Wood Waste Turned Into Value Added Products : Thermal Plasticization by Benzylation Process

Sawdust is usually considered as waste in wood-using industries. These materials can be converted into value added thermoplastics by means of benzylation. Products can be utilized in different applications where plastics are used. Thermoplasticization process was carried out with benzyl chloride under different alkaline conditions, 15, 25 and 35 %, respectively. Alkali ions and concentration affect the substitution reaction. Tailored material structure was remarkably changed. In order to detect changes, crystallinity index of the materials and thermal properties were analyzed. In FTIR spectra, the peaks appeared at 698 cm-1 and 740 cm-1, which indicates the aromatic C-C angular deformation. Multiple peak appears at 3030 cm-1, which indicates benzylation of the materials. The peak increase can be observed at 1596 cm-1 due to the aromatic deformation. Benzyl groups attached to hydroxyl to form ether groups increase the peak intensity. As a result of that, hydrogen bond energy changes and crystallinity of the materials is reduced. This substitution of functional groups changes the decomposition temperature of modifi ed materials. It reduces the decomposition temperature to between 330 and 350 oC. Thermogravimetric analysis revealed that modifi ed products were characterized by poorer thermal stability compared to raw materials.


Materijali
Turkish red pine (TRP) sawdust were obtained from the Isparta region in Turkey.Materials were dried under room temperature.Meal samples were prepared using a Wiley mill and ground to pass various mesh screens (60-80 mesh).

Alkali treatment 2.2.1. Lužnata obrada
Sawdust was treated with different concentrations of sodium, lithium, potassium hydroxide and guanidine for 24 hrs at room temperature.After treatment, materials were rinsed and dried at 102±3 ºC and tested with Fourier transform infrared spectroscopy (FTIR).

Benzylation process 2.2.2. Proces benzilacije
Benzylation process was used similarly to Hon and Ou process.Dried and ground samples (3 grams) were pretreated with various alkali concentrations (15, 25, 35 %) for preswelling.The slurry was transferred to a 250 ml round bottom fl ask containing benzyl chloride (BC) (27.6 ml).The reaction was conducted at 110 ºC for 6 hours with continuous stirring.The crude benzylated material was collected by fi ltration and exhaustively washed with water to remove any residuals and fi nally washed with ethanol to remove any residual benzyl alcohol.The fi nal product was dried overnight at 40 ºC.

Fourier transform infrared spectroscopy (FTIR) 2.2.3. Fourierova transformacija infracrvene spektroskopije
FTIR spectra were obtained on untreated and benzylated substrates from KBr pellet using Perkin Elmer spectrum one model FTIR spectrometer.Each sample was scanned 10 times between 4000 and 400 cm -1 and changes in the chemical structure were recorded.

UVOD
Increased utilization of wood results in more waste due to debarking, cutting, shaving, sanding, etc.How to deal with this waste is an important issue.Environmental concern and defi ciency in natural resources impose solutions that involve reducing waste and recovering and recycling this material to conserve natural resources.Progress has been made in efforts to reduce waste, but additional works need to be done to solve this problem.
Sawdust and wood shavings are produced by a number of sectors and this raw material is part of the municipal waste stream.A tremendous range of products can be obtained from these lignocellulosic waste materials due to complexity of cell wall structure.Lignocellulosic materials refer to woody and nonwoody plants that are composed of cellulose, hemicellulose, and lignin.Chemical properties of these materials make them suitable for a large number of products.The utilization of lignocellulosic materials in the production of plastic and composites is becoming more and more attractive (Biswas et al., 2006;Bodirlau et al., 2008;Çöpür et al., 2007;Ebringerova and Heinze, 2000;Hassan et al., 2001;Hon and Luis, 1989;Hon and Ou, 1989;Pereira et al.,1997;Rowell, 1990;Su et al., 2015).
Plastics are being favored for many applications in place of other materials due to formability, light weight and strength properties (Hon and Shiraishi, 2001).In order to plasticize, lignocelullosic materials are chemically modifi ed.Chemical modifi cation of cell wall polymers is usually carried out either in acidic or alkali conditions (Chen et al., 2012;Huang et al., 2014;Qu et al., 2014).Chemical alteration of hydroxyl groups can reduce the interaction among the chain segments, creates free volume and changes the thermal properties of the material (Nakano, 1994).New modifi ed lignocellulosic materials have thermoplasticity, when large or many side-chains are introduced by chemical modifi cation.
Thermoplastic materials are usually produced from petrochemicals, which is dependent on limited source of fossil fuels whose price is fl uctuating and may be running out.In addition to that, fossil fuels release gases which cause the greenhouse effect.One solution is to use tailored renewable resources.Therefore, the objectives of this paper were to explore the chemical modifi cation of Turkish red pine sawdust via etherifi cation to impart thermoplasticity.Thermo-

Thermal properties 2.2.4. Toplinska svojstva
Perkin Elmer Diamond model thermogravimetric analyzer (TGA) was used to study the thermal properties of etherifi ed samples.The heating rate was set at 10 ºC/min and the temperature ranged from 25 to 600 ºC.Measurements on 4 mg samples were carried out under nitrogen atmosphere (100 ml/min).

REZULTATI I RASPRAVA
The degree of crystallinity is an important parameter for plasticization of lignocellulosic materials.Cell wall polymers contain signifi cant amounts of hydroxyl groups.Chemical modifi cation of lignocellulosic materials usually takes place between these hydroxyl groups of the cell wall polymers and chemical reagent with or without catalyst (Rowell, 1990).Tailored hydroxyl groups can help lignocellulosic materials to exhibit thermoplastic properties due to change in hydrogen bonding ability.
Introducing new chemicals to cell wall polymers causes breaking up of some hydrogen bonds and changes crystallinity.This change indicates the possibility of plasticization and can be detected with FTIR spectroscopy.In order to detect the change in crystallinity, different peak ratios and hydrogen bond energy can be used (Poletto et al., 2013;Akgul et al., 2007).The ratio between the heights of the bands at 1370 cm -1 and 2900 cm -1 was used to determine the total crystalline index (TCI), and the ratio between the areas of the bands at 1430 cm -1 and 896 cm -1 was used to determine lateral order index (LOI) of the materials (Akerholm, et al., 2004;Ma, 2007).The energy of the hydrogen bonds EH for the OH stretching band was calculated using equation 1: Where ν o is the standard frequency corresponding to free OH groups (3650 cm -1 ), ν is the frequency of the bonded OH groups, and K is a constant (1/ K = 2.625 • 10 2 kJ).
In order to increase reactivity and swell lignocellulosic materials before modifi cation, the material was treated with alkaline solution.Alkaline treatments contracts microfi brils in the cell wall and changes the dimension (Nakano, 2010).The mechanism of microfibril contraction and anisotropic dimensional changes of cells in wood are treated with aqueous NaOH solution.As a result, chemical reagent can reach and react with hydroxyl groups on cell wall polymers.In untreated materials, there are free, intra and inter hydrogen bonded hydroxyl groups available (Figure 1).The intramolecular hydrogen bond in lignin can be observed at 3560-3580 cm -1 (Kondo, 1997;Poletto et al., 2012).Intramolecular hydrogen bond in cellulose appears around 3430 cm -1 and 3340 cm -1 (Kondo, 1997;Poletto et al., 2014).After alkaline treatment, these hydroxyl groups affected crystalline structure changes.Table 1 shows the crystallinity and hydrogen bond energy change after alkaline treatment (Table 1).
There is a small difference in crystallinity index and hydrogen bond energy (EH) of the materials.TCI   After alkali treatment, the slurry was transferred to a round bottom fl ask containing benzyl chloride.The benzylation process proceeded with continuous stirring.Untreated and chemically treated samples show different FTIR spectra (Figure 2).Benzylation of the materials caused a reduction of hydroxyl peaks at 3400 cm -1 and an increase of the aromatic C-C axial deformations around 1595 cm -1 (Figure 3).In addition to that, aromatic multiple peak appeared at 3030-3100 cm -1 .This could be due to monosubstituted benzyl rings.Guanidine showed spectra similar to those of untreated materials.The peak at 670 cm -1 gives information on C-OH out of plane bending (Ma, 2007).Spectra of the samples showed a reduction of peak intensity at 670 cm -1 .In contrast, peak appears at 698 cm -1 due to aromatic C-C angular deformation in treated materials (Figure 5).In addition to that, benzyl group can be detected at 740 cm -1 .The guanidine peak is lower compared to others.Even though it is strong alkali, the size of the molecule may restrict the entrance into the cell wall.After the reaction, an increase of aryl ether band at 1265cm -1 and of alkyl ether band at 1155-1060 cm -1 (due to C-O stretch from the substituted benzyl ether) was observed.(Figure 5).This absorbance band implied the substitution of hydroxyl groups in materials with benzyl groups.
Cellulose is the main component in wooden materials and it controls the thermal properties of wood (Hon and Shiraishi, 2001).Hydrogen bonds between cellulose chain and in the chain shift to melting temperature over decomposition temperature.Modifi cation of wood helped to disrupt any hydrogen bonds between adjacent chains and in the chain.Therefore, it helps wood to become thermoformable.
Figure 7 shows differential thermogravimetric analysis (DTGA) curves of alkali treated with different alkali ions, concentration and untreated materials.The fi rst step of weight loss, from room temperature to 120 °C, was related to the evaporation of absorbed water.The second step ends near 410 °C, and can be described by an abrupt mass loss stage that was related to the main thermal decomposition process.A derivative weight loss curve can be used to tell the point at which weight loss is most apparent (Figure 8).According to the results obtained, raw materials begin to decompose at a higher temperature (T i = 380 °C) when compared to modifi ed materials (T i = 330-340 °C).
It was seen that there was a signifi cant difference between modifi ed and untreated materials in relation to their respective thermal decomposition temperatures, which may be related to the difference in crystallinity between untreated and modifi ed materials.Tailored hydroxyl groups change the crystalline structure of the materials, when the intra and intermolecular hydrogen bonds between chains are broken.Rearrangement of the bonding ability of the treated materials reduces the decomposition temperature.As a result, the crystalline domains in the untreated materials show a higher thermal stability, when compared to modifi ed materials.

ZAKLJUČAK
Sawdust is a very promising source of raw materials for commercial products such as cellulose, plastics, etc. for many countries due to its availability and abundance.However, it is considered as waste.Thermoplasticization can be achieved by benzylation.Alkaline species and alkali concentration affect the substitution reaction and change the material properties.These changes are signifi cant with NaOH, and it can be detected with crystallinity, hydrogen bond energy change and thermal analysis.Hydroxyl groups were substituted with benzyl groups and this caused the change of FTIR spectra.Guanidine shows different trends.This could be due to the molecule size.It cannot penetrate the pore on the cell wall, because the pore size could be smaller than the molecule size.Na Li and K are effective on thermoplasticization. Multiple peaks appear at around 3030 cm -1 indicating benzylation of the materials.The appearance of the peak at 698 cm -1 and 740 cm -1 indicates the aromatic C-C angular deformation.Thermogravimetric analysis revealed that modifi ed products were characterized by poorer thermal stability compared to raw materials.Deformed crystallinity of the materials reduced signifi cantly the decomposition temperature, and the reduction of the decomposition temperature ranged between 40 to 60 o C.