Acrylic scrap recycle
Acrylic, also known as poly methylmethacrylate (PMMA), is a clear, colorless transparent plastic with a higher melting point, better impact strength, and better weather resistance than polystyrene (PS). It is widely used in many areas like transparency roof, automobile parts, etc. and produced principally through extrusion and casting.
The cell casting process, of sheet manufacture, which consists of two flat glass plates separated by an elastomeric gasket, is generally used for the manufacture of transparent acrylic sheets. In general, the gasket is used only once and has to be removed from the finished product by cutting in order to make the required sheet size. Residual acrylic material sticking around unusable gaskets, generated during cutting step, comprises approximately 10% of total final production, and becomes an industrial waste. Acrylic plastic is not easily recycled and is therefore not collected for recycling in many countries.
Scrap Acrylic is an industrial waste, not only having a significant impact on the environment but also on the cost of production of Acrylic Sheets. Acrylic plastics are not easily biodegradable. Some acrylic plastics could be highly flammable. PMMA scrap with technological additives can, however, be recycled and re extruded to produce new PMMA sheet in spite of its amorphous structure.
Industrial PMMA scrap can be divided into two groups, pure acrylic plastic scrap which forms about 20% and reinforced acrylic plastic scrap forming about 80% of the total amount.
Recycling Scrap by Pyrolysis
The process generally consists of heating the acrylic scrap with certain chemicals to a temperature of 4000-4500ºC in a mild steel distillation still. The heating results in the depolymerisation of PMMA to Methyl meth acrylate monomer which is condensed and redistilled to get the pure regenerated monomer. A mixture of the pure monomer and regenerated monomer (generally up to 5%) is then mixed with Benzyl peroxide (catalyst) and heated. After the desired degree of polymerization, the viscous mass is cooled, mixed with colours and poured into molds. It is then heated and dipped in a hot water bath to complete the polymerization process.
PMMA has also been successfully depolymerised by contacting with molten lead resulting in MMA with a purity of more than 98%, but from an environmental point of view the use of lead many be undesirable.
Recycling Scrap by Melting
It is also claimed that acrylic scrap can be melted in a high temperature furnace after separation and grinding. The molten liquid is put in mold plates and then taken to a pressurized oven for a period of 12 hours, making the acrylic plates again. The acrylic sheets can be used to create various types of products, furniture, decorative items, Car parts etc. It is reported that this is cheaper by 30% than the manufacture of the conventional Acrylic Plates.
Reprocessing of reinforced plastic scrap
Composite plastic scrap (vacuum formed acrylic plastic with glass fibre reinforcement) has low density and thus has to be pre crushed to save transportation and land filling costs.
Reprocessing of problematic plastic scrap (composite plastics) by using mechanical methods like milling by collision in disintegrators, has been tried successfully. For the milling of composite plastic scrap, different disintegrator mills are used for the size reduction of the acrylic plastic constituent and the separation of the glass fibre constituent. Plastic powder with a particle size of about 1–2 mm can be produced by two step milling and 95 mass % of the glass fibre content can be separated by final selective milling. The total amount of separated Glass Fibre particles (GFP) was 45 mass %. 55 mass % of acrylic plastic from the composite plastic scrap (GFP) can be, therefore, reused in the production of polymeric concrete products as reinforcement. Heating up an acrylic plastic material over glass, transition temperature (100 °C), converts the plastic into a rubber-like state, which makes this material ideal for vacuum forming. Continued heating causes thermal degradation of the material instead of melting.
Acrylic powder has found application as a new filler material in the Solid Surface casting technology for producing bathroom washbasins. Commonly, washbasins are made from a composite material consisting of a binder agent (unsaturated polyester resin), a filler material (dolomite powder) and a catalyst agent added to the resin to accelerate hardening. The mixing ratios of the binder agent and the filler material are 25/75 mass %. The traditional filler material, used in the casting technology, is a high-white dolomite filler. Acrylic powder was used to substitute for the high white dolomite filler. The best flow characteristics of the mixture were obtained with 50 mass % of acrylic filler and 50 mass % of matrix, but the best surface quality and hardness after polishing was achieved with a mixture of 66 mass % of the acrylic filler and 34 mass % of the resin matrix. Reprocessed plastics washbasins, produced from the new composite material, increase the wear resistance of the working surface. At the same time, as compared to the dolomite filler, double reduction in weight can be achieved.
Recycled scrap vs. virgin MMA Acrylic sheets – Properties
Concentrations of acrylic waste scrap mixed with the acrylic monomer solution in the range of 4% and 5%, give the viscosity values in the range of 500-1611 cp. which are appropriate for pouring into casting cells and conform to the standard viscosity prescribed for molding.
In experimental studies the acrylic waste scrap did not affect the impact strength and hardness properties of the acrylic cast sheet product although the tensile strength property of the acrylic cast sheet product increased with increasing the amount of acrylic waste. The acrylic waste scrap did not affect the transparency property of the acrylic cast sheet. Acrylic waste scrap affects the UV resistance property but did not affect the heat resistance property. However, the UV resistance property of the acrylic cast sheet product mixed with the acrylic waste scrap can be improved by the addition of UV stabilizer additive, which is usually added to the final product of acrylic cast sheet before sale to customer.
Recycled Acrylic Products
Recycled Acrylic products find use in the following application.
- Construction- Sound proof windows and doors, windows mining masks and telephone both.
- Medical- baby incubators, medical and surgical devises.
- Public Goods- Handicrafts, sanitary facilities, cosmetics frames.
- Surface of instrument Panel and Cover.
- Lighting- Fluorescent-lamps, chandeliers, street lamps.
- Advertising –Light boxes, signage, exhibition.
- Transport – Cars, trains and other vehicles, doors and windows.
Reutilization of acrylic scrap in the Acrylic sheet manufacturing process results in a decrease in the environmental impacts and processing costs. In an experiment carried out at the Pan Asia Industrial Company in Thailand using 16000 Kg. of methyl methacrylate monomer in a batch reactor, 1600 Kg. of scrap was generated and 800 Kg. (5%) of this scrap was recycled. This brought about a 6 to 7 % saving in total costs. In addition it resulted in decrease in pollutants and national resource consumption as follows-
Environmental Aspects Unit
Raw Material (Acrylic Monomer) 800 kg/day
Coal 208 kg/day
Oil 472 kg/day
Natural Gas 576 kg/day
Co2 2640 kg/day
Nox 1208 kg/day
Sox 14.4 kg/day
Clty 10.4 kg/day
Dust 2.5 kg/day
BOD 281600 mg/day
Land Conversion 32 m2/800 kg