Development and Performance Analysis of a Mini Twin-Shaft Shredder for Efficient Polyethylene Terephthalate (PET) Bottle Recycling

Abstract

Polyethylene terephthalate (PET) stands out as the most widely recycled plastic globally. However, in the Philippines, the processes associated with PET recycling, particularly the transportation of PET bottles from collectors and consolidators to processing plants, demand significant time, monetary resources, and effort due to the lack of appropriately sized shredder machines in local junkshops to reduce bulkiness. As a response, this study aimed to design a mini twin-shaft PET bottle shredder. The design took into account the constraints and prerequisites of local junkshop proprietors, municipal and barangay local government units, and non-government organizations. The machine was comprised of five essential components: the hopper, shredding chamber, power transmission, prime mover, and frame. Post-consumer PET bottles were employed as test materials for experimentation at different treatment speeds: 30, 40, and 50rpm. The experimental layout followed a completely randomized design (CRD). Performance metrics, including shredding capacity, shredding efficiency, and energy demand, were scrutinized based on shaft speed alterations through analysis of variance testing. Additionally, comparison among means was executed using the least significant difference (LSD) method, with a significance level of 5%. Results indicated that the highest shredding input capacity of 34.07 kg/hr was attained at a shaft speed of 50rpm, along with a shredding efficiency of 91.3%. The presence of unshredded materials was identified as the primary cause of device inefficiency, constituting 6.44% of the total test materials input. The energy demand was calculated at 0.132 kW-hr/kg. The resulting product dimensions primarily ranged between 25-50mm. A cost analysis demonstrated that the machine would need to shred a cumulative 6,889kg of PET bottles to reach the breakeven point, given a custom rate of Php7/kg ($0.12/kg). The initial investment cost of Php124,383 ($2,194.71) could be recuperated in a mere 1.91 years, yielding an added net income of Php210,000/yr ($3,705.40/yr) for PET collectors and/or consolidators.