Essential work of fracture testing of PC-rich PET/PC blends with and without transesterification catalysts

0.7 mm sheets of blends of polycarbonate (PC) with polyethylene terephthalate (PET) rich in PC in the presence and absence of three different transesterification catalysts have been obtained using reactive extrusion-calendering processing method in order to evaluate the fracture toughness of these materials applying the essential work of fracture (EWF) approach which has not been previously reported in the literature. The morphology has been characterized by scanning electron microscopy (SEM). In addition, the tensile properties of these materials were determined. There is a decrease on the essential term (w _e) values of PC/PET blends without transesterification catalysts while blends with transesterification catalysts present an increment in comparison with neat PC which may related to the product of the transesterification that plays like an emulsifier/compatibilizing agent to reduce the interfacial tension between the components of the blend and reduce the interfacial tension between the two immiscible or incompatible component phases to get a better fracture behavior. This is confirmed by the tensile test results obtained which demonstrate higher values for E and σ _y in the case of blends with transesterification catalysts compared with neat PC. For non-essential term of fracture (βw _p), blends without catalysts exhibit an increase compared with neat PC by increasing the amount of PET which may due to the lowering of the yielding stress. In contrary, the presence of transesterification catalysts and especially Zn-based shows decrease as a consequence of the restriction that occurred on the movement of PC segments during the transesterification reactions or as a decohesion of the dispersed phase during the test.     

Effects of composition and transesterification catalysts on the physico-chemical and dynamic properties of PC/PET blends rich in PC

Melt blending of polycarbonate (PC)/poly(ethylene terephthalate) (PET) rich in PC at absence/present of different type of tranesterification catalysts was carried out by using reactive extrusion method. The thermal, dynamic, and morphological properties were studied. It was found that all blends are formed by a PC matrix and a semicrystalline (12–20% of crystallinity) of PET dispersed phase. The addition of a catalyst in the mixing process promotes a refined and homogeneous dispersion of PET, as well as it enhances the dynamicmechanical behavior of PC/PET blends compared with PC. These effects are attributed to the emulsifying effect of the PC–PET copolymer generated by transesterification. Additionally, this copolymer contributes to the miscibility between phases as demonstrated by the glass transition (T _g) shift of PC phase and PET phase.     

具有高界面压应力的高分子共混物Ⅱ.拉伸过程中形态演化与增强机理

研究了聚对苯二甲酸乙二醇酯(PET)/聚乙烯(PE)和聚碳酸酯(PC)/PE共混物在拉伸过程中形态的演化和增强机理.结果表明,高界面压应力是共混物在基体加工温度成型时,从成型温度冷却到室温过程中基体收缩比分散相大产生的;两种共混物在拉伸中有不同的形态演化过程:PC粒子原位形成了微纤,粒子与基体间没有明显的界面滑动,而PET粒子只产生较小的塑性变形,成为椭球状粒子,粒子与界面间存在滑动.PC对基体PE的增强效果比PET的更好,因为PC/PE共混物拉伸过程中形成了良好增强作用的原位微纤.在拉伸过程中,PET/PE试样的细颈在靠近非浇口端形成,并从此扩展开.部分拉伸后,PC/PE试样比PET/PE试样的弹性回复大,回复到平衡状态时间长,这是两种共混物分散相变形机理不同引起的.     

具有高界面压应力的高分子共混物Ⅰ.制备和拉伸性能

考察了高界面压应力对不相容聚对苯二甲酸乙二醇酯(PET)/聚乙烯(PE)和聚碳酸酯(PC)/PE共混物拉伸性能的影响.高界面压应力是共混物低温成型(PE的成型温度)时,分散相与基体从加工温度冷却到室温过程中基体的收缩比分散相粒子大产生的.尽管PET/PE和PC/PE共混物极不相容,但拉伸强度和模量随着PET和PC含量增加而增加.PET与PC含量相同时,PC/PE的拉伸强度和模量高于PET/PE的.采用Takayanangi方程计算共混物的拉伸模量时,具有高界面压应力的PC/PE共混物的拉伸强度高于界面有良好粘结的共混物的理论值,表明在不添加增容剂时,可通过控制加工条件改善共混物界面相互作用,提高共混材料的性能.     

Morphology and properties of ASA/PET blends

This study examines the morphology and mechanical properties of acrylate styrene acrylonitrile (ASA) and polyethylene terephthalate (PET) blends. The morphology of the 60/40 and 40/60 ASA/PET blends reveals a dispersed phase morphology verging on co-continuity, whilst the 50/50 blend appears to be completely co-continuous. Processing temperature has no effect on blend modulus or tensile strength and there is no statistically significant difference in mechanical performance between the three blend ratios. Charpy impact resistance decreases with increasing processing temperature. The fracture surface reveals a similar mushroom fibril morphology found for the ASA/polybutylene terephthalate (PBT) system, but is less extensive. Thermal analysis shows a marked drop in glass transition temperature for the blends compared to the component polymers.     

Fracture toughness and fracture mechanisms of polybutylene-terephthalate/polycarbonate/ impact-modifier blends

A series of polybutylene-terephthalate/polycarbonate (PBT/PC) blends with different compositions were prepared using a twin-screw extruder. The morphologies of the blends were revealed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It was found that a 50/50 PBT/PC blend possessed a bicontinuous structure and the other blends had a dispersed phase of either PBT or PC depending on which was the minor component. A relatively strong interface was observed in the blends with 20%, 40% and 50% PBT; but poor interfacial adhesion was found in the blends with 60% and 80% PBT. The strength of the interfacial boundary was believed to depend on the composition and blending conditions of the individual blend. Fracture experiments showed that the sharp-notch fracture toughness of PC could be significantly increased by mixing with up to 50% PBT without losing its modulus and yield stress. The toughening mechanisms involved in the fracture processes of the blends were studied using both SEM and TEM together with single-edge-double-notched-bend (SEDNB) specimens. It was found that in the toughened blends the growing crazes initiated by the triaxial stress in front of the crack tip were stabilized by the PC domains. The debonding-cavitation mechanism occurred at the PBT/PC interface, which relieved the plane-strain constraint and promoted shear deformation in both PBT and PC. This plastic deformation absorbed a tremendous amount of energy. Crack-interface bridging by the PC domains was clearly verified by the TEM study. Thus, the PC domains not only stabilized the growing crazes they also bridged crack surfaces after the crack has passed by. This effect definitely caused a large plastic-damage zone and hence a high crack resistance. Poor crack resistances of the blends rich in PBT was caused by the poor interfacial adhesion between PBT and PC. In these polymer blends, the growing crazes easily developed into cracks, which subsequently passed through the weak interface of PBT/PC and finally produced fast unstable fracture.     

PET/PC共混物配比对其高压结晶行为的影响

利用SEM及W AXD等测试手段研究了配比对PET/PC共混物高压结晶行为的影响。SEM观察表明,随PC比例的增加,共混物高压下主要结晶形态以伸直链晶体,生长成熟的立体开放球晶,大尺寸球晶的方式变化。拟合分峰法和W arren-A verbach傅氏分析法的计算结果表明,随PC含量的增加,高压结晶共混物的结晶度降低,PET的平均晶粒尺寸总体呈减小趋势,晶粒尺寸分布则变窄,而晶格畸变平均值在一定PC比例范围内达到极大值。     

Processing conditions, morphology and properties of a polycarbonate + a thermotropic polymer liquid crystal blend

We have investigated phase structure – properties relationships of polycarbonate (PC) + a polymer liquid crystal (PLC) blends processed in a twin-screw extruder at several conditions. The PLC is PET/0.82 PHB – a copolyester of poly(ethylene terephtalate) and p -hydroxybenzoic acid. For comparison the blend was additionally extruded in a wide range of shear rates in a capillary rheometer at two different spinning rates and compression-molded. The blend processed in the rheometer exhibits lower values of modulus and tensile strength than the blend extruded due to destruction of the initial orientation and dispersion level gained during extrusion. The orientation of PLC-rich islands increases up to the shear rate of 50–100 s^–1, whereas deformation at higher shear rates exhibits a droplet–breakup phenomenon, confirmed by SEM micrographs. The rheological measurements (oscillation mode) evidence a high shear thinning of the PLC. By contrast, the influence of the deformation rate on the viscosity for PC and the blend is negligible, suggesting also a low interaction level in the interfacial area. This conclusion was confirmed by dynamic mechanical measurements. As expected, our experiments prove that structure and properties of the blend are affected by processing (shear and elongation) conditions. Increasing shear rate leads to elongation of dispersed domains but exceeding critical values can lead to droplet breakup and destruction of created structure. The unique morphology created during extrusion can be destroyed during additional processing (in rheometer). Formation of fibrils is also dependent on additional treatment – spinning speed. Optimized spinning speed can lead to 50% increase in stiffness of the blend. Electronic Publication     

Morphology-tensile behavior relationship in injection molded poly(ethylene terephthalate)/polyethylene and polycarbonate/polyethylene blends (I) Part I Skin-core Structure

The skin-core structure of injection molded poly(ethylene terephthalate) (PET)/polyethylene (PE) and polycarbonate (PC)/PE blends was investigated. The results indicate that both shape and size of the PET and PC phases depended not only on the nature properties of PET/PE and PC/PE blends, but also on the injection molding parameters such as injection speed and the positions in the molded bars. The morphology in the section perpendicular to the melt flow direction included four layers, surface, sub-skin, intermediate layers as well as core zone. The surface layer was ignored in the present study. The sub-skin layer contained more or less fibrous structure and its thickness gradually decreased along the molded bar from the gate toward the non-gate end. At the same injection speed, the concentration of the injection-induced fibers in PC/PE blend was much higher than that in PET/PE blend. In the core region, the dispersed phase was mainly composed of spherical particles whose diameter increased along the melt flow pathway. Between these two layers, there was an intermediate layer where the dispersed particles mainly assumed the form of fibers, ellipsoids or spheres. Generally, no matter whether the dispersed particles were elongated or not during injection molding, the PET particles were larger than PC ones.     

PC／PET共混体系的形态,结构和性能及催化剂对它们的影响

本文研究了PC/PET熔融共混体系组分比和酯交换反应对共混物形态、结构和性能的影响。结果表明:随PET含量增加,体系中两个组分的互容性增加。酯交换反应可以增大两个组分的互容性。加入催化剂所引起的酯交换反应改变了共混物的结构,使共混物的力学性能有所下降。     

Tuning the localization of functionalized MWCNTs in SAN/PC blends by a reactive component

The influence of the reactive component (N-phenylmaleimide styrene maleic anhydride) on the blend morphology, the localization of functionalized multiwalled carbon nanotubes (MWCNTs), and the electrical resistivity of MWCNT filled blend systems of polycarbonate (PC) and poly(styrene-co-acrylonitrile) (SAN) was investigated. SAN, PC, amino-functionalized MWCNTs (Nanocyl™ NC3152) and the reactive component (RC) were melt mixed in a DSM Xplore microcompounder using different mixing sequences. The RC containing maleic anhydride (MA) groups is miscible with SAN and is assumed to act as linking agent to the functionalized MWCNTs.The morphology of the SAN/PC blends was studied depending on the concentration of the RC. Thereby co-continuous morphologies were found for all blends with 40 wt.% SAN and 60 wt.% PC. In all nonmodified blends the MWCNTs were localized within the PC phase. After the addition of RC the MWCNTs migrated completely into the miscible SAN–RC phase. Consequently, the electrical resistivities of the blends changed in dependence on the localization. Whereas the SAN/PC/MWCNT blends showed low electrical resistivity values, much higher values were found for SAN–RC/PC/MWCNT blends. This was assigned to a coupling or strong interaction of MA groups to the nanotubes disturbing electrical contacts and percolation between them. The occurrence of the MWCNT migration from PC towards SAN was found to be dependent on the concentrations of RC and MWCNTs. By adapting that ratio and the mixing strategy, the localization of the carbon nanotubes in the blend phases can be tuned. The investigations indicated that MWCNTs once coupled with the RC remain in the SAN–RC phase. Thus, a chemical reaction or strong interactions seem to be the driving forces for localization of the MWCNTs in the SAN–RC blend phase.     

Morphology-tensile behavior relationship in injection molded poly(ethylene terephthalate)/polyethylene and polycarbonate/polyethylene blends (II) Part II Tensile behavior

The tensile behavior of injection molded poly(ethylene terephthalate) (PET)/polyethylene (PE) and polycarbonate (PC)/PE blends was investigated. For the same blend, due to the difference in the elongated dispersed particle concentration, the specimens molded at higher injection speed had slightly higher tensile strength and modulus than those molded at lower speed. Moreover, the reinforcement effect of PC to PE matrix was more noticeable than PET to PE. For the stress-strain behavior, while the PET/PE blend behaved like a common injection-molded immiscible blend the PC/PE blend unusually underwent twice yielding regardless of the cross head speed. For the PET/PE blend, obvious debonding between the dispersed PET particles and the matrix PE occurred upon elongation, resulting in large grooves and voids behind the particles. The PET particles experienced slight plastic deformation from spheres to ellipsoids. The stress whitening first appeared in the necking zone then extended along cold drawing zone. For the PC/PE blend, the PC particles in the core layer experienced considerable plastic deformation throughout the tensile test. Consequently, most of PC particles in the fractured specimen were deformed into fibers. Owing to comparatively high amount of injection-induced fibers that distributed or transferred the external stress, the specimen of PC/PE blend first deformed evenly in the entire tested zone, characterized by stress whitening in the entire specimen. Then after the first yielding, the stress decreased slowly while the elongation continued. When the elongation reached a certain point, the fibers in the sub-skin layer could no longer endure the external stress, and accordingly the second yield took place. Additionally, the fibrillation of the spherical PC particles in the core layer appeared right after the second yielding point.     

Morphological control of LCP/PET blends using a melt mixer equipped with a milling part

The morphology of liquid crystalline polymer (LCP)/poly(ethylene terephthalate) (PET) blends using a melt mixer equipped with a gap-adjustable milling part was investigated. From the scanning electron microscopic (SEM) observation, the isotropic structure in which spherical LCP domains were dispersed homogeneously in a PET matrix was attained in this study, if the LCP component was 50% or below. The wide-angle X-ray diffraction (WAXD) pattern of the LCP/PET=50/50 blend extrudate suggested that the LCP phase had an unoriented structure, showing a single reflection of 0.45 nm. In the case of the LCP/PET=50/50 blend extrudate, the difference between the linear expansion coefficient (α) parallel to the machine direction, α (MD), and that perpendicular to the MD, α (TD), was estimated to be very small; the α (TD)/α (MD) ratio was 1.153. These results are in agreement with the results of the WAXD profile, and clearly suggest that the anisotropy in the α of the blend extrudate is significantly reduced by the use of a melt mixer equipped with a milling part.     

Structural-mechanical relationship of epoxy compatibilized polyamide 6/polycarbonate blends

Polyamide 6 (PA6)/polycarbonate (PC) blends compatibilized with solid epoxy resin (bisphenol type-A) were prepared by extrusion followed by injection molding. The effects of epoxy resin on the microstructure, tensile, impact and compatibility of the PA6/PC blends were investigated. The results showed that both the tensile modulus and elongation at break of PA6/PC blends were inferior as compared to their parent polymers. This resulted from incompatibility between the PA6 and PC phases. SEM observation revealed that the introduction of 0.5 part per hundred (phr) epoxy resin into the PA6/PC75/25 blend yields a finer dispersion of PC phase in PA6 matrix. The boundaries between the PC domains and PA6 matrix became obscure with the incorporation of 1 phr epoxy resin. Such an improvement in compatibility was suggested to be resulted from the formation of in situ epoxy bridged PA6-PC block copolymer in the blend during compounding. Consequently, the tensile modulus, yield strength and impact strength of the PA6/PC 75/25 blend improved considerably with increasing epoxy content.     

用SEM观察PE/PC共混物在拉伸和冲击作用前后的形态

介绍了典型的极不相容共混物（ＥＩＢ）聚乙烯／聚碳酸酯（ＰＥ／ＰＣ）体系的形态受组成的影响,以及共混物在受到拉伸前后,冲击前后的形态。通过扫描电子显微镜（ＳＥＭ）观察发现,组成不仅影响分散相粒子的大小,形状,还决定分散相与连续相的转变,共混物在受到拉应力（拉伸）和剪切应力（冲击）后,前者较多球状粒子变形成为有利于提高拉伸性能的纤维状,后者粒子和基体都发生了能提高抗冲击韧性的塑性变形。     

PET／PC共混物的形态结构的研究

用偏光显微镜、X-ray衍射仪和示差扫描量热计(DSC)研究了聚对苯二甲酸乙二酯/聚碳酸酯(PET/PC)共混物的形态结构。结果表明:在PET/PC共混物中,当PC含量在50％以下时,PC的晶粒与PET的球晶分别分散在非晶区中;当PC含量在50％以上时,PET的晶柱与PC的晶粒分别分散在非晶区中。随着PC含量的增加,PET晶体的完整性被破坏,晶粒变小,结晶度下降,熔点降低。     

Effect of composition on transcrystallization with reorientation of polypropylene in drawn PET/PP blend

The crystallization behaviour of three blend compositions of poly(ethylene terephthalate)/polypropylene (PET/PP), namely 30/70, 50/50 and 70/30 wt.% was studied. The samples were heated up to temperature between the melting temperatures of the blend components and then cooled to 30 °C. X-ray pictures were taken at every stage and it was shown that a recrystallization with reorientation of the PP crystallites took place during the nonisothermal recrystallization. The PP crystallites in the PET/PP blend reorient with molecular axis tilted at aprox. 49° against the FA during the recrystallization. The amount of PP in the blend does not directly affect the process of trancrystallization with reorientation but has only a masking effect. Such reorientation was observed for all three blends. No reorientation occurs if the PET crystallites have been melted before the recrystallization, i.e., when oriented they induce the reorientation of the PP crystallites.     

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.     

Fracture toughness and fracture mechanisms of PBT/PC/IM blends: Part V Effect of PBT-PC interfacial strength on the fracture and tensile properties of the PBT/PC blends

To investigate the effect of PBT-PC interfacial strength on the fracture toughness and toughening mechanisms of the PBT/PC system, a series of PBT/PC blends with different content of in situ formed PBT-PC copolymers were made by melt blending. The in situ copolymer was separately prepared via reactive blending of the PBT and PC in the presence of a transesterification catalyst in a twin-screw extruder for a few minutes. The reactive extrudate (RE) was studied using a DSC and the existence of the PBT-PC copolymer in the RE was confirmed. Microstructure characterizations of the PBT/PC/RE blends revealed that the domain sizes of the PBT and PC decrease and the PBT-PC interfacial strength increases with the RE content. Compared with the PBT/PC blend, all the PBT/PC/RE blends have higher yield strength, elongation at break as well as tensile modulus. The quasi-static fracture tests show that fracture toughness of the blends increases with the RE content. Since the highest toughness was obtained with the blend having the highest RE content (7.5%), it is not certain at this stage whether adding more than 7.5% RE will further improve the fracture toughness. The impact toughness of the PBT/PC/RE blends was found to decrease with the increase of the PBT-PC interfacial strength, which confirms the failure mechanisms proposed in the Part-4 of this series.     

PC／PET共混物的非等温结晶动力学

采用等速变温ＤＳＣ法对ＰＣ／ＰＥＴ共混体系的非等温结晶动力学进行了研究，结果表明，从玻璃态结晶时，随着ＰＣ含量的增加，ＰＥＴ组分的结晶速率先增加后降低。耐从熔体结晶时，体系的结晶速率随着ＰＣ含量的增加而增加，讨论了ＰＣ对ＰＥＴ组分结晶过程的影响。