Tez özetleri Astronomi ve Uzay Bilimleri Anabilim Dalı

Effect of Storage Conditions of Wood Chips Pile on Physical and Mechanical

Properties of Fiberboard
Although the number of wood-based panel manufacturers in Turkey has been increased year by year, the native wood resources could not supply enough wood material. In particular, the manufacturers in Marmara region supply their wood material as chips by ships from overseas countries such as USA, Canada, Venezuela due to the raw material deficiency in this region. There is no any study about effect of outdoor chip pile storage on the quality of fiberboard. In this study, effect of outdoor chip pile storage on physical and mechanical properties was investigated. It was aimed to share the results with the literature and the fiberboard manufacturers.
Pine wood chip as raw material used in this study since it is the most piled wood specie on the woodyard of the fiberboard manufacturers in Turkey. Turkish fiberboard manufacturers import mostly bark free pine wood chips from overseas and stored outdoors. This research was carried out at Gebze Factory of Kastamonu Integrated Wood Company. For this aim, it was prepared a normal size pile from pine wood (Pinus palustris, Southern pine) chips imported from USA. The dry process high density fiberboards (HDFs) were manufactures from the piled chips at different storage times such as 1. day, 15. day, 30.day, 45 days, 60 days, 90. days, 120 days, and 180 days. The pH values and moisture contents of the wood chips for each storage time were measured. Two HDF panels with dimensions of 2081 mm x 2632 mm x 8 mm were manufactured for each storage time.
Physical properties of experimental boards such as moisture content density, thickness swelling, and formaldehyde emission; and mechanical properties such as bending strength, modulus of elasticity in bending, and internal bond strength were performed on the test specimens. The pH value of the HDF panels decreased from 5.66 to 3.93 as the chip piles storage time increased to 180 days. Moisture content of the panels decreased from 101.2% to 80.8% as the chip piles storage time increased to 180 days. It was concluded that this was caused by the degredation of wood chips due to bacteria and fungi activities, and egzotermic reactions.
There was no significant difference (p<0.05) among the HDF groups in terms of moisture content (8.13-8.32%) and density (871-874 kg/m³). The moisture content and density of the boards were compared with EMB/PS/HDF (1997) standard of Association of European Producers of Laminate Flooring since there was no any information in TS 64-5 EN 622-5 standard. The values of moisture and density met the requirement of EMB/PS/HDF (1997). It was found a significant difference among the HDF groups in terms of thickness swelling ratio. The thickness swelling values of HDF panels increased from 7.32% to 9.69% as the chip piles storage time increased to 180 days. The thickness swelling values of all panel groups were between the values (4-11%) specified by EMB/PS/HDF (1997). The pile storage conditions significantly affected the formaldehyde emission of the HDF groups. As the chips pile storage increased to 180 days, the formaldehyde emission of HDF panels increased from 7.14 mg/100g to 9.78 mg/100 g. The formaldehyde emission of all HDF panels, except for the HDF panels made from the chips piled beyond 15 days, met the maximum value (8 mg/100 g) of E1 class HDF panels specified by EMB/PS/HDF (1997). The increment in the formaldehyde emission of the HDF groups was mainly attributed to the decrement in the pH value and and biological degradation of the piled wood chips. The increment in the pH values of the chips results in the precuring of the mat with resin and this causes to the increment formaldehyde emission of the panels.
The mechanical properties of the HDF panels were negatively affected by the chips pile conditions. As the pile storage time increased to 180 days, the bending strength of the panels decreased from 46.96 N/mm² to 38.11 N/mm² and modulus of elasticity in bending decreased from 4117.8 N/mm² to 3373.5 N/mm². All the HDF panels, except fort he HDF panels made from chips piled 180 days, met the minimum bending strength value (40 N/mm²) of EMB/PS/HDF standard. All the panels met the minimum modulus of elasticity value (2700 N/mm²) of EMB/PS/HDF standard. Internal bond strength of the HDF panels decreased from 1.71 to 1.04 N/mm² due to the piles storage conditions.
All the HDF panels, except fort he HDF panels made from chips piled 180 days, met the minimum internal bond strength value (1.20 N/mm²) of EMB/PS/HDF standard. During the storage of wood chips, bacterial and fungi activities cause the degradation of hemicellulose, cellulose, and lignin, and decreasing pH and increasing pile temperature cause to the weaking of cell wall, low bonding performance between wood fibers in the panel, decreasing to mechanical adhesion of urea-formaldehyde resin to wood fibers, the precuring of the resin applied to the wood fibers before hot pressing and decreasing of polymerization of cellulose, and finally concluded that these factors decreased the HDF panel quality. Based on the findings obtained from the present study, it can be said that the wood chips should not be piled beyond 1 month to minimize negative effects of storage conditions on the HDF quality and should be paid attention to the preparation of chips pile and its control.