# Recycling Technology of Fiber-Reinforced Plastics Using Sodium Hydroxide

K Baba, T Wajima

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K Baba, T Wajima. Recycling Technology of Fiber-Reinforced Plastics Using Sodium Hydroxide. Mechanics, Materials Science & Engineering MMSE Journal. Open Access, 2017, 9, 10.2412/mmse.8.14.523. hal-01503670

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Submitted on 7 Apr 2017

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Distributed under a Creative Commons Attribution 4.0 International License
# Recycling Technology of Fiber-Reinforced Plastics Using Sodium Hydroxide

K. Baba¹, a, T. Wajima¹

1 – Department of Urban Environment System, Chiba University, 1-33, Yayoi-cho, Chiba 263-8522, Japan

a – afsa3284@chiba-u.ac.jp

<figure><img src="image_2.png" /></figure>

DOI 10.2412/mmse.8.14.523 provided by [Seo4U.link](https://link.springer.com/10.2412/mmse.8.14.523)

**Keywords:** fiber-reinforced plastics, sodium hydroxide, pyrolysis, silica extraction.

**ABSTRACT.** Glass fiber-reinforced plastics (GFRP) are high strength materials by reinforcing resin with glass fiber, and are increasing annually because FRP is a light weight with high corrosion resistance. However, disposal treatment of it is difficult due to its high stability, and cause illegal waste dumping of big GFRP products, such as ship, bath, tank and so on. In this study, we attempted to convert plastic and glass fiber in the FRP into gas, oil and water glass using sodium hydroxide reaction, respectively. GFRP was cut into the peace with the diameter of 1 cm. Sample peaces (4g) and sodium hydroxide (2g - 12g) put into the reactor, and the reactor was heated with an electric furnace while flowing nitrogen (160 mL/min). After heating to setting temperature (300 - 450 °C) for 1 h, the reactor was naturally cooled to room temperature. The generated gas and oil during the reaction was collected by gas pack and oil trap, respectively. After cooling, the residue inside the reactor was washed with distilled water, and filtrates to obtain the residual substance, and silicon concentration in the filtrate was measured to calculate the silicon extracted content from GFRP. By using pyrolysis with sodium hydroxide, GFRP can be decomposed by correcting the resin into the gases, such as hydrogen and methane, and glass fiber into soluble salt in order to be extracted into the solution. GFRP can be decomposed by pyrolysis with NaOH above 400°C.

**Introduction.** Glass fiber-reinforced plastic (GFRP) is light weight, high strength and high durability, and is widely used worldwide for bath tubs, automobile parts, railway car parts, small ships, etc [1]. In Japan, GFRP has been used since 1955 and its production has gradually declined after reaching 480,000 ton in 1996. On the other hands, the amount of discarded FRP is increasing year by year. Most of waste GFRP is disposed of by incineration or landfill, and 2% of waste GFRP is recycled as cement raw fuel or concrete additive [2, 3]. GFRP is molded by combining an organic matter of a thermosetting resin, such as an unsaturated polyester resin, and an inorganic material of glass fibers. It is difficult to recycle FRP. Because the resin does not reform is not soluble in any solvents, the amount of heat generated by GFRP is too small to use as fuel due to the glass fiber contents. Therefore, in Japan, the development of resource recycling technology of GFRP is promoted by enactment of law on recycling. As a current GFRP recycling method, a chemical recycling method of decomposition using a solvent [4] or subcritical water [5] has been studied. However, these chemical recycling methods for waste GFRP are the high cost by high temperature and high pressure, so it has not yet been put into practical use.

In this study, we attempted to develop a new recycling technology for thermal decomposition method using sodium hydroxide for recovering gas, oil and glass from waste GFRP at normal pressure and low temperature.

**Material and Methods.** The sample used in this study is waste GFRP obtained from one of the intermediate treatment contractors in Japan. GFRP was cut for use as a sample (size: 1.0 × 1.0 × 0.05 cm) as shown in Fig. 1.
The experimental apparatus is shown in Fig.2. GFRP(4g) and NaOH(2 – 12g ) put into the reactor, and heated to setting temperatures with an electric furnace while flowing nitrogen (160 mL/min). After heating to setting temperature, the reactor was heated for 1-h, and then naturally cooled to room temperature. Since the residual substance was included in fused salt solid, it dissolves in distilled water, and filtrates to obtain the residual substance in the reactor. After filtering, the residue remaining on the filter paper was observed, and the weight of the residual was measured to calculate residual weight ratio. The amount of silicon extracted into the filtrate was analyzed by an atomic absorption spectrophotometers (AAnalyst200, Perkin-Elmer). During the experiment, the gas generated in the reactor pass through the water bubbling bottle to capture the halogen content in the gas, then the passing gas was collected in gas pack. The collected gas was analyzed by a gas chromatograph (GC-2014ATF, SHIMADZU).

<figure><img src="image_3.png" /><figcaption>Fig. 1. Photo of GFRP samples(left) and GFRP after cutting (right).</figcaption></figure>

<figure><img src="image_4.png" /><figcaption>Fig. 2. Experiment apparatus.</figcaption></figure>

**Result and discussion.** Figure 3 shows the photos of the residues with various NaOH addition. The reaction time is 1-h and the reaction temperature is 400 °C. Without addition of NaOH, GFRP could not be decomposed and remained piece with glass fiber can be observed (Fig.3(a)). With addition of NaOH(Fig.3(b)~(d)), the resin and the glass fiber were not observed due to the decomposition of resin and glass fiber by pyrolysis with NaOH.

<figure><img src="image_5.png" /><figcaption>Fig. 3. The residue after the pyrolysis with addition of NaOH of (a) 0 g, (b) 4 g, (c) 8 g and (d) 12 g.</figcaption></figure>
Figure 4 shows the residual weight ratio of the residue after pyrolysis with without NaOH addition. While 90% weight of raw sample was remained by pyrolysis without NaOH, the residue weight decreases by pyrolysis with sodium hydroxide.

<figure><img src="image_6.png" /><figcaption>Fig. 4. Residual weight ratio of the residual after pyrolysis with different NaOH addition.</figcaption></figure>

Figure 5 shows the product gas during the experiment (Fig. 3(a) ~ (d)). Production of gas without NaOH is lower than those with NaOH. Production of hydrogen gas and methane gas was confirmed, and the production of hydrogen and methane gas increased with increasing sodium hydroxide addition.

<figure><img src="image_7.png" /><figcaption>Fig. 5. The product gas from GFRP using pyrolysis with sodium hydroxide.</figcaption></figure>

Figure 6 shows Si content extracted from the residue of the pyrolysis. While Si content could not be extracted from the residual of the pyrolysis without NaOH. Si content could be extracted from the residue of the pyrolysis with sodium hydroxide. With increasing NaOH addition, a larger amount of Si can extracted into the solution.

The weight of GFRP was reduced by decomposing the resin into gas and extracting the glass fiber into the filtrate by pyrolysis with NaOH. Figure 7 shows the photos of the residue of the pyrolysis with NaOH at various temperatures. The reaction time is 1-h and NaOH addition is 1 g/g. At 300°C, the form of GFRP remained, and decomposition of the resin and the glass fiber could not be observed
(Fig. 7(e)). At 350°C, decomposition of the resin could be observed, and decomposition of the glass fiber could not be observed (Fig. 7(f)). At 400 and 500°C, decomposition of both resin and glass fiber was observed (Fig. 7(h)).

<figure><img src="image_8.png" /><figcaption>Fig. 6. Si content extracted from residue after the experiment.</figcaption></figure>

<figure><img src="image_9.png" /><figcaption>Fig. 7. The residue after the experiment at (a) 300°C, (b) 350°C, (c) 400°C and (d) 500°C.</figcaption></figure>

Figure 8 shows the residual weight ratio of the pyrolysis at various temperatures. With addition of sodium hydroxide with increasing the reaction temperature, the residual weight decrease.

<figure><img src="image_10.png" /><figcaption>Fig. 8. Residual weight ratio of the residue of the pyrolysis at different reaction temperatures.</figcaption></figure>
Figure 9 shows the product gas by pyrolysis at various temperature, with NaOH addition. Regardless of reaction temperatures production of hydrogen gas and methane gas was confirmed by pyrolysis with sodium hydroxide. A larger amount of methane and hydrogen gases can be generated, with increasing the reaction temperature.

<figure><img src="image_11.png" /><figcaption>Fig. 9. Product gas from the GFRP using pyrolysis with sodium hydroxide at different temperature.</figcaption></figure>

Figure 8 shows Si content extracted from the residue of the pyrolysis at various temperature. Si can be extracted from the residue of the pyrolysis with NaOH above 400°C, while at 300°C and 350°C, extracted Si content was not confirmed.

<figure><img src="image_12.png" /><figcaption>Fig. 10. Si content extracted from the residue of the pyrolysis with NaOH at various temperatures.</figcaption></figure>

From these results, GFRP can be decomposed by the pyrolysis with NaOH above 400°C.

**Summary.** In this study, we attempted to decompose GFRP using pyrolysis with sodium hydroxide. By using pyrolysis with sodium hydroxide, GFRP can be decomposed by correcting the resin into the gases, such as hydrogen and methane, and glass fiber into soluble salt in order to be extract into the solution.

**References**
[1] K. Shibata, FRP Recycling Technology, NetworkPolymer, Vol.28 (4), 2007, 43-48. DOI: 10.11364/networkpolymer1996.28.247

[2] A. Kondo, Development of Light Weight Materials with Low Thermal Conductivity by Making Use of Waste FRP, J. Soc. Powder Technol, Vol.47, 2010, 768-772 DOI: 10.4164/sptj.47.768

[3] F. Yoshimichi, I. The Present Conditions of GFRP which Aimed at the Environmental Load Reduction, The Society of Materials Science, Vol.57(6), 2008, 621-625, DOI: 10.2472/jsms.57.621

[4] T. Iwata, Recycling of fiber Reinforced Plastics Using Depoly-merization by Solvothermal Reaction with Catalyst, Journal of Materials Science, Vol.43, 2008, 2452-2456, DOI: 10.1007/s10853-007-2017-8

[5] T. Nakagawa, FRP Recycling Technology Using Subcritical Water Hydrolysis, NetworkPolymer, Vol.27, 2006, 88-95, DOI: http://doi.org/10.11364/networkpolymer1996.27.88

Cite the paper

K. Baba, T. Wajima, (2017). *Recycling Technology of Fiber-Reinforced Plastics Using Sodium Hydroxide*. Mechanics, Materials Science & Engineering, Vol 9. Doi 10.2412/mmse.8.14.523