Development of a process for the recycling of PET fabric waste and its applications

Abstract

The use of silica-coated PET fabrics, specially designed for printing, is continuously increasing and its waste causes serious environmental problems. Pretreatment process including NaOH reaction was developed to remove surface impurity from the fabric wastes as the reaction can dissolve hydrophilic fumed silica. The pretreated PET fabrics can be used to produce commercially valuable items.

In this study, the mechanism of the pretreatment process was proposed and verified. The lab-scale and bench-scale pretreatment processes of silica-coated PET fabric waste were developed based on the dissolution of fumed silica in NaOH solution. The wastewater treatment process was developed by using coagulation-flocculation method with aluminum sulfate (alum). Also commercially valuable products were fabricated with pretreated PET fabrics.

Experimental results from lab-scale pretreatment process showed excellent removal of surface impurity including fumed silica with 5% NaOH reaction in 25 min at $85^\circ C$. The rate constants for dissolution of fumed silica in NaOH solution were evaluated by using the pseudo-first-order reaction model. The ratio of fabric samples to NaOH solution was 1:8 and NaOH solution could be recycled at least 10 times. Results from bench-scale pretreatment process showed successful removal of surface impurity with 5% NaOH solution. Optimized condition was 25 min at $85^\circ C$ with 1:8 ratio of fabric samples to NaOH solution, 60% loading of NaOH solution to drum capacity. To sufficiently remove dye and residual NaOH from fabric samples, the pretreated PET fabrics should be washed at least 4 times.

Results from wastewater treatment process showed that the wastewater generated from the pretreatment of silica-coated PET fabric waste can be treated with conventional coagulation-flocculation process using alum. The optimal pH and coagulant dose for the wastewater treatment were pH 8 and 600 mg/L to give 99.3% color removal. In addition, composition of treated water was within acceptable level for effluent discharge according to the Enforcement Degree of the Water Quality and Ecosystem Conservation Act. from Ministry of Environment.

The glycolysis of pretreated PET fabric to BHET monomer was studied with ethylene glycol (EG) and zinc acetate (ZnAc) catalyst. The experiment results showed that higher BHET monomer yield (89.21% compared to 60.39%) was achieved by the pretreatment process and the purity of BHET monomer was confirmed by qualitative analysis.

In conclusion, pretreatment process of silica-coated PET fabric waste was developed to solve environment problems by recycling of pretreated PET fabrics. Based on the lab-scale and bench-scale experiment results in this study, it was confirmed that scale-up can be applied to develop pilot-plant process. Also NaOH and wash solutions could be re-used to minimize water usage. The wastewater can be treated cost-effectively with alum. The pretreated PET fabrics can be processed by both physical and chemical recycling methods to produce commercial product.