Synthesis of carbon material via pyrolysis and hydrothermal carbonization of rubberwood and its effect on thermal and mechanical properties of medium density fiberboard/ Tanveer Ahmed Khan

Faculty of Chemical & Natural Resources Engineering

Thesis (Doctor of Philosophy in Chemical Engineering) -- Universiti Malaysia Pahang – 2015

Bibliography : p. 160-180

The medium density fiber boards (MDF) provide an alternative to structural materials from furniture to flooring to crown molding. It is made from a slurry containing wood fibers and a thermoset resin usually urea formaldehyde (UF) bonded under heat and pressure. An MDF board should have high dimensional stability and high mechanical strength under adverse atmospheric conditions of temperature and humidity; these requirements strongly depend on the board processing conditions. Wood fibers have low thermal conductivity thereby imposing severe inhomogeneity during the curing process and leads to low internal bonding, poor modulus of rupture and low dimensional stability. The thermal conductivity of the wood fiber could be increased by nano/micro structured fillers. It is hypothesized that carbon materials, such as carbon black, carbon nanotubes, carbon fibers would offer high thermal conductivity considering the carbon–carbon bonding between wood fibers and carbon materials. In this work, the carbon material was synthesized by pyrolysis and hydrothermal carbonization (HTC) of rubber wood fibers and characterized by CHNOS analyzer, Xray diffraction (XRD), Brunauer, Emmett and Teller (BET) and scanning electron microscope (SEM). The carbon material and yield percentage obtained from pyrolysis method (operated at 500 °C for 4 hours) was 76.22 and 22 respectively. In addition, the carbon material and yield percentage of HTC method (operated at 260 °C for 7 hours and 35 times water) was 68.10 and 59.7 respectively. The prepared carbon materials were used as fillers in urea-formaldehyde adhesive in different weight concentration up to 5%. The dispersion of carbon materials into UF resin matrix were evaluated using Thermo gravimetric Analysis (TGA), Differential Scanning Calorimetry (DSC), Fourier Transform Infrared (FTIR), X-ray diffraction (XRD) and solution rheology. The uniform dispersion of the carbon material in the resin undertaken by mechanical stirring is confirmed on curing. The result from the curing reaction showed an increasing trend with the addition of carbon material concentration. The X-ray-based measurement of CrI indicates that carbon material increased the crystallinity of UF resin, whereas the maximum value was observed at CF-1 for both pyrolysis and HTC method i.e., 86.6% and 87.3 %. The MDF was prepared by mixing of rubber wood fibers and UF/carbon material, resin at different weight percentages, i.e. 1, 2.5, 3.5 and 5. The mixing of carbon materials enhanced the heat transfer during the hot pressing of MDF. The core temperature reached 100 °C in 72 seconds on the board made using carbon material synthesized by pyrolysis, whereas, it reached in 74 seconds in the case of carbon material synthesized by HTC. These values are on the lower side compared to the control board made without carbon material i.e., 84 seconds. The internal bonding (IB) strength and the modulus of rupture (MOR) estimated for the MDF is observed to have a maximum of 1 wt. % concentration of carbon material prepared by both pyrolysis and HTC method. The IB and MOR values of boards made by 1 wt. % of carbon material synthesized by pyrolysis and HTC are 0.71 MPa, 0.72 MPa and 37.63 MPa, 37.72 MPa, respectively which are significantly higher than the boards made without carbon material i.e, IB and MOR values are 0.56 MPa and 32.31 MPa respectively. The HTC method was optimized in order to obtain the best synthesis conditions. The best operating conditions such as temperature, time and water were investigated using response surface methodology. The carbon content % was taken a response and maximum carbon content % was observed at temperature 260 °C, water 35 times and time 7 hours.