Recycling of Glass Fiber Reinforced Polyester (GRP) Waste

Turkchem 05 Feb 2018 42 7 dk okuma

TURKCHEM

Abstract

Glass fiber reinforced plastic (GFRP) composite production generates various sizes of end-of-life waste during processes such as edge trimming, molding and assembly hole drilling. Turkey generates approximately 2,500 tons of GFRP waste annually, while worldwide production amounts to around 166,000 tons. These waste materials are typically disposed of by reducing their size, incineration, landfilling, or with additional cost, used as filler material in cement and construction sectors, though this is uncommon. This study systematically examined parameters such as particle size and waste content when ground waste was incorporated into newly produced GFRP-based products, evaluating their effects on material properties.

1. Introduction

Polymeric composites are polymeric matrices reinforced with adequate amounts (by length and weight) of glass fiber and/or other reinforcement materials in thermoset or thermoplastic form, providing single or multi-directional reinforcement properties. Glass fiber reinforced plastic (GFRP), produced from unsaturated polyester resin reinforced with glass fiber, is a high-strength composite material. Applications in aerospace/defense and sports/recreation sectors represent the highest value-added applications for GFRP [1]. GFRP composite production generates various sizes of end-of-life waste during processes such as edge trimming and molding. Polin Waterparks generates approximately 200 tons annually, Turkey generates 2,500 tons, and worldwide production amounts to 166,000 tons. These waste materials are typically disposed of by reducing their size followed by incineration and landfilling, or less commonly, used as filler material in cement and construction sectors with additional disposal costs. Currently, procedures applied nationally and internationally for waste disposal and recovery show similarities. During incineration, carcinogenic micronized carbon particles, polycyclic aromatic hydrocarbons (PAH), carbon monoxide and CO2 gas contributing to global warming are released. Landfilling causes soil contamination [2]. Literature on GFRP waste reuse is generally divided into two categories: studies on direct use of ground waste and studies on fiber recovery. In studies by Correria and Almeida, finely ground (<100 μm) waste GFRP powder was tested as a sand substitute in concrete mixtures at 0, 5, 10, 15, 20 percent by volume. Usage up to 5% showed that GFRP powder improved concrete elasticity, thereby reducing crack tendency [3]. In research by Cunliffe and Williams, GFRP underwent pyrolysis in a fixed-bed reactor at 450°C. It demonstrated that up to 20% of recovered glass fiber from waste could replace virgin glass fiber in DMCs (dough molding compounds) [4]. Iwaya and colleagues worked with supercritical solvents capable of effectively depolymerizing polyester resin in GFRP and separating fiber from filler and resin. Polyester conversion accelerated as the catalyst/solvent molar ratio increased in the presence of catalyst [5]. In research by Kao and colleagues, the effect of recovered glass fibers on mechanical performance was examined using solvolysis (hydrolysis) technology. Subcritical water was used in the chemical reaction for dissolving polyester resin and recovering glass fiber [6]. In research by Kennerley and colleagues, glass fiber was separated from SMC waste using a fluidized-bed reactor at 450°C. No significant changes in physical and mechanical properties were observed up to 50% usage [7]. Although numerous studies addressed complete or partial GFRP recovery, the vast majority followed the framework outlined above. No systematic study in the literature was found where both fiber and resin were jointly evaluated in new formulations. This study systematically examined parameters such as particle size and waste content when ground waste was incorporated into newly produced GFRP-based products, evaluating their effects on material properties. It is considered that incorporating these high-value waste materials into newly produced GFRP products at appropriate particle sizes and/or by improving compatibility to increase matrix-waste interaction could make a significant contribution to increasing waste value-added content and eliminating adverse environmental effects.

2. Method

Waste material was prepared by direct grinding of production scrap. Ground waste at 300 μm, 1 mm and 3 mm particle sizes was added to fresh polyester resin at 5, 10, 15 and 20 percent by weight. Composite samples were prepared by hand lay-up method by processing felt fiber with waste-containing resin. Tensile, three-point bending, impact, short beam strength and ash furnace combustion tests were conducted for characterization of samples containing ground waste. Additionally, gel and cure times and peak cure temperature measurements were performed to investigate the effect of waste addition on the resin cure profile. Compositions and codes of prepared composite samples are given in Table 2.1.

Table 2.1 Compositions and codes of prepared composite samples

3. Results and Discussion 3.1. Mechanical Properties

Mechanical properties of prepared composite samples are given in Table 3.1. With increasing waste content, expected partial reductions in material mechanical strength were observed. This can be explained by weak waste-matrix interfacing, as GFRP waste undergoes only physical recovery and lacks chemical interaction with fresh polyester resin, thus reducing crosslinker concentration in the mixture. At 20% usage of 3 mm waste, average reductions of 50% in tensile and bending strength and 45% in impact strength were observed. Additionally, increasing waste particle size generally resulted in mechanical property losses. Reduction in mechanical strength can be minimized by reducing particle size. Another important effect of waste addition is increased matrix viscosity, requiring higher resin amounts for wetting the same fiber content. Ash furnace testing was performed on prepared composite samples at 650°C to determine their fiber content. While fiber content in the composite was 45.3% when no waste was used, this value decreased with increasing waste usage and particle size. When 20% waste at 3 mm particle size was incorporated into the composite material, fiber content measured 24.3%. This can be explained by GFRP waste containing approximately 25% fiber on average, and with increased waste ratio in the resin, increased viscosity requires more resin for fiber wetting. Since fiber ratios in composites decreased with waste usage, to evaluate the effect of fresh waste and polymeric matrix ratios on mechanical properties at constant fiber ratio, test results were normalized to constant fiber ratio and tensile, bending and impact strength were re-evaluated (Figure 3.1, Figure 3.2, Figure 3.3). Examination of normalized graphs shows that property losses from waste utilization alone are actually at more reasonable levels compared to variations reported in Table 2. Although this effect is similar on impact strength of tested samples, a notable finding is that the rate of impact strength loss decreases with increasing waste particle size. Morphological examinations of fracture surfaces continue to clarify the fracture mechanism during impact.

3.2. Physical Properties

To investigate the effect of waste usage on the resin cure profile and physical properties, gel time, peak cure temperature, peak cure duration, viscosity, linear shrinkage and hardness of reference and waste-containing resins were measured. According to test results, gel and cure times decreased with waste addition. This can be attributed to the presence of crosslinker in the waste. Reduction in peak cure temperature results from decreased bulk polyester content with increasing waste ratio. Increased viscosity and hardness values were observed with waste usage increase. When examining linear shrinkage values before and after post-cure application, waste addition was found to behave like filler in the mixture, reducing polyester linear shrinkage values. Physical properties of waste-containing and waste-free resins used in preparing composite samples are given in Table 3.3.

4. Conclusions

This study systematically examined parameters such as particle size and waste content when ground waste was incorporated into newly produced GFRP-based products, evaluating their effects on material properties. Both increased waste ratio and particle size in composite samples resulted in reduced mechanical strength. Since GFRP waste undergoes only physical processing to powder form and does not participate in chemical bonding, it reduces crosslinker concentration in the mixture. This causes mechanical strength reduction. With GFRP waste containing approximately 25% fiber on average and increased resin viscosity with increasing waste ratio, more resin is required for fiber wetting. This leads to decreased fiber content with increased waste usage and particle size. For this reason, mechanical values were normalized by keeping fiber ratio constant, and when fiber content was identical to the case without waste usage, tensile and bending strengths close to reference composite values were obtained. In continuation of the study, artificial neural networks will be used for modeling to determine the GFRP composition containing the highest waste content while maintaining acceptable physical and mechanical properties. A broad range of application areas for waste-containing products will be prepared, and alternative product spectra will be defined. Sibel Yıldız R&D Engineer Polin Waterparks Selen Gül Güzeliş R&D Engineer Polin Waterparks Assoc. Prof. Dr. Bağdagül Karaağaç Chemical Engineering Department Kocaeli University