熊本大学学術リポジトリ. Kumamoto University Repositor

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1 熊本大学学術リポジトリ Kumamoto University Repositor Title Recycling of arbon Fiber and Epoxy arbon Fiber Reinforced Plastics Author(s) 柴田, 勝司 itation Issue date Type URL Thesis or Dissertation Right

2 Recycling of arbon Fiber and Epoxy Resin from arbon Fiber Reinforced Plastics March 2014 Katsuji Shibata Graduate School of Science and Technology KUMAMT UNIVERSITY 1

3 Recycling of arbon Fiber and Epoxy Resin from arbon Fiber Reinforced Plastics ( 炭素繊維複合材料から回収した炭素繊維及びエポキシ樹脂のリサイクル技術の開発 ) Abstract(within 1600 words) 1. Introduction Since fiber reinforced plastics (FRP) have high strength and durability in lightness, these have been widely used for sporting goods, bathtubs, automobiles, railway vehicles, boats, etc. owever, because thermosetting resins (thermosets) used for FRP neither melt nor dissolve, recycling of FRP is very difficult. We have developed the technology to recover materials from FRP by dissolving the resins. FRP is classified by the types of the reinforced fibers. GFRP using glass fiber has the highest market share. Next, there are a lot of FRP that uses carbon fiber. The common chemical recycling technologies of thermosets are pyrolysis and solvolysis. They are often carried out with supercritical fluids. Pyrolyses damage fiber and filler because of high temperature. Supercritical fluid methods require high-pressure vessels that are usually expensive. Solvolyses are carried out under mild conditions. But they need long treatment time without appropriate catalysts and solvents, or require crushers and grinders. 2. Previous Works Printed wiring board (PWB) wastes are composite of metals, glass fiber, paper, fillers, devices and plastics. In studying reactions of epoxy resins for glass-epoxy laminates, we found depolymerization of brominated epoxy resins. We tried to apply this reaction to recycling of PWB, then found the effective catalysts for this depolymerization. Finally, we applied these solutions to PWB wastes made of brominated epoxy-glass cloth laminate, obtaining separated recyclates such as electronic devices, glass cloth, copper foil depolymerized epoxy resin. In the next stage, we applied the method of dissolving resins under ordinary pressure to GFRP. In this method, tripotassium phosphate (K 3P 4) is used as a catalyst and benzyl alcohol (BZA) as a solvent at 190 under ordinary pressure. These chemicals are both food additives. Depolymerized resins, fibers, fillers and metals are separated and recovered by this method. The processing time is from 5 to 20 hours. This method needs no preprocessing such as grinding or crushing. We treated helmets made of GFRP treated by the method then obtained GF, filler and depolymerized UP. GF recovered from GFRP is 20 mm or more in length. Nonwoven fabric of the recovered GF can be made by the dry process or the wet process. In the dry process, a carding machine which is usually used to manufacture futon cotton is useful. In the wet process papermaking machine can be used. The tensile strength of recycled GFRP that uses nonwoven 2

4 fabric was lower than new one by 30 %. But, it is applicable to some uses which do not require high strength. AFRP is used for aircraft materials and concrete reinforcement. AF is difficult to separate from AFRP molded with EP. Since AF decomposes at about 500, EP cannot be removed from AFRP by pyrolysis or supercritical fluids. The method of dissolving resin under ordinary pressure is the only method to recover AF from AFRP. Aramid rods made of AFRP are used for concrete telephone poles. They were treated for 25 h at 190, then AF was recovered. With recovered AF, nonwoven fabric is made by the same dry process as GF and F. 3. Recovering F and EP from FRP Epoxy resin cured with acid anhydride is mainly in FRP matrix. This is applied to golf club, tennis racket and aerospace parts, but is difficult to recycle. We estimated that cured epoxy resin can be depolymerized by transesterification with mono alcohols, and then be dissolved in solvent. Various FRP products could be dissolved by depolymerization under ordinary pressure. For example, tennis rackets and badminton rackets were dissolved in 8 hours. The nonwoven fabrics were produced by the dry or wet process similar to GF from the recovered cotton-like F. We produced the recovered F nonwoven fabric using a carding machine. 4. Recycling of Recovered F The investigated materials are non-woven fabrics of F (rf) recovered by our method from depolymerized FRP-moldings and tennis rackets. We compared the properties of the non-woven fabric of our recovered F by depolymerization with those of the commercially available TRAYA Mat and the recovered F by pyrolysis process. The resin used was Bisphenol-A type EP cured with anhydride. We evaluated the tensile properties and the surface of F monofilaments. The tensile properties of F monofilaments were measured in accordance with JIS R The surfaces of the rfs were not damaged and clean as TRAYA. We produced non-woven fabric of rfs by using a carding machine. The recycled FRP (rfrp), which is composed of non-woven fabric and Bisphenol-A type EP cured with anhydride, was manufactured by compression molding. The volume content of fiber (Vf) was between 0 % and 40 %. The thicknesses of FRP-m, Racket and TRAYA increase with increasing Vf when Vf is larger than 30 %. We speculated that when the density of non-woven fabric is low, the 3

5 compression molding does not proceed properly due to the bulkiness of the fabric. n the contrary, in the case of Takayasu, which has high density, the thickness of FRP was almost constant even at the high Vf of 40 %. Looking at the cross-section, some voids were observed in FRP-m and Racket of 40 % Vf. We considered the cause of the void was that EP couldn t be impregnated properly due to bulkiness of the fabric which hinders the compression of the resin and fabric. In the FRP of Takayasu and TRAYA, voids were not observed. So, it may be necessary to improve the density of the fabric to enhance the moldability of rfrp. We dissolved rfrp and evaluated the F length varying Vf from 10 % to 40 % after compression molding. The length of F of 40 % Vf was shortened by about 1 mm~2 mm comparing with the length of about 30 mm at Vf of 10 % in FRP-m, Racket and TRAYA. We thought that the breaking of fiber may be caused by the increased contact point of fibers of high Vf. n the other hand, the ratio of cut fiber was low in Takayasu. We evaluated mechanical properties of rfrp using non-woven rf fabrics following JIS K 7073 (tensile properties), JIS K 7074 (flexural properties) and JIS K 7077 (harpy impact strength). The mechanical properties increased with increasing Vf, but after reaching a maxima, decreased with further increase in Vf. We thought that the cause of the non-linear relation was the imperfect molding and increased ratio of shortened fibers. 5. Recycling of Recovered EP Acid anhydride (Ah) cured EP (EP/Ah) usually used as the matrix resin of FRP has ester bond by the reaction between epoxy group and anhydride. So, we investigated the depolymerization of EP/Ah under ordinary pressure and found that EP/Ah easily dissolves into BZA in standard conditions, finally recovering the carbon fiber. We used model compounds of EP/Ah for analysis. The model epoxy was phenylglycidylether (PGE) and the model Ahs were succinic anhydride (ScAh), cis-1, 2-cyclohexanedicarboxylic anhydride (hah), cis-4-cyclohexene-1, 2-dicarboxylic anhydride (heah). The model compounds consisting of PGE and Ahs were introduced in a test tube. The reactive mixture was heated at 80 for 1.0 h followed by heating at 150 for 1.0 h. In order to analyze the depolymerization, the model compounds, BZA and K 3P 4 were introduced in a test tube, then were heated at 180 for 10.0 h. For identification of products, we used 1 NMR and 13 NMR. Model compounds were dissolved in d6-dimethylsulfoxide (d 6-DMS). The model compounds were synthesized stoichiometrically by the reaction between PGE and Ahs with catalyst. While, the depolymerization of PGE/Ah model compounds, we found that dibenzylester and bisdiol are formed by the depolymerization of the thermosets under ordinary 4

6 pressure. The depolymerization mechanism of PGE/Ah was the transesterification with BZA, so we concluded that the depolymerization were mainly transesterification reaction accelerated with K 3P 4. We have developed the depolymerization of thermosets by using subcritical fluids. Insoluble or slightly soluble thermosets like Am cured EP was possible to be depolymerized in a short time by this method. In order to analyze the mechanism of EP/Am depolymerization, bisphenol A diglycidylether (DGBPA) was used as the model matrix. Isophrondiamine (IPDA) and 2,4,6-tris(dimetylaminomethyl) phenol (DMAmP) were used as the curing agent and catalyst. The selected model compounds of Ams were dicyclohexylamine (DhAm), N,N-dicyclohexylamine (DhMeAm), dibenzylamine (DBzAm) and tribenzylamine (TBzAm). DGBPA, IPDA and DMAmP of the ratio of 100:25:2 were mixed, then were heated at 80 for 0.5 h. The additional heating was 150 for 1.0 h. The obtained cured EP of about 5 mm thick was cut into 10 mm 15 mm for further testing. A piece of a model matrix, BZA and K 3P 4 were introduced into tube bomb reactor, then heated at 250 to 325 for 1.0 h to 4.0 h. To depolymerize Am compounds, BZA and K 3P 4 were introduced in the reactor, then heated at 280 for 6.0 h. The test pieces dissolved perfectly after 4.0 h at 325. It was difficult to analyze the depolymerization products of EP which has cross-linked three-dimensional networks. To identify the structure of products, Am compounds and depolymerization products were measured with NMR. The cleavage of the -N bond didn t occur in alicyclic Am by the depolymerization reaction. n the other hand, we found that there was the possibility of cleaving the -N bond in aromatic Am compounds with the depolymerization reaction by subcritical fluids. Because IPDA is alicyclic Am,the cleavage of the ether linkage (--) or transetherification may occur. 5

7 Table of ontents Abstract 1. Introduction Previous Works Recycling of Printed Wiring Board (PWB) Recycling of Fiber Reinforced Plastics (FRP) Recovering F and EP from FRP Recycling of Recovered F Recovered F Nonwoven Fabric Recycled FRP Recycling of Recovered EP Anhydride ured EP Amine ured EP onclusion References 6

8 1. Introduction 1.1 Background Since fiber reinforced plastics (FRP) have high strength and durability in lightness, these have been widely used for sporting goods, bathtubs, automobiles, railway vehicles, boats, etc. owever, because thermosetting resins (thermosets) used for FRP neither melt nor dissolve, recycling of FRP is very difficult. We have developed the technology to recover materials materials from FRP by dissolving the resins. FRP is classified by the types of the reinforced fibers. GFRP using glass fiber has the highest market share. Next, there are a lot of FRP that uses carbon fiber. AFRP using aramid fiber is used in an architectural field. These FRPs can be recycled by the method of dissolving thermosets under ordinary pressure. 1.2 omparison with onventional Technologies The common chemical recycling technologies of thermosets are mainly pyrolysis and solvolysis (Table 1). Table 1 omparison of chemical recycling methods of thermosets Method Pyrolysis Supercritical Solvolysis Gas phase Vegitable oil Fluid Liquid phase Glycolysis ur method Temperature 250~ ~ ~ ~ Pressure closed,ordinary ordinary 2~22MPa ordinary~ 2MPa ordinary~20mpa ordinary Solvent no vegetable oil water,alchol, phenol hydrogen donor solvent glycol alcohol atalyst no no no salt acid or alkali salt Grinding size <10mm <5mm <1mm <5mm <1mm - Recyclate gas,oil oil monomer monomer,oil ligomer ligomer Japan arbon Fiber Manufacturers Association (JMA) started working on FRP recycling in ). JMA made a FRP pyrolysis plant for recovering milled F at muta ity, Fukuoka Prefecture, that are taken over by Toray Industries, Inc., Toho Tenax o., Ltd. and Mitsubishi Rayon o., Ltd..from kajima et al. 2), 3) developed FRP recycling to decompose EP with supercritical methanol or acetone at 250 for 2 h in a 5 L pressurized vessel. The decomposed products are obtained by the ester bond cleaved selectively. 7

9 M. Goto et al. 4), 5) at Kumamoto University investigated recycling of FRP with subcritical benzyl alcohol at This method needed lower pressure than the methods with other supercritical or subcritical fluids. S. J. Pickering et al. 6), 7) at University of Nottingham have developed the method of recovering F from FRP with supercritical propanol. This method needs lower temperature than one with supercritical water. M. Kubouchi et al. 8) at Tokyo Institute of Technology have investigated dissolving amine cured EP with nitric acid at 80 for 100 h. The cured EP that consisted of 25 % recovered EP and 75 % fresh EP with anhydride as curing agent had higher glass transition temperature and higher bending strength than that of all fresh EP. Mizuguchi et al. 9) at Shinshu University have developed the FRP recycling technology on the basis of the thermal activation of semiconductors (TAS). TAS enables to decompose polymer matrices of FRP into 2 and 2 in min at about , yielding F or GF without damage. Pyrolyses damage fiber and filler because of high temperature and oxygen. Supercritical fluid methods require high-pressure vessels that are usually expensive. Solvolyses are carried out under mild conditions. But they need long treatment time without appropriate catalysts and solvents, or require crushers and grinders. We regard cost efficiency as most important to put a recycling technology to practical use; consequently we have been searching for a simple recycling process. 8

10 2. Previous Works 2.1 Recycling of Printed Wiring Board (PWB) 9)-14) Printed wiring board (PWB) wastes are composite of metals, glass fiber, paper, fillers, devices and plastics. These components consist of various kinds of raw materials. Moreover, plastics used in PWB often contain halogens for flame retardancy. As they are difficult to separate into recyclable materials and to incinerate, they are mainly landfilled. Laminates used for PWB are divided broadly into paper-phenol laminates and glass-epoxy laminates. The former is used more than the latter, but the latter has been increasing recently for IT instruments. In studying reactions of epoxy resins for glass-epoxy laminates, we found a depolymerization of brominated epoxy resins or brominated polyhydroxyethers made from bifunctional epoxy resins and bifunctional phenols. We tried to apply this reaction to glass-epoxy laminates recycling, especially for the separation of materials used in PWB. First, we studied the mechanism of these polymers' degradation, then we clarified the mechanism of depolymerization into raw materials, epoxy resins and phenols. Then we found the effective catalysts for this depolymerization. Finally, we applied this technology to PWB wastes Experimental (1) Materials hemicals used as solvents and catalysts are shown in Table 2. Table 2 hemicals used as solvents and catalysts hemicals abbr. Phenylglycidylether PGE Tribromophenol TBPh N,N-Dimethylformamide-d7 DMF-d7 yclohexanone N Diethylene glycol monomethyl ether DGMM N-methyl-2-pyrrolidone NMP Potassium hydroxide K Potassium iodide KI Potassium bromide KBr Potassium chloride Kl Sodium hydrogen carbonate Na3 Sodium iodide NaI Sodium bromide NaBr Sodium chloride Nal Lithium hydroxide Li Lithium iodide LiI Lithium bromide LiBr Lithium chloride Lil 9

11 All the chemicals used were reagent grade supplied by Kanto hemical o., Inc. Japan. Brominated epoxy polymer model compound 1-(2,4,6-tribromo-phenoxy)- 3-phenoxy- 2-propanol (TBPP) was prepared in our laboratory by reaction of phenylglycidylether with 2,4,6-tribromophenol. (2) Laminates Preparation Laminates No. 1 and No. 2 shown in Table 3 were commercial products by itachi hemical o., Ltd. Japan. Laminate No. 3 was prepared from brominated epoxy resin, brominated polyphenol and glass cloth with molding press. (3) NMR Analysis 13 -NMR spectra were measured at room temperature on a Brucker 400 Mz NMR spectrometer. Previously NMR spectra of TBPP solution in DMF-d7 were measured. The samples were heated at 120 for 4.0 h and measured every hour. (4) Molecular Weight Determination Weight-average molecular weights of polymers were determined with a gel-permeation chromatograph supplied by Tosoh o. Ltd. Japan. Standard polystyrenes used for calibration and columns of styrene gel were also from Tosoh o. Ltd. Japan. (5) Solubility Measurement Table 3 Laminates omposite No.1 No.2 No.3 commercial commercial prepared uring Agents Polyphenol Dicy Polyphenol Br contents 15% 20% 28% Fiber Resin contents uring Temp. E-glass cloth 47% 170 /90min Laminates were in the form of 10 mm X 30 mm test pieces. Each had a thickness of about 0.2 mm. The test pieces were weighed and put into the solutions at for h. The pieces were taken out from the solution, then dried and weighed again. Solubility of laminates was calculated by the next equation Results and Discussion (1) Model ompound Decomposition The decomposition of 1-(2,4,6-tribromo-phenoxy)-3-phenoxy-2-propanol (TBPP) as a model 10

12 compound of brominated epoxy polymer was observed with Li as a catalyst at 120 for 4.0 h. In Table 4, 13 -NMR spectrum data of reactant and reaction products are shown. Before heating, there were only signals of TBPP. Upon heating, TBPP signals gradually weakened, and new signals appeared. Table NMR spectra of TBPP decomposition (in DMF-d 7, at 120 ) ppm h h h h The new signals are found to be ones of phenylglycidylether (PGE) and lithium 2,4,6-tribromophenolate (TBPh-Li), with a small amount of by-product, 1-phenoxy- 2,3-propandiol (PPD). TBPh-Li will be able to change into TBPh by reacting with water. PGE and TBPh are the raw materials of TBPP, so this reaction seems to be a reversible reaction. TBPP decomposition is described schematically in Figure TBPP Br Br Br PGE PPD Li Br Br Br TBPh-Li Figure 1 Scheme of TBPP decomposition (2) Depolymerization of Brominated Epoxy Polymer As TBPP can be cleaved at the oxygen atom linked with a brominated benzene ring, epoxy polymers can also be cleaved at the ether linkage. Depolymerization of brominated epoxy polymer at several concentrations of Li as a catalyst are given in Figure 2. The molecular weight (Mw) of brominated epoxy polymer did not change without a catalyst, but increasing the concentration of a catalyst, Mw of the polymer decreased more rapidly. Moreover, the 11

13 concentration of a catalyst decided the Mw at the end points of the depolymerized polymers. Mw of this particular polymer decreased from 332,000 to 35,000 with 0.10 mol catalyst at 120 for 6.0 hr. (3) Solubility Measurement PWB wastes from electronic instruments were mainly made of brominated epoxy polymers, glass cloths and copper circuits. If epoxy polymers dissolve into some solution, glass and copper easily separate. In the mechanism of brominated epoxy depolymerization, bromine content (Br content) influences the rate of the depolymerization. shows a relationship between bromine content and solubility of laminates. As Br content increased, solubility of laminates also increased. 28% Br content laminate has high solubility, compared to lower Br content laminates. But 20% Br content laminates are most common now, so that type was used next. The laminate solubility in the solutions of alkali metal compounds as catalysts are shown in Figure. It shows K, Na 3 and Lil are better catalysts for the solubility of 20% Br content laminates. Not only alkali metal hydroxide, but alkali metal salts are also Mw (*1000) Solubility (%) 40 atalyst : Li 0mol mol mol 0.20mol 0.10mol mol eating time (h) Figure 2 Depolymerization of brominated epoxy polymers with various amount of Li as catalyst Br ontent (%) Figure 3 Relationship between bromine content and solubility of brominated epoxy laminates 12

14 useful. Without a catalyst, the solubility value was as low as 1%. The effect of combinations of catalysts and solvents are shown in Figure. atalysts No atalyst K KI KBr Kl Na3 NaI NaBr Nal LiI LiBr Lil Solubility (%) Figure 4 Solubility's of brominated epoxy laminates with various alkali metal compounds as catalysts atalysts No atalyst K Lil LiI N DGMM Solubility (%) NMP Figure 5 Solubility of brominated epoxy laminates with combination of catalysts and solvents 13

15 NMP is a good solvent for K catalyst, and N is good for LiI. Figure 6 shows the relationship between temperatures and the solubility of brominated epoxy laminates. In these investigations K in NMP and LiI in N were used as catalysts in solutions. K / NMP was able to dissolve the laminates more rapidly than LiI / N. The solubility in both solutions are much higher over 140 than at lower temperatures. Figure 7 Relationship between catalyst concentration and solubility of brominated epoxy laminates shows the relationship between concentrations of catalysts and the laminate solubility. This chart indicates the difference in the solubility between two solutions. The solubility for K / NMP increased, along with an increase in concentration. Whereas, LiI / N had the maximum solubility at the concentration of 3.0 mol /1000 g solvent Solubility (%) 40 Solubility LiI/N 30 K/NMP 30 K/NMP LiI/N Temperature (deg ) oncentration (mol/1000 g solvent) Figure 4 Relationship between temperature and solubility of brominated epoxy laminates Figure 5 Relationship between catalyst concentration and solubility of brominated epoxy laminates Application to PWB Waste Finally, we applied these solutions to PWB wastes made of brominated epoxy-glass cloth laminate. Figure 8 shows separated recyclates from a PWB waste with electronic devices. The recyclates are electronic devices, glass cloth, copper foil depolymerized epoxy polymer.. 14

16 PWB waste with electronic devices Separated devices on glass cloth Separated electronic devices Separated glass cloth Separated circuits chiefly made of copper Depolymerized brominated epoxy polymer solution in NMP with Lil as a catalyst Figure 6 Recyclates from PWB waste with electronic devices 15

17 2.2 Recycling of Fiber Reinforced Plastics (FRP) 15)-23) The method of dissolving resins under ordinary pressure In this method transesterification reaction is used to dissolve the resins of FRP at 190 under ordinary pressure. Tripotassium phosphate (K 3P 4) is used as a catalyst and benzyl alcohol (BZA) as a solvent. These chemicals are both food additives. Depolymerized resins, fibers, fillers and metals are separated and recovered by this method. The processing time is from 5.0 h to 20.0 h, depending on the thickness, the kind of resins and manufacturing process of FRP. If FRP is previously ground, the processing time can be shortened remarkably, but the recovered GF is also shortened resulting in the low reinforcement for FRP. This method needs neither preprocessing such as grinding nor an autoclave, and so it is more economical than other recycling methos. In addition, as the method is dust free, there is no risk of pneumoconiosis and dust explosion. Thus, this method is advantageous in the health and safety Glass fiber composite material (GFRP) GFRP is mainly made from glass fiber (GF), unsaturated polyester resin (UP) and filler. It is necessary to separate these materials in order to recycle GFRP. Each material can be separated and recovered by the method of depolymerizing and dissolving UP under ordinary pressure. Figure 9 shows helmets made of GFRP treated by the method with the passage of time. 16

18 Before treatment After 0.5 h After 2.5 h After 5.0 h Figure 7 FRP helmets treated by the dissolving method GF recovered from GFRP is 20 mm or more in length. owever, the recovered GF is a form of cotton, which is not applicable to GFRP, while nonwoven fabric of the recovered GF made by the dry process or the wet process can be applicable to FRP. In the dry process, a carding machine which is usually used to manufacturing futon cotton is useful. In the wet process papermaking machine can be used. The recovered GF nonwoven fabric made with dry process is shown in Figure

19 Figure 8 Recovered GF nonwoven fabric The tensile strength of recycled GFRP that uses the nonwoven fabric was lower than new one by 30 %. But, it is applicable to some uses which do not require high strength Aramid fiber composite materials (AFRP) 14) Aramid fiber (AF) has two kind of chemical structures which are para-aramid and meta-aramid. Para-aramid which has high strength and high modulus is used for tire cords, conveyer belts, protective clothing, etc. While meta-aramid which has flame retardancy and heat resistance is used for filters, wire coverings, and flame retardant clothing, etc., it is hardly used as composite materials. As for AFRP, para-aramid is chiefly used, and there are a lot of use of aircraft materials and concrete reinforcement. AFRP molded with EP is difficult to separate AF. Since AF decomposes at about 500, EP cannot be removed from AFRP by pyrolysis. Supercritical fluids also degrade AF remarkably, and are not applicable for the recovering. The method of dissolving resin under ordinary pressure is the only method that is announced to be able to recover AF from AFRP. Aramid rods made of AFRP are used for concrete telephone poles. They were treated for 25.0 h at 190, then AF was recovered. The recovered AF is shown in Figure

20 Before treatment After 20.0 h Figure 9 An aramide rod made of AFRP treated by the dissolving method With recovered AF, nonwoven fabric is made by the same dry process as GF and F. AF nonwoven fabric currently made with a carding machine is shown in Figure 12. Before carding Recovered AF nonwoven fabric Figure 10 Recovered AF nonwoven fabric with a carding machine 19

21 2.2.4 Pilot Plant for FRP Recycling We have constructed the pilot plant for FRP recycling that can be used also for other composites recycling. The FRP recycling process is shown in Figure 13. The pilot plant for FRP recycling is shown in Figure 14, that was constructed with subsidy from the Ministry of Economy, Trade and Industry of Japan. FRP Wastes Treating Tank FRP Washing Tank Solid Washing Tank Solid Filtration Distillation Drying Recovered Recovered Recovered Resin Filler Fiber Figure 11 FRP recycling process by the dissolving method Figure 12 The pilot plant for FRP recycling by the dissolving method 20

22 3. Recovering F and EP from FRP 3.1 Method of Dissolving EP under rdinary Pressure 24)-26) Epoxy resin (EP) cured with acid anhydride is mainly used for a matrix of FRP. This is applied to golf club, tennis racket and aerospace parts, but is difficult to recycle. We estimate that cured epoxy resin can be depolymerized by transesterification with mono alcohols, and then be dissolved into a solvent. 3.2 Depolymerization of FRP Various FRP products could be dissolved by the depolymerization under ordinary pressure. For example, tennis rackets and badminton rackets made of FRP were dissolved in 8.0 h respectively (Figure 15) FRP badminton rackets FRP tennis rackets Figure 13 FRP rackets treated by the dissolving method 21

23 4. Recycling of Recovered F 27)-42) 4.1 Recovered F Nonwoven Fabric The nonwoven fabrics using the recovered cotton-like F were produced by the dry or wet process as same as GF nonwoven fabrics of recovered GF (Figure 15). The recovered F nonwoven fabric currently produced with a carding machine is shown in Figure 16. Recovered F nonwoven fabric Before carding Figure 14 Recovered F nonwoven fabric with a carding machine 22

24 4.2 Recycled FRP Materials The investigated materials are non-woven fabrics of F (rf) recovered by our method from depolymerized FRP-moldings and tennis rackets. The dissolving process of tennis racket is shown in Figure 17. We compared the properties of the non-woven fabric of our recovered F by depolymerization with those of the commercially available TRAYA Mat (TRAY Industries Inc.) and the recovered F by pyrolysis process (Takayasu o., Ltd.). The EP used was Bisphenol-A type EP cured with anhydride. Table 5 shows materials in this study. Figure 15 Recovered Fs from a racket and a molding 23

25 Table 5 Materials Item Product name ontent Abbreviation Manufactuer Non-woven fabric Recycle F Recovered from depolymerized FRP-m this study non-woven fabric (1) FRP-moldings Recycle F Recovered from depolymerized Racket this study non-woven fabric (2) Tennis racket Recycle F Recovered from Pyrolysis Takayasu Takayasu o.,ltd non-woven fabric (3) process TRAYA Mat ommercial product TRAYA TRAY Industies Inc. Resin jer 828 Bisphenol-A type EP - Mitsubishi hemical orp. N-2200 Anhydride type hardner - itachi hemical o., Ltd 2E4MZ-N ardening accelerator - Shikoku hemicals orp Evaluation of F monofilaments We evaluated the tensile properties and the surface of F monofilaments. The tensile properties of F monofilaments were measured in accordance with JIS R Table 6 characterizes tensile strength (T), tensile modulus (E) and fiber diameters (φ) of F monofilaments, comparing with the Takayasu and TRAYA. Type of F T (MPa) E (GPa) φ(μm) FRP-m Racket Takayasu TRAYA Table 6 omparison of tensile properties of Fs The rfs had tensile properties close to the Takayasu and TRAYA. The differences of tensile strength and tensile modulus among Fs seemed to be due to the differences of the original fibers properties. Figure 18 shows the images scanning electron microscopic (SEM) images of rfs, Takayasu and TRAYA. As obviously shown, the surfaces of the rfs and Takayasu were not damaged and clean as TRAYA. 24

26 mm mm mm mm FRP-m Racket Takayasu TRAYA Figure 16 SEM images of rfs (5000 ) omparison with density of F non-woven fabric We produced non-woven fabric of rfs by using a carding machine. Table 7 show the densities and the bulkiness of non-woven fabrics (Vf = 40 %). As shown, the density of rf non-woven fabric is lower than those of Takayasu and TRAYA. Table 7 omparison of bulkiness of non-woven fabric Type of Thickness Fabric weight Density non-woven fabrics (μm) (g/m 2 ) (g/m 3 ) FRP-m Racket Takayasu TRAYA Mat

27 4.2.4 Molding Recycled FRP The Recycled FRP (rfrp) composed of non-woven fabric (Figure 19) and Bisphenol-A type EP cured with anhydride was manufactured by compression molding. The condition of compression molding and molding process of rfrp are shown in Table 8 and Figure 20. The volume content of fiber (Vf) was between 0 % and 40 %. Figure 17 Non-woven fabric of rf Table 8 onditions of ompression Molding Item onditions Pressure 12 MPa Temperature 150 Time 2 h EP resin Impregnation of EP resin Appearance of rfrp Figure 18 Molding process of rfrp 26

28 4.2.5 Moldability of rfrp The dependence of FRP thickness on the volume content of fiber (Vf) is shown in Figure 21. As shown, the thicknesses of FRP-m, Racket and TRAYA increase with increasing Vf when Vf is larger than 30 %. 5 :Takayasu :FRP-m FRP Thickness (mm) :TRAYA :Racket Vf (vol%) Figure 19 Relationship between Vf and thickness of rfrps We speculated that when the density of non-woven fabric is low, the bulkiness of the fabric increases with the increase of Vf, and the compression molding does not proceed properly due to the bulkiness of the fabric. Thus thickness of FRP has increased with increasing Vf. n the contrary, in the case of Takayasu whose density is high, the thickness of FRP was almost constant even at the high Vf of 40 %. 27

29 Table 9 ross-section observation of rfrps Item FRP-m Racket Takayasu TRAYA Vf=10% Vf=40% void As shown in the Table 9, some voids were observed in FRP-m and Racket of 40 % Vf. We considered the cause of the void was that EP couldn t be impregnated properly due to bulkiness of the fabric which hinders the compression of the resin and fabric. In the FRP of Takayasu and TRAYA, voids didn t occur. So, it may be necessary to improve the density of the fabric to enhance the moldability of rfrp F length of rfrp We dissolved rfrp and evaluated the change of the F length varying Vf from 10 % to 40 %. The optical microscopy images of F of rfrp are shown in Table 10. Table 10 length of rf Item FRP-m Racket Takayasu TRAYA 0 Vf=10 % μm Vf=40 % 500 μm 28

30 As shown, the length of F of 40 % Vf was shortened about 1 mm~2 mm comparing with the length of about 30 mm at Vf of 10 % in FRP-m, Racket and TRAYA. We thought that the breaking of fiber may be caused by the increased contact point of fibers of high Vf. n the other hand, the ratio of cut fiber was low in Takayasu Mechanical properties of rfrp We evaluated mechanical properties of rfrp using non-woven rf fabrics following JIS K 7073(tensile properties), JIS K 7074(flexural properties) and JIS K 7077(harpy impact strength). The results are shown in Table 11 and Figure 20-Figure 22. As shown, the mechanical properties increased with increasing Vf, but after showing the maxima and decreased with the increasing Vf. We thought that the cause of the non-linear relation was the imperfect molding and increased ratio of shortened fibers. Table 11 The results of mechanical properties of rfrp Item Unit FRP-m Racket Pyrolysis TRAYA Fiber form - F non-woven fabric Matrix resin - Anhydride cured Bisphenol-A type EP Tensile strength MPa Tensile modulus GPa Flexural strength MPa Flexural modulus GPa harpy impact strength kj/m

31 200 Tensil strength (MPa) :FRP-m :TRAYA :Racket 0 :Takayasu Volume content of fiber (vol%) 8 7 :Racket Tensil modulus(gpa) :TRAYA :FRP-m :Takayasu Volume content of fiber (vol%) Figure 20 Tensile properties of rfrps 30

32 :FRP-m :TRAYA Flexural strength(mpa) :Takayasu :Racket Volume content of fiber (vol%) 25 :Takayasu :TRAYA Flexural modulus(gpa) :FRP-m :Racket Volume content of fiber (vol%) Figure 21 Flexural properties of rfrps 31

33 30 harpy impact strength (kj/m 2 ) :FRP-m :TRAYA :Takayasu :Racket Volume content of fiber (vol%) Figure 22 harpy impact strength of rfrps onclusion The mechanical properties of rf and rfrp using rfs recovered from waste FRP was investigated. The mechanical and surface properties of the recovered F monofilament was as the same as the fresh one. The mechanical properties of rfrp increased with the increasing volume content of fiber, but there were maxima and did not have a linear relation to the volume content of F. We thought that the causes of the non-linear relation were both imperfect molding and increase in the ratio of shortened fibers. The mechanical properties of rfrp is equal to that of Takayasu and TRAYA. 32

34 5. Recycling of Recovered EP 5.1 Anhydride ured EP 43)-46) Acid anhydride (Ah) cured EP (EP/Ah) usually used as the matrix resin of FRP has ester bond by the reaction between epoxy group and anhydride. So, we investigated the depolymerization of EP/Ah under ordinary pressure and found that EP/Ah easily dissolves into BZA in standard conditions, finally recovering carbon fiber (Figure 25). + Epoxy resin Acid anhydride transesterification prepolymers monomers Figure 23 Depolymerization of epoxy resin cured with acid anhydride Experimental Materials The model epoxy was a commercial phenylglycidylether (PGE). The Ahs were succinic anhydride (ScAh), cis-1, 2-cyclohexanedicarboxylic anhydride (hah), cis-4-cyclohexene-1, 2-dicarboxylic anhydride (heah) purchased from Tokyo hemical Industry o., Ltd. The hardening accelerator was 2,4,6-tris (dimethylaminomethyl) phenol purchased from Tokyo hemical Industry o., Ltd. K 3P 4 and BZA were commercially available from Taiyo hemical Industry o., Ltd and Sun hemical o., Ltd, respectively Synthesis of a model compounds The model compounds that consist of PGE and Ahs were introduced in a test tube. The 33

35 reactive mixture was heated at 80 for 1.0 h followed by the heating at 150 for 1.0 h. An oil bath was used to heat the mixture in a test tube Depolymerization of a model compounds The model compounds, BZA and K 3P 4 were introduced in a test tube. The reactive mixture was heated at 180 for 10.0 h in an oil bath haracterization 1 NMR and 13 NMR spectra were measured at a room temperature with a JEL AL-400 (400 Mz) NMR spectrometer. Model compounds were dissolved in d 6-dimethylsulfoxide (d 6-DMS). In a suffix of signals, alphabet shows the degree of signal intensity (s: strong, m: middle, w: weak) and numerals show number of signals. "Spectra Database for rganic ompounds SD'S" was used to assign the NMR spectrum. This is a free site organized by National Institute of Advanced Industrial Science and Technology (AIST), Japan Results and discussion Polymerization reaction of model compounds The model compounds were synthesized stoichiometrically by the reaction between PGE and Ahs with a catalyst. NMR signal assignment of PGE, ScAh, hah and heah are shown in Figure 26, and the estimated model polymerization reaction between PGE and Ah is shown in Figure / ~ PGE 49.96, ,1.50/ ,2.85/ ,1.81/1.90 hah 28.34, ,3.14/ ScAh , / heah Figure 24 Assignment of PGE, ScAh, hah and heah in NMR (Italic: 1 NMR, Bold: 13 NMR) 34

36 R = PG 2 + R Ahs R R PGE/Ah 2 Figure 25 Estimated model polymerization reaction between PGE and Ah haracterization of the polymerization products (1) PGE/ScAh The NMR signal assignment of PGE/ScAh is shown in Figure 26 and NMR signals of polymerization product, PGE and ScAh are shown in Table 12 and Table 13. The disappearance of epoxide signals of PGE at both σ 2.72 ppm and σ 2.86 ppm of 1 NMR and at both σ ppm and σ ppm of 13 NMR indicates the cleavage of epoxides and progress of polymerization reaction. 1 NMR signal at σ 3.39 ppm and 13 NMR signal at σ ppm may suggest the possibility of unreacted materials or polymerization reaction between PGEs (e) (d) (c) (b) (a) Figure 26 Assignment of PGE/ScAh in NMR( alphabet : 1, numeral : 13 ) 35

37 Table 12 Signal assignment and chemical shifts in 1 NMR Assignment 1 NMR σ(ppm) PGE/ScAh PGE ScAh (a ) 2.58s s (d ) 3.93w (d ) 4.02w2 (b ) 4.12m (b) 4.29m1 (c) 5.30m1 (e ) 6.94s (e ) 7.27m Table 13 Signal assignment and chemical shifts in 13 NMR Assignment 13 NMR σ(ppm) PGE/ScAh PGE ScAh m m m w m s m s m m The NMR signal assignment of PGE/ScAh is shown in Figure 29 and NMR signals of a polymerization product, PGE and hah are shown in Table 14 and Table

38 (g) (c) (b) 2 2 (f) (e) (d) (a) Figure 27 Assignment of PGE/hAh in NMR( alphabet : 1, numeral : 13 ) Table 14 Signal assignment and chemical shifts in 1 NMR Assignment 1 NMR σ(ppm) PGE/hAh PGE hah (b ) 1.32m (b ) 1.67m1 (c ) 1.84m (c ) 1.92w (a ) 3.34s (f ) 3.85w (f ) 4.06w1 (d ) 4.24w (d ) 4.30w4 (e ) 5.26w1 (g ) 6.95m (g ) 7.30m

39 Table 15 Signal assignment and chemical shifts in 13 NMR Assignment 13 NMR σ(ppm) PGE/hAh PGE hah w w w w w m m s m s m m The disappearance of epoxide signals of PGE at both σ 2.72 ppm and σ 2.86 ppm of 1 NMR and at both σ ppm and σ ppm of 13 NMR indicates the cleavage of epoxides and progress of polymerization reaction. 1 NMR signal at part of σ 3.34 ppm and 13 NMR signal at σ ppm may suggest the possibility of unreacted materials or polymerization reaction between PGEs. 38

40 (2) PGE/heAh The NMR signal assignment of PGE/heAh is shown in Figure 30. And NMR signals of a polymerization product, PGE and heah are shown in Table 16 and Table 17. Table 16 Signal assignment and chemical shifts in 1 NMR Assignment 1 NMR σ(ppm) PGE/heAh PGE heah (b ) 2.27m (b ) 2.36m (a ) 3.02m1 3.36s (f ) 3.89w (f ) 4.03m1 (d ) 4.22w (d ) 4.30w2 (e ) 5.24w1 (c ) 5.56m (g ) 6.88m (g ) 7.24m

41 Table 17 Signal assignment and chemical shifts in 13 NMR Assignment 13 NMR σ(ppm) PGE/heAh PGE heah w m w w w w s m m s m w (g) (c) (b) 2 2 (f) (e) (d) (a) Figure 28 Assignment of PGE/heAh in NMR( alphabet : 1, numeral : 13 ) The disappearance of epoxides signals from PGE at both σ 2.72 ppm and σ 2.86 ppm of 1 NMR and at both σ ppm and σ ppm of 13 NMR indicated the cleavage of epoxides and progress of polymerization reaction. σ 3.36 ppm of 1 NMR signal and σ ppm of 13 NMR signal may suggest the possibility of unreacted materials or polymerization reaction between PGEs. 40

42 Proposed depolymerization mechanism In Figure 31, we showed the proposed mechanism of the depolymerization of thermosets under ordinary pressure by the BZA. As shown, the most probable mechanism is thought to be transesterification. Following the proposed mechanism shown in Scheme 2, the depolymerization products with BZA may be dibenzyl ester compounds from the Ah and 3-phenoxy-1, 2-propanediol from PGE. R R PGE/Ahs 2 R = phenoxy-1, 2-propanediol + Transesterification 2 R 2 Dibenzyl ester compounds Figure 29 Estimated model depolymerization reaction of PGE/Ah haracterization of the depolymerization products (1)Depolymerization of PGE/ScAh (DEP(PGE/ScAh)) The NMR signals of DEP(PGE/ScAh), PhPD and DbSuc are shown in Table 18 and Table 19. NMR signal assignment of DEP(PGE/ScAh) is shown in Figure 32. Spectra always contain signals of BZA as a solvent. 41

43 Table 18 Signal assignment and chemical shifts in 1 NMR Assignment 1 NMR σ(ppm) DEP(PGE/ScAh) PhPD DbSuc BZA 2.50w (i ) 2.63m (h ) 3.39w (d ) 3.47w (d ) 3.85w (f ) 3.94w (g ) 4.01w (e ) 4.12w m (j ) 5.19w (a ) 6.93m (c ) 6.94 (b ) 7.23w (k) 7.32s

44 Table 19 Signal assignment and chemical shifts in 13 NMR Assignment 13 NMR σ(ppm) DEP(PGE/ScAh) PhPD DbSuc BZA m s m w w w m m s m w w m m m w w (b) (c) (a) (d) (e) (g)(h) (f) PhPD (i) (j) (k) (l) DbSuc 2 Figure 30 Assignment of depolymerization products in NMR 43

45 As a result of NMR analyses, the signals of DEP(PGE/ScAh) consisted with those of PhPD and DbSuc. So we thought that DEP(PGE/ScAh) consists of PhPD and DbSuc. (2) Depolymerization of PGE/hAh(DEP(PGE/hAh)) The NMR signals of DEP(PGE/hAh) are shown in Table 20 and Table 21. NMR signal assignment of DEP(PGE/hAh) is shown in Figure 33. Table 20 Signal assignment and chemical shifts in 1 NMR Assignment 1 NMR σ(ppm) DEP(PGE/hAh) PhPD Dbp BZA (l ) 1.26w (m ) 1.34w (j ) 1.66w (k ) 1.85w m (i ) 2.60w (i ) 2.80w (h) 3.43w (d ) 3.50w (d ) 3.78 (f ) 3.80w (g ) 3.90w (e ) 4.07w s (n ) 5.21m (a ) 6.92m (c ) 6.94 (b ) 7.23m (o ) 7.31s

46 Table 21 Signal assignment and chemical shifts in 13 NMR Assignment 13 NMR σ(ppm) DEP(PGE/hAh) PhPD Dbp BZA w w w w w w s w w w w w m w s m m m w s w w (b) (c) (a) (d) (e) (g)(h) (f) PhPD (i) (j) (k) (l) (m), (n) 15 (o), (p) 16 Dbp 2 Figure 31 Assignment of depolymerization products in NMR 45

47 As a result of NMR analyses, the signals of DEP(PGE/hAh) consisted with those of PhPD and Dbp. So we thought that DEP(PGE/hAh) consisted of PhPD and Dbp. n the other hand, signals of σ ppm, σ ppm, σ ppm and σ ppm of 13 NMR were not assigned to PhPD and Dbp, suggesting the existence of the side reaction products. (3)Depolymerization of PGE/heAh (DEP(PGE/heAh) The NMR signals of DEP(PGE/heAh), PhPD and DbTp are shown in Table 22 and Table 23. NMR signal assignment of DEP(PGE/heAh) is shown in Figure 34. Table 22 Signal assignment and chemical shifts in 1 NMR Assignment 1 NMR σ(ppm) DEP(PGE/heAh) PhPD DbTp BZA (m ) 2.29w (m ) 2.38w w w1 (h ) 3.40w (d ) 3.47w (d ) 3.78 (f ) 3.80w (g ) 3.92w (e ) 4.07w s (m ) 5.20w (l ) 5.61w (a ) 6.91m (c ) 6.94 (b ) 7.23m (o ) 7.31s

48 Table 23 Signal assignment and chemical shifts in 13 NMR Assignment 13 NMR σ(ppm) DEP(PGE/heAh) PhPD DbTp BZA w m s w w w w w w w s m w m w w m w w (b) (c) (a) (d) (e) (g)(h) PhPD (f) (i) (j) (k) (l) (m), (n) DbTp 15 (o) 16 2 Figure 32 Assignment of depolymerization products in NMR 47

49 As a result of NMR analyses, the signals of DEP (PGE/heAh) consisted with those of PhPD and DbTp. So we thought that DEP (PGE/heAh) consisted of PhPD and DbTp. n the other hand, signals of σ 3.03 ppm of 1 NMR was not assigned to PhPD and DbTp, suggesting the existence of the side reaction products onclusions In this work the chemical recycling of the epoxy resin cured with Ahs were investigated. Synthesis of a model compounds enable to study the polymerization and depolymerization reaction. The polymerization and depolymerization products were almost identified by NMR analyses. From the NMR analyses of depolymerization of PGE/Ah model compounds, we found that dibenzylesters and bisdiols are formed by the depolymerization of Ahs reacted with model EP under ordinary pressure. The depolymerization mechanism of PGE/Ah was the transesterification with BZA, so we estimated that the depolymerization reaction of EP cured with Ah under ordinary pressure occured mainly transesterification reaction accelerated with K 3P 4 as a catalyst. 48

50 5.2 Amine ured EP 47)-50) We have developed the depolymerization of thermosets under ordinary pressure. This method uses tripotassium phosphate (K 3P 4) as a catalyst and benzyl alcohol (BZA) as a solvent to depolymerize anhydride cured epoxy resin (EP) and unsaturated polyester resin (UP). It is possible to recycle thermosets based on transesterification. Although depolymerization of resins takes more time, our method is also applicable to depolymerize amine (Am) cured EP often used for FRP. Besides we have developed the depolymerization of thermosets by using subcritical fluids. Insoluble or slightly soluble thermosets like Am cured EP was possible to be depolymerized in a short time by this method. Am cured EP doesn t have ester bond, so we investigated the depolymerization mechanism of Am cured EP Experimental Materials Bisphenol A diglycidylether (DGBPA), the epoxy resin of epoxy equivalent weight (EEW) , was used as the model matrix. Isophrondiamine (IPDA) and 2,4,6-tris(dimetylaminomethyl) phenol (DMAmP) were used as the curing agent and catalyst. In order to analyze the depolymerization mechanism, we investigated the reactions of secondary and tertiary Am as the model compound of Am cured EP. The selected Ams were Dicyclohexylamine (DhAm), N,N-Dicyclohexylamine (DhMeAm), Dibenzylamine (DBzAm) and Tribenzylamine (TBzAm) Synthesis of a model matrix DGBPA, IPDA and DMAmP of the ratio of 100 : 25 : 2 were mixed in the aluminum plates. This reactive mixture was heated at 80 for 0.5 h. The additional heating was 150 for 1.0 h. The obtained cured EP of about 5 mm thick was cut into small pieces (size: 10 mm 15 mm ) for further testing Depolymerization of a model matrix and model Am compounds Piece of a model matrix, BZA and K 3P 4 were introduced into a tube bomb reactor. The reaction temperatures ranged from 250 to 325 in an inert gas oven and reaction time was from 1.0 h to 4.0 h. Am compound (DhAm, DhMeAm, DBzAm, TBzAm), BZA and K 3P 4 were introduced in the reactor, and then the reactor was heated at 280 for 6.0 h in an inert gas oven. 49

51 haracterization 1 and 13 NMR spectra of test pieces in DMS and Dl 3 were measured with JEL AL 400 operating at 200 Mz sing Results and discussion Depolymerization of a model matrix The solubility of the test pieces were measured changing the temperature from 250 to 325. The solubility (%) was calculated by the next equation. Solubility (%) = (A-B)*100/A A (g):mass of a test piece before treatment B (g):mass of a test piece after treatment The results are shown in Table 24 and Figure 33, Figure 36 shows the temperature profile. The test pieces before / after the treatment were shown in Figure 37 and Figure 36 respectively. Table 24 Solubility of test pieces Treatment time (h) Treatment temperatuer ( ) Solubility (%)

52 120.0 Solubility (%) Treatment time (h) Figure 33 Solubility of test pieces Figure 34 Temperature profile of subcritical fluids process Figure 35 A test piece before treatment 51

53 1.0 h 2.0 h 3.0 h 4.0 h Figure 36 Test pieces after treatment As shown in Table 24 and Figure 35, the test pieces dissolved perfectly after 4.0 h at 325. It was difficult to analyze the depolymerization products of EP cured with Am which has cross-linked three-dimensional networks. So we analyzed the depolymerization mechanism by using secondary and tertiary Am as model compounds of Am cured EP Depolymerization of model Am compounds To identify the structure of products, Am compounds and depolymerization products were characterized by NMR. In a suffix of signals, the alphabet shows the degree of signal intensity and numerals show the number of signals. The results of NMR analyses are as follows Alicyclic Am compounds The NMR signals of before and after the depolymerization reaction of DhAm and DhMeAm are shown in Table 25 and Table 26. The attributions of NMR signals are shown in Figure