Stabilization of Recycled Materials

Fillers such as carbon black, titanium dioxide, and other pigments are extremely effective light protectors. Many rubber compounds come with high carbon black or other mineral filler loads and thus require no further UV stabilization. Titanium dioxide Is also effective, provided that a light-stable type Is used. In cases where high filler loads are not advisable for the final application of the finished parts, other types of stabilizing additives have to be utilized, such as UV absorbers and HALS [544]. 

In order to UV-stablllze elastomers, the elastomer selection Is as decisive as the choice of additives. Highly unsaturated elastomers such as butadiene polymers and co-polymers should be avoided. For example, styrene-ethylene-butadlene-sty-rene (SEES) is characterized by clearly superior weathering resistance than the analogous SBS block copolymer [544]. 

Formulations for recycled materials meet specifications with the help of a wide range of available additives. Polymeric additives, reinforcing substances, and especially functional additives are used. Table 3.13. Special developments for recycled plastics are only available for compatibilizers and stabilizers. Compatibilizers and stabilizers are also the additives most often used and described in operation [533]. 

Fillers (talcum, wollastonite, calcium carbonate, wood flour) Pigments 

The amount of stabilizer in a recycled material that is consumed during the first application has to be at least replaced, if comparable service and quality requirements have to be fulfilled. However, this is usually not sufficient recycled plastics from short-term applications, such as food packaging, certainly do not contain enough residual stabilizers or light stabilization to satisfy subsequent application in long-term service. Pre-damage and the molecular changes induced, mainly by oxidation, as well as the influence of mixtures and contaminations also reduce the stability of recycled compounds, so that post-stabilization may have to take these influences into account [533]. 

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Chemical re-stabilization of recycled material against the thermal and light-induced degradation is essential. Addition of 0.1-0.5 wt% of a sterically hindered phenol and a phosphite at a ratio varying from 10 1 to 1 10 is recommended [Pauquet et al., 1994]. For outdoor applications, hindered amine light stabilizers with UV-absorbers of the benzotriazole type are to be used [Herbst et al., 1995,1998]. Examples of blends used for polymer recycling are listed in Table 1.81. For more details see Chapter 16 in this book. 

An additive system was developed for poly(vinyl chloride) for medical applications. The additives include primary stabilisers (Ca-Zn stearate and Zn stearate), secondary stabilisers (epoxides) and lubricants (ethylene bisamide and high density polyethylene), to improve melt processing and heat stability. The use of the stabilisers resulted in reduced equipment down-time, increased the level of recycled material which could be incorporated, and enhanced the product characteristics, including colour, clarity, blush, aqueous extractables and particle generation. 5 refs. 

The choice of plastic material for automotive parts is influenced by its potential recyclability. One recent example shows that the use of recycled material gave the added benefit of an approximately 10% reduction in weight. This involved the use of recycled material in the Chrysler Neon rear spoiler. Major considerations in this respect are thermal and UV stabilities of the reprocessable material combined with low weight and mechanical protection performance characteristics. 

PS exhibits a natural thermostability. Antioxidants are only added to it if low damage levels due to use of recycling material is an important issue. Phosphites and polyphenols of medium molar mass in additive amoxmts of 0.1-0.4 % are usually selected. PS is sensitive to photooxidation. Yellowing and embrittlement can only be prevented by UV stabilization. 

K. Ziegler, H. Breil, H. Martin, E. Hozkamp, Ger. Offen. 973,626, 14 Apr 1960, Appl. 17 Nov 1953 U.S. Patents 3,257,332, 21 June 1966, Appl. 15 Nov 1954, to K. Ziegler A. Zletz, U.S. Patents 2,692,257, 19 Oct 1954, Appl. 28 Apr 1951, to Standard Oil of Indiana H. Zweifel, Recycling of Polymers for Reuse, Recovery Experiences, Trends and Case Studies, NATO-ASI on Polymer Recycling, Antalya 16-27 June 1997 H. Zweifel, Stabilization of polymeric materials (Springer, Berlin, 1998)... 

One problem related with doping in catalysis is stability of the material, meaning that doped G should not xmdergo any variation during the catalytic cycle. It is very common that since the dopant element is involved in the catalysis, a proportion of it can become detached from the G and can be transformed into a different species. This leaching of the dopant element due to the instability of the doped G in the catalysis can be a cause of deactivation of the material upon recycling of the catalyst. 

S.4.4 Wall Base Extruded vinyl wall base is opaque and generally in black or dark colors, some product is produced through coextrusion techniques. Here, the top coat can be very colorful, while the base material contains a lot of recycled material. It is important that the level of recycled material be controlled because of its impact on extmdabihty (gauge variations and dimensional stability problems). Exceptionally high levels of lubricant are often used to improve processability. 

Traditionally carpet tile backings have been made from bitumen, PVC or polyurethane. There are problems with the environmental impact of these materials and they are difficult to recycle. Shaw industries developed their EcoWorx carpet tile backing using a polyolefin resin. This has superior environmental profile to PVC and is easier to recycle than bitumen and the cross-linked polyurethane backings. EcoWorx has lower toxicity, better adhesion and good dimensional stability. It is easy to recycle and can be separated from any fibre type used in the carpet tile. It works particularly well with nylon-6 fibres. EcoWorx tiles contain 40% recycled content and Shaw have established a collection and return scheme to close the loop. 

Recyclable materials Combustion residence time Heat treatment Stability of the process Atmospheric emissions Solid wastes from the process Waste from separation Up to 4 s at about 1,200°C Integrated process Without caloric restriction Much less than the legal limits Cement furnaces Waste from separation 2 s up to 850°C Only incineration Minimum CP of 1,400-1,600 kcal/kg Within the legal limits Sanitary landfills... 

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