The Effects of Boric Acid on Fiberboard Properties

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The growing awareness of health towards the environmental implications associated with building materials 13 has increased the attention towards natural materials. However, Tthe natural fibers have often been 14 reported to have good insulation properties, have no harmful effects on health, and are available in large 15 quantities often as a waste product of other production cycles [1]. In recent years, natural fibers which are 16 have considered as environmentally friendly materials have been considered raw materials for producing 17 insulation panels (i.e. sound or heat) at a reduced cost. For that reason, those materials are becoming an 18 important alternative to traditional synthetic ones for building applications [2]. A number of researchers have 19 already reported that panel products from secondary fibers exhibit appropriate properties, often more 20 advantageous than synthetic fibers [2][3][4][5][6]. 21 Based on their microscopic configurations, porous absorbing materials have been classified as cellular, 22 fibrous, and granular [7]. The fibrous materials generally include a series of tunnel like openings that are 23 formed by interstices in material fibers. However, pores that a continuous channel of communication with 24 the external surface of the material called "open pores" allow sound absorption properties some level [7]. It 25 has is well established that in order to absorb sound, materials should have high porosity to allow the sound 26 entering in their matrix, and facilitate its for dissipation. Nevertheless Moreover, there is still little knowledge 27 about the sound absorption behavior of cellulosic fibers especially secondary fibers from various sources. 28 On the other hand, thermal insulation has become important issue for housing and building constructions 29 worldwide. Therefore However, numerous insulation products have been already developed with 30 technological advances. The legislations have acted as the basic requirements under the building 31 constructions in many countries. These products vary in terms of color, surface finish and texture, core 32 composition and, most importantly, performance. Moreover, cellulose based products have already 33 reported to be good insulation products in building applications [7][8][9][10]. Yet the market is still dominated by 34 synthetic insulating materials. It has already well established that cellulosic fibers are have defined as high 35 wettability and absorbability as an open pore structures. Due to their special structure, the cellulose based 36 materials need to be protected/modified against abiotic and biotic biological attacks (e.g. against fungi, sun, 37 rain, heat, etc.,) [11]. Nevertheless, the negative properties of cellulosic materials may be largely modified 38 by chemical treatments. 39 An understanding of the phenomena of noise, materials used for its suppression, and the characterization 40 of those materials for predict their acoustic performance is necessary while successfully developing 41 materials for acoustic absorption applications [10]. Following literature reviews of previous studies about 42 the insulation properties of some natural materials, it was considered that the porous structure of medium 43 density cellulosic composites might give advantage for insulation purposes.

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However, the secondary fibers are typically shorter and stiffer (rigid) than the original fibers. However, as a 46 result of recycling process, the fibers are undergoing various modifications. Some of the important 47 modifications are; length of fibers has shortened, surface areas narrowed, and the bonding potentials 48 decreased. Theoretically, it is known that long fibers have higher strength, surface area and bonding 49 properties than short fibers. Those clearly influenced swelling/plasticizing and hydrogen bonding potential 50 of fibers. Thereby, the mixture of wood fiber and secondary fiber is used to improve strength properties of 51 boards and evaluate effects of secondary fiber content in furnish.

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This study presents the basic knowledge and approaches for determining the acoustic and thermal 54 performance of cellulosic composites that were produced from recovered secondary fibers in a manner that 55 may help materials researchers new to this area gain the understanding and skills necessary to make 56 meaningful contributions to this field of study. 57 58

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The post-consumer waste papers (office and newspaper) and old corrugated container products (OCC) 61 were obtained from local waste paper trader, Isparta, Turkey. The boric acid was supplied directly from 62 Etibor A.Ş, as laboratory purity, Bandırma-Turkey. 63 The waste papers were carefully sorted according to their inherent properties. That are; office papers coded 64 as A; newspapers coded as B; and OCC coded as C. These waste materials separately were converted to 65 pulp using a 5 L. capacity, laboratory type standard disintegrator in water. 66 The first step of this study was to prepare boards from recycled secondary fibers individually in order to 67 determine the suitability of these waste materials for insulation purposes. The second step was to determine 68 the effects of secondary fiber proportions (A/B/C) in wood fiber (W) and boric acid addition (BA,%) on the 69 performance of the boards. large tube is used for measuring low-frequency sound absorptions (between 50 Hz and 1.6 kHz). In this 78 sense, samples with a diameter of 100 mm are prepared for large tube measurements. However, a small 79 tube is useful for measuring sound absorption coefficient in the 1.6 kHz to 6.4 kHz frequency range. Hence, 80 samples with a diameter of 29 mm are prepared to make measurements in a small tube as well [15]. In 81 based on the impedance method, the sound absorption coefficient (∝) is expressed by the following formula 82 (1, 2) [16,17]. 83 Where, R: sound pressure reflectance coefficient, Zs: surface impedance (Pa s/m), Ρ0: characteristic 86 impedance (Pa s/m), c: sound velocity (m/s). 87 Table 1 Table 2. It can realize that the sound absorption properties of boards were generally better in 95 high frequencies. This is important for considering board's sound absorption coefficient influenced by 96 frequencies. In this regard, these materials could be utilized in specific sound or frequency level as sound 97 barrier materials. 98 When the sound absorption coefficient was measured by the impedance tube method, even thin samples 99 (10 mm) utilized, it was observed that the board's sound coefficients have increased at the 1000-2000 Hz 100 impedance range. It is important to note that peak sound absorption coefficient increase at 0.81 levels of 101 the boards made from secondary OCC fibers at 2000Hz range. Similarly, boards made from boards made 102 from secondary office fibers and newspaper fibers were shown 0.60 and 0.56 sound absorption coefficient, 103 respectively at same impedance range (2000 Hz). It looks like there is a positive correlation between 104 frequency and sound absorption properties. It could be concluded that it is possible to use boards made 105 from secondary paper fibers as a sound absorbent material in the constructions with specific range. 106 In order to examine the effect of fiber type and boric acid content at various frequencies, the sound 107 properties of boards are shown in Figures 1-3. The sound absorption of board appears to be well correlated 108 secondary fiber/wood fiber proportions. However, the sound absorption values of boards made from office 109 secondary fiber/wood (Fig. 1) show a sound damping that it was steady increase up to 3000 Hz and then 110 decreasing. Interestingly, boards made from mixture of secondary newspaper and OCC fibers with wood 111 shows more less similar shape (Figs. 2-3). It is clear that at middle level frequencies and lower boric acid 112 addition (5.0%), the boards made from equal proportion of wood and secondary OCC and newspaper fibers 113 show markedly improved sound barrier properties. It was also realized that the sound absorption shows a 114 various level of increase and decrease with some variables but in high frequencies it shows sudden 115 increase in all conditions. It may be suggested that at middle level noise frequencies, the boards made from 116 equal proportion of wood and secondary newspaper (Fig. 1) and OCC shows (Fig. 3) markedly improved 117 sound properties some level. The presented data clearly show that the sound frequencies, fiber mixture 118 proportions and non-fibrous content in furnish (boric acid) influenced board's sound absorption properties. 119 Moreover, these comparisons between the boards and the measured results reveal that the secondary 120 fibers response of a board with initial sound properties similar to wood (Table 2) up to 4000 Hz and beyond  121 this level, the sound absorption markedly decreased (Figs. 1-3). 122   In thermogravimetric analysis, the mass (weight) of specimen is monitored continuously as the ambient 157 temperature reaching to 1200 ºC. During these heating, the graph drawn by the mass lost against the 158 temperature is called "thermogram". This thermogram is used for qualitative and quantitative analyses of 159 samples. The thermogravimetric analyzer has a precision analytical technique and provided with furnace, 160 temperature controller, computer based program and a recorder. The recorder save data and drawn graphs 161 of the sample mass modification against the temperature. It has conducted in an inert gas atmosphere. In 162 TGA technique, purity, degradation behavior under various temperature and chemical kinetics of sample 163 are examined. 164 165 (Above comment should be placed in the Materials and Methods section) 166 167 A typical TGA and DSC diagrams for boards made from secondary newspaper's fibers (B) are shown 168 in Figure 5 and Figure 6, respectively. It can be realized that increasing boric acid content has negative 169 positive impact on thermal degradation that decomposition temperature was increased in all boric acid 170 (5.0-10%) addition conditions (Fig. 5), compare to boards that made without boric acid (0%). This is an 171 important result considering boric acid affects improving board's thermal resistance. However, this 172 might be expected considering a number of literature findings on composites containing boric acid's 173 thermal resistance properties. In TGA micrographs, regions were determined for the approximate 174 starting and ending points of the TGA curve, which shows the breakdown of the organic matter and 175 volatiles [20]. Initially, up to 100 ˚C, 7-10% mass loss occurs due to vaporization of moisture in the 176 material. However, at the range of 110-220 ˚C, the mass remains approximately constant, with no water 177 remaining in the cell wall. After this point, the organic matters started to warm up and two disruptions 178 occurred. There is progressive increase of mass lost between 300-360 ˚C and total mass of sample 179 reached to 75-80%. Increasing temperature from 400 to 900 ˚C, the passage to the gas flow is 180 accelerated and the cell wall is degraded by the internal pressure. This is occurring at lower slope than 181 the other temperatures and the mass loss reached to 90%. At this level (900 ˚C) the evaporation of cell 182 wall constituents has completed and pure carbon remains. It is important to note that the endothermic 183 peaks at 71 ºC, 266 ºC and 333 ºC for DSC (Fig. 6) have clearly consisted with TGA curves. The summary data of TGA analyses are shown in Table 4. It could be seen that increasing boric acid has 200 negative positive impact on thermal degradation that decomposition temperature was increased for all 201 boards manufactured with secondary fiber and boric acid content. This is clear effects for improving 202 degradation against thermal of boards made with boric acid.

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The results presented in Table 4 show the samples had different decomposition temperatures. It can be 204 realized that thermal stability of boric acid treated samples increased as compared to control samples (A0,

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B0, C0). However, this increasing for 10% BA addition is higher than 5.0% BA added panels. As a result,

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there were some differences between samples treated with BA in different concentration. It was also found 207 that the changes in TGA curves for samples were somewhat similar shape, but there was usually less 208 weight loss of 10% BA treated samples. properties compare to materials that generally utilized in construction for sound absorbing purposes.

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However, as a result of the measurements made on the boards, we could be summarize that the increase 232 the amount of secondary fiber content in furnish usually positively effects in terms of sound barrier 233 properties while boric acid has not shown any improvements of that properties. Thus, fibers from waste 234 paper products could be support and provide functional benefits for sound insulation purposes in buildings.  Moreover, the boards made from secondary cellulosic fibers could be used for some building applications 249 regarding thermal and acoustic insulation purposes. Because, these fibers are competitive materials thanks 250 to their low density, good mechanical properties, easy processing, high quantity availability, low price, and 251 reduced environmental impacts for their production. 252 253