Functional Properties and Morphology of Recycled Post-consumer WEEE Thermoplastic Blends
Doctoral thesis, 2015

This work concerns a waste electrical and electronic equipment blend of recycled plastics (WEEEBR), reprocessed from a low density thermoplastics batch (600 kg) by removal of non-thermoplastic contamination (1.2 weight % (wt%)). Some well-distributed inorganic domains (mainly 5-20 µm) containing Ca, Na, Mg, Fe or Ba still remained in the WEEEBR after melt-filtration. The WEEEBR consisted of high impact polystyrene (HIPS, 42 wt%), acrylonitrile-butadiene-styrene copolymer (ABS, 38 wt%), polypropylene (PP, 10 wt%) and other thermoplastics (10 wt%). Although PP was a minor component in the blend, the phase separation of the polymers and the shear yielding observed in the fracture surfaces indicated the existence of partial co-continuous structures at appropriate mixing times, viscosity ratios and temperatures. Co-continuity of WEEEBR was suggested as a transitory morphological state, which was only observed by twin screw extrusion under certain processing conditions (around 60 rpm, 200 oC). These processing conditions resulted in a yield point and an elongation at break (εb) at about 5 %. Increasing the screw rotation rate by only 30 rpm or increasing the barrel temperature by only 20 oC resulted in a WEEEBR material without a yield point and about half the εb-value. The processing conditions in single screw extrusion or injection moulding were not observed to yield a co-continuous PP phase. Furthermore, injection moulding resulted in a layered structure with a small variation in composition in the layered structure. In addition, single screw extruded WEEEBR contained a significant amount of voids (50-300 µm), reducing the load-bearing cross-sectional area and probably giving rise to stress concentrations. The WEEEBR was already chemically degraded in the as-received state, which was indicated by a smaller than expected exotherm associated with the lower activation energy and the antioxidants were mainly de-activated (consumed). An increase in stiffness and a significant decrease in ductility were observed after reprocessing, which could to some extent be attributed to physical ageing caused by the cooling conditions used. The ductility of WEEEBR was significantly improved by compatibilisation, which was expected to promote the shear yielding deformation mechanism, particularly around defects and inclusions. Among four studied compatibilisers, the addition of only 2.5 wt% SEBS was found to increase the εb-values of uncompatibilised WEEEBR more than 5 times.

morphology

melt-blending

compatibilisation

extrusion

SEBS

WEEE

physical ageing

TOF-SIMS

co-continuous

chemical degradation

plastics recycling

HC1
Opponent: Sigbritt Karlsson

Author

Erik Stenvall

Chalmers, Materials and Manufacturing Technology, Polymeric Materials and Composites

Elektronikskrot är en ökande avfallsfraktion i samhället. Innehållet är ungefär en tredjedel plast, med en stor variation av olika plaster som är svåra att separera från varandra. Därtill används mycket tillsatser som ytterligare komplicerar sammansättningen och därmed återvinningen. I denna avhandling har möjligheten att återvinna blandade plaster från elektronikskrot studerats samt vilka mekaniska och termiska egenskaper man kan förvänta sig från en sådan blandning. Att återvinna blandade plaster får ses som ett kostnads- och energieffektivt alternativ där man undviker separationen av olika plaster från varandra. Användning av blandade plaster vid återvinning kan leda till att en större andel plaster materialåtervinns, istället för att förbrännas eller i värsta fall deponeras. Återvinning av blandade plaster kräver ändå några separationssteg, där ett viktigt steg är att separera ut icke smältbara andelar, som annars kan försämra egenskaperna avsevärt. I den här studien har det gjorts genom en kombination av smältbearbetning och smältfiltrering. Den på detta sätt framställda blandningen ser helt homogen ut, men visade sig vara temperaturkänslig. I allmänhet hade plast blandningen ett sprött beteende, men sprödheten kunde minskas avsevärt genom tillsats av kompatibilisatorer, som skapade en seg fas i det spröda materialet och band samman blandningen bättre.

Subject Categories

Polymer Chemistry

Manufacturing, Surface and Joining Technology

Polymer Technologies

Other Environmental Engineering

Textile, Rubber and Polymeric Materials

Materials Chemistry

Areas of Advance

Materials Science

ISBN

978-91-7597-181-0

Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie

HC1

Opponent: Sigbritt Karlsson

More information

Created

10/7/2017