JEC COMPOSITES MAGAZINE - Issue #61 - November/December 2010 - 39

FRP recycling technology using subcritical water hydrolysis
Background

Fig. 3: Concept of FRP thermo-setting resin recycling using sub-critical water hydrolysis

Environment

valuable materials such as carbon fibres, resins and other components. Chemists have been trying to develop certain “degradation and rebuilding technologies” with synthetic resins from composites matrices, using supercritical or subcritical water systems. With these technologies, the "bumper to bumper recycling” dream will hopefully come true.

Osaka Prefecture University. Subcritical water is hightemperature, high-pressure water under the critical temperature (374°C). It is known to have a significant hydrolytic capability with high resin affinity due to its ion product content, which is 1,000 times higher than at ordinary temperature, and its low dielectric constant equal to organic solvents.

FRP recycling concept using subcritical water hydrolysis
Figure 3 shows the concept for the subcritical water hydrolysis recycling process applied to the thermosetting resin in FRP . First, unsaturated polyester (UP) is obtained through a dehydration reaction with glycol and organic acid. It is cured with styrene as cross-linking agent, glass fibre and inorganic filler. During cure, styrene develops a styrene cross-linking moiety to form a lattice molecular structure of thermosetting polyester resin. The resin’s ester bonds can be hydrolysed using the significant hydrolytic capability of subcritical water to generate resin raw materials and styrene-fumaric acid copolymer (SFC). The same monomers of resin raw materials are obtained since the ester bonds were generated through dehydration.

Fibre-reinforced plastics are defined as composite materials made of a thermosetting resin and inorganic materials such as inorganic fillers or glass fibre. They are widely used for many products such as bathtubs or pleasure boats due to their lightness and high mechanical strength. They are used in automotive parts to save weight and thus reduce C02 emissions, and trials applying them for automotive body parts have also been conducted. However, their constituent thermosetting resin cannot be re-shaped after the final cure. In addition, they are very difficult to burn since their inorganic material content is about 50-70 wt.%. The total amount of FRP waste in Japan reaches 400,000 metric tons annually and most of it is landfilled, Ieading to a wasteful use of Iimited oil resources. To reduce waste amounts and utilize exhaustible oil resources more efficiently, these materials (including the thermosetting resins) should be recycled, which would be more conducive to a sustainable society. However, there is no effective method available to recycle FRP materials along with the thermosetting resin so, in spite of its weight-saving advantages, FRP is no longer widely accepted because improved recycling rates are now required for automotive parts. Our research aims at establishing an effective horizontal recycling technology that includes thermosetting resin so as to solve the above-mentioned environmental issues. We focused on subcritical water hydrolysis of thermosetting resins and were instructed by Professor Hiroyuki Yoshida of

No61 November - December 2010 / jec composites magazine
Fig. 4: Sub-critical water hydrolysis experiment

Optimizing reaction conditions for subcritical water hydrolysis

Figure 4 shows the experimental results of subcritical water hydrolysis. The experiment started with a reaction temperature higher than 300°C. The reaction liquid collected was black at 360°C for 20 min. Only 20% of the resin can be recycled, and 70% of the decomposing organic ingredients appear to be substances derived from pyrolysis of the styrene

Before reaction

Reaction liquid (360°C, 20min.)

Reaction liquid (230°C, 4h.)

JEC COMPOSITES MAGAZINE - Issue #61 - November/December 2010

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