废弃塑料包装物的管理及资源、环境评价

由于塑料包装材料具有明显的资源优势,而获得广泛应用。但塑料材料的原料——石油,目前面临枯竭窘境。同时,塑料包装废弃物的处理存在巨大的环境压力。焚烧包括塑料包装废弃物在内的生活垃圾,用于发电,是日本曾经采取的方法。近年来,因存在难以逾越的生态环境问题,而逐渐废止。工业生态学的材料流的循环利用模式,是解决资源耗尽、废物充斥的理想方法。源头分离是城市固体废弃物资源化的前提条件。按塑料品种分类回收,以材料形式重复利用,保留了塑料的材料价值,还需要解决,再加工过程造成材料力学性能下降的问题。将单一品种塑料转化成单体,不同塑料品种的单体转化率有很大差距,缩合聚合物较高,而PP、PE等则不然。混合塑料的热裂解可获得化工原料和燃料,又达到减少垃圾总量和石油资源循环利用的效果,具有开发潜力。填埋方式占用土地又人为阻碍了有机垃圾回归生物圈。控制性堆肥对避免大量使用化肥、农药造成的生态环境灾难,再建农业生产的可持续性模式,发挥重要作用。生物降解塑料袋对堆肥的实施,具有特殊价值。PET和E-CO在食品包装某些应用领域有优势,而PVC食品包装物的使用和废弃后再利用都存在问题。

Management of discarded plastic packaging and its assessment from the angles of resources and environment

Owing to the fact that plastic packaging materials possess distinct superiority in environment and resources aspects,they have largely replaced those traditional materials.The raw material resources of the plastic industry(oil and gas) are limited.At present,the resources are confronted with exhausted circumstances and the disposal of post-consumer plastics has brought huge pressure to the environment.In some countries,notably Japan,the heat produced by incineration of waste polymers is used for the generation of power.Incineration once was the major method of disposing of combustible waste products from domestic sources.Recently,because of unsolvable problems with ecological environment,it is being abolished gradually.The model of cyclic materials flows of the industrial ecology is an ideal way of solving the problems of used-up resources and glutted with waste.Preseparation is prerequisite for the resources of the municipal solid waste.Relatively uncontaminated single polymer types can be re-used by reprocessing.This method preserves most of the material value of the wastes.During reprocessing,the polymer chains in the plastic are sheared,and the mechanical property is reduced.For real recycling,the problem must be solved.Some polymers,notably condensation polymers,can act as the raw material of new monomers or oligomers which are produced by hydrolysis and alcoholysis.For example PMMA and PET can relatively produce good yields of the original monomer provided they can be segregated from the polymer wastes,but PP and PE are not the case yet.Another recycling method,chemical or thermal treatment has been using to transform mixed waste plastics into chemical feedstocks and fuels.It would be advantageous to reduce the volume of plastic that is send to landfills,conserve non-renewable petroleum resources and has great potentials.Composting has value well beyond that of managing waste.Compost increases organic matter in the soil,feeding soil microorganisms and increasing water-and nutrient-holding capacities;it provides a slow release of nutrients;it suppresses plant pathogens and provides an alternative to raw manures that may introduce pathogens;and it reduces erosion.The end results are increased crop yield and quality,reduced dependence on chemical fertilizers and pesticides,and reduced need for water.There is growing realization that in the future its most important value will be in supporting long-term sustainable agriculture.Landfill occupies land and cannot achieve composting which returns the fundamental components of waste to their natural carbon cycles.Degradable plastics would have special value as bagging for compostable garbage,including yard waste and food waste.PET and E-CO resins show more environmental superiority in some respects of food packaging.The practical use and the reused of PVC as food-packaging bring many problems.