TECHNICAL FIELD

This invention is in the field of the Forest Products Industry.

It provides stabilization of the low-thickness high-density fiberboards’ dimensional changes that occur in contact with moisture and water. These fiberboards are used as carrier layers in the laminate flooring product group in the Wood Based Board Industry, which has an important place in the Forest Products Industry.

The invention is a product and consists of combining the glued lignocellulosic fibers, produced with the systems already available in the fiberboard sector, with polystyrene-based waste used in packages of different qualities and a coupling agent during the production of fiberboard.

BACKGROUND

Wood-based boards such as particleboard, medium-density fiberboard (MDF), and high-density fiberboard (HDF) are used as laminated surfaces in interior applications. Especially, laminate flooring consists of different layers, which are a carrier layer (used high-density particle board or HDF), a decor paper on the upper surface, an overlay paper protecting this decor paper, and a balance paper on the lower surface.

Fiberboard, which is one of the wood-based boards, is a building material formed by drying or pressing the mat formed by the lignocellulosic fibers obtained in various pulping methods by themselves or with the help of an adhesive (Eroglu ve Usta, 2000).

Laminate flooring is a type of composite material consisting of different layers (Kara et al. 2016). High-density fibreboards (HDFs) greater than 800 kg/m3 (ISO 818:1975) are often used as the carrier panel layer for laminate flooring. Therefore, the dimensional stability and mechanical strength values of HDF panels are important for the production of laminate flooring and often require some additional requirements (Kara et al. 2016). In addition to lignocellulosic fibers, glue, and hardeners, paraffin and/or additional special chemicals are used to increase the resistance to humidity, especially for using fiberboards in the carrier layer of laminate flooring.

The use of plastics in the forest industry in the last 20 years is an important approach to solving the environmental problems that waste plastics (Kaymakci et al. 2012; Sommerhuber et al. 2016). Wood plastic composites (WPC), which is the result of this approach, is a new type of composite material formed by combining lignocellulosic material and polymer (Ashori 2008; Chaharmahali, et al. 2008; Aynlmi§ ve Kaymakgi 2013; Keskisaan ve Karki 2018; Gulitah ve Liew 2019). One of the main application areas of WPCs is their use as flooring materials, such as laminate flooring (Gao et al. 2016; Machado et al. 2016).

The main result found in various studies on WPCs produced using virgin polymers is that the increase in the amount of polymer used in composite materials increases the water resistance and mechanical strength (Huuhilo et al. 2010; Ayrilmis and Jarusombuti 2011 ; Cademartori et al., 2015; Rao et al. 2018). It is possible to use different lignocellulosic based materials such as hazelnut shells, wood shavings, MDF waste, etc. as fillers for plastics (Jayaraman ve Bhattacharyya 2004; Faruk et al. 2008; Karaku§ 2008; Aynlmi§ ve Buyuksan 2010; Necefi ve Islam 2011 ; Akba§ et al. 2013; Aynlmi§ et al. 2013; Chavooshi ve Madhoushi 2013; Ozmen et al. 2014; Arnanda et al. 2017; Narlioglu et al. 2018).

In their studies, Karaman et al. (2006) preferred PET wastes as a plastic source. In accordance with other studies in the literature, they stated that the moisture and water absorption problems, which are the disadvantages of wood material, can be solved by adding waste plastic material.

Aynlmi§ and Kaymakgi (2013) used polypropylene (PP) waste plastic material at the rates of 30%, 40%, and 50% and maleic anhydride (MA) as a coupling agent at the rate of 3% in their study. They obtained positive values from the swelling test results for the thickness of the boards obtained from this mixture. Aynlmi§ and Buyuksan (2010) obtained positive results in dimensional stability values according to Turkish standards, concluded from the results of the WPC material's water absorption and swelling to thickness tests obtained with the addition of PP. In parallel with the work subject to the patent, Binhussain and El-Tonsy (2013) produced boards using 50% PS and 50% palm leaf in their work. They stated that the water absorption rate in softwood wood was 42.4% and the water absorption rate in hardwood wood was 29.2%. As a result of the experiments, they determined the water absorption rate of WPC boards at 9.9%. In Karaman et al. (2006), it was concluded that the problem of swelling to the thickness of the wood material can be solved by using plastic material and the obtained products can be used, especially in areas of use where humidity is high. Karaku§ (2008) stated that as a result of their studies, they obtained positive results in the bending tests of non-compliance removers on composite boards and that a bonding agent should be used.

Contrary to this result, Tayyar and Ustun (2010) found that PET and HDPE showed a homogeneous distribution on the board, and the percentage of strain under maximum load decreased as the PET ratio increased. They emphasized that the increase in the PET ratio also contributes to the increase in the modulus of elasticity. It can be said that this is due to the fact that PETs in HDF cannot provide chemical bonding.

As a result of mechanical tests, Muehl, Krzysik, and Chow (2004) obtained the result that the mechanical properties of the boards made with PP have better values than the boards made with PET. Also, Nemati et al. (2013) produced a composite material with recycled PS and wood fiber. As a result of the experiments, they stated positive improvements in the product’s mechanical properties thanks to PS and that they observed significant increases in quality.

When the literature studies were examined in general, they stated that the mechanical properties of the composite materials were improved when the polymer ratios increased (Karaman et al., 2006; Aynlmi§ and Kaymakgi, 2013; Aynlmi§ et al., 2013).

Due to the natural structure of wood, wood-based materials (composites, boards, etc.) are products that interact with the humidity in the air. As a result of this interaction, dimensional changes (shrinkage and swelling) in the material occur; in this case, dimensional instability occurs.

Due to this situation, the research and production of alternative materials in the building sector have been questioned. There are many studies in the literature on composite production using wood-based materials with different plastics and plastic processing tools.

However, today, in the fiberboard sector, which has become as big an industrial branch as the plastics sector, there has not been much work on producing composite boards by adding plastics to wood fiber with mechanical recovery. It is estimated that the melting method cost will be eliminated by not using it, and an additional contribution will be made to the forest products industry. Generally in the literature studies, polyethylene terephthalate (PET) was preferred. However, the melting temperature of PET is quite high, and this temperature is not suitable for wood fibers. Because wood material deteriorates structurally above 200°C therefore, the use of non-combustible. However, melting polymers (PE, PP, and PS) from thermoplastics at temperatures between 150 and 200°C can prevent the thermal deterioration of wood material (Chaharmahali et al. 2008; Najafi 2013). Although dimensional stability has been achieved in studies on board production on this subject, the mechanical properties of the material have not been improved. One of the main disadvantages of plastic waste is that it has a heterogeneous structure when recycled and composite material is produced. The melting temperature (Tm) and glass transition temperature (Tg) change in parallel with the density. Tg value is a more important parameter in PS processing because it has an amorphous structure (Chanda 2017). Glass transition temperature (Tg) and melting temperature (TM) values of polystyrene were given in Table 1. Because it stands out with its low processing temperature and widespread use in the packaging industry, polystyrene was preferred in this invention.

When the literature is examined, Nemati et al. (2013) produced a nano clay composite material by combining wood fiber and recycled polystyrene (PS). As a result of the investigations, they concluded that the matrices, namely PS polymer, made positive changes in the mechanical properties of the composite product and provided significant increases in its quality.

As a result, the wood-based composite industry (particle board, plywood, etc.) is as big as the plastic material industry. Wood-based composites are more commonly used in homes than wood-plastic composites (Ritter de Souza Barnasky et al. 2020). For this reason, the effects of the materials used in HDF production on these values are important in terms of determining the usability of the materials. The wood-based composite industry is directly dependent on forest resources. Therefore, the use of plastic waste as reinforcement material in HDF is a more effective solution in reducing environmental problems (Karaman et al., 2006; Aynlmi§ and Jarusombuti, 2011 ; Tayyar and Ustun, 2010; Binhussain and El-Tonsy, 2013; Necefi, 2013; Nemati et al. 2013; Rahman et al. 2013; Lopez et al. 2018).

DESCRIPTION OF THE INVENTION

The mentioned invention eliminates the disadvantages described in the state of the art and meets the needs.

The invention relates to the grinding of waste polystyrene in a raw state without using an extruder device and incorporating it into the HDF composition in order to stabilize the dimensional stability of the high-density fiberboard.

The main purpose of this study is to determine the usability of industrial polystyrene (PS) wastes as reinforcement material for laminate flooring carrier panels in HDF production. For this purpose, PS, which is a widely used plastic material, was added in different proportions to be added to the HDF production system, and the values of density, water absorption, swelling to its thickness, elasticity modulus, bending strength, and adhesion strength were determined in HDF panels.

The main advantages of the present invention are:

• The forest products industry has a very wide area and includes the production of many products. Wood-based products change their dimension over time, depending on their environment. It swells in contact with water. Eliminating these and similar disadvantages by using waste polystyrene and wood gave positive results.

• With this invention, customer complaints, where high-density fiberboard (HDF) is used, will decrease, especially in the parquet sectors.

• Besides HDF, it can be used in areas such as MDF and OSB production.

• The fiberboards’ dimensional stability will be improved. • The dimensional instability of the products made from these boards will be minimized.

• It will be a solution for the fiberboards to be used in open environments.

• It will help in balancing the moisture of the wood. • It will increase the water resistance of the material.

• Because the waste polystyrene materials will be used, it will also contribute to solving environmental problems.

• Waste PS materials were ground in a willey-type mill and the melting process was carried out during the press. This will reduce energy savings and investment costs for the industry. DETAILED DESCRIPTION

High density fiberboard (HDF) with improved dimensional stability made from waste polystyrene is the subject of this invention.

This study aims to combine the polymers with different properties and fibers obtained by grinding plastic waste with the help of MA (maleic anhydride) and evaluate them as raw materials in the HDF production process, thus minimizing the dimensional instability in the boards and recycling the waste plastics.

The following process steps were carried out in the production of high density fiberboard (PSAHDF) with improved dimensional stability with thewaste polystyrene of the present invention: a-Waste PS raw material was brought to the laboratory area and the coarse dirt on it was cleaned. b- Waste PS raw material was divided into as small pieces as possible. c- The reduced pieces were brought to an average size of 5*5cm in equal measure. d- The sized pieces were ground in a Wiley Type Laboratory Mill. e- The process was continued with the samples obtained after the grinding process. f- The milled wastes were subjected to the sieving process. (The remaining raw materials above 60 mesh were used. This was done to achieve homogeneity in the size of the waste. g- Ready-to-use fibers from the industry and milled waste PS were mixed. h-Binding agent (maleic anhydride) was used to bind the fibers and waste PS polymers. These three substances were homogenized with the help of a mixer. i-Thickness boards and dimension drafts were created. j- The prepared mixture was put into the draft. k-Pre-press was applied.

I- Press operation was performed.

In this study it is aimed to combine the polymers with different properties and fibers obtained by grinding plastic waste with the help of MA (maleic anhydride) and evaluate them as raw materials in the HDF production process, thus minimizing the dimensional instability in the boards and recycling the waste plastics.

Three trial groups were created: 25% PS content HDF, 50% PS content HDF, and 75% PS content HDF. In addition, HDF consisting of 100% fibers was produced as the control group. The trial plan is given in Table 2.

It was established to evaluate the PS foams, which were used as a protector for the goods collected as waste PS. Very large waste foams were cut into approximately 5x5x5 cm dimensions with various cutting tools for the grinding process.

The grinding process was applied twice for each waste plastic. After the final sieving process, the products above 60 mesh are reserved for use. The plastics remaining on the coarse sieve are re-ground and made ready for use.

The use of plastic waste as an additive in the forest products industry will be an alternative solution to minimize the dimensional instability of fiberboards and reduce environmental pollution. In this study, waste polystyrene (PS), which has various properties and significant potential, was added to high density fiberboard (HDF) as a reinforcing material to better bind wood fibers together. It was mixed with glued fibers purchased from the industry at the ratios of 25/75, 50/50, and 75/25 (w/w). The changes in some properties of the boards, such as density, water absorption, swelling in thickness, modulus of elasticity (MOE), bending strength (MOR), and internal bonding strength, were determined. It was determined that the water absorption and swelling to the thickness of the plastic waste added boards were lower than the control samples. In addition, the mechanical properties of the samples manufactured from plastic waste were determined to be as good as those of the control samples. The results show that PS wastes can be evaluated in the production process of HDF reinforced with different mixing ratios for different usage areas.

The physical and mechanical properties of prototype boards developed at the laboratory level are shown in Table 3, along with the results of the tested parameters of the HDF samples. Depending on the polymer type and ratio, the densities of all boards were found to be close to the target density. Small differences from the target density can be explained by various properties of the plastic waste used.

An ANOVA test was applied to determine the effect of polymer type and polymer mix ratio on HDF board. According to the results, while the polymer type, polymer mixing ratio, and the combination of the two factors were statistically significant in the MOR results, only the polymer type had a significant effect on the MOE and internal adhesion strength results. It was observed that the mixing ratio of polymer with wood fiber was also statistically significant on water absorption and swelling to thickness results.

According to the Duncan test results, the water absorption (WA (%)), swelling to thickness (TS (%)), and bending strength (MOE) values of the tested panels were statistically affected by changing the polymer ratios. The 24-hour dewatering test results were clearly improved with the increase in plastic waste. All plastic-added groups are lower than control groups and meet standard requirements. Thickness swelling results are similar to water absorption test results.

Although there is not much difference between the absorption and thickness swelling values of the plastic reinforced boards after 24 hours of waiting, this difference is higher in the test samples than in the control sample. According to this result, it was observed that PS material reduces the water absorption ratios of the boards and makes the boards better quality. In terms of modulus of elasticity (MOE) values, it was observed that the values of the group using PS waste did not change significantly from the values of the control group. The tensile strength results perpendicular to the surface are similar to other mechanical test results. In terms of mechanical properties, it was determined that PS wastes can be used for HDF production at different mixing ratios. It was observed that the fibers in the control group sample were regularly distributed and their morphology was well preserved. In terms of groups containing waste plastic, it was observed that the groups made of polystyrene were distributed quite well as a matrix on the boards. The PS waste shows good compatibility with the fibers, according to the microstructure photographs.

After soaking in water for 24 hours, the best results were obtained with the addition of 75% PS. The main reason for this situation can be shown that the very low melting point of PS and the homogeneous distribution of PS particles among the wood fibers. In addition, since PS has a low Tg point, it is possible to reduce the energy costs of the hot press by lowering the press temperatures applied in HDF production. HDF, which is used in the production of laminate flooring, can be produced with PS used plastic waste to a higher quality in terms of some mechanical and physical properties. Thus, it is possible to reduce the pressure on forest resources by reducing both environmental pollution and the need for wood.

A lab-level prototype of the product was developed. Experimental studies were done on it. However, it has not been transferred to the industry.

Tests:

The conformity of the density of the produced boards to TS EN 323 standards was examined. Three test specimens were created for each fiberboard group. The dimensions of these samples were 5x5x1 ,1 cm. Sample boards were weighed on a precision balance with a sensitivity of 0.01 g. Then thickness, width, and height measurements were made. The density of the control sample is 0.85 gr/cm3. The density value of a board with a PS ratio of 25% is 0.83, the density value of a board with a PS ratio of 50% is 0.84gr/cm3, and the density value of a board with a PS ratio of 75% is 0.83gr/cm3. These values are compatible with the TS EN 323 standard.

Measuring the humidity of the boards (24 hours): the humidity of the produced boards was examined with TS EN 323 standard. It was kept in an oven at 103 ± 2oC until it reached a constant weight. Cooling of samples removed from the oven after twenty-four hours was shown. The humidity value of the control sample was 6.79%.

The humidity value of the board with a 25% PS ratio was 5.01 %, the humidity value of the board with a 50% PS ratio was 3.06%, and the humidity value of the board with a PS ratio of 75% was 2.02%. Control sample values and humidity values in samples with a PS ratio of 25% were between 4 and 11 % and were compatible with the standards. The moisture values of the samples with 50% and 75% PS content were below the standard. This was proof that the dehumidification rate of the boards decreased. This result was important for the forest products sector.

Water absorption (%) over a 24-hour period: the humidity of the produced boards was examined with TS EN 317 standard. The weight of 50x50x11 mm samples was measured with a 0.01 precision balance and kept in a water bath device at 20 ± 2oC. The samples, which were kept for 2 hours and 24 hours, were measured at the end of the period.

The water absorption rate of the control sample, which was kept in water for two hours, was 19.97%. The water absorption rate of the board with a PS ratio of 25% is 1 1 .21%, the water absorption rate of the board with a PS ratio of 50% is 7.53%, and the water absorbtion rate of the board with a PS ratio of 75% is 3.74%.

The water absorption rate of the control sample, which was kept in water for 24 hours, was 67.09%. The water absorption rate of the board with a 25% PS rate is 35.33%, the water absorption rate of the board with a 50% PS rate is 21.10%, and the water absorption rate of the board with a PS rate of 75% is 16.24%. It was observed that the water absorption rate decreased as the PS ratio increased.

After analyzing all of the data, it was determined that the control sample had the highest water absorption rate, and the sample with the lowest water absorption rate was the 75% PS sample. This is important in terms of ensuring the dimensional stability of the plastic material and wood fiber boards. The maximum water absorption rate in HDFs is 35% according to the TS EN 317 standard. According to this data, it has been determined that the boards with 75% PS, 50% PS, and 25% PS are suitable for use. ThicknessSwelling Test: ThicknessSwelling experiments of the samples were performed with TS EN 317 standard. Sample dimensions were prepared as 50x50x1 1 mm. The thickness of the samples was measured with a digital caliper. It was kept in a water bath device at a temperature of 20oC. The samples, which were kept for 2 hours and 24 hours, were measured at the end of the period.

The swelling ratio to the thickness of the control sample, which was kept in water for two hours, was 7.34%. The swelling ratio to the thickness of the board with a PS ratio of 25% was determined as 2.61 %, the swelling ratio to the thickness of the board with a PS ratio of 50% was determined as 2.1 1%, and the swelling ratio to the thickness of the board with a PS ratio of 75% was determined as 96%.

The swelling ratio to the thickness of the control sample, which was kept in water for 24 hours, was 28.43%. The swelling ratio to the thickness of the board with a PS ratio of 25% was determined as 8.73%, the swelling ratio to the thickness of the board with a PS ratio of 15% was determined 5.44%, and the swelling ratio to the thickness of the board with a PS ratio of 75% was determined as 2.65%. It was observed that as the PS ratio increased, the swelling ratio to the thickness decreased.

When all of the data was analyzed, it was discovered that the control sample had the most swelling to its thickness, and the sample with 75% PS added had the least swelling to its thickness. This was important in terms of ensuring the dimensional stability of the plastic material and wood fiber boards. According to the TS EN 317 standard, the swelling ratio to thickness in HDFs was limited to a maximum of 28%. According to this data, it was determined that the boards with 75% PS, 50% PS, and 25% PS were suitable for use.

Modulus of Elasticity and Bending strength (N/mm2): Compliance of the samples with TS EN 310 standards was investigated. The Universal Tester was used to evaluate samples measuring 50x310x1 1 mm. The distance between the support points is determined as 200mm.

The control sample's average load can resist being deformed elastically determined as1784.26 N/mm2. The average load that the PS ratio of 25% group can resist being deformed elastically determined as 1462.58 N/mm2. The average load the 50% PS ratio group can resist being deformed elastically determined as 1775.04 N/mm2 and for 75% PS ratio group as 1874.86 N/mm2. When the results were investigated, it was determined that the elastic modulus values increased with the increase in the PS ratio.

The average bending strength value of the control sample was determined as 17.76N/mm2, the 25% PS samples value was determined as 17.78N/mm2, the PS 50% group value was determined as 21 ,46N/mm2 and 75% PS value group was determined as 25.64N/mm2. When the data were examined, the control sample was determined as the sample with the lowest bending strength value. The highest bending strength value was determined from groups of 75% PS. However, the fiberboards must meet a minimum of 40 N/mm2 according to the TS EN 310 standard, the all fiberboard sample values were not meet this requirement. This situation was thought to be due to laboratory conditions, and it was decided that it would be appropriate to compare it with the control sample.

Internal Bonding strength: the sample values were determined and investigated according to TS EN 319 standards. Samples were prepared from the boards as 50x50x1 1 mm produced in accordance with the standard. These prepared samples adhered to the aluminum blocks with hot silicone. Finally, the prepared samples were evaluated using the Universal Tester in a tensile test perpendicular to the surface.

The averange internal bonding strength values were found for the control group as 0.67N/mm2, for 25% PS groups as 0.63N/mm2, for 50% PS as 25.74N/mm2, and 75% PS as 0.97N/mm. It was observed that the lowest internal bonding strength was determined from 25% PS samples, while the highest internal bonding strength was determined from 75% PS group. When the values were examined, it was determined that the internal bonding strength increased with an increase in the PS ratio.

The mean, standard deviation, maximum and minimum values of the data obtained from the results of all experiments were determined in the Microsoft Excel program. RESULTS

In this study, PS and wood fiber were used as raw materials. Waste plastics were cut, ground, and sieved. Three groups of samples were produced with different ratios brought to standard sizes PS (25%, 50%, and 75% PS). As a control sample, the boards were produced from 100% wood fiber. Maleic anhydride was added to wood fibers during the test board production. The produced boards were resized for physical and mechanical tests. Several mechanical and physical features were determined according to the appropriate standards, which are TS EN 323 for density properties, TS EN 322 for moisture properties, TS EN 317 for water absorption properties and swelling to thickness properties, and TS EN 310 for elasticity modulus and bending strength properties.

When the density results of PS added samples were evaluated, the highest result was obtained in the group with 50% PS. When the humidity values were compared, the group with 75% PS received the lowest humidity. When the water absorption values were compared, the best results were obtained for the 75% group for the two-hour and 24-hour water absorption values.

When the thickness swelling values were compared, the lowest thickness swelling ratio was determined in the 75% group for two and twenty-four hours values.

It was determined that the 75% PS group had the highest bending strength value.

As a result of all these results, improvements were observed in the board properties of PS wastes added to wood fiber at different rates. In particular, its positive effect on dimensional stability is an important advantage for the fiberboard industry.

It was determined that the problems of moisture absorption, water absorption, and swelling to the thickness of HDF boards used in flooring can be solved to some extent by using waste plastic material.

It was considered that the evaluation of PS wastes in HDF production created an alternative raw material source as an additive for HDF production. It was anticipated that it will positively contribute to the HDF production system by reducing raw materials and production costs. It can be said that PS-added HDF boards will be widely used for the positive dimensional stability data of the composite material and will be produced with appropriate techniques. In addition, it aims to benefit the environment and the economy by evaluating plastic waste in this way. In addition, it is foreseen that Turkiye will provide significant advantages for fiberboard industry companies in international competition.