Recycled-plastic properties

Recycled poly(ethylene terephthalate) (PET), which offers excellent properties at potentially lower cost, is finding wider use as a raw material component and meeting increasing demands for environmentally compatible resins (see POLYESTERS,THERMOPLASTIC Recycling, PLASTICS). 

Recycling polymers is one way to minimize the disposal problem, but not much recycling occurs at present. Only about 25% of the plastic made in the United States is recycled each year, compared with 55% of the aluminum and 40% of the paper. A major obstacle to recycling plastics is the great variation in the composition of polymeric material. Polyethylene and polystyrene have different properties, and a mixture of the two is inferior to either. Recyclers must either separate different types of plastics or process the recycled material for less specialized uses. Manufacturers label plastic containers with numbers that indicate their polymer type and make it easier to recycle these materials. Table 13-5 shows the recycling number scheme. 

Suitably recycled plastics can have properties that are good enough for many applications, with a noticeable economic advantage. Table 3.22 compares properties of virgin and recycled polyamides. These data are examples only and cannot be considered as representative. 

Post-industrial waste and sorted post-consumer wastes (PCW) are suitable raw materials. However, they contain different amounts of inhomogeneities formed during the service life and non-polymeric impurities. These contaminants account for differences in mechanical properties and ageing resistance between recyclates and the respective virgin plastics. Recycled plastics are often used in low-grade applications, and it is generally believed that the mechanical performance of recyclates is lower than that of virgin materials. 

The objectives of this paper are to discuss and present some examples of how polymer characterisation must be used in order to determine a range of important polymeric properties in recycled plastics. These properties in turn are used to define the quality of recycled plastics. 

Online separations are often based on spectroscopic identification of polymeric type, but seldom give any indications of polymeric properties (e.g. melt index, crystallinity, mechanical properties) or of the level of low molecular weight compounds. A complicating factor when trying to define properties of recycled plastics has to do with the word contamination . Depending on the context and also the person it may imply as vastly different things as dirt or low molecular weight compounds. 

Some undesirable impurities deteriorate the material properties of recycled plastics by reducing their stability. These contaminants consist not only of residues of polymerisation catalysts, but also of salts of metals introduced during polymer processing and exploitation [34, 35]. Metallic impurities arise from contaminated filler as well. Ions of copper and iron belong to the most dangerous species. They catalyse homolysis of hydroperoxides and increase the consumption of phenolic antioxidants or phenolic moieties of UV absorbers by their oxidation into dienoide compounds [36, 37, 38]. Residues of titanium and aluminium polymerisation catalysts can form coloured salts with phenolic antioxidants. 

It is generally known that only a very limited number of packaging materials such as glass or metal provide absolute protection properties concerning the penetration of chemical compounds from layers behind or from the environment. In the case of multi-layers with plastics materials as functional barriers there occurs, in most cases to a certain extent, an unavoidable mass transfer from the plastics layers into the product. This must be understood as a functional quantity which, however, must comply with food regulations. Therefore it is necessary firstly to understand functional barrier characteristics and mechanisms and, secondly, to define the functional barrier efficiency in relation to food safety and to establish appropriate test methods. This is especially important with those food packaging applications where recycled plastics are covered by plastics functional barriers. 

Explain sustainable development and the triple bottom line. (P) How does polymer regeneration differ from standard recycling methods 10) Are the properties of recycled plastics as good as the properties of virgin plastics 11) Discuss the life cycle of plastics and why reducing is better than recycling and reusing. 12)... 

This has particular significance due to the fact that the materials came from recycled plastic wastes. This not only alleviates pollution of the environment, but also reduces the cost of the polymer concrete. These two kinds of recycled polymer can complement each other to produce excellent properties. 

Rebeiz, K., Fowler, D.W., Paul, D. (1991) An Overview on the Properties of Polymer Concrete Using Recycled Plastics, University of Texas at Austin. 

In this investigation, the short-term behaviour of the protected waterproofing has been studied. It should be pointed out, however, that, due to the plastic properties of the recycled material, including migration of plasticizers, modificators, and so on, the long-term behaviour of the system is also of importance and requires due attention. 

In this entry, the effect of blending recyclable poly-(propylene) (PP) and poly(ethylene terephthalate) (PET) with lignin on carbon fiber production is presented. We discuss the effects of lignin structure and specific intermolecular interactions on lignin thermal properties as well as the effect of blend composition on surface morphology, mechanical properties, and the manufacturing process of lignin/recyclable plastic-based carbon fibers. 

Table 4 Typical mechanical properties of HKL and HKL/recyclable plastic carbon fiber...

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