Polymer waste, additives

The most creative application of the secondary cathode approach was described by Schelles and Van Grieken [24], who investigated its ability to determine the elemental constituents of polymeric materials. Mass spectrometric analysis has almost exclusively been directed at the determination of molecular weights and disparity characteristics secondary ion mass spectrometry (SIMS) [53,54] and matrix assisted laser desorption ionization (MALDI) [55,56] have carried the major share of the workload. Growing concerns over the fate of polymeric materials in the environment and the leaching of heavy metals into ground waters have necessitated the development of methods that permit the elemental analysis of bulk polymers. In addition, the use of polymers as immobilization media for waste remediation is also pressing these developments. 

No single method of recycling provides a practical method for handling polymer waste. To be effective, processes must be based on sound science and technology. In addition, a recycling program must make economic sense. There must be incentives for companies willing to participate to make a profit. Fed-... 

The chemical composition of recycled polymer waste material (in Germany mainly from packing materials) can be described only for random samples, as the portions of different polymers, additives, and contaminations may differ considerably, depending on... 

There are other alternatives for the improvement of polymer stability starting with polymer wastes [147, 148]. The presence of sulphur in irradiated HR increases the crosslinking level up to 100 kGy. The addition of stabilizers is a solution for flie protection of materials for further oxidation [149]. 

Thermoplastics processing operations produce emissions into the air, wastewater, and solid waste resulting from both polymers and additives. Most important are volatile organic compounds emitted from heated cylinders and molds. The identification of such volatiles and the development of analytical techniques for measuring their concentration in the workplace are of paramount importance to establish or revise threshold limit values that would minimize exposure to hazardous chemical substances. Environmental issues in polymer processing are reviewed in References 18 and 19. 

PLA could make a significant contribution to reducing the environmental problems associated with polymer waste. PLA can provide similar mechanical properties as conventional polymers, while leaving a lower environmental footprint [137, 138]. In addition, PLA has adequate impact resistance, good processability, and food contact acceptance. However, this desirable polymer has also disadvantages, such as poor thermal stability, brittleness, and lower gas and water vapor barrier properties. The permeability of currently available PLA is adequate for specific applications where gas and water vapor barriers are not needed, or when storage requirements are short. 

It would appear that the use of laser-aided polymer waste sorting [137] (eventually in combination with LIBS) and fluorescent tracer systems (cfr. Chp. 1.4.2) [152] are technologically the most attractive, with the latter technology more geared towards the identification of polymers than additives. 

Additionally, the recycling of plastics usually requires a suitable separation method in which plastic materials in the mixed solid wastes are separated into a homogeneous stream. A homogeneous plastic material demonstrates better properties, which results in the wider application of recycled products. In other words, the incompatibility of different polymer wastes leads to problematic processing and poorer mechanical-physical properties of the obtained materials. 

With the objective of a successful and economical recycling process in which the recycled polymer has largely acceptable properties, considerable effort must be made to encompass all the aspects of recycling in future studies to enhance the competitiveness of these systems. The first step could be the improvement of interfacial adhesion in prepared nanocomposites to achieve better physical and mechanical properties from recycled polymer wastes. Many procedures such as compatibilisation, functionalisation and surface modification could be developed in the future. Furthermore, the addition of effective nanofillers including available nanofillers or a combination of nanofillers will provide further progress and new opportunities in these systems. In addition, the development of fabrication techniques and also, the optimisation of available methods such as melt mixing should be performed, due to its important role in the final properties of recycled products. 

Incineration and landfill as additional treatment techniques for residual waste are mentioned for completeness. The content of pollutants and harmful substances in residual waste is almost always determined by waste fractions other than biodegradable materials. Therefore the established rules for incineration and landfill will cover biodegradable polymers well additional considerations of ecotoxicological impacts are not needed. 

---