塑料食品包装制品中多环芳烃的分析及检测

通过模拟向聚酯(PET)、聚碳酸酯(PC)两类包装材料中添加回收塑料,探索了塑料食品包装中多环芳烃(PAHs)的来源,并对样品中的PAHs进行分析检测.由新料加工制成的样品中不含PAHs;添加回收料的样品中出现了PAHs的累积与放大;添加回收料并引入氯源(PVC)的样品,经反复加工,其有害物质的含量增加,组分更趋复杂.结果表明,添加回收塑料的包装制品中含有大量有害物质,如萘、苊烯、苊等2～3环的多环芳烃.     

Adsorption of a lignosulphonate polymer onto PVC and PET surfaces: Evaluation by XPS

As part of the separation by froth flotation of PVC and PET from waste bottles before recycling, the adsorption mechanism of a lignosulphonate used to selectively render one of the plastics hydrophilic has been studied. As the 'rest' method is not sufficiently sensitive for this purpose, X-ray Photoelectron Spectroscopy analysis was conducted. A method of calculating the surface coverage of both plastics by the reagent is proposed based on the fact that the lignosulphonate contains sulphur whereas PVC and PET do not. The results show that a greater quantity of lignosulphonate adsorbs on PET than PVC, leading to a higher surface coverage of LS on PET. The surface coverage values are a function of the lignosulphonate macromolecular configuration. For the sphere and film configurations hypothetised, the surface coverage values remain less than 1, which is consistent with the patchy adsorption assumed in the calculations.     

Weathering of injection-moulded glassy polymers: changes in residual stress and fracture behaviour

Injection-moulded bars made from poly(methyl methacrylate) (PMMA) polystyrene (PS), polycarbonate (PC) and poly(vinyl chloride) (PVC), have been weathered outdoors in Jeddah, Saudi Arabia, for varying periods. The residual stresses in the bars have been found to vary considerably with exposure and in some cases the surface stress has reversed, becoming tensile. With PS and PVC, significant surface damage developed on exposure and the presence of surface flaws together with tensile residual stresses at the surface can be expected to reduce the resistance to fracture, especially in the case of PS which suffers considerable molecular weight reduction near the surface. The changes in residual stress in PMMA and PC were smaller, and the surface deterioration, examined by scanning electron microscopy, was much less than with PS and PVC. The performance of PMMA and PC in fracture tests generally declined less with weathering than did that of PS and PVC but the materials used were all commercial grades designed for use in Europe and the results obtained here should not be taken to indicate the relative weatherability of the different polymers. The significance of the results relate to the mechanism of failure involving the interaction of reversed residual stresses and surface flaws.     

A study of polymer fracture surface features and their relationship to toughness

The aim of this study was to research fracture surface features for polymers of different toughness and type. The materials chosen provided for an interesting comparison of fracture surfaces. Two brittle amorphous thermoplastics (SAN & PMMA) of the same toughness had very different fracture surfaces. An amorphous thermoplastic (PC) exhibited similar features as both SAN and PMMA but had a higher toughness. Two semi-crystalline thermoplastics (PE1 & PE2) had similar fracture surface features but one was twice the toughness of the other. A rubber toughened polymer (ABS) showed a very different fracture surface to SAN (the host material) and all the other polymers studied. A particular interest was to use the comparison of the fracture surfaces of the above materials to investigate the toughening effects of rubber particles in ABS.     

Quartz crystal microbalance and infrared reflection absorption spectroscopy characterization of bisphenol A absorption in the poly(acrylate) thin films

The absorption process of bisphenol A (BPA) in a number of poly(acrylate) thin films, such as poly(2-methoxyethyl acrylate) (PMEA), poly(ethyl acrylate) (PEA), poly(n-butyl methacrylate) (PBMA), and poly(methyl methacrylate) (PMMA), has been investigated by quartz crystal microbalance (QCM) and infrared reflection absorption spectroscopy (IRRAS) measurements. Both QCM and IRRAS measurements show that the BPA molecules absorb in PMEA, PEA, and PBMA thin films but not in PMMA thin film. The differences in the BPA absorption behavior are mainly attributed to the difference in the glass transition temperature (T(g)) between these polymers. This absorption behavior also depends on the BPA concentration and polymer film thickness. Furthermore, IRRAS characterization demonstrates that the hydrogen bonding is formed between the hydroxyl group in BPA and the carbonyl group in the poly(acrylate) thin films. BPA molecule absorbed in these polymer thin films can be removed by ethanol rinse treatment. By optimizing experimental conditions for the QCM electrode modified by PMEA thin film, detection limitation of approximately 1 ppb for BPA can be realized by the in situ QCM measurement. This method is expected to be a sensitive in situ detection way for trace BPA in the environmental study.     

Shear strength of polymers under hydrostatic pressure: Surface coatings prevent premature fracture

The effect of surface rubber coatings on the stress-strain behaviour in shear of polymethylmethacrylate (PMMA), polyethylene terephthalate (PET) and polyethylene has been examined. Uncoated PMMA fractures without yielding at high pressure, while it is ductile at lower pressures. The high pressure fracture is thought to be due to pressure fluid penetrating into surface cracks allowing them to grow in spite of the applied hydrostatic pressure. Coating in rubber prevents such penetration and PMMA remains ductile up to 7 kbar. PET and polyethylene are normally ductile at all pressures, and coating in rubber has no effect on their behaviour. Failure here is due to internal flaws.     

Influence of substrates on the structural and optical properties of chemically deposited CdS films

Cadmium sulfide (CdS) films were chemically deposited on glass, polycarbonate (PC), polyethylene terephthalate (PET), and Si wafer. Effects of substrate types on the structural and optical properties of the films were investigated. There is a preferential orientation of the crystallites in the film grown on the glass along the c-axis (perpendicular to the plane of the substrate) producing a strong hexagonal (0 0 2) or cubic (1 1 1) peak, regardless of the presence of ITO coating. However, such preferential orientation decreases or disappears when the deposition was made onto PC or PET substrates. The crystallinity of CdS films on glass and Si is better than that of the other ones. The average transmittance of the films on PC and PET is about 50% and 55%, respectively, and increases up to 70% for glass substrate. The improvement of the transmittance was obtained from ITO-coated substrates.     

Functionalization of PEG-PMPC-based polymers for potential theranostic applications

The synergistic effect of polyethylene glycol (PEG) and poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC) can effectively reduce the protein absorption, which is beneficial to theranostics. However, PEG–PMPC-based polymers have rarely been used as nanocarriers in the theranostic field due to their limited modifiability and weak interaction with other materials. Herein, a plain method was proposed to endow them with the probable ability of loading small active agents, and the relationship between the structure and the ability of loading hydrophobic agents was explored, thus expanding their applications. Firstly, mPEG–PMPC or 4-arm-PEG–PMPC polymer was synthesized by atom transfer radical polymerization (ATRP) using mPEG-Br or 4-arm-PEG-Br as the macroinitiator. Then a strong hydrophobic segment, poly(butyl methacrylate) (PBMA), was introduced and the ability to load small hydrophobic agents was further explored. The results showed that linear mPEG–PMPC–PBMA could form micelles 50–80 nm in size and load the hydrophobic agent such as Nile red efficiently. In contrast, star-like 4-arm-PEG–PMPC–PBMA, a monomolecular micelle (10–20 nm), could hardly load any hydrophobic agent. This work highlights effective strategies for engineering PEG–PMPC-based polymers and may facilitate the further application in numerous fields.     

Modification on crystallization of poly(vinylidene fluoride) (PVDF) by solvent extraction of poly(methyl methacrylate) (PMMA) in PVDF/PMMA blends

The crystallization modification of poly(vinylidene fluoride) (PVDF) was investigated for the blend films of PVDF and poly(methyl methacrylate) (PMMA). The mass crystallinity (χ_c) and further, the β-phase content (F_(β)) of PVDF, were studied for the as-prepared blend films with different mass ratios. In addition, the variations of χ_c and F_(β) were systematically probed once the PMMA component was removed from the related blend systems. DSC, FTIR and XRD measurements all indicated that 1) χ_c, F_(β) and even the content of α-phase (F_(α)) decreased with the addition of PMMA; 2) with the extraction of PMMA, both χ_c and F_(β) increased while F_(α) decreased. It is worth noting that the increase of χ_c and F_(β) depended on the relative amount of extracted PMMA (E_PMMA), i.e., the more PMMA was removed, the more χ_c and F_(β) increased. These results reveal the hindrance effect from the PMMA constituent to the crystallization of PVDF, and consequently, this restriction would be released when the PMMA was extracted.     

聚丙烯腈/聚甲基丙烯酸正丁酯共混体系的相容性及流变性能

采用溶解度参数法预测聚丙烯腈(PAN)/聚甲基丙烯酸正丁酯(PBMA)为部分相容体系,并通过黏度法、红外光谱法(FT-IR)、动态力学分析法(DMA)和差示扫描量热法(DSC)进一步判断PAN与PBMA的相容性。结果表明,二者属于部分相容体系,与理论预测相符。以N,N-二甲基乙酰胺(DMAc)为共溶剂,研究了PAN/PBMA共混溶液的流变性能,研究表明,共混溶液的流动性与其组成、温度以及浓度有关,通过改变上述因素可以有效调控共混溶液的流动性,这为后续制备具有吸附功能的PAN/PBMA共混纤维奠定了理论基础。     

Evaluation of oriented poly(lactide) polymers vs. existing PET and oriented PS for fresh food service containers

Poly(lactide) (PLA) polymers have garnered increasing attention in the last few years as food packaging materials because they can be obtained from renewable resources; their production consumes quantities of carbon dioxide; they can be recycled and composted; and their physical and mechanical properties can be tailored through polymer architecture. As a consequence, PLA is becoming a growing alternative as a ‘green’ food packaging material. PLA's optical, physical and mechanical properties have been compared to those of polystyrene (PS) and polyethylene terephthalate (PET), although studies comparing and showing the actual performance of PLA, PS and PET plastics containers are scarce. The purpose of this study was to investigate and compare the role of PLA in package sustainability for the food service industry. Two of the commonly used materials to make containers to package fresh food, PET and oriented polystyrene (OPS), were compared with oriented PLA (OPLA) and OPLA with 40% recycled content from the industrial trimming process. The recycled OPLA provides an opportunity for full material utilization and lower costs. This study involved a number of tests to quantify the physical, mechanical, barrier and compatibility properties that would affect the selection criteria for containers to be used for food service applications. Based on the data collected, OPLA, OPLA + 40% regrind, OPS and PET performances were evaluated. Exposure of the four materials to vegetable oil and weak and strong acids show a minimal reduction in the performance of these polymers. At ambient temperature, PET has the highest impact resistance, followed by OPLA, OPS and OPLA + 40% regrind. In terms of barrier properties, PET shows the highest oxygen barrier, followed by OPLA, OPLA 40% recycled content, and OPS. Thus, OPLA and OPLA with 40% recycled content can be used for fresh food applications as well as OPS and PET, and in many situations it performs better than OPS and PET. Copyright © 2005 John Wiley & Sons, Ltd.     

脆性塑料改性PVC体系中相界面的作用

将ＰＶＣ体系分别与ＰＶＣ／ＰＳ、ＰＶＣ／ＰＭＭＡ体系相对比,观察到两类不同体系的拉伸及冲击性能具有相当的一致性。认为在用脆性塑料改性ＰＶＣ时,分散相对基体间的界面起很重要的作用,实验表明具有核／壳结构的分散相粒子对ＰＶＣ的影响主要取决于分散相壳层与基体间界面的性质。     

聚对苯二甲酸乙二醇酯的结晶成核改性研究进展

聚对苯二甲酸乙二醇酯(PET)因其重复结构单元中含有刚性苯环而成核慢、结晶度低,从而导致综合力学性能与耐热性较差,限制了其工程化应用,故对PET进行成核改性以提高结晶速率与结晶度成为亟待解决的问题。综述了PET的4大类成核剂:无机填料、有机小分子、有机高分子及复合型成核剂;在此基础上,提出机理上不同于异相成核的"离子簇集诱导成核"的概念,即与离子共价相连的聚合物链段因离子簇集而在离子簇近围紧密堆砌,从而诱导"拥挤"链段结晶成核。无机填料类成核剂包括粘土、氧化物与氢氧化物、无机盐、Si_3N_4及碳纳米管/石墨等,其成核机理均为异相成核。有机小分子类成核剂涉及羧酸盐、二胺、双酰胺及改性山梨醇等,其中羧酸盐成核机理为离子簇集诱导成核,而其它均属于异相成核。有机高分子类成核剂分为结晶性聚合物、液晶高分子、嵌段共聚物及离子交联型聚合物等;其中前三者属异相成核,后者为离子簇集诱导成核。复合型成核剂为两种以上成核剂(或成核机理)配合使用协同促进PET结晶成核。对比发现,有机高分子与复合型成核剂效果较好,且不会引起PET的降解,为PET优良成核剂。异相与离子簇集诱导耦合高分子成核剂为PET结晶成核改性未来的重点发展方向之一。     

聚氯乙烯／聚丙撑碳酸酯共混相容性研究

分别用溶液法和熔融法制得聚氯乙烯（ＰＶＣ）与聚丙碳酸酯（ＰＰＣ）共混试样，用ＤＳＣ证明ＰＶＣ／ＰＰＣ不相容，但它们不相容的程度受分子量、共混比例及共混方法等因素的影响，并根据玻璃化转变温度计算出溶液２共混试样ＰＰＣ富相中ＰＶＣ的质量百分含量。用ＤＭＡ说明了ＮＢＲ／ＰＰＣ对ＰＶＣ／ＰＰＣ共混体系具有良好的增容作用，共混体系中ＰＰＣ的用量对共混体系相容性有一定程度的影响，加入适量的ＰＰＣ可提高共混试样     

An Investigation on Vibration Welding of Amorphous and Semicrystalline Polymers

Vibration welding technique has been used to study the weld zone of thermoplastic polymers using ABS (amorphous), PC (amorphous), PMMA (amorphous), and PBT (semicrystalline). Polymers were welded using alike components and combinations of semicrystalline polymer with different amorphous polymers. Mechanical testing of welded polymers has proved that the tensile strength, elongation at break, and deformation was highest for PC–PC weld and least for ABS–ABS weld, when alike polymers were welded. However, welding of semicrystalline and amorphous polymer shows enormous reduction in its tensile strength as well as other tensile properties. Also, the tensile fracture of PBT with other amorphous polymers always occurred at weld zone which was not always in case of alike polymer welds. The weld strength of these polymers was observed to be dependent on the mechanical interlocking among the layers and not on interfacial bonding. This phenomenon may be due to the difference in glass transition temperatures of semicrystalline and amorphous polymers. XRD, FESEM, and AFM have been used in this study to observe the morphology of welded surfaces.     

Triboelectrostatic separation of granular plastics mixtures from waste electric and electronic equipment

The efficiency of the electrostatic separation of insulating granular mixtures depends on the electric charge carried by the particles. The first objective of this work was to characterize the tribocharging properties of various plastic materials in the composition of waste electric and electronic equipment: polyvinyl chloride (PVC), “high-impact” polystyrene (HIPS), acrylonitrile butadiene styrene (ABS), “high-density” polyethylene (HDPE), polycarbonate (PC), polyamide (PA). Thus, in a first series of experiments, 15 samples composed of binary mixtures of above plastics were initially charged in a fluidized bed device, then separated using a free-fall electrostatic separator. The six plastics could be ordered in a specific triboelectric series: PVC, HIPS, ABS, PEHD, PC, PA. The second objective was to evaluate the efficiency of three tribocharging devices: a static charger, a fluidized bed, and a fan-type device. The triboelectrostatic separation experiments performed with four different binary mixtures (PVC/PA, PC/PA, HIPS/PA, and HIPS/ABS) showed that the fluidized bed is the most effective.     

PMMA、SAN改性PVC/CPE共混体的研究

研究了刚性聚合物(PMMA、SAN)对PVC/CPE共混体力学性能、冲击断面形貌及流变性的影响。结果表明,PMMA对PVC/CPE=100/10、100/15体系,SAN对PVC/CPE=100/10体系都具有显著的增韧作用和一定的增强作用;初步的测定显示,刚性聚合物能改善共混熔体的流变性,促进PVC/CPE共混体系中CPE网络结构的形成和分散性。     

分子结构对增塑聚氯乙烯性能的影响

研究了聚合度、分子量分布和支化结构对增塑聚氯乙烯加工流变性能和物理力学性能的影响。结果表明，增塑ＰＶＣ的加工流变性能随聚合度的增加而恶化；拓宽分子量分布和引入支化结构均有利于加工流变性能的提高；增塑ＰＶＣ的拉伸强度随聚合度的增加而提高，而压缩永久变形却随之减小；分子量分布对物理力学性能的影响不大；支化ＰＶＣ的拉伸强度略有下降。     

How does fly ash mitigate alkali–silica reaction (ASR) in accelerated mortar bar test (ASTM C1567)?

ASTM C1567 [1] is a commonly used accelerated test method to determine the required dosage of supplementary cementitious materials (SCMs) to mitigate alkali–silica reaction (ASR) in mixtures containing reactive siliceous aggregates. Past research suggested that fly ash and other SCMs inhibit ASR, primarily through alkali dilution and binding. In ASTM C1567, however, the alkalinity of the pore solution is largely influenced by the penetration of NaOH from the external soak solution; and this could erase the beneficial effects of alkali dilution and binding. To better understand why fly ash inhibits ASR in this test, the present study performs a quantitative evaluation of six potential ASR mitigation mechanisms: (1) alkali dilution, (2) alkali binding, (3) mass transport reduction, (4) increasing tensile strength, (5) altering ASR gel, and (6) reducing aggregate dissolution rate. The results suggest that (2), (3), (4), and (6) are the primary mitigation mechanisms, while (1) and (5) show a negligible impact.     

Permeability of naphthalene in different types of polymeric food packaging materials

The relative permeabilities of naphthalene through different types of common polymeric food packaging materials were determined by migration studies in a controlled environment. The results illustrate that polyolefins, such as low density polyethylene (LDPE), have a higher relative permeability than other polymers, such as polyethylene terephthalate (PET) or polyvinylchloride co-polymer (PVC). This was explained by the correlation between the permeability of the migrant and the glass transition temperature (Tg) of the different polymers, as well as their polarity.