Effect of Pretreatment and Production Variable on the Sorption and Strength Properties of Cement Bonded Board

This study was carried out to investigate the effect of pretreatment on the sorption and strength properties of board manufactured from Gliricidia sepium sawdust. Twenty four (24) experimental boards were produced at three pretreatment levels of hot water (1 h), cold water (2 weeks and 4 weeks), three mixing ratios (1:1, 2:1 and 1:2), and one board density 700 g/m 3 . and test for their bonding strength by physical (water absorption-WA and thickness swelling-Th.S) and mechanical properties (modulus of elasticity-MOE, modulus of rupture-MOR). Data obtained was analyzed using analysis of variance at α = 0.05. The result showed that board produced from mixing ratio 1:2 (sawdust to cement) of hot water for 1 h pretreatment is more dimensionally stable since it has the least mean values 44.10 and 50.23 % for water absorption and 1.17 and 2.76 % for thickness swelling in 1 and 6 h immersion and highest mean values of 68.94 and 0.33 N/mm 2 for modulus of rupture and elasticity respectively. However, the analysis of variance shows that pretreatment levels and production variables have a significant effect on the physical and mechanical properties examined thus increase in pretreatment and mixing ratio resulted in the improvement of dimensional stability and increase in the strength properties of the board produced. of cement-bonded board from Gliricidia sepium sawdust.


Introduction
Wood is a natural organic material, a composite of cellulose fiber embedded in amatrix of lignin which resists compression (Kermani 1998). Its waste is residues derived during various conversion processes and is in the form of trimmings edgings slabs shavings, sawdust, etc. These wastes or residues are generated in large quantities as reported by Ajayi (2006) and the bulk of these waste generated in Nigeria was estimated to be 1.72 million cubic meters in 2001 and we can be sure to have doubled up the figure by now.
In view of the importance of saving energy and conversion of resources, efficient recycling of all wood waste is now a global concern requiring extensive works towards exploring newer application and maximizing use of existing technologies for a sustainable and environmentally sound management. It is therefore necessary to develop ways to utilize sawdust and reduce pollution with carbon dioxide emissions. A strategy of converting this wastes into value-added products must be imbibed like pyrolytic oil (Adegoke et al. 2014).
According to the end uses of wood wastes and their possible reuse products, particle boards have found typical applications like flooring, wall and ceiling panels, office dividers furniture, cabinets among others (Wang & Sun 2002;Adedeji 2011). Particleboard is a composite panel product traditionally produced from wood and its wastes (Erakhrumen et al. 2008) as this is the most common way to reuse these wastes (Yang et al. 2007;Lykidis & Grigoriou 2008). To manufacture particleboards with good strength, smooth surfaces, and equal swelling, the use of homogeneous raw material is required, so wood-cement bonded boards come into play. These are made from the combination of wood particles bonded with inorganic binding agents like cement, magnetite, gypsum, and water with or without the catalyst.
Wood-cement board (WBC) despite having its advantages as a major problem which is the inhibitory effects caused by wood on the cure of the cement and the high density of the final product, this is due to mainly to the extractives and polysaccharides inherent in wood (depending on its nature) which affects reactions between it and cement resulting in boards of low quality (Jorge et al. 2004). To solve this problem of inhibition, inorganic accelerators are added and also pretreatment of the wood particle which is the basis of this research work. This study therefore aimed at investigating the effect of pre-treatment and mixing ratio on strength and sorption properties of cement-bonded board produced from Gliricidia sepium sawdust.

Pretreatment of Sawdust
The sample was presented to remove inhibitory substance between woods, a lignocellulose material and cement, and inorganic binder before board formation. The treatments included hot water treatment and cold water treatment. Hot water treatment was carried out by boiling the water to 100 ͦ C poured unto the sawdust and leave for a period of 1 h and also for cold water treatment, the sawdust was left in cold water for a soaking period of two weeks and four weeks respectively in a plastic bowl. Thereafter, the water was drained off and the sample was air-dried to a moisture content of 12 %. It was then sieved with 2 mm mesh and kept in a sealed polythene bag against any further moisture.

Calculation of Weight of Materials
The quantities of the materials used for the production of the boards having the size 200 ×200 ×10 mm was calculated and measured out according to the level of combination in the experiment. The sawdust and ement were calculated based on the sawdust/cement ratio of (1:1, 2:1, and 1:2) using the formulae: ⁄ Where; D = density of board produced in g/m 3 , M = mass in g; V = volume in m 3 Water used in mixing the cement into a slurry form was also calculated. 0.30 0.60 Where; Wt=Weight of water (g); W=Wood dry weight (g); MC=Moisture Content (%); C=Weight of cement (g)

The Blending of Production Variable, Board Formation, and Pressing
The blended stock was transferred and formed on the dimensioned mold (200×200 ×10 mm) covered with a polythene sheet to form the mat, while another polythene was placed at the top of the formed mat before it was covered with plywood at the top. The formed mat was transferred to the cold press and pressed under pressure to the required thickness for 24 h.

Curing, Condition and Trimming
The formed mat was demoulded and left to dry for 21 days to allow for proper curing of the cement. The boards were then trimmed and edged to sizes and a test specimen was cut from the boards. The boards were strengths tested for strength and sorption properties (Falemara et al. 2014).  Badejo et al. 2011. The test samples used were trimmed to 50 × 50 mm and immersed in cold water for 1 h and 6 h. The water absorption of the samples was measured and recorded before and after immersion in cold water. The percentage of water absorption for each sample was calculated as: %

Data Analysis
The experiment adopted 3 3 factorial experiments in completely randomize design replicated 3 times making 27 boards altogether. The mixing ratio (1:1, 2:1 and 1:2); The pretreatment (hot water for 1 h; cold water for 2 weeks cold water for 4 weeks).
Analysis of variance (ANOVA) was conducted to estimate the relative importance of various sources of variation (mixing ratio and pretreatment) on the physical and mechanical properties of cement boarded boards produced. When the ANOVA indicated a significant difference among factors and levels, a comparison of the means was conducted, employing Duncan Multiple Range Test (DMRT) to identify which groups were significantly different at α = 0.05.

Results and Discussion
3.1 Physical Properties 3.1.1 Water Absorption (WA) Water absorption gives an idea of how wood cement boards behave when used under severe humidity conditions (Noor et al. 2012). The mean value of water absorption property was presented in Table 1. The value ranged from 44.10 -99.15 % and 50.23 -101.30 % at 1 h and 6 h respectively. The values for percentage water absorption property showed that board with hot water pretreatment at mixing ratio 1: 2 (fibre cement) has the lowest value of 44.10 % at 1 h and 50.23 % at 6 h of immersion. Conversely, the range of value recorded was higher than the range obtained by Amiandamhen & Izekor (2013) who both found out that the absorption of water by sawdust board and rice husk fine board was 25.96 -40.95 % in a ratio of cement to the particle of 70:30 while a board with the highest water absorption is from the pretreatment of cold water (4weeks) at mixing ratio of 2:1 of 99.15 % at 1 hour and 101.30 % at 6 h of immersion.
The board with the lowest water absorption might be possibly due to its maximum binding force between the sawdust and the cement and nearly complete filling of the pores by the cement which could limit the absorption by capillary action Davies & Davies 2017). The board with higher water absorption was detected to be more porous and absorbed more water. This phenomenon was attributed to the void spaces created by a small quantity of cement available to blind the sawdust fiber. These void spaces are easily stocked by penetrating water thus increasing the board's weight after soaking.
In general, it was observed that the behavior of the boards to water intake revealed that increase in pretreatment level (hot water at 1 h) and maxing ratio (1:2) produced boards that re more dimensionally stable than others and it showed highest resistant to movements; as similarly observed by Ajayi & Aina (2012). Boards with a pretreatment level (cold water at 4 weeks) and mixing ratio of 2:1 were observed to be more permeable and absorbed more water. Table 2 and 3 show the results of the analysis of variance conducted on the water absorption after 1 h and 6 h water immersion. The results show that all factors are significant in water absorption at 1 h and only mixing ratio is significant in 6 h immersion but pretreatment and interaction of the two factors is not significant at 5 % probability level in 6 h immersion.

Thickness Swelling (Th.S)
The result after 1hr and 6 hrs of cold water immersion is shown on the Table 1 which ranges from 1.17 -4.37 % at1 h, then 2.76 -6.52% at 6 h immersion. The high results obtained can be attributed to high compression ratio and compatibility, and also strong bond formation Ajayi (2013) due to the quantity of binder present in the board. This is similar to what was obtained by Kaplon, 2009& Terry 2011. The analysis of variance conducted on thickness swelling after 1 and 6 h of cold water immersion at 5% level of probability shown in Table 3 shows that there is a significant difference at the mixing ratio level of 1 h but none between pre-treatment, mixing ratio and interaction between the two factors at 1 and 6 h of immersion.   Table 4 below with mean values ranging from 0.1 -0.33 N/mm 2 . The highest value was observed to be from the mixing ratio level of 1:2 at hot water (1hr) pretreatment while the lowest was observed at a mixing ratio level 2:1 at cold water (4wks). However, it was observed that these values obtained were far lower than those observed by Ma et al. (2012) whose values range from 3 -3.5 N/mm 2 which may be due to the high resin content of the sawdust sample used. This result obtained is far lower even compared with the standard or minimum required for panels of general-purpose and interior fittings (Gokay & Aytak 2007). ANOVA revealed that MOR at 5 % probability level was not significantly different for both the pretreatment and mixing ratio but significant at the interaction of the two. 3.1.2. Modulus of Elasticity This is also presented in Table 4, and it ranges from 26.16 -68.94 N/mm 2 . The MOE values were high boards produced with hot water pretreatment (1 h) and mixing ratio 1:2 while its lowest at cold water pretreatment (4 wks) and mixing ratio 2:1. This may be because reinforcing particles being stiffer than the binder matrix which is contrary to most reports by several authors (Mehmet & Ayhan 2008). T his may also be due to the high resin content of the sawdust used.
The ANOVA result shows that MOE wasn't significant at a 5 % level of probability in pretreatment and mixing ratio but only significant in the interaction between the two factors (

Conclusion
The present study investigated the effect of pre-treatment and mixing ratio on strength and sorption properties of cement-bonded board produced from G. sepium sawdust hence it was observed that the board produced from the mixing ratio1:2 (sawdust to cement) with the pretreatment level of hot water (1hr) has more dimensional stability and strength properties. This shows that mixing ratio and pretreatments has a positive influence on both dimensional stability and strength properties of the board, but the sawdust to be used should be less resinous.