聚酯热稳定性的研究

在合成聚酯试验之后,利用聚合试验装置搅拌器扭矩变化来表征聚酯加工过程中的热稳定性,比热失重法更接近聚酯加工过程,比粘度降法减少了干扰因素。研究结果表明:稳定剂种类、添加量和调配方式等均影响聚酯的热稳定性。     

Structure‐mechanical properties relationship of poly(ethylene terephthalate) fibers

The correlation between the fiber structure and mechanical properties of two different poly(ethylene terephthalate) fiber types, that is, wool and cotton types produced by three producers, was studied. Fiber structure was determined using different analytical methods. Significant differences in the suprastructure of both types of conventional textile fibers were observed, although some slight variations in the structure existed between those fibers of the same type provided by different producers. A better‐developed crystalline structure composed of bigger, more perfect, and more axially oriented crystallites was characterized for the cotton types of PET fibers. Crystallinity is higher, long periods are longer, and amorphous domains inside the long period cover bigger parts in this fiber type in comparison with the wool types of fibers. In addition, amorphous and average molecular orientation is higher. The better mechanical properties of cotton PET fiber types, as demonstrated by a higher breaking tenacity and modulus accompanied by a lower breaking elongation, are due to the observed structural characteristics. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3383–3389, 2003     

Thermoluminescence of poly(ethylene terephthalate) films

Thermoluminescence of γ-ray-irradiated poly(ethylene terephthalate) (PET) films in the temperature range from 77K to 300 K is studied. Three glow peaks were observed in this temperature range, at 102 K, 257 K, and 277 K, which preferentially emit at 365, 326, and 304 nm, corresponding to usual fluorescence peaks of normal PET films. The cause may be seen in the self-trapping mechanism which is involved during irradiation of the PET films by γ-rays. A simultaneous observation of the effect of thermal release and photobleaching on thermoluminescence glow intensity supports this mechanism. Energy required to release the electrons from trapping centres also supports this observation.     

Dynamic thermomechanical and tensile properties of chain-extended poly(ethylene terephthalate)

A series of chemically modified poly(ethylene terephthalate) (PET) samples was received after chain extension of a virgin sample at different reaction times with a new diepoxide as chain extender. These samples showed different intrinsic viscosity and degrees of branching or crosslinking. The effect of this differentiation on thermal properties was studied by dynamic mechanical thermal analysis and the determined T_g values were found to be in good agreement with those obtained by differential scanning calorimetry and thermomechanical analysis. Also, the branching or crosslinking exhibited significant improvement in tensile mechanical properties, which were studied, and the results are discussed. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 797–803, 1998     

聚酯(PET)的混料和共混改性

就聚酯加工应用中混料和共混改性一些基本的技术原理进行讨论 ,如间歇法生产中不同批次的混料方法 ,新料与回收料的共混 ,白料与色母料的共混 ,还有PET改性共混涉及到的相容、结晶相分离等问题     

Effect of recycling on the properties of poly(ethylene terephthalate) films

Different proportions of recycled poly(ethylene terephthalate) (PET) films were blended with virgin PET and evaluated for physicomechanical, chemical, thermal, optical and barrier properties. The safety evaluation of the films for food contact applications has also been carried out. The variations in properties, such as tensile behaviour, impact strength, tear resistance, burst strength, gloss, haze, barrier properties, crystallization temperature and melting temperature, are reported. © 2000 Society of Chemical Industry     

Processing and characterization of multilayer films of poly(ethylene terephthalate) and surface-modified poly(tetrafluoroethylene)

Multilayer films were prepared from poly(tetrafluoroethylene) (PTFE) and poly(ethylene terephthalate) (PET) films together with using an adhesion promoting layer (tie-layer) consisting of ethylene-methyl acrylate-glycidyl methacrylate (E-MA-GMA) terpolymer and low density polyethylene (LDPE) blend. Na/naphthalene treatment and subsequent acrylic acid grafting were applied on the surfaces of PTFE for chemical modification. FT-IR spectroscopy, XPS analysis and surface energy measurements were performed to characterize the modified PTFE films. The analyses showed defluorination and oxidation of PTFE surface, and supported the acrylic acid grafting. The surface energy of modified surfaces enhanced with respect to unmodified one, which promoted adhesion. The multilayers were subjected to T-peel tests to measure the adhesion strength between PET and modified PTFE. Peel strength between the films increased with increasing E-MA-GMA amount in the tie-layer. A proportional dependence of peel strength on Na/naphthalene treatment time was observed for multilayers containing acrylic acid grafted or ungrafted PTFE. From SEM analysis, it was observed that the texture of the PTFE surface after modifications became rougher when compared to untreated PTFE. The peeled surfaces were also analyzed by SEM. The micrographs evidence that the energy absorbing mechanism is the plastic deformation of the tie-layer, which is responsible for obtaining high peel strengths.     

Preparation and characterization of poly(vinyl alcohol) nanocomposites made from cellulose nanofibers

A method using a combination of ball milling, acid hydrolysis, and ultrasound was developed to obtain a high yield of cellulose nanofibers from flax fibers and microcrystalline cellulose (MCC). Poly(vinyl alcohol) (PVA) nanocomposites were prepared with these additives by a solution‐casting technique. The cellulose nanofibers and nanocomposite films that were produced were characterized with Fourier transform infrared spectrometry, X‐ray diffraction, thermogravimetric analysis, scanning electron microscopy, and transmission electron microscopy. Nanofibers derived from MCC were on average approximately 8 nm in diameter and 111 nm in length. The diameter of the cellulose nanofibers produced from flax fibers was approximately 9 nm, and the length was 141 nm. A significant enhancement of the thermal and mechanical properties was achieved with a small addition of cellulose nanofibers to the polymer matrix. Interestingly, the flax nanofibers had the same reinforcing effects as MCC nanofibers in the matrix. Dynamic mechanical analysis results indicated that the use of cellulose nanofibers (acid hydrolysis) induced a mechanical percolation phenomenon leading to outstanding and unusual mechanical properties through the formation of a rigid filler network in the PVA matrix. X‐ray diffraction showed that there was no significant change in the crystallinity of the PVA matrix with the incorporation of cellulose nanofibers. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Characterization of poly(vinylpyrrolidone)–konjac glucomannan blend films

Blend films of konjac glucomannan (KGM) and poly(vinylpyrrolidone) (PVP) were prepared by using a conventional solvent‐casting technique and dried at room temperature. The structure and physical properties were studied by infrared spectroscopy (IR), wide‐angle X‐ray diffraction (WAXD), thermogravimetric analysis (TGA), differential thermal analysis (DTA), scanning electron microscope (SEM), and by measurement of mechanical properties. The changes of carbonyl stretching bands of KGM and PVP and hydroxyl stretching region of KGM were detected by FTIR analysis. WAXD analysis revealed that the film KP‐2 got the lowest crystallinity of all the films. The tensile strength and breaking elongation of the blend films reaches the maximum value at 10 wt % PVP content. The DTA curves indicated the existence of interaction between two kinds of macromolecules. Higher thermal stability was attained by konjac glucomannan through blending with PVP. These improvements are attributable to the existence of a certain degree of interaction between KGM and PVP molecules resulted from intermolecular hydrogen bonds. Air surface morphology of the films observed by SEM was consistent with the results mentioned above. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 1049–1055, 2001     

Functional modification of poly(ethylene terephthalate) with an allyl monomer: Chemistry and structure characterization

Radical grafting of biocidal precursor monomer 3-allyl-5,5-dimethylhydantoin (ADMH) onto poly(ethylene terephthalate) (PET) fabric was investigated. Based on SEM pictures, it was suggested that benzoyl peroxide could generate macromolecular radicals on PET when it was delivered to the areas properly. The macroradicals were in a form of benzoyl structure which can react with ADMH to form a short chain graft. It seems the reaction occurred at the end of polymers or defect areas with terephthalate groups at the end. After being converted to N-chloramide structure, the poly(ADMH)-g-PET fabric demonstrates total kill of 10⁵-10⁶ CFU/mL Escherichia coli at a contact time of 2 h.     

Sequence distribution,thermal properties,and crystallization studies of poly(trimethylene terephthalate‐co‐1,4‐cyclohexylene dimethylene terephthalate) copolyesters

A series of novel poly(trimethylene terephthalate‐co‐1,4‐cyclohexylene dimethylene terephthalate) (PTCT) with various compositions were synthesized by melt polycondensation of 1,3‐propanediol, 1,4‐cyclohexanedimethanol and dimethyl terephthalate. The resulting copolyesters were characterized using ¹³C and ¹H nuclear magnetic resonance. The average length of both trimethylene terephthalate (TT) and cyclohexylene dimethylene terephthalate (CT) sequences varies from 1 to 10, and the chain structure is statistically random. The crystallization was investigated using wide angle X‐ray diffractometer (WAXD) and differential scanning calorimeter. The WAXD patterns can be divided in two groups according to the composition: copolyesters with less than 35 mol % CT content exhibit PTT‐type lattice, and those with CT unit content higher than 42 mol % crystallize with the PCT‐type lattice. The crystallizability of CT sequence is higher than that of TT sequence. Thermodynamic analysis shows that the comonomer is excluded from the PTT‐type or PCT‐type crystal of the copolyesters. The thermal decomposition temperature of copolyesters increases with increasing CT content, and their thermal stability is improved as compared to that of PTT. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Chitosan modified by poly(ethylene oxide): Film and mixture properties

Chitosan + poly(ethylene oxide) mixtures and films prepared from these mixtures were studied by rheological, absorption of solvent vapors, SANS, and mechanical testing methods. At a stoichiometric chitosan:poly(ethylene oxide) monomer:monomer composition, the mechanical properties of chitosan + poly(ethylene oxide) film are the best as compared with those of the initial components or of other compositions. This film composition is shown to be less heterogeneous. Chitosan and poly(ethylene oxide) are proved to be slightly incompatible polymers. This is supposed to induce the two components to align and to order at their stoichiometric composition, leading to the improvement in the mechanical properties. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1114–1122, 2002; DOI 10.1002/app.10319     

Surface nature of UV deterioration in properties of solid poly(ethylene terephthalate)

We investigated the changes in the molecular weight and also in the mechanical properties with the distance to the exposed surface of the irradiated stacked poly(ethylene terephthalate) (PET) film samples. A relation between the molecular weight and the mechanical properties of the irradiated PET was established. The relation demonstrates that the decrease in molecular weight is one of the main origins causing the deterioration in the mechanical properties. The photodegradation process developing in PET was quantitatively studied by investigating the degradation kinetics of stacked PET film samples. Our results show that the strongest degradation takes place at the exposed surface, and the degradation rate decreases with increasing the distance. This further implies that the capability to bear a tensile stress in the area near the exposed surface is much lower than that in bulk. Therefore, irradiated PET may be fractured in a lower stress. These results indicate the surface nature of ultraviolet deterioration in the physical properties of PET. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67: 705–714, 1998     

Permeability coefficient of proton-irradiated poly(ethylene terephthalate) thin films

The principle of operation of an apparatus developed to study gas permeation through thin films is described, and the measurement method is discussed. Use is made of diffusion theory to obtain an expression for the permeability coefficient as a function of the rate of increase of the pressure in the receiving volume. The activation energy for permeation of helium through PET is determined. The permeability coefficient for helium is found to increase significantly with the range of the implanted protons although the incident charge has been kept constant. The hypothesis of structural modifications of the proton implanted PET seems to be confirmed by small-angle X-ray scattering experiments on the irradiated samples.     

Sorption of lower alcohols in poly(ethylene terephthalate)

This paper presents equilibrium sorption and kinetics of lower alcohols in a 1.5 μ thick, biaxially oriented PET film. Methanol, ethanol, n-propanol and iso-propanol have been studied for the solubility and sorption kinetics in this film to understand how these properties change with penetrant size and branching. It is observed that n-propanol shows dual mode characteristics at all activities whereas the other three penetrants show Flory-Huggins uptake at high activities. Infinite dilution solubility is estimated and compared with that of esters, ketones and other hydrocarbons previously reported. The dispersive solubility parameter, δ_d is found to correlate well with the solubility of penetrants with the same functional group. The hydrogen bonding parameter, δ_h is observed to influence the solubility of penetrants with the same carbon number but different functional groups. This correlation with the solubility parameters may be extended to other functional groups and used to predict the infinite dilution solubility of larger penetrants in PET. Diffusion coefficients in the Fickian kinetics regime and Berens-Hopfenberg parameters in the non-Fickian kinetics regime have been evaluated. Diffusivity increases with concentration and decreases with size. Diffusion coefficient of iso-propanol is an order of magnitude lower than that of n-propanol due to branching effects.     

X-ray low-angle scattering from oriented poly(ethylene terephthalate) films

Low-angle x-ray scattering data are used to deduce the morphology of oriented polymeric films. Generally, the structural models proposed to explain these patterns have been extrapolations of observations made from solution-grown polymer single crystals or from highly crystalline bulk polymers. These models and explanations may not be applicable broadly to oriented systems having only modest amounts of crystallinity or to those generated from precursor states that are grossly different. Poly(ethylene terephthalate) (PET) was chosen as a model polymer system for study. A systematic series of uniaxially and biaxially deformed films were produced from this polymer, made from the initially glassy or crystalline states. The low-angle x-ray scattering patterns generated from these films were studied as a function of (a) the sequence of deformation, (b) the precursor structure, (c) molecular orientation, and (d) the direction of observation. Optical diffraction and model structures were used to aid in the interpretation of the morphology produced. At least three different-sized domains are developed upon deformation, ranging from that of the unit cell (about 10 Å) to large laminar domains of average size 2,000 Å × 10,000 Å. This structure is shown to be substantially different from that developed in an oriented polyethylene film.     

Flame-retardant poly(ethylene terephthalate)

Poly(ethylene terephthalate) containing hexabromobenzene, tricresyl phosphate, or a combination of triphenyl phosphate and hexabromobenzene, pentabromotoluene, or octabromobiphenyl was extruded or spun at 280°C into monofilaments or low-denier yarn, respectively. Only combinations of the phosphorus- and halogen-containing compounds resulted in flame-retardant poly(ethylene terephthalate) systems, without depreciating their degree of luster and color quality. The melting temperature, the reduced viscosity, and the thermal stability above 400°C of these flame-retardant systems were in most cases comparable to those of poly(ethylene terephthalate) itself. Phosphorus-bromine synergism was proposed with flame inhibition occurring mostly in the gas phase.     

The effect of physical ageing on the properties of poly(ethylene terephthalate)

Physical ageing rates of poly(ethylene terephthalate) have been measured, and ageing is interpreted to be associated with the conventional glass formation process, which occurs at a more rapid rate at higher temperatures. Ageing is accompanied by a marked change in mechanical properties, increased tensile yield stress and drawing stress, more localized yielding of the polymer and a marked decrease in impact strength. The fracture results have been attributed to the increased yield stress and a change in contribution of plane stress and plane strain conditions in the samples. Fracture surfaces show evidence of mixed modes of fracture.     

化学反应平衡对聚酯扩链增粘的影响

用化学反应平衡的方法对开环扩链型扩链剂的增粘作用进行理论分析 ,推导出扩链剂用量与聚酯特性粘数变化的关系 ,发现反应平衡常数直接影响扩链效率 ;分析了实现扩链的必要条件和扩链剂的最佳投料量 ;利用推导出的理论关系计算出常见扩链剂参与扩链反应的平衡常数。