Plastic waste disposal problems

This article highlights the growing problem of plastics waste disposal and then investigates modes of polymer degradation - thermal, chemical, mechanical, photodegradation, bio-degradation, solvolysis andglycerolysis. 4 refs. 

The naturally biodegradable polymers such as starch, chitosan and cellulose derived from natural sources have produced a number of interesting NR blends and IPNs. These blended systems have an advantage in that they create fewer waste disposal problems compared to the petroleum based polymeric materials. The use of stareh blends to enhance the biodegradability of conventional plastics has been reported by many researchers in order to reduce the environmental impaet of petroleum based plastic products and waste. The NR/maize stareh blends exhibited a decrease in their mechanical strength due to the speeifie properties of starch. However, the blended polymers showed a low interfaeial interaetion between the two phases due to the different polarity behaviour of the hydrophobic NR and the hydrophilic starch. 

Plastics waste disposal can cause problems, especially as plastics are usually mixed up with other types of waste such as paper, metals and food. For recycling they really need to be sorted into individual types such as polythene, polyst)0 ene or PVC before being mixed with virgin material. Otherwise they have no strength if remoulded, and may literally fall apart. Sorting can be very difficult. 

Catalysts play an important role in the synthesis of fuels and chemicals as well as on the reaction systems hence, the catalytic cracking of polyolefins over solid acids needs to be explored. In this method a suitable catalyst is used to carry out the cracking reaction. The addition of a catalyst enhances the conversion and fuel quality, and lowers the reaction temperature and time. Reuse of catalysts and the use of effective catalysts in lesser quantities can optimise this option. It also enables an increased level of the cracking of plastics and a lower concentration of solid residue in the product. The cost should be further reduced to make the process more attractive from an economic perspective in order to solve the acute environmental problem of plastic waste disposal [2]. 

Based on the literature it can be stated that plastic waste management currently operates four fundamental methods incineration, landfill, reuse and recycling via energy production [12]. Unfortunately, both landfilling and incineration are currently the mostly commonly used methods for solid and plastic waste disposal. However, it is also well known that neither deposition, nor combustion should be the long-term solution for the problem of waste plastic treatment. 

The persistent problem of conventional plastic waste disposal grows ever more severe as landfills approach capacity with these highly degradation-resistant substances (Section 12-15). Biodegradable plastics provide an option for nonre-usable items such as plastic bags, wraps, and bottles. A recently developed and commercialized biobased and biodegradable plastic is poly(jS-hydroxybutyrate-co-/3-hydroxyvalerate) (PHBV), a copolymer of 3-hydroxybutanoic acid and 3-hydroxypentanoic acid. PHBV is a polyester that is produced by bacterial fermentation of mixtures of acetic and propanoic acids. The ratio of the two hydroxy acids controls the properties of the plastic—it is more flexible with more... 

Solutions to the solid waste disposal problems facing the world will include recycling, incineration and land fill where feasible. However, in those instances where collection is prohibitive such as roadside and beach littering, and on the oceans and other large bodies of water, photodegradable plastics will remain a viable solution and will find additional applications, repeating the success of E-CO as the material of choice for the Hi-Cone carrier for beverage cans. 

Another factor potentially affecting the market for halogenated fire retardants is the waste disposal of plastics (see Wastes, industrial). As landfiU availabihty declines or becomes less popular, two alternatives are incineration and recycling (qv). The nature of the combustion products from halogenated products requires carefiil constmction and maintenance of incinerators (qv) to avoid damage to the incinerator itself and a pubHc health problem from the exhaust. The ease of recycling used products also has a potential effect on fire retardants. 

---