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81.
Reactively Compatibilized Cellulosic Polylactide Microcomposites 总被引:3,自引:0,他引:3
Birgit Braun John R. Dorgan Daniel M. Knauss 《Journal of Polymers and the Environment》2006,14(1):49-58
Poly(lactic acid) (PLA) possesses a suite of favorable material properties that are enabling its penetration into diverse
markets (e.g., as packaging material or textile fibers). In order to increase the range of applications for this material,
it is necessary to modify its properties and for certain applications, reduce its cost. The introduction of fibers into a
polymeric matrix is an established route towards property enhancement provided good dispersion and intimate interfacial adhesion
can be achieved. In addition, cellulosic microfibers are obtainable at low to moderate cost. In this study, reactive compatibilization
of cellulosic fibers with PLA is pursued. Hydroxyl groups available on the surface of cellulosic fibers are used to initiate
lactide polymerization. Various processing strategies are investigated: (1) blending preformed PLA with the fiber material,
(2) through a one-step process in which lactide is polymerized in the presence of the fibers alone, or (3) reactive compatibilization
in the presence of preformed high molecular weight polymer. The results show that materials prepared by simultaneous introduction
of lactide and preformed high molecular PLA at the beginning of the reaction possess superior mechanical properties compared
to composites made by either purely mechanical mixing or solely polymerization of lactide in the presence of fibers. The modulus
of materials containing 25% fibers which are prepared by reactive compatibilization of 30% preformed PLA and 70% lactide (30/70
P/L) improves by 53% compared to the homopolymer, whereas 36% reinforcement can be achieved upon purely mechanical mixing.
A further increase to 35% fiber loading leads to a reduction in modulus due to an excess in initiating groups. The same trend
was observed in systems containing 65% preformed PLA and 35% lactide (65/35 P/L) with an overall achievable reinforcement
that was slightly lower. 相似文献
82.
Goal and Scope
Type III Environmental declarations (Environmental product declarations, EPD) are intended to inform interested parties about the environmental performance characteristics of products. They are based mainly on LCA according to ISO 14040ff, provide its results as inventory or impact category indicators and thus describe the product system under investigation. ISO 14025 is out for ballot as FDIS. The concept of EPD has found a market in particular in the construction sector. It has a considerable part in the European Integrated Product Policy, e.g. documentation of improvement in design for environment, documentation of compliance with green procurement requirements.Main Features
EPD are a means to communicate the results of a LCA-study according to ISO 14040ff in a comparable and harmonised way. ISO (FDIS) 14025 describes how to develop and document consistent and comparable data sets. This report exemplifies three levels in the development of EPD for which the standard provides requirements. 1. Framework for the development of an EPD program including verification procedures for EPD. 2. Defining the rules for conducting the LCA according to ISO 14040ff as well as additional information for defined product categories (product category rules). 3. Development and documentation of EPD according to the PCR.Results and Conclusions
After quite a few years of standardisation work the new standard ISO (FDIS) 14025 will provide a systematic approach to documenting and communicating LCA results in an EPD. This will support propagating LCA from its academic origin to a practical tool for the assessment of the environmental performance of a product system. An essential part will be the participation of LCA experts in EPD programs.Recommendations and Outlook
An enormous effort for developing appropriate conventions will have to be taken by all interested parties to come up with consistent and comparable EPD in different branches. In some areas defining such conventions has been shown to be possible. An important part is the development of quality criteria for modelling as well as for the databases used to calculate the LCA. To find sufficient credibility at economically acceptable conditions with a minimum of bureaucratic effort more practical experience will have to be gained. This holds especially for the trust in the EPD results based on the independence of the review, transparency of procedures and the participation of interested parties. There is a demand on education for SME developing EPD for their products as well as for the users of EPD on how to document EPD transparently and apply them properly. 相似文献83.
北京夏季高温高湿和降水过程对大气颗粒物谱分布的影响 总被引:26,自引:8,他引:26
2004-07-13~2004-08-23使用TDMPS-APS系统在线测量颗粒物的数浓度谱分布,并于07-16~07-18选取了高温闷热夜晚、日间高温高湿和雨后晴朗干洁3种天气条件,使用多级串联撞击式采样器(MOUDI)测量颗粒物的质量浓度谱分布,结果表明,高温高湿天气条件下颗粒物的污染、尤其细粒子污染严重,导致很低的能见度(2.5km);PM1.8和PM10的质量浓度分别为170.68μg/m3和249.35μg/m3,细粒子质量浓度占PM10的68%;粒径为50~100nm颗粒物的数浓度最高,为2×104~3×104个/cm3;降雨过程对粗粒子和细粒子均有去除作用,对细粒子的去除作用尤为明显;降雨后PM10和PM1.8浓度分别比降雨前降低3倍和6倍;降雨过后的晴朗干洁天气有利于新粒子(3~20nm)的生成,生成的新粒子快速长大到50~100nm;随着污染物的累积,以后几天内又变为污染天气. 相似文献