ABSTRACT
Solid waste management is a major problem in Nigeria just like most other developing countries. The major substances composing municipal solid waste include plastic wastes which unlike other solid waste constituents is not biodegradable. Developing a technology such as compression moulding for recycling plastic wastes will be of huge economic benefit to Nigeria. Thus, in this project work, a compression mould with a mould square shaped articles to curing at a very low temperatures less than 80oC is developed. This was done in order to increase the number of articles with higher compressive and flexural strength to be moulded per time, as well as prevent excess material loss during compression is designed and fabricated.
Three conceptual designs for the compression mould were drawn based on selected considerations and requirements. The best conceptual design was selected for detail design and fabrication using decision matrix. A manually actuated hydraulic compression mould machine for the recycling of plastic wastes was designed and fabricated for the compression moulding of electrical wall plates and other related wares. The machine consists of key components such as hydraulic press, the mould, electrical heating element and melting crucible. The fabricated compression mould had a length, width and height of 400mm by 150mm by 900mm respectively and was made with U-section mild steel. It had a movable platen carrying the upper mould and sitting on top of a hydraulic press which pushes it towards a fixed platen carrying a lower mould during compression of the molten plastic. The lower platen also had an electric heater which keeps it from solidifying prior to compression and a water-cooling reservoir to reduce the curing time during compression. The machine was tested and evaluated for performance using several types of plastics wastes. During operation, molten plasticize stock were poured into a mould of dimension 100 mm x 100 mm x 100 mm and were subjected to compression, then cooled under a water shield in a cooling tank and their curing time and temperature observed.
The compression mould was fabricated with mild steel with each of its structural members welded, while the cooling tank was fitted in order to perform experimental studies for observing curing temperature and time by using ambient air or water. Findings from the research showed that the machine throughput capacity was computed as 82% when air cooled and 84% when cooled by water. Similarly, the required total surface area and volume of plastic waste the mould can take was determined as 0.56 m2 and 0.024 m3. It was observed that the finished product after compression moulding weighed a little below the feed stock. Also, the feedstock and product weight ratio was high resulting in minimal material waste. During the operation, the use of polyvinyl chloride (PVC) materials led to improper melting which produces a highly, non-flow viscous molten rubber which solidifies with little exposure to air. The polyethylene terephthalate (PET) was brittle in nature, and during compression it resulted to breaking, cracking and shattering. The high density polyethylene plastics (HDPE), low density polyethylene plastics (LDPE) and polypropylene plastics (PP) melted, flowed and solidified well on heating, compression and forming. The HDPE, LDPE and PP materials melted on heating in 25 minutes while solidification in atmospheric condition took 90 minutes and 15 minutes when cooled by water.
More so, it was observed that the curing time and temperature greatly reduced for specimens that were cooled under a water shield in the cooling tank. It was therefore concluded that the compression mould machine was suitable for plastic forming with less post compression shaping with the use of less compression force, hence should be useful in plastic waste recycling.
