塑料食品包装材料添加剂迁移的数值模拟

应用有限元法建立塑料包装材料添加剂向食品迁移的数学模型和计算仿真模型.以BHT向模拟食品(酒精)的迁移为例,分析了塑料包装材料在共挤和储存过程以及溶胀情况下添加剂的扩散.建立的模型可用来预测混合边界条件下的添加剂迁移,给出了食品包装中添加剂迁移的解决方案,简化了迁移的研究手段.     

多类型食品包装材料的迁移研究

食品应具备的首要品质就是食用安全性,可目前与食品接触的包装材料中添加剂的迁移成为了一个关于健康问题的隐患.国外学者研究了各种类型的食品接触包装材料中化学物向食品(模拟物)的迁移,对研究进展进行了概述,简介了迁移的有关基础知识:迁移极限的规定、食品模拟物的选择、(加速)迁移试验要求、迁移机理、迁移预测模型.介绍了国外研究者在各迁移研究领域所进行的研究现状及结论,包括常规使用条件下塑料、再生塑料、纸和纸板、金属罐,非常规使用条件如微波加热、γ辐射、高压处理下包装材料中化学物成分的迁移.     

基于机理模型的质子交换膜燃料电池动态特性分析

详细分析了质子交换膜燃料电池(PEMFC)的机理模型,在此基础上运用Matlab的Simulink仿真工具建立PEMFC电堆的动态仿真模型.通过所建立的电堆动态仿真模型,就能够研究主要运行参数对电堆动态特性输出的影响.当电堆输出电流出现阶跃变化时,仿真分析了电堆的输出电压、输出功率、消耗功率、电堆等效内阻和电堆效率的动态响应.仿真结果和已知文献的实验数据基本一致,表明建立的电堆模型是正确、可操作和有效的.该研究有助于实现对PEMFC电堆的实时分析和动态优化,为PEMFC的实际应用提供了帮助.     

原油处理过程短期生产计划的辅助仿真

石化炼油企业原油处理过程的短期生产计划是一个挑战性的问题,至今为止没有可应用于实际的方法和工具.因此,开发一种仿真方法消除计划人员的复杂计算以便致力于决策过程非常必要.本文在分析问题的动态特性的基础上,建立了原油处理过程的混合Petri网模型.基于模型所给出的运行逻辑,提出了一个有效的仿真模型.应用该模型进行仿真可以验证计划的可行性,也可估计计划的性能,这使得计划人员的工作大大简化.     

可口可乐增加再生塑料 使用甘蔗有机原料制环保瓶

<正>未来,再生塑料使用即将成为消费者接受、环保人士推崇和政府大力支持的流行趋势。可口可乐公司也认识到这一点,宣布增加再生塑料使用,加盖环保标签,增加消费者满意度。新环保塑料瓶使用甘蔗树有机原料制成。近期,可口可乐印尼公司推出名为"实惠小巧耀眼包装"的新技术,该创新技术已证实可减少印尼塑料使用量至40%,相当于每年减少800吨塑料。该技术使用甘蔗     

相邻场群上有迁移的动物疫病传播模型分析

本文主要研究不同距离场群之间疫病的交叉感染和动物的迁移对动物疫病传播的影响.首先,根据疫病的传播基理,建立了相邻场群上有动物迁移的一类动物疫病传播模型.其次,利用微分方程定性稳定性理论,讨论了系统无病平衡点和地方病平衡点的存在性,证明了系统的无病平衡点是全局渐近稳定的.最后,对结果进行数值分析,定量分析了基本再生数对于不同参数的敏感性.结果表明,个体与环境细菌的接触传染系数以及个体从非相邻场群的迁入系数对基本再生数的影响较大.     

可再生塑料资源的利用大有可为

包装是塑料最大的应用领域.废旧塑料的回收应加快速度,加大力度.有人在误解,塑料把人类惯坏了.因为塑料太便宜了,人们将塑料到处乱扔.认为塑料与环保是对立的.还有种说法:20世纪最糟糕的发明就是塑料,塑料被称为白色污染.其实这是错误的.塑料的可回收利用率是很高的,再生塑料比再生纸的能耗要降低30%.即使用到不能再生,也可以焚烧.不是简单的焚烧方式,而是把它变成无害的液体.     

一类带有治疗的HIV传播模型的定性分析

根据对携带HIV病毒的患者实施治疗的策略及HIV传播的发展情况,建立了一类带有治疗的HIV传播模型.在该模型中,考虑了被治疗后的HIV患者行为改变情况.借助再生矩阵求得了所建模型的基本再生数.当基本再生数小于1时,疾病最终灭绝;当基本再生数大于1时,疾病持续存在.还分析了治疗期对基本再生数的影响.     

欧盟委员会(EC)No 282/2008法规解析

本文针对再生塑料是否可用于与食品接触这一热点问题,解析欧盟对拟与食品接触的再生塑料和制品的主要要求,包括拟与食品接触的再生塑料材料和制品的范围的设定,再生工艺的许可条件、再生工艺许可程序、监督检查要求、对符合性声明的要求等。     

国际资讯

<正>欧盟委员会启动"循环塑料联盟"欧盟委员会启动了一个新的关键行业利益相关者联盟,涵盖整个塑料价值链,作为其努力增加再生塑料份额和刺激欧盟市场创新的一部分。欧盟委员会希望通过这个新平台,为欧洲塑料战略目标做出贡献,该目标是到2025年在欧盟市场上将至少有1000万吨再生塑料用于新产品。该联盟将追求三个主要的业务目标:1.鼓励主要行业利益相关方采取短期、自愿和统一的行动和投资。欧盟委员会表示,这些行动和投资     

多因素对再生混凝土力学性能及抗冻性的影响

为研究不同因素、不同水平对再生混凝土力学性能的作用。该文通过正交试验研究钢纤维掺量、再生粗骨料掺量和粉煤灰掺量对再生混凝土力学性能(抗压强度、劈裂抗拉强度和抗折强度)的影响,确定各因素对再生混凝土力学性能的影响程度,并加以量化表征,并提出多因素共同作用下再生混凝土力学性能的多元非线性回归模型且进行验证。在此基础上,该文进一步研究再生混凝土的抗冻性。结果表明:再生混凝土的力学性能随钢纤维掺量的增加而提高;随粉煤灰掺量增加而降低;再生粗骨料掺量对再生混凝土的力学性能影响较小。钢纤维的掺入可提高再生粗骨料的掺量。再生混凝土力学性能的实测值与通过建立的回归模型得到的计算值的最大误差在6.5%以内。此外,钢纤维的掺入和减少再生粗骨料的掺量均可以提高再生混凝土的抗冻性。     

Experimental direct evaluation of functional barriers in PET recycled bottles: comparison of migration behaviour of mono‐ and multilayers

Recycling of used bottles into new bottles is associated with possible migration of pollutants arising from the previous life of the packages. To reduce or delay such migration, the recycled resin is depolluted or a functional barrier layer made of virgin plastics is used. Testing migration from such recycled bottles relies on the use of model pollutants (surrogates). In order to enable modelling of migration kinetics, each step of the use of surrogates is carefully investigated here in the case of PET. First, criteria underlying the selection of surrogates are carefully examined; together with volatility, polarity and diffusion behaviour, it is shown here that their solubility in the food simulant and their chemical stability strongly influence migration results. For aqueous test media, 2,4‐pentanedione and phenol should be used as surrogates. Second, a procedure is developed to impregnate surrogates at very large concentrations (several thousands of mg/kg PET) which are necessary to monitor migration kinetics. This procedure, which uses dichloromethane as solvent, allows a quick and reproducible impregnation, not sensitive to temperatures between 11–23°C, factors which favour its use at a plant scale. Third, flakes impregnated with this procedure are processed into bottles, and their physicochemical properties are compared to those of commercial bottles. Last, monolayer and tri‐layer polluted bottles (model pollutants in inner layer) are tested for migration for more than 1.5 years. With multilayers, the migration lag time of the fastest surrogates is 6 months with 3% acetic acid and 3 months with ethanol as the simulant, due to plasticization of PET by ethanol. The sequence of migration of surrogates is different with monolayer and multilayer bottles, which shows that partition effects (solubility) play an essential role, especially with monolayer materials. Copyright © 2005 John Wiley & Sons, Ltd.     

Application of a computer model to evaluate the ability of plastics to act as functional barriers

A simulation model computer program, which accounts for not only the diffusion process inside the polymer but also partitioning of the contaminant between the polymer and the contacting phase, was developed based on a numerical treatment, the finite element method, to quantify migration through multilayer structures. The accuracy of the model in predicting migration was demonstrated successfully by comparing simulated results to experimental data. For this study, three‐layer co‐extruded high density polyethylene (HDPE) film samples, having a symmetrical structure with a contaminated core layer and virgin outer layers as the functional barriers, were fabricated with varying thickness of the outer layers and with a known amount of selected contaminant simulant, 3,5‐di‐t‐butyl‐4‐hydroxytoluene (BHT), in the core layer. Migration of the contaminant simulant from the core layer to the liquid food simulants was determined experimentally as a function of the thickness of the outer layer at different temperatures. The computer program, developed as a total solution package for migration problems, can be applied not only to multilayer structures made with the same type of plastics but also to structures with different plastics, e.g. PP/PE/PP. This work might provide the potential for wider use of recycled plastic, especially polyolefins, which have lower barrier properties, in food packaging, and simplification of the task of convincing the FDA that adequate safety guarantees have been provided. Copyright © 2003 John Wiley & Sons, Ltd.     

方钢管玄武岩纤维再生混凝土短柱偏压性能研究

为研究方钢管玄武岩纤维再生混凝土短柱的偏压性能,以再生粗骨料取代率、玄武岩纤维掺量、再生混凝土强度等级、偏心距为变化参数,设计并制作8个短柱试件,进行偏压静力加载试验.观察了试件破坏过程及形态,获取了荷载-位移、荷载-应变等重要关系曲线.分析了设计参数对试件承载力的影响趋势,建立了试件偏心受压的有限元分析模型,并建议了...     

型钢再生混凝土柱保护层厚度力学分析

结合型钢再生混凝土受压柱的破坏特征以及再生混凝土的材料特性,根据板的弹塑性稳定理论,对型钢再生混凝土柱受压区再生混凝土保护层不发生失稳时的最小保护层厚度进行了理论推导;同时从再生混凝土保护层开裂的角度,依据力扩散原理和拉断破坏模型,分析了型钢再生混凝土临界开裂保护层厚度的计算方法。研究表明:型钢再生混凝土柱保护层厚度主要与再生混凝土强度等级、型钢再生混凝土柱高、型钢翼缘宽度、再生粗骨料取代率有关。     

重复使用下聚碳酸酯饮水桶中双酚A的迁移规律

目的研究重复使用条件下聚碳酸酯(PC)饮水桶中双酚A(BPA)的迁移规律及主要影响因素,为日常生活中PC饮水桶的正确使用提供参考。方法采用高效液相色谱方法,研究了重复使用时间、温度和换水间隔对收集的5只饮水桶中BPA迁移行为的影响,同时分析新桶与使用1年的旧桶的区别。结果 PC饮水桶中BPA的迁移主要受重复使用时间和温度的影响,并且随使用时间的延长和温度的升高而增加;间隔换水时间对BPA迁移影响较小;已使用过的PC旧桶中BPA迁移量显著高于新桶。结论在PC桶的日常使用中,应注意在常温下短期使用,避免高温长期使用,使用一段时间的PC桶应注意废弃回收。     

型钢再生混凝土框架-再生砌块填充墙结构恢复力模型试验研究

对7榀1/2.5比例单层单跨型钢再生混凝土框架-再生砌块填充墙模型进行低周反复荷载作用下的抗震性能试验研究,分析了墙体设置形式、填充墙砌块强度、拉筋构造形式、轴压比以及墙体宽高比等设计参数对该种结构抗震性能的影响。研究了模型的典型破坏形态、荷载-位移曲线、承载能力以及位移延性等。结果表明:试验模型的典型破坏形态均符合“强柱弱梁”的破坏模式,框架部分的破坏程度随墙体全高填砌而减轻;在框架中加设墙体后可明显提高结构承载力和初始刚度,墙体填充率越大、填充墙砌块强度越高、拉筋间距越小、轴压比越高、墙体宽高比越大,结构承载力与初始刚度提高越明显;结构的位移延性均值达到6.26,高于钢筋再生混凝土框架-填充墙、普通钢筋混凝土框架-填充墙以及钢筋混凝土异形柱框架-填充墙等结构,抗倒塌能力较强。在试验研究的基础上,通过有限元与试验结合的方法,建立了相应的四折线恢复力模型,可用于型钢再生混凝土框架结构的弹塑性地震反应分析。     

A macro model for usage and recycling pattern of steel in Japan using the population balance model

Abstract

A macro model for evaluating the steel flow in Japan is proposed. The steels are classified into four types; virgin steel for machinery and for construction and recycled steel for machinery and for construction. The steel is assumed to be discharged from the society in accordance with the lifetime distribution of each usage. The amount of recycled steel and the accumulation in society are calculated using a population balance model. The comparison with the calculated results and statistics ensures the validity of the model. Since the amount of recycled steel mainly supplied for construction will increase and be oversupplied, recycled steel will have to be used for machinery. The required amount and the available amount to supply recycled steel for machinery are considered from the point of allowable copper concentration for machinery use. Copper contaminates steel during the recycling process of steel used for machinery and the contamination ratio is evaluated with the model. The copper concentration in the recycled steel and the amount of CO₂ emission are predicted for various scenarios. The relationship between recycling ratio and contamination ratio, which enables us to supply recycled steel for machinery, and the allowable CO₂ emission to decrease the contamination ratio are discussed. © 2000 Published by Elsevier Science Ltd.     

Water Absorption and Thickness Swelling Behavior of Polypropylene Reinforced with Hybrid Recycled Newspaper and Glass Fiber

This study aims to investigate the moisture absorption of recycled newspaper fiber and recycled newspaper-glass fiber hybrid reinforced polypropylene composites to study their suitability in outdoor applications. In this work composite materials were made from E-glass fiber (G), recycled newspaper (NP) and polypropylene (PP), by using internal mixing and hot-pressing molding. Long-term water absorption (WA) and thickness swelling (TS) kinetics of the composites was investigated with water immersion. It was found that the WA and TS increase with NP content in composite and water immersion time before an equilibrium condition was reached. Composites made from the NP show comparable results as those made of the hybrid fiber. The results suggest that the water absorption and thickness swelling composite decrease with increasing glass fiber contents in hybrid fiber composite. It is interesting to find that the WA and TS can be reduced significantly with incorporation of a coupling agent (maleated polypropylene) in the composite formulation. Further studies were conducted to model the water diffusion and thickness swelling of the composites. Diffusion coefficients and swelling rate parameters in the models were obtained by fitting the model predictions with the experimental data.