The effect of combined modification of blue warm nano silver on pressing time and functional properties of particle board

Dissertation for receiving a master's degree in the field of preservation and modification

Abstract

In this research, the effect of colloidal nanosilver-hot water combined modification on heat transfer from hot press plates to the heartwood of beech (Fagus orientalis), physical and mechanical properties Chipboard and chemical changes of treated chipboard were investigated through FTIR spectroscopy. The treatment was carried out in 4 control groups, warm water, nano and nano-warm water. Of course, hot water and nano-hot water treatments were performed at two heat levels of 150 and 170 degrees Celsius and two time levels of 30 and 45 minutes. A total of 10 treatment levels were obtained. Colloidal nanosilver with a concentration of 100 ppm was prepared. The mechanical resistance of the boards including modulus of elasticity, modulus of elasticity and internal adhesion were measured according to DIN-68763 standard and the physical properties of the boards including water absorption and thickness shrinkage after 2 and 24 hours immersion in water were measured according to EN-317 standard. In order to investigate the effect of silver nanoparticles on heat transfer, boards were made with a pressing time of 5 minutes and the temperature in the middle layer of the chipped cake was recorded every 30 seconds by thermocouple. Electron microscope (SEM) images have clearly proven the presence, size and proper distribution of colloidal silver nanoparticles in wood chips. The results of FTIR spectroscopy show the breakdown of acetyl groups of hemicelluloses and the reduction of hydrophilic areas of wood chips modified by hydrothermal and nano-hydrothermal methods. Combined nano-hot water modification accelerated the heat transfer rate to the middle layers of the cake. Nano-hot water treatment at high temperature (170 degrees Celsius) and also in the last minutes of the press showed a significant improvement in heat transfer compared to the control and hot water samples. Also, boards containing nanosilver reached the temperature of 100 degrees Celsius in less time (92 seconds) than all the treatment levels. The results showed that the nano-hot water treatment led to a decrease in modulus and internal adhesion, an increase in modulus elasticity, a decrease in water absorption, and an improvement in the thickness of the boards. The greatest improvement in physical properties was observed in boards made with wood chips treated with nano-hot water method at 170 degrees Celsius for 45 minutes. With the increase of temperature and treatment time, the reduction of MOR and improvement of MOE became more noticeable, but with the increase of treatment time, it showed a further decrease at a temperature level of IB. Also, all the physical and mechanical properties of boards made with nano-saturated wood chips were higher than the control.

Key words: Nano colloidal silver-hot blue, chipboard, heat transfer, physical and mechanical properties

Part I Introduction and Generalities

1-1- Introduction

Wood has always been considered as a very important material since the beginning of man. In recent years, the market for the consumption of compressed wood has expanded significantly. One of the main reasons is the special advantages of wooden panels, such as uniformity of functional properties on the surface of the panel, the possibility of production in large dimensions and a smooth surface with good quality (Toman [1] et al., 2010). Among the various products made from wood products, chipboard is of special importance due to its variety of uses, relatively simple production process and flexibility of raw materials. This industry was industrialized in the early 20th century and developed significantly with the production of synthetic resins in the 40s to 60s (Fathi et al., 2009). In addition to the unique features of chipboard, this material has undesirable features such as dimensional instability that results from the exchange of moisture with its surrounding environment. This feature changes the dimensions of wood and affects its mechanical, thermal, acoustic and electrical properties. Also, this material has characteristics such as biodegradation, weathering, flammability and so on. It is.

As a result, if wooden products are used under unfavorable conditions (especially for outdoor use) without any corrective treatment, their quality will be affected and their useful life will be limited. In order to improve the properties, treatments should be applied to composite wood products to increase their use.In recent years, more wood modification methods are used to solve environmental problems, and improve the properties of wood and its products, and heat treatment is one of these methods (Hale [2], 2006). In thermal decomposition, hemicelluloses are more susceptible to degradation than other wood polymers (Stam[3], 1964; Allen[4] et al., 2002). Degradation of cellulose occurs at higher temperatures than hemicellulose, although sometimes at low temperatures the degradation of hemicellulose is very slow (Hill, 2006). By heating wood in air to more than 120C, the degree of polymerization (DP) decreases (Fengel and Wegner [5], 1984). In the initial stages of the treatment, an increase in the degree of crystallinity and the extent of the crystalline areas were observed, but as the treatment time increases, both decrease (Hale, 2006).

Heat treatment leads to changes in various physical properties, such as a decrease in equilibrium moisture (Obataya et al., 2000; Obataya and Tomita[6], 2002), a decrease in hygroscopic properties (Metsa Kortlinen[7] et al., 2006;), improvement in adhesion (Fulreich[8] et al., 2006), improvement in natural durability (Bonestra[9] et al., 2006; Hanger[10] et al., 2002; Siler[11] et al., 2000), increased crystalline areas[12] of cellulose (Boyan[13] et al., 2000; Tejada[14] and et al., 1997; Odaka and Ferno[15], 2003) and the apparent amount of lignin (Kamdem[16] et al., 2002; Nupenen[17] et al., 2004). On the other hand, heat treatment reduces the strength and resistance of wood (Avimi and Westermark [18], 2005; Hong and Lin [19], 2000; Kamdem et al., 2002), and the amount of this reduction is related to the treatment time and the type of wood. The reduction of resistances is more in conifers than in broadleaves (Bengtson [20] et al., 2002). In the process of making chipboard, the pressing stage is very important, which has a direct impact on the functional properties of the product as well as the production efficiency (Dosthosseini, 2010). Examining the effect of heat transfer of the press and its relationship with the physical and mechanical characteristics of the product helps us in achieving the best quality. In recent years, many efforts have been made to reduce the press time and increase the efficiency of the production line. In this regard, the progress of science has gained a significant speed with the advent of nanotechnology.

The use of nanotechnology in various sectors of wood industry is increasing (Selikar[21], 2005; Taghiyari, 2010). It has been proven according to various researches. Adding metal nanoparticles to wood and its products improves physical properties (Bahmani, 2011; Ebrahimenjad, 2010; Siahpasht, 2010; Yekekhani, 2010), increases wood resistance (Bahmani, 2011; Rangavar et al., 2013; Akhtri et al., 2012) and improves heat transfer (Laighi et al., 2019; Farajollahpour, 2012; Taghiari et al., 2011; a2012). On the other hand, heat treatment after saturating wood with metal nanoparticles transfers heat faster and causes more changes in wood characteristics due to its thermal conductivity (Siahpasht, 2010; Taghiyari, 2010). For this reason, in this research, the effect of hot water treatment on chipboard saturated with nanoparticles will be investigated.

1-2- Research hypotheses:

1- Nanosilver-hot water combined treatment will significantly improve the physical properties of chipboard compared to hot water treatment.

2-Nano silver-hot blue combined treatment changes the mechanical resistance of wood.

3- Nano silver increases heat transfer in wood chips, it is possible to apply heat treatment at lower temperatures and reduce pressing time.

1-3- Research goals:

Decreasing hot pressing time during construction Board.

Maintaining the mechanical resistance of modified chipboard at the standard level.

Increasing the dimensional stability of modified chipboard using the combined nano-thermal method.

In this research, broadleaf beech wood native to Iran was used due to the wide coverage of forests in the north of the country.

In this research, the effect of silver nanoparticles with high thermal conductivity on hot water treatment of beech wood chips was studied.