matrix, compared with the plain PP and PA matrices. On the other hand an increase in fracture toughness was observed when 25 wt% of PP was added to the PA matrix. This was explained by the differences in thermal expansion of PP and PA. The fracture toughness of the long-glass-fibre (LGF) composites were not affected by the glass-fibre sizing up to a PA/PP ratio of 50/50. After the phase inversion from a continuous PP to a continuous PA phase in the matrix (between PA/PP ratios of 50/50 and 75/25) the PA glass-fibre sized composite showed higher fracture toughness than the PP sized. This was explained by the change of the fibre-related failure mechanism from frequent fibre pull-out to fibre fracture. In addition the matrix affected the fracture toughness of the PA/PP75/25 blend with PA glass-fibre sizing in a positive way, resulting in the highest fracture toughness observed in this study.     

Polyethylene/clay nanocomposites prepared by polymerization compounding method

A new technique for the preparation of high density polyethylene/clay nanocomposite, "polymerization compounding," is reported. This technique was based on the chemical anchoring of a Ziegler-Natta catalyst on organically modified clay surface containing an ammonium cation bearing primary hydroxyl groups. The polymerization of ethylene was initiated after adequate activation and the growing polyethylene chains are directly adsorbed on to the clay surface through the hydroxyl-functionalized surfactant. Finally, the nanocomposite was prepared by diluting polyethylene adsorbed clay in the high density polyethylene (HDPE) matrix using a batch mixer at 180 degrees C. The as-synthesized nanocomposite was typically characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM) that revealed the formation of intercalated nanocomposite. Tensile property measurements exhibit substantial increase in stiffness (approximately 50%) and strength (approximately 20%) of nanocomposite as compared to that of neat HDPE. Dynamic mechanical analysis under molten state revealed 25% increase in storage modulus when compared to that of neat HDPE.     

Processability of PVDF/PMMA blends studied by torque rheometry

The processing characteristic of blends of poly(vinylidene fluoride) (PVDF) and poly(methyl methacrylate) (PMMA), in different compositions, were studied by torque rheometry. The polymers were mixed in a batch mixer in proportions of 20, 40, 60 and 80% by weight of PVDF, at 190 °C using rotor speeds of 30, 60 and 100 rpm. The results have shown that the increase of the PMMA content improved the processability of the blends, in spite of an increase of the activation energy of flow. Higher speeds of blending caused a reduction of the homogenization blending times of the blends. The PMMA processing at different speeds studied by parallel plate rheometer showed that a similar behavior and did not affect considerably the degradation of PMMA, according the Carreau model.     

有机蒙脱土调控ABS/PA6共混体系的共连续结构

采用熔融共混的方法制备了不同配比的有机蒙脱土(OMMT)填充丙烯腈-丁二烯-苯乙烯(ABS)/尼龙6(PA6)共混物。通过抽提、SEM、TEM、XRD等表征手段研究了OMMT在PA6相中的定向分散现象及共混体系相结构的演变规律。结果表明,OMMT可以定向分散在ABS/PA6共混物的PA6相中,使形成共连续结构的聚合物比例范围变宽;随着OMMT含量的增加,形成共连续结构所需的PA6的含量降低,同时相尺寸减小;OMMT的临界含量(m(OMMT))和形成共连续PA6的质量分数(m(PA6))存在近似的反比关系,其特征参数n值约为8,据此可根据共混体系中PA6的含量,推算形成相反转所需的OMMT添加量,为相关共混物的制备提供有益的借鉴。     

高聚物材料动态本构关系对PP/PA共混物的应用研究

用霍布金森实验技术(SHPB)研究了两种PP/PA共混高聚物材料在高应变率(102～103s-1)下的粘弹性力学行为.实验表明,PP/PA共混高聚物材料的动态应力-应变曲线能用一个简单实用的非线性粘弹性本构方程(ZWT方程)较好地表达;通过最小二乘法拟合了材料参数;在加载过程中,理论计算值与实验结果较吻合.     

三元乙丙橡胶接枝马来酸酐共聚物对PA6/PP共混物结构和性能的影响

通过Molau实验、扫描电子显微镜(SEM)观察和力学、热学性能测试,研究了三元乙丙橡胶接枝马来酸酐共聚物(EPDM-g-MAH)增容剂在PA6/PP共混物中的作用.重点讨论了PA6/PP配比、EPDM-g-MAH用量对共混物结构、冲击强度、热变形温度和吸水率的影响.实验结果表明:EPDM-g-MAH是一种反应型增容剂.适量的EPDM-～MAH加入可很好地改善PA6和PP两相的相容性,减小PP分散相的粒径,提高PA6、PP两相界面的相互作用.当PA6/PP/EPDM-g-MAH质量比为80/20/(10～15)时,共混物综合性能最好.和纯PA6相比,共混物冲击强度提高3倍以上,热变形温度提高7℃以上,吸水率减少2/3.     

纳米蒙脱土/PP/PVC共混物的性能研究

对纳米蒙脱土(nano-MMT)/聚丙烯/聚氯乙烯(PP/PVC)共混物的性能进行了研究,讨论了纳米MMT用量对PP/PVC(40/60)共混物性能的影响.研究结果表明:随着加入纳米MMT量的增加,共混物的拉伸强度也逐渐增加;当共混物中加入纳米MMT 5份时,共混物的拉伸强度达到最大值;随着加入纳米MMT的增加,共混物...     

Tensile dilatometry of injection-moulded HDPE/PA6 blends

In order to understand the mechanism of deformation of injection-moulded HDPE/PA6 (25 vol% /75 vol%) blends both with and without compatibilizer, the volume change has been monitored using tensile dilatometry. Dog-bone specimens were either directly moulded or cut from rectangular plaques. Both neat materials and their blends were tested. For the directly moulded dog-bone specimen, a pure shear yielding mechanism was observed for all materials tested, i.e. PA6, HDPE, and their blends in the same proportion as above. In the case of a deformable minor phase (HDPE), the dispersed phase appeared to bear its share of stress and the flow-induced orientation mimics the effect of interfacial modification. This was not the case of a rigid minor phase (glass beads) at the same concentration; the effect of surface treatment changed the mechanism of deformation from mixed mode cavitation shear yielding (45%) to almost pure shear yielding (85%). Machined specimens made of neat PA6 and HDPE deformed through pure shear yielding. The addition of 25 vol% HDPE to PA6 resulted in a mixed mode cavitation (55%)/shear yielding mechanism of deformation in the transverse direction, while in the longitudinal case, the mechanism which prevailed was almost pure shear yielding (80%). This can be attributed to the flow-induced orientation as above. When adding 10% (based on the weight of the dispersed phase) of an ionomer as a compatibilizer, the blend deformed via shear yielding (85%) and in the longitudinal direction both compatibilized and non-compatibilized blends display similar behaviour. Varying the specimen thickness by changing the mould cavity, led to a significant variation in the dilatational behaviour. Dilatometric behaviour is shown to be closely related to the morphology generated as a result of flow-induced orientation. The skin/core ratio, which is an indication of the proportion of the oriented dispersed phase to the non-oriented one, plays a key role in influencing the mechanism of deformation involved.     

Toughening mechanism of PA1010/ester-based TPU blends

To improve the notched impact strength of polyamide-1010 (PA1010), it was modified with a thermoplastic poly (ester urethane) elastomer (ester-based TPU). The notched impact strength of PA1010/ester-based TPU blends was investigated by using an impact tester and the fracture morphology of PA1010/ester-based TPU blends was investigated by means of SEM. In the impact experiments, it was found that the notched impact strength of the blends is obviously higher than that of pure PA1010, and the fracture surfaces of the blends show a corrugated and oriented structure. The results indicate that the brittle-to-tough transition of the blends occurs when the content of ester-based TPU is 20 wt.% and there is a new toughening mechanism, which is the multi-layer crack extension mechanism, besides the crazing with a shear-yield mechanism in the process of fracture for the blend samples under impact.     

PP/PA6/OMMT纳米复合材料的非等温结晶动力学

采用熔融插层法制备了聚丙烯(PP)/尼龙6(PA6)/蒙脱土(OMMT)纳米复合物材料,并用差示扫描量热法(DSC)对体系的非等温结晶动力学进行了研究.结果表明,PA6和OMMT的加入,对PP有异相成核的作用,能提高PP的结晶速率和结晶度;运用莫志深方法处理纯PP和PP/PA6/OMMT复合材料的非等温结晶动力学,结果...