Surface modification of poly(ethylene terephthalate) by plasma polymerization of poly(ethylene glycol)

Poly(ethylene glycol) (PEG) was ‘polymerized’ onto poly(ethylene terephthalate) (PET) surface by radio frequency (RF) plasma polymerization of PEG (average molecular weight 200 Da) at a monomer vapour partial pressure of 10 Pa. Thin films strongly adherent onto PET could be produced by this method. The modified surface was characterized by infra red (IR) spectroscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM), cross-cut test, contact angle measurements and static platelet adhesion studies. The modified surface, believed to be extensively cross-linked, however showed all the chemical characteristics of PEG. The surface was found to be highly hydrophilic as evidenced by an interfacial free energy of about 0.7 dynes/cm. AFM studies showed that the surface of the modified PET became smooth by the plasma polymerized deposition. Static platelet adhesion studies using platelet rich plasma (PRP) showed considerably reduced adhesion of platelets onto the modified surface by SEM. Plasma ‘polymerization’ of a polymer such as PEG onto substrates may be a novel and interesting strategy to prepare PEG-like surfaces on a variety of substrates since the technique allows the formation of thin, pin-hole free, strongly adherent films on a variety of substrates.     

NMR analysis of poly(ethylene naphthalate) + poly(butylene terephthalate) blends

Melt blends of poly (butylene terephthalate) (PBT) and poly (ethylene naphthalate) (PEN) with 30, 40, 50, 60 and 70 wt% PEN were prepared using a single screw extruder and injection moulding machine. ¹³C and ¹H nuclear magnetic resonance (NMR) spectra were obtained with a Bruker DRX-400 instrument, on solutions prepared by dissolving samples of the homopolymers and each blend in deuterated trifluoroacetic acid + chloroform mixtures (1:1 by volume). The absence of new signals in ¹H and ¹³C spectra, that would be expected to result from transesterification reactions in the PBT + PEN blend system, provides convincing evidence that such reactions do not occur in these blends under the melt processing conditions that were used. In the light of published work on solid-state NMR studies of these and related blend systems, and our observations of partial miscibility with a very small domain size, together with substantial enhancement of the mechanical properties of PBT by blending with PEN, we conclude that the improvement in mechanical properties arises from molecular scale mixing of the homopolymers and strong but non-covalent bonding interactions over the very large interfacial area between the PBT-rich and PEN-rich phases.     

Stiffening of poly(ethylene terephthalate) by means of polyamide 6 nanocomposite fibers produced during processing

Polymer nanocomposites based on poly(ethylene terephthalate) (PET) with up to 40% polyamide 6 (PA6) reinforced with up to 7% of a fully dispersed organoclay were obtained in the melt state presenting a highly fibrillar morphology of the dispersed phase. The organoclay was located in the dispersed PA6 phase, as was expected given the nature of the chemical modification of the organoclay and the mixing procedure selected. Fibrillation was possible thanks to the presence of some PA6 in the PET-rich phase which assured compatibility and allowed the development of these high surface/volume ratio structures. The increases obtained in the elasticity modulus were higher than any previously observed in PET matrix Ncs. This indicated that the location of the organoclay in the dispersed fibrillated phase was more effective in terms of stiffening than a location in the matrix.     

Crazing behaviour in oriented poly(ethylene terephthalate)

A study has been made of the two types of crazes formed in oriented sheets of poly(ethylene terephthalate). The crazes have been termed tensile crazes and shear crazes. The tensile crazes formed parallel to the initial draw direction (IDD) whereas the shear crazes formed in a direction close to that of the deformation bands observed when the material yields.The possibility of applying a yield criterion to shear craze formation has been examined and there appears to be fairly good agreement between theory and experiment. Measurements of crazing stress on the tensile crazes indicated that the criterion for tensile craze formation is not purely dependent on the component of stress normal to the extended chains.It is concluded that the two types of crazes are formed by two quite different mechanisms, although the exact nature of these mechanisms is still uncertain.     

Orientation in poly(ethylene terephthalate) drawn by solid state coextrusion

The development of uniaxial orientation by solid-state extrusion at 60 to 90° C has been evaluated for both the amorphous and crystalline components of a polyethylene terephthalate). Analyses involved X-ray diffraction, birefringence and visable dichroism. The dichroism was evalulated from a host dye molecule. The initial PET film for draw was amorphous and isotropic. Orientation functions for the amorphous and the developed crystalline phases are reported at a series of draw ratios up to 4.4.     

Structural changes during photodegradation of poly(ethylene terephthalate)

An investigation has been conducted into the effects of photodegradation on the structure of poly(ethylene terephthalate) (PET). Films, with and without ultraviolet absorbers and prepared by biaxial orientation after extrusion, have been exposed in the laboratory for periods of up to 1020 hours. The samples were investigated by differential scanning calorimetry (DSC), X-ray diffraction and size exclusion chromatography. The appearance of a cold crystallization peak during DSC heating scans was noted for exposed samples and this was considered to be a result of released molecules in the amorphous region that could rearrange into a crystalline phase. From X-ray analysis, a loss of crystalline orientation was observed after degradation and an interpretation was given based on relaxation in the mesophase region. In samples containing the photostabilizer additive the magnitude of changes in structure was lower, possibly due to segregation effects during film production making the non-crystalline region relatively immune to degradation effects.     

Nonisothermal crystallization kinetics of poly(ethylene terephthalate) nanocomposites

This article reports the nonisothermal crystallization kinetics of poly(ethylene terephthalate) (PET) nanocomposites. The non-isothermal crystallization behaviors of PET and the nanocomposite samples are studied by differential scanning calorimetry (DSC). Various models, namely the Avrami method, the Ozawa method, and the combined Avrami-Ozawa method, are applied to describe the kinetics of the non-isothermal crystallization. The combined Avrami and Ozawa models proposed by Liu and Mo also fit with the experimental data. Different kinetic parameters determined from these models prove that in nanocomposite samples intercalated silicate particles are efficient to start crystallization earlier by nucleation, however, the crystal growth decrease in nanocomposites due to the intercalation of polymer chains in the silicate galleries. Polarized optical microscopy (POM) observations also support the DSC results. The activation energies for crystallization has been estimated on the basis of three models such as Augis-Bennett, Kissinger and Takhor methods follow the trend PET/2C20A < PET/1.3C20A < PET, indicating incorporation of organoclay enhance the crystallization by offering large surface area.     

Molecular orientation of poly(ethylene terephthalate) and poly(butylene terephthalate) probed by polarized Raman spectra: a parallel study

Poly(ethylene terephthalate) (PET) and poly(butylene terephthalate) (PBT) samples uniaxially drawn above Tg and beyond the yield point exhibit significant differences in their molecular orientation behavior as probed by polarized Raman spectra. The quasi-amorphous PET samples, drawn close to the Tg, manifest considerable molecular orientation development; however, when drawn above Tg + 30 degrees C, they exhibit significant molecular orientation relaxation. The semi-crystalline PBT samples maintain prominent molecular orientation even when drawn 110 degrees C above Tg. The drawing process, in PET samples, when resulting in molecular orientation, is accompanied by a gauche-trans transformation of the glycol linkage and a concurrent initiation of crystallinity development. In PBT specimens, it gives rise to a coexistence of alpha- and beta-type crystalline phases. Phase alpha is predominant at high draw temperatures, i.e., Tg + 110 degrees C, while phase beta dominates at low draw temperatures, i.e., Tg + 10 degrees C. PBT samples, with beta-phase predominance, left at relevant draw temperatures without stress, exhibit a beta-alpha phase change though no molecular orientation relaxation occurs. A note is made of the fact that complete molecular orientation analysis of PBT segments utilizing the depol method gives more reliable results than the simplified analysis assuming a cylindrical tensor for the 1614 cm(-1) symmetric stretch of the para-disubstituted benzene ring of PBT. In this context, segments of PBT specimens rich in alpha-phase exhibit higher molecular orientation than those with beta-phase predominance.     

Viscoelastic properties of poly(butylene terephthalate)/poly(ethylene naphthalate) blends

Melt blends of poly(butylene terephalate) (PBT) and poly(ethylene naphthalate) (PEN) with 30 and 60 wt% PEN were prepared using a single screw extruder and an injection moulding machine. Stress relaxation tests for the specimens of PBT/PEN blends and the homopolymers were carried out using an Instron testing machine in an Instron environmental chamber. The Taguchi method of experimental design analysed how different levels of temperature, PEN content and initial stress affected the relaxation behaviour of PBT/PEN blends and homopolymers. From the response tables and analyses of main and interaction effects, it was shown that the most significant factor was temperature, followed by PEN content and then the initial stress. Consequently, high temperature, low PEN content and high initial stress speeded up stress relaxation rate of specimens. Interaction effects between factors were insignificant. To fit the relaxation curves of the PBT/PEN blends and the homopolymers at different temperatures, PEN contents and the initial stresses, four different equations were attempted with Matlab™, which determined the coefficients of these functions using the experimental data of stress change with time. The simulated curves from the most suitable function among them were shown using the calculated coefficients to predict the relaxation behaviour of PBT/PEN blends (50% PEN) at temperatures of 30 and 60°C with an initial stress of 7 MPa.     

Physical ageing studies in semicrystalline poly(ethylene terephthalate)

The physical ageing of semicrystalline poly(ethylene terephthalate) (c-PET) of different crystallinities and morphological structures was studied using differential scanning calorimetry. Samples of c-PET of crystallinity content _c = 0.12, crystallized at low temperatures (105 °C for 13 min), submitted to physical ageing in a temperature range between 50 and 65 °C for different periods of time, showed two endothermic peaks. The first peak (P₁) of higher intensity, appeared at a temperature close to the glass transition temperature, T _g, of the amorphous PET, and the other peak (P₂) of lower intensity, merged as a shoulder of the first one, at a higher temperature. These peaks have been attributed to the enthalpy relaxation process of two different amorphous regions: one amorphous phase outside the spherulitic structure (interspherulitic amorphous region) and another amorphous phase inside the spherulites (interlamellar amorphous region). The separation between P₁ and P₂ indicates that DSC, via enthalpy relaxation, is a good technique to detect the real double glass transition of the semicrystalline PET. However, the physical ageing of a semicrystalline PET of _c = 0.32, crystallized at 114 °C during 1 h, showed a main endothermic peak shifted to a higher temperature, which probably corresponds to the enthalpy relaxation of the more restricted interlamellar amorphous region, and a small endothermic peak at lower temperature which could be a reflection of the hindered interspherulitic amorphous region.     

长支链支化制备高熔体强度PET研究进展

主要介绍了采用多官能单体以及扩链/支化剂在PET主链上引入长支链的方法,论述了长支链结构对PET熔体强度、熔体流变行为和结晶行为的影响.     

Morphological instability of poly(ethylene terephthalate) cyclic oligomer crystals

The mechanism of formation of depressions and cavities in the middle of the basal faces of hexagonal plates of poly(ethylene terephthalate) oligomer single crystals upon growth during heat treatment is investigated. It is proposed that this effect is caused by two simultaneously occurring processes: supersaturation inhomogeneity in the centre of the plates and formation of the kinematic (shock) waves at the edges of the plates.     

Self-reinforced poly(ethylene terephthalate) composites by hot consolidation of Bi-component PET yarns

Self-reinforced polymer composites or all-polymer composites have been developed to replace traditional glass-fibre-reinforced plastics (GFRP) with good lightweight, mechanical and interfacial properties and enhanced recyclability. Poly(ethylene terephthalate) (PET) is one of the most attractive polymers to be used in these fully recyclable all-polymer composites, in terms of cost and properties. In this work, unidirectional all-PET composites were prepared from skin–core structured bi-component PET multifilament yarns by a combined process of filament winding and hot-pressing. During hot-pressing, the thermoplastic copolyester skin or sheath layers were selectively melted to weld high-strength polyester cores together creating an all-PET composite. Physical properties of the resulting composites including thickness, density and void content were reported. The effect of processing parameters, i.e. consolidation temperature and pressure on mechanical properties and morphology was investigated in order to balance good interfacial adhesion with residual tensile properties of the composite.     

The conductive polyaniline/poly(ethylene terephthalate) composite fabrics

Conductive composite fabrics were prepared by chemical polymerization of aniline on poly(ethylene terephthalate) (PET) fabrics in the aqueous hydrochloride acid solutions using potassium dichromate as the oxidant. The effect of the polymerization conditions such as temperature, oxidant, aniline and hydrochloride acid concentrations was investigated on the electrical surface resistance and polyaniline (PAn) content of PAn/PET composite fabrics. The maximum PAn content and the lower electrical resistance of composite fabrics were observed at the HCl concentrations of 0.25 M and 1.5 M, respectively. The electrical surface resistance of the PAn/PET composite fabrics was decreased under vacuum five-fold more than the ones kept under in air. The properties of PAn/PET composite fabrics such as density, diameter and moisture regain were also investigated in comparison with the those of pure PET. The conductive composite fabrics were characterized by surface resistance, FTIR and TGA techniques.     

The use of poly(ethylene terephthalate)–poly(aniline) composite for trypsin immobilisation

This paper presents trypsin immobilisation on strips of poly(ethylene terephthalate)–poly(aniline), activated with glutaraldehyde (PET–PANIG) composite. The photomicrography of the material showed changes corresponding to the chemical modifications produced in the steps of synthesis. The immobilisation process was very efficient under optimal conditions (18.6%). The immobilised and free enzyme presented the same pH and temperature optimum. PET–PANIG-trypsin was able to hydrolyse casein, albumin, gelatine, and skimmed milk. Km_app value for PET–PANIG-trypsin was very close to Km of the free enzyme for casein. Immobilised trypsin showed higher stability than the free enzyme, with 100% activity after 14 days of storage at 4 °C and 100% operational stability after 4 cycles of use.     

Surface properties of poly(ethylene terephthalate) foils of different thicknesses

Surface properties of commercially available poly(ethylene terephthalate) (PET) foils of different thicknesses (3, 13, 23, 50, and 100 μm) were characterized using different analytical methods. Surface roughness and morphology were determined by atomic force microscopy, goniometry was used for determination of contact angle (wettability of surface) and electrokinetical analysis (zeta potential) for characterization of surface polarity and conductivity. X-ray photoelectron spectroscopy was used for characterization of PET surface chemistry. Infrared spectroscopy and differential scanning calorimetry (DSC) were used for determination of crystallinity portion. By DSC analysis, it was confirmed that the crystallinity portion depends on the foil thickness. Most important result of this study is that the surface properties of PET foils depend not only on the foil thickness but also on the foil side under study. This finding may be of importance for future experiments performed on PET foils and for their application in tissue engineering or microelectronics.