Influence of soaking temperature time on the ability prepared liquefaction of wood from cashew nut shell waste

Use your smartphone to scan this QR code and download this article ABSTRACT Liquefied wood is one of the phenolic resin. However, unlike commercial phenolic resins that are normally synthesized by the chemical reaction between phenol and formaldehyde, liquefiedwood is usually produced by reacting phenol with wood-derived materials, and catalyst at 120-180◦C. Depending on whether the catalyst is a base or a acid, the formed resin is a thermoset or a thermoplastic. In this study, wood liquefaction was prepared from a cashew nut shell waste (CNSW), phenol, and sulfuric acid catalyst. The cashew nut shell waste is taken from Binh Phuoc province Vietnam and crushed to a size of less than 500 μm. Phenol and sulfuric acid catalyst are chemical experiments. The powder of cashew nut shell waste, phenol, and sulfuric acid were mixed and reacted at 150oC for different soaking times. An optimal soaking temperature time was determined through a cashew nut shell waste residue content in wood liquefaction products. The wood liquefaction products also were determined by a number average molecular weight (Mn) and a weight average molecular weight (Mw) by Gel permeation chromatography method (GPC); the function groups by Fourier Transform Infrared method (FT-IR). The results showed that the formed resin is thermoplastic and the optimal soaking time to prepared liquefied wood is 180 minutes. This sample has a residual cashew nut shell waste ratio of 9.44%, a number average molecular weight of 7552, and a weight average molecular weight of 10640. The liquefied wood from cashew nut shell waste can be used as a binder in the manufacture of the medium density fiberboard (MDF) or as a material to promote the sintered process in the production of woodceramic materials. In addition, the liquefied wood can also be pyrolyzed to form carbon fiber. Carbon fiber can be applied as reinforcing materials for ceramic products.


INTRODUCTION
Phenolic resin is a resin synthesized from the phenol and formaldehyde. It was commercialized and was put into industrial production in the early 20th century. Phenolic resin has good thermal stability, capable of binding and high carbon content. When decomposed at high temperatures, the phenolic resin can transform into carbon fiber structures 1 . Carbon fiber can be applied as reinforcement materials 1,2 . There are many methods for synthetic phenolic resin. Liquefied wood is one of the methods that have been studied 3 . By this method, the wood will be transformed into a high-molecular material with a strong odor and dark black color by giving the phenol or multi-functional alcohol to react with a catalyst. This transformed process is complicated and has many products to form. There have been many studies to fabricate wood liquefaction such as: using wood to react with polyethylene glycol/ glycerol/ polyhydric alcohol, and catalytic sulfuric acid at 150 o C to create wood liquefaction [4][5][6] . In addition, ethylene glycol, sulfuric acid, and wood are also combined to make wood liquefaction [7][8][9] . Several studies have also used phenol and acid catalysts such as sulfuric acid, phosphoric acid to make wood liquefaction from the wood pulp at 120 -180 o C 10,11 . Regarding wood materials for fabricating wood liquefaction, studies often use agricultural waste to fabricate wood liquefaction. Types of agricultural waste can be mentioned as the fruit of oil palm 12 , the wood of Japanese cedar 13 , waste paper 14 , bagasse 15 , corn stover 16 .
It can be seen that these research directions consider wood liquefaction made from wood-based raw materials as renewable resources to replace fossiloriginated plastic. It contributes to addressing concerns about fossil fuel exhaustion issues and environmental pollution. In agriculturally developed countries like Vietnam, this research direction is even more important in the use of industrial waste products to make wood liquefaction into a product of economic value.
In Vietnam, cashew is one of the important industrial trees. Due to exporting cashew nuts only, cashew nut shell has become one of the waste items in the cashew industry. Cashew nut shell is often pressed to get cashew oil. However, the cashew nut shell after pressing (often called the cashew nut shell waste) is still a waste to be treated. There have been some studies using cashew shell waste to fabricate ceramic 17,18 . Other studies have also used cashew shell waste to make wood liquefaction 19,20 . This research will study the influence of soaking temperature time on the ability to prepared wood liquefaction from cashew nut shell waste.

Raw materials
CNSW was taken from Binh Phuoc. Chemical composition was shown in Table 1 and Table 2. CNSW was washed and crushed to a size of less than 500 µm. Phenol (1.07 g/cm 3 , Merck) and 98% sulfuric acid (1.84 g/cm 3 , Merck) were also used to fabricate wood liquefaction from CNSW. Phenol, CNSW were mixed with the ratio of 2/1 (wt.) and 5% sulfuric acid According to the amount of phenol used. The mixed mixtures were placed in the drying oven and soaked at 150 • C for different time periods to make wood liquefaction. The soaking temperature times are shown in Table 3. Optimum soaking time was determined by analyzing properties such as vibrational units of functional groups by FT-IR method; Wood liquefaction reaction efficiency through assessment of residual CNSW ratio; The number average molecular weight (M n ) and the weight average molecular weight (M w ) by Gel chromatography (GPC) method.

Fourier-transform infrared spectroscopy (FT-IR):
The vibration of the functional groups of wood liquefaction was analyzed by Fourier-transform infrared spectroscopy (FT-IR -Model Nicolet 6700, Thermo, USA). The scanning step was 0.9642 with a scanning angle of 500 to 4000cm −1 . The binder was KBr. The test method was a transmittance spectrum.

Determine a residual CNSW:
Phenolic resin is crushed, filtered, and washed to remove residual phenol in the resin. The washed resin is dried at 70 o C. The sample was then weighed 2,00 ± 0.01 gram, contained in Erlen, added about 40 ml of ethanol, and swirled well. The sample is filtered slowly through the filter paper and weighed to determine the mass of the filtered sample. After filtration is complete, the filter paper containing the residue is placed in a drying cup and dried to constant weight. The residual CNSW is determined from the following formula: m gd -the percentage of residual CNSW (%) m s -the weight of filter paper and insoluble residue (gram) m gl -the weight of dry filter paper (gram) m o -the weight of the original phenolic resin (gram)

Gel permeation chromatography (GPC):
The number average molecular weight (M n ) and the weight average molecular weight (M w ) were determined by Gel permeation chromatography method (GPC -Model PL-GPC 50, POLYMERLAB, USA). The used soluble solvent is Dimethyl -Formamide (DMF). The wood liquefaction samples were dissolved in DMF solvent at a concentration of 0.10 mg/ml. The dosage for each sample injection was 50µl.

THE RESULTS AND DISCUSSIONS Vibrational units of functional groups by FT-IR spectrum
Wood liquefaction samples at different soaking times were determined functional groups by FT-IR method. The results of the FTIR spectrum of the samples were similar. Comparison with the FTIR spectrum of previous studies showed that there was wood liquefaction formation in all samples 2,3,21,22 . In this case, it is difficult to estimate the optimal retention time for wood liquefaction generation at 150 • C. Therefore, the determination of residual CNSW and the GPC method was used to evaluate this factor.

Determine residual CNSW
Results from the graph in Figure 2 showed that the residual CNSW of liquefied wood decreased as the soaking time increases. When the retention time increased, the reaction time for creating wood liquefaction was prolonged, the reaction performance also increased. The residue of CNSW was reduced rapidly    when extending the retention time from 90 to 180 minutes corresponding to the model ST90 to ST180 (from 29.68% to 9.44%). If the soaking time was prolonged, the residue of CNSW would be difficult to reduce further (from 9.44% to 9.02%). When the heat retention time was prolonged, the chemical reactions between phenol, CNSW, and the acid catalyst would take place more thoroughly. As a result of this process, the amount of CNSW involved in the reaction to create the resin was more, the amount of CNSW remaining after the reaction also was less. However, besides the resin-forming reaction, there was also the thermal decomposition of CNSW 23 . Therefore, when the heat retention time was longer than 180 minutes, the result of CNSW residue decreases very little. The CNSW residue result showed that at 150 o C the optimal soaking time was 180 minutes.

Determine M n and M w by GPC
The results of the GPC analysis of the samples were presented in Table 5 and Figure 3. According to the   Table 5 and Figure  Kensuke Naka pointed out that polymer had a molecular weight of more than ten thousand and oligomer had a molecular weight of several thousand or less 23 . GPC results showed that region 1 with M w value over 10000 was the distribution region of the polymer and region 2 with M w value from 1545 to 1755 was the distribution region of the oligomer. The W n was used to determine the formation of the liquefied wood at different thermal retention time. When holding the heat at 150 o C from 90 minutes to 180 minutes (ST90 -ST180 samples), the oligomers linked together to form polymers. The W n value of the polymer region would increase and the oligomer region would decrease. Conversely, if the holding time was too long (ST210 sample), the W n value of the polymer region would decrease and the oligomer region would increase. This result demonstrated that prolonging the soaking time also would sever the molecular circuit of the newly formed polymer. This result combined with the residual CNSW ratio ( Figure 1) and the relative intensity ratio of the peaks on the FT-IR spectra (Figure 2) showed that the formed wood liquefaction at different soaking times

CONCLUSIONS
In this study, the effect of soaking time at 150 o C on the ability to prepared wood liquefaction was investigated. The FTIR results showed that there was LW formation in all samples at different soaking times. When increasing the soaking time, the residual CNSW ratio in resin decreased. However, when increasing the retention time of more than 180 minutes, the residual CNSW ratio did not decrease significantly. M w and M n values in the GPC results showed that the samples had coexistence of the polymer and oligomer and 180 minutes was the optimal time to fabricate wood liquefaction from CNSW at 150 o C. The ST180 sample had the residual CNSW ratio of