Improving the transparency of stretched poly(ethylene terephthalate)/polyamide blends

Compatibilized blends of poly(ethylene terephthalate (PET) with an aromatic polyamide such as poly(m‐xylylene adipamide) (MXD6) have good transparency (T) because the constituent refractive indices (RIs) match closely. However, haziness is observed when the blends are stretched. This study demonstrated that stretching imparted a greater RI anisotropy to PET than to the aromatic polyamide. The resulting RI mismatch was responsible for the loss in T. Analysis of the strain‐dependent birefringence revealed that different molecular deformation models described the intrinsic birefringence of the PET and aromatic polyamides. Hydrogen bonding of the polyamide may have been responsible for the difference. On the basis of these results, three approaches for improving T of stretched PET blends were attempted. Blends with a lower molecular weight MXD6 exhibited slightly higher T after stretching; however, they did not compare with stretched PET. Increasing the amount of compatibilizer reduced the particle size; however, the dimension of even the smallest particles exceeded the quarter wavelength after biaxial stretching transformed the spherical particles into platelets. Copolyamides based on MXD6 that incorporated isophthalate were designed to increase the RI of the polyamide and thereby reduce the RI mismatch with stretched PET. Unexpectedly, the poor T of stretched copolyamide blends was attributed to the high glass‐transition temperature of the copolyamide, which hampered the molecular orientation. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 225–235, 2006     

Transparency of polymer blends

Polymer blending is useful for improving physical properties. Blends of transparent polymers are generally hazy. However, transparency is required in many products such as packages (especially PET bottles). The miscible blends, PET (polyethylene terephthalate)/PBT (polybuthylene terephthalate), maintain transparency in almost all cases regardless of the blending ratio, whereas the immiscible blends, PET/MxNYLON (MXD6 nylon, i.e. polymethaxylirene adipamide) and PET/PMAI (polymethacril imide, i.e. N‐methyl dimethyl glutarimide) become hazy as the blending ratio increases. The reason for this haze is the number and size of the dispersed particles. Differences in the refractive indices of various polymers also have a large influence on haze. Stretching makes even the transparent blends hazy in the case of PET/MxNYLON. One reason for this phenomenon is that stretching increases the size of the dispersed particles in the sheet plane. A second reason is that the difference in the anisotropic refractive indices of the matrix and the dispersed phase is increased by stretching. These effects are very consistent with light scattering theory.     

Improving gas barrier of PET by blending with aromatic polyamides

Improvement of gas-barrier properties of poly(ethylene terephthalate) (PET) by blending with an aromatic polyamide, either poly(m-xylylene adipamide) (MXD6) or a copolyamide based on MXD6 in which 12 mol% adipamide was replaced with isophthalamide (MXD6-12I), was studied. Incorporating a small amount of sodium 5-sulfoisophthalate into the PET matrix compatibilized the blends and reduced the polyamide domain size to 100-300 nm. Thermal analysis showed that the polyamides had a nucleating effect on PET crystallization, whereas crystallization of the polyamides was inhibited especially in compatibilized blends. Without orientation, blending with 10 wt% MXD6 or MXD6-12I reduced oxygen permeability of PET by a factor of about 0.8 (P/P_PET) when measured at 43% relative humidity (RH), in accordance with the Maxwell model prediction. However, after biaxial orientation, oxygen permeability of blends with 10 wt% MXD6 was reduced by 0.3 at 43% RH, and permeability of blends with 10 wt% MXD6-12I was reduced by 0.4. Even at 85% RH, oxygen permeability was reduced by 0.4 and 0.6 for blends with MXD6 and MXD6-12I, respectively. Blending with an aromatic polyamide was even more effective in reducing carbon dioxide permeability of oriented PET. Transformation of spherical polyamide domains into platelets of high aspect ratio increased tortuosity of the diffusion pathway. The platelet aspect ratio predicted by the Nielsen model was confirmed by atomic force microscopy. Higher aspect ratio of MXD6 domains was ascribed to a lower T_g compared to MXD6-12I. Similar reduction in oxygen permeability was achieved in bottle walls blown from PET blends with MXD6 or MXD6-12I.     

Improving oxygen barrier properties of poly(ethylene terephthalate) by incorporating isophthalate. I. Effect of orientation

The present study examined poly(ethylene terephthalate) (PET) and a series of statistical and blocky copolymers in which up to 30% of the terephthalate was replaced with isophthalate by copolymerization and melt blending, respectively. Some level of transesterification during processing of melt blends resulted in blocky copolymers, as confirmed by NMR. Random and blocky copolymers exhibited similar properties in the glassy state, including a single glass transition, due to miscibility of the blocks. However, random copolymerization effectively retarded cold‐crystallization from the glass whereas blocky copolymers readily cold‐crystallized to a crystallinity level close to that of PET. The polymers were oriented at four temperatures in the vicinity of the T_g and characterized by oxygen transport, wide‐angle X‐ray diffraction, positron annihilation lifetime spectroscopy, and infrared spectroscopy. Orientation of all the copolymers resulted in property changes consistent with strain‐induced crystallization. However, blocky copolymers oriented more easily than random copolymers of the same composition and after orientation exhibited slightly lower oxygen permeability, higher density, and higher fraction trans conformers. Analysis of oxygen solubility based on free volume concepts led to a two‐phase model from which the amount of crystallinity and the amorphous phase density were extracted. Dedensification of the amorphous phase correlated with the draw temperature. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1615–1628, 2005     

PET/PA nanocomposite blends with improved gas barrier properties: Effect of processing conditions

The aim of this research is to develop nanocomposite polyethylene terephthalate‐polyamide blends (PET/MXD6 blends) with low oxygen permeability. Particular attention has been paid to the relation between barrier properties and the processing route adopted and therefore four different strategies were considered. Mechanical characterization shows that clay may effectively act as reinforcing filler in PET/MXD6 blends. Morphological characterization shows the strong effect of the processing strategy on clay dispersion and its distribution between the PET and polyamide phases. Barrier properties of PET/MXD6 nanocomposite blends are enhanced with respect to neat PET polymer as well as PET/MXD6 blends. The significant effect of processing techniques on barrier properties is also revealed. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011.     

Improving oxygen barrier properties of poly(ethylene terephthalate) by incorporating isophthalate. II. Effect of crystallization

The present study examined crystallization of poly(ethylene terephthalate) (PET) and a series of random and blocky copolymers in which up to 30% of the terephthalate was replaced with isophthalate. Isothermal crystallization kinetics and direct observation of the spherulitic morphology revealed that the blocky copolymers crystallized more rapidly than PET, at least in part, as the result of enhanced spherulite nucleation. The statistical copolymers with 10 and 20% isophthalate achieved almost the same level of crystallinity as that of the blocky copolymers. The statistical copolymers with 10% isophthalate crystallized almost as fast as PET, although the statistical copolymer with 20% isophthalate crystallized much more slowly. Crystallization substantially reduced the oxygen permeability. Analysis of oxygen‐transport parameters in terms of a two‐phase structural model that considered a dispersion of lower‐permeability spherulites in an amorphous matrix of higher permeability revealed that dedensification of the PET interlamellar amorphous regions was responsible for the unexpectedly high oxygen solubility of crystallized PET. In contrast, copolymerization with isophthalate prevented dedensification of the interlamellar amorphous regions. As a result, crystallization was more effective in reducing the oxygen permeability. It was speculated that segregation of kinked isophthalate units to the amorphous regions of the spherulite relieved constraint on the interlamellar amorphous chain segments. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1629–1642, 2005     

Morphology development and non isothermal crystallization behaviour of drawn blends and microfibrillar composites from PP and PET

Microfibrillar composites (MFC) were prepared from the blends of polypropylene (PP) and poly (ethylene terephthalate) (PET) at a fixed weight ratio of 85/15. The blending of the mixture was carried out in a single screw extruder, followed by continuous drawing at a stretch (draw) ratio 5. The stretched blends were converted into MFC by injection moulding. Scanning electron microscopy (SEM) studies showed that the extruded blends were isotropic, but both phases possessed highly oriented fibrils in the stretched blends, which were generated insitu during drawing. The PET fibrils were found to be randomly distributed in the PP matrix after injection moulding. The non isothermal crystallization behaviour of the as extruded blend, stretched blend and MFC was compared. The analysis of the crystallization temperature and time characteristics revealed that the PET fibrils in the stretched blend had a greater nucleating effect for the crystallization of PP than the spherical PET particles in the as extruded blend and short PET fibrils in the MFC.     

Microstructure and crystallization of melt‐mixed poly(ethylene terephthalate)/poly(ethylene isophthalate) blends

Physical blends of poly(ethylene terephthalate) (PET) and poly(ethylene isophthalate) (PEI), abbreviated PET/PEI (80/20) blends, and of PET and a random poly(ethylene terephthalate‐co‐isophthalate) copolymer containing 40% ethylene isophthalate (PET₆₀I₄₀), abbreviated PET/PET₆₀I₄₀ (50/50) blends, were melt‐mixed at 270°C for different reactive blending times to give a series of copolymers containing 20 mol % of ethylene isophthalic units with different degrees of randomness. ¹³C‐NMR spectroscopy precisely determined the microstructure of the blends. The thermal and mechanical properties of the blends were evaluated by DSC and tensile assays, and the obtained results were compared with those obtained for PET and a statistically random PETI copolymer with the same composition. The microstructure of the blends gradually changed from a physical blend into a block copolymer, and finally into a random copolymer with the advance of transreaction time. The melting temperature and enthalpy of the blends decreased with the progress of melt‐mixing. Isothermal crystallization studies carried out on molten samples revealed the same trend for the crystallization rate. The effect of reaction time on crystallizability was more pronounced in the case of the PET/PET₆₀I₄₀ (50/50) blends. The Young's modulus of the melt‐mixed blends was comparable to that of PET, whereas the maximum tensile stress decreased with respect to that of PET. All blend samples showed a noticeable brittleness. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3076–3086, 2003     

Primary structure and physical properties of poly(ethylene terephthalate)/poly(ethylene naphthalate) resin blends

The morphology and properties of blends of poly(ethylene naphthalate) (PEN) and poly(ethylene terephthalate) (PET) that were injection molded under various conditions were studied. Under injection molding conditions that make it possible to secure transparency, blends did not show clear crystallinity at blending ratios of more than 20 mol% in spite of the fact that crystallinity can be observed in the range of PEN content up to 30 mol%. Because both transparency and crystallinity could be secured with a PEN 12 mol% blend, this material was used in injection molding experiments with various injection molding cycles. Whitening occurred with a cycle of 20 sec, and transparency was obtained at 30 sec or more. This was attributed to the fact that transesterification between PET and PEN exceeded 5 mol% and phase solubility (compatibility) between the PET and PEN increased when the injection molding time was 30 sec or longer. However, when the transesterification content exceeded 8 mol%, molecularly oriented crystallization did not occur, even under stretching, and consequently, it was not possible to increase the strength of the material by stretching. PET/PEN blend resins are more easily crystallized by stretch heat‐setting than are PET/PEN copolymer resins. It was understood that this is because residual PET, which has not undergone transesterification, contributes to crystallization. However, because transesterification reduces crystallinity, the heat‐set density of blends did not increase as significantly as that of pure PET, even in high temperature heat‐setting. Gas permeability showed the same tendency as density. Namely, pure PET showed a substantial decrease in oxygen transmission after high temperature heat‐setting, but the decrease in gas permeability in the blend material was small at heat‐set temperatures of 140°C and higher.     

Synthesis and characterization of copolymers of poly(m-xylylene adipamide) and poly(ethylene terephthalate) oligomers by melt copolycondensation

Poly(m-xylylene adipamide)/poly(ethylene terephthalate)(MXD6/PET) copolymers are synthesized by melt copolycondensation with 1–5 wt% low molecular weight PET oligomers into the MXD6 oligomers at 260 °C.FR-IR and1 H NMR analysis results indicate that the interchange reaction has occurred between MXD6 oligomers and PET oligomers. The thermal behavior of copolymers shows that the melting temperature of MXD6/PET copolymers decreases with the increasing of amount of PET oligomers, while the crystallization temperature accordingly increases. And the equilibrium temperature Tm0 is evaluated to be 251.8 °C for the copolymers with5 wt% PET oligomer adding, which is very close to that of neat MXD6. The tensile and impact strength of MXD6/PET copolymers are significantly improved than that of pure MXD6 by mechanical properties test, and the microfibril structure in the impact fracture sample's surface reveals the feature of ductile fracture.     

Effect of compatibilization on the oxygen‐barrier properties of poly(ethylene terephthalate)/poly(m‐xylylene adipamide) blends

The improvement of the oxygen‐barrier properties of poly(ethylene terephthalate) (PET) via blending with an aromatic polyamide [poly(m‐xylylene adipamide) (MXD6)] was studied. The compatibilization of the blends was attempted through the incorporation of small amounts of sodium 5‐sulfoisophthalate (SIPE) into the PET matrix. The possibility of a transamidation reaction between PET and MXD6 was eliminated by ¹³C‐NMR analysis of melt blends with 20 wt % MXD6. An examination of the blend morphology by atomic force microscopy revealed that SIPE effectively compatibilized the blends by reducing the MXD6 particle size. Thermal analysis showed that MXD6 had a nucleating effect on the crystallization of PET, whereas the crystallization of MXD6 was inhibited, especially in compatibilized blends. Blending 10 wt % MXD6 with PET had only a small effect on the oxygen permeability of the unoriented blend when it was measured at 43% relative humidity, as predicted by the Maxwell model. However, biaxially oriented films with 10 wt % MXD6 had significantly reduced oxygen permeability in comparison with PET. The permeability at 43% relative humidity was reduced by a factor of 3 in compatibilized blends. Biaxial orientation transformed spherical MXD6 domains into platelets oriented in the plane of the film. An enhanced barrier arose from the increased tortuosity of the diffusion pathway due to the high aspect ratio of MXD6 platelets. The aspect ratio was calculated from the macroscopic draw ratio and confirmed by atomic force microscopy. The reduction in permeability was satisfactorily described by the Nielsen model. The decrease in the oxygen permeability of biaxially oriented films was also achieved in bottle walls blown from blends of PET with MXD6. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1361–1370, 2005     

Melting and crystallization behavior of poly(ethylene terephthalate) and poly(m‐xylylene adipamide) blends

The crystallization and melting behaviors as well as the crystalline morphologies of Poly(ethylene terephthalate)/Poly(m‐xylylene adipamide) (PET/MXD6) blends have been examined and characterized with the aid of differential scanning calorimetry (DSC) and wide angle x‐ray diffraction (WAXD). The isothermal and nonisothermal crystallization behaviors of the blends were studied as functions of the contents of MXD6, catalyst concentrations, and the effects of the interchange reactions between PET and MXD6. Wide angle x‐ray scattering has been used to examine the crystalline morphologies of the PET/MXD6 blends, to characterize their crystalline and amorphous phases, and to determine crystallite sizes in the blends. Results indicate that the catalyst has both catalyzing and nucleation effects on the PET/MXD6 blends, with the extents of each effect dependent upon the content of catalyst. In addition the crystalline morphology was found to be dominated by the MXD6 content as well as the crystallization temperature. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Rheological behavior comparison between PET/HDPE and PC/HDPE microfibrillar blends

The rheological behaviors of in situ microfibrillar blends, including a typical semicrystalline/semicrystalline (polyethylene terephthalate (PET)/high‐density polyethylene (HDPE)) and a typical amorphous/semicrystalline (polycarbonate (PC)/HDPE) polymer blend were investigated in this study. PET and PC microfibrils exhibit different influences on the rheological behaviors of microfibrillar blends. The viscosity of the microfibrillar blends increases with increased PET and PC concentrations. Surprisingly, the length/diameter ratio of the microfibrils as a result of the hot stretch ratio (HSR) has an opposite influence on the rheological behavior of the two microfibrillar blends. The stretched PET/HDPE blend exhibits higher viscosity than the unstretched counterpart, while the stretched PC/HDPE blend exhibits lower viscosity than the unstretched blend. The data obtained in this study will be helpful for constructing a technical foundation for the recycling and utilization of PET, PC, and HDPE waste mixtures by manufacturing microfibrillar blends in the future. POLYM. ENG. SCI., 45:1231–1238, 2005. © 2005 Society of Plastics Engineers     

封闭型异氰酸酯齐聚物及与PET反应性共混

合成了一系列由聚乙二醇、芳香族二异氰酸酯以及乙醇、异丙醇、苯酚组成的封闭型异氰酸酯齐聚物（ＴＩＯ）；应用差示扫描量热法、红外光谱、特性粘数测试等手段，表征了这些ＴＩＯ的解封闭特性，进而在哈克流变仪上进行聚对苯二甲酸乙二酯与ＴＩＯ反应性共混，初步研究了共混物的特性粘数和热性能。     

Strain-induced crystallization of poly(ethylene terephthalate)

The fabrication of poly(ethylene terephthalate), PET, into fibers, films, and containers usually involves molecular orientation caused by molecular strain, which may lead to stress- or strain-induced crystallization (SIC). The SIC of PET was studied by the methods of birefringence, density, thermal analysis, light scattering, and wide-angle X-ray. The development of crystallinity is discussed in relation to the rate of crystallization, the residual degree of orientation, and stress relaxation. The experimental procedure involves stretching samples at temperatures above the glass transition temperature, Tg, to a given extension ratio and at a specific strain rate of an Instron machine. At the end of stretching, the sample is annealed in the stretched state and at the stretching temperature for various periods of time, after which the sample is quickly quenched to room temperature for subsequent measurements. During stretching, the stress strain and the stress relaxation curves are recorded. The results indicate that the SIC of annealed, stretched PET can proceed in three different paths depending on the residual degree of orientation. At a low degree of residual orientation, as indicated by the birefringence value, annealing of stretched PET leads only to molecular relaxation, resulting in a decrease of birefringence. At intermediate orientation levels, annealing causes an initial decrease in birefringence followed by a gradual increase and finally a leveling off of birefringence after a fairly long period of time. At higher orientation levels, annealing causes a rapid increase in birefringence before leveling off. The interpretation of the above results is made using the measurements of light scattering, differential scanning calorimetry, and wide-angle X-ray. The rate of the SIC of PET is also discussed in terms of specific data analysis.     

The interchange reaction between poly(ethylene terephthalate) and poly(m‐xylylene adipamide)

The interchange reaction in blends of poly(ethylene terephthalate) (PET) and poly(m‐xylylene adipamide) (MXD6) has been characterized in terms of changes observed in spectra obtained with a 600‐MHz ¹H‐NMR. The selective degradation of PET components in the blends was carried out in the NMR tubes prior to evaluation. Results indicate that there is no chemical reaction between the PET and MXD6 in the absence of sodium p‐toluenesulfonate catalyst. The presence of the catalyst activates the interchange reaction between these two resins. A mathematical method was applied to calculate the degree of randomness of PET‐MXD6 copolymer. In addition, the reaction degree was found to be affected by exposure temperature, time, shear rate, and catalyst concentration. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Study of compatibilization of HDPE–PET blends by adding grafted or statistical copolymers

The reactive compatibilization of blends of HDPE–PET [high‐density polyethylene–poly(ethylene terephthalate)] was investigated in this study. The compatibilizers used were two grafted copolymers prepared by reactive extrusion containing 1.20–2.30 wt % GMA such as HDPE‐g‐GMA and one statistical copolymer containing 1 wt % GMA such as Lotader AX8920. HDPE was successfully functionalized using a melt free‐radical grafting technique. Grafting was initiated in two ways: adding an initiator in the polymer–monomer mixture or activation by ozone of polymer. Ozonization of HDPE by the introduction of a peroxide lead to a better grafting yield and to better grafting efficiency of the samples. The effects of the three compatibilizers were evaluated by studying the morphology and the thermal and mechanical properties of HDPE–PET (70/30 wt %) blends. Significant improvements were observed, especially in morphology, elongation at break, and Charpy impact strength of the compatibilized blends. A more pronounced compatibilizing effect was obtained with the statistical copolymer, for which the elongation at break and the impact strength were increased by 100%, while the uncompatibilized blends showed a 60% decrease in the Young's modulus and the strength at break. We also were able to show that the grafting yield increase of 1.20–2.30 wt % of GMA did not affect the properties of the blends because the grafted copolymers possess very similar chemical structures. However, compatibilization of blends with grafted copolymers is an interesting method, particularly for recycled blends, because the synthesis of these compatibilizers is easy and cheap in comparison to statistical copolymer. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2377–2386, 2001     

Effect of copolymers containing glycidyl methacrylate functional groups on the rheological,mechanical, and morphological properties of poly(ethylene terephthalate)

The aim of this work was to investigate the effect of ethylene‐glycidyl methacrylate (EGMA) and ethylene‐methyl acrylate‐glycidyl methacrylate (EMAGMA) copolymers on the rheological, mechanical, and morphological properties of Poly(ethylene terephthalate) (PET). The results of torque rheometry showed an increase in the torque of PET with the addition of EGMA and EMAGMA copolymers due to the reactions between the GMA groups present in the copolymers and the carboxyl and hydroxyl groups present in PET. The torque of PET/copolymer blends increased with the increase in the copolymer content and was more pronounced for the blends containing EGMA copolymer. X‐ray diffraction and differential scanning calorimetry analyzes showed that neat PET and the PET in PET/copolymer blends are amorphous. The addition of EGMA and EMAGMA copolymers delayed the crystallization of PET. Rheological measurements showed an increase in the viscosity at low frequencies with the addition of EGMA and EMAGMA copolymers to PET. This increase was more pronounced for PET/copolymer blends containing higher amount of copolymers and for the blends containing EGMA, corroborating the results obtained by torque rheometry. The impact strength of PET/EMAGMA blends was higher than that of PET/EGMA blends. Morphology analysis by SEM showed that PET/EMAGMA blends presented higher average dispersed phase domains size than PET/EGMA blends. POLYM. ENG. SCI., 59:683–693, 2019. © 2018 Society of Plastics Engineers     

PET/PP共混改性研究进展

综述了聚对苯二甲酸乙二酯(PET)和聚丙烯(PP)共混的研究进展。重点阐述了以不同方式共混时,共混体系的相容性、形态和性能。     

Properties and morphology of oriented ternary blends of poly(ethylene terephthalate), high density polyethylene,and compatibilizing agent

Oriented blends of poly(ethylene terephthalate) (PET) and high density polyethylene (HDPE) with and without compatibilizing agent have been studied with regard to orientation temperature, stretch rate, extension ratio, mode of orientation, and blend composition. These oriented blends have been characterized using infrared spectroscopy and differential scanning calorimetry. The tensile and tensile impact properties were also investigated. The results show that blends with compatibilizer show strain hardening upon orientation, whereas the blend without compatibilizer does not strain harden upon orientation. The blends with less PET content have been difficult to orient. The morphology of these blends show fibril structure, highly oriented in the direction of stretch. Infrared measurements show that PET within the blend has undergone strain induced crystallization upon orientation. It has also been observed that the mechanical properties, such as the modulus and ultimate stress, show improvement upon orientation. Simultaneously stretched blends show better physical properties than sequentially oriented blends.