Mechanical and thermal properties of recycled WEEE plastic blends
Doktorsavhandling, 2016

Electronic waste is the fastest growing waste stream today, and the recycling of the plastics from waste electrical and electronic equipment (WEEE) has attracted great attention recently for environmental reasons and to comply with the European Union’s (EUs) WEEE Directive. The plastics fraction in WEEE is between 20 and 35 weight % (wt%). The WEEE plastics contain up to 15 different types which makes it difficult and costly to separate the plastics from each other, which is how plastics material recycling mainly is done today. In this work the opposite approach has been taken and the possibility to do a plastics blend of all the WEEE plastics has been investigated. This has been done in means of characterizing different WEEE plastic waste streams regarding the mechanical and thermal properties and enhance the mechanical properties of the recycled material with the addition of compatibilizers and/or gamma irradiation. The WEEE plastics study was based on a 600 kg batch of blended post-consumer recycled WEEE plastics (WEEEBR). This low-density, brominated flame retardant free blend was melt-filtered to remove contaminants, mostly thermosets such as rubbers (1.2 wt%). The composition analysis showed that the WEEEBR consisted of three main thermoplastics constituents: high impact polystyrene (PS/HIPS, 42 wt%), followed by acrylonitrile-butadiene-styrene copolymer (ABS, 38 wt%), and lastly polypropylene (PP, 10 wt%). The remaining 10 wt% were other thermoplastics, thermosets and contaminants such as wood and paper. Antimony leaching from an ABS computer casing showed that sodium hydrogen tartrate in dimethyl sulfoxide (DMSO) worked as a leaching medium with almost 50 % leaching efficiency. The hypothesis that gamma irradiation of ABS should enhance the mechanical properties by creating free radicals and making crosslinks in the plastics was not confirmed. Instead the plastics became brittle and degraded with lower mechanical properties compared with non-irradiated ABS. The melt flow rate (MFR) of gamma irradiated WEEEBR showed a decrease in viscosity of up to 100 kGy (indicating chain scissoring of the polymer chains) and then an increase in viscosity of up to 600 kGy (indicating crosslinking of the polymer chains). The WEEEBR went from being brittle to becoming a ductile material by adding only a small amount (2.5 wt%) of a styrene-b(ethylene-co-butylene)-b-styrene copolymer (SEBS) containing compatibilizer. A considerable increase in the impact strength was seen, from 2.1 kJ/m2 to 3.8 kJ/m2 with 5 wt% compatibilizer. Based on the achieved results, WEEEBR and similar blends can potentially be used as a replacement for virgin plastics when they have been melt-blended, melt-filtrated and a suitable compatibilizer has been added.

SEBS

HIPS

extrusion

WEEE

WEEEBR

melt-blending

plastics recycling

gamma irradiation

PP

ABS

compatibilization

polymer degradation

KC
Opponent: Michele Edge

Författare

Sandra Tostar

Industriell materialåtervinning

The Influence of Gamma Irradiation on Repeated Recycling and Accelerated Acrylonitrile Butadiene Styrene Terpolymer Aging

International Journal of Waste Resources,; Vol. 4(2014)

Artikel i vetenskaplig tidskrift

The influence of extrusion conditions on mechanical and thermal properties of virgin and recycled PP, HIPS, ABS and their ternary blends

International Polymer Processing,; Vol. 28(2013)p. 541-549

Artikel i vetenskaplig tidskrift

Elektronikavfall är den snabbast växande avfallsfraktionen som finns i samhället, och cirka en tredjedel av den består av plast. Plasten i sig är uppdelad i upp till 15 olika sorter vilket gör att separering av dessa för materialåtervinning är svårt. I detta arbete har vi undersökt möjligheten att återvinna de olika plastsorterna från elektronikavfallet och göra en blandplast av dem alla med hjälp av smältbearbetning och smältfiltrering. Att kombinera dessa metoder är ett kostnads- och energieffektivt sätt, då man slipper flera separationssteg och minskar restfraktionerna som bildas i de olika stegen. För att veta vilka plaster som den aktuella materialströmmen som vi arbetade med bestod av, gjordes en kompositionsanalys. Baserat på denna analys valdes en specifik typ av plast för att kunna simulera återvinning och åldrande av plaster. Studier har också gjorts på de mekaniska och termiska egenskaperna av de ingående plasterna och blandplasten som sådan. En process för att laka ut värdefulla material ur plasterna har också utvecklats och visat sig vara effektiv. Plastblandningen var generellt spröd, vilket krävde en tillsats av en kompatibilisator. Detta ämne kan binda ihop plastfaserna bättre vilket gör att plasten blir mera elastisk och därmed förbättrar hållfastheten på den.

Electronic waste (E-waste) is the fastest growing waste stream in the society today and approximately one third of it is plastics. The plastic itself contains up to fifteen different types which makes separation of them for material recycling difficult. It is further more complicated since different fillers are added to the plastics which complicates the composition and therefore the recycling. In this work we have investigated the possibility to recycle the different plastic types from the E-waste and do a plastic blend of them by melt-blending and melt-filtration. Combining these methods is an energy and cost-effective way, due to the reduction of several separation and cleaning steps, and also the rest fractions are reduced which are created in the different steps. To know the composition of the blend constituents we worked with, a composition analysis was made. Based on this data, a specific plastic was chosen to simulate recycling and ageing of plastics. Mechanical and thermal studies have also been made on the plastic constituents and the blended plastic. A process has been developed for leaching out a valuable material, antimony, from the plastics and it turned out to been successful. The plastics blend was brittle in general, while a compatibilizer was added to combine the phases within the different plastics better. The plastics blend became more ductile and the mechanical properties were increased.

Ämneskategorier

Textil-, gummi- och polymermaterial

Styrkeområden

Materialvetenskap

ISBN

978-91-7597-303-6

Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 3984

KC

Opponent: Michele Edge