Recycling of plastic waste.

Abstract

The majority of wastes both industrial and urban including plastic waste, goes to landfill sites. Waste disposal has now emerged as the priority public concern in most countries, not only because it is finally recognised that we are running out of landfill space but perhaps even more importantly because landfills represent an uncontrolled source of toxins and contaminants which have the potential to ruin our water and food supplies. The plastic proportion of waste volume is almost double the weight fraction, so it is the volume of plastics which fills landfills, and pick-up vehicles. Certainly improved compacting of plastics will help but it is not sufficient. Plastics represent the fast growing portion of municipal waste in most countries for example in United States the waste stream has increased by weight from 1% in 1960 to 2.7% in 1970, 7.2% by 1984 and it is predicted that plastics will account for almost 10% of the municipal waste stream by the year 2000. This rapid rise in the use of plastic reflects their unique advantages in term of physical and chemical properties especially for packaging. This situation is also present in Malta. The household waste fraction of Textiles, Plastics and Wood has increased from 6% in 1970 to 11% in 1986, to 14% in 1989 according to the Malta National Waste Study Interim Report (p 2.12 Table 2.6). This is estimated to increase in the near future as it is clear that plastic will continue to displace paper metal and glass in many applications. Thus it is necessary that viable recycling technologies and economically feasible commercial recycling businesses are developed and established. Other solutions include refurbishing degradability, design of plastic parts and energy recovery. However there is no simple solution to waste disposal as it is a complex problem. Most plastics are extremely resistant to biodegradation. This phenomenon starts to create significant economical and environmental problems when landfill sites starts to overflow, with plastic a visible part of the problem. Paper, wood and other remnants slowly decompose. Plastic however, may stay intact for a long time. There is still a problem, whether or not degradable plastics should be introduced as this may create problems in the recycling stream, because the quality and lifetime of plastic articles may be contaminated by degradable resin. There are two basic categories of degradable plastics which are : a) Biodegradable and b) Photodegradable plastics. Biodegradable plastic is decomposed by the action of micro-organisms while photodegradable plastic decomposes on exposure to ultra-violet radiation. However degradation is not a magic solution for the plastic waste disposal problem and degredation in certain conditions is not as fast as expected. At present however only a limited amount of degradable plastics can be found in the market place.