ABSTRACT
The effect of mixing flax shives with casuarina particles as raw material on physical and mechanical properties of laboratory three layers particleboards was studied. Mixtures of Casuarina glauca particles and flax shives with ratios of 1:1, 1:3 and 3;1, respectively, were used in different combinations in surface or in core and/or in the three layers of the boards. The particles was blended with 3 and 10% urea-formaldehyde resin (based on oven-dry weight) for core and surfaces, respectively. Hand-made mat was formed and pressed at 22 kg/cm a and 150°C for 7 min.
Mechanical properties in static bending and internal bond as well as thickness swelling and water absorption were determined for the control and mixed boards.
A. The construction variables were as follows:
1- Board size: 30 by 30 cm by 12 mm in thickness.
2. Face-core-back weight ratio: 25; 50: 251.
3. Binder: Commercial urea-formaldehyde, 40 percent resin solids.
4. Resin solid content: Face 10% and Core 8% (based on ovendry (OD) weight of the mixture).
5- Wax content: 0.5% for core and one percent for face and back layers (based on OD weight of the mixture).
6. Catalyst: 1.5% (liquid-to liquid weight basis) of the following solution: 16.8% ammonium chloride, 14.8% hexamethyl ethylene tetramine and 68.4% water.
7. Mat moisture content: 8 and 10% for core and surface layers, respectively.
8. Pressing conditions:
Press temperature: 150°C
Press time : 7 min. including one min. closure time,
Pressure : 22 Kg/cm2
B. Board Manufacture:
The raw material of C. glauca was prepared using a ring flaker at Modern Arab for Timber Industry Co. (MATIN), Alexandria. The particles were taken after drying at about 4% moisture content and screening. The flax shives were taken from Tanta Company for Flax and Oils. The screen analysis of C. glauca wood and flax shives are
presented in Table 1.
Constant weight were used for each of core and surface layers of a board. The percentages of wood particles were 25, 50, 75 and 100% which was replaced with the equivalent OD weight of flax shives. The particleboards were prepared in a random order according to the following procedure:
(a) The particles were blended in a drum-type blender designed and manufactured at the faculty of Agriculture, Alexandria University, that provided a uniform distribution of the resin on the particles and/or shives.
(b) Resin, wax and catalyst were nixed together and applied by spraying.
(c) After removing particles from the blender, the moisture content, and correct weight for face and core were determined. Then the mat was hand-filted with random orientation onto stainless steel plate having dimensions of 30 by 30 cm. The formed mat was loaded into single opening hot press (Carver 2669) and pressed to 12 mm thickness. After
pressing, the finished board was allowed to cool. The boards were not sanded.
C. Preparation of Specimens and Testing
Three specimens were used (one for each board) to determine the average modulus of elasticity (MOE), modulus of rupture (MOR) in static bending and Internal bond (IB) . Three specimens also were utilized for thickness swelling (TS) and water absorption (WA) tests.
The test specimens for mechanical properties were conditioned at 20 C and 65% relative humidity (RH) before testing according to the procedure outlined in ASTM D-1037 (1978) with some modification due to the small size of the board.
The dimensional stability tests consisted of measuring the change in weight and thickness from equilibrium condition to water soak at 20°C for 2 and 24 hr. Specimens were weighed to the nearest 0.01 g. Thickness were measured to the nearest 0.05 mm at the center of each specimen.
RESULTS AND DISCUSSION
The averages of strength and dimensional stability properties of particleboard made of a mixture of C. glauca particles and flax shives using different percentages of flax shives are presented in Table (2) . In addition, the analysis of variance is presented in Table (3). It is obvious from the analysis of variance that there is a significant difference between the properties of particleboards processed from the different mixtures of C. glauca particles and flax shives. The effect of addition of flax shives on the different properties is also shown in Figs (1,2,and 3).
The highest values of MOR, MOE and IB Strength were obtained when 75% of flax shives are mixed in back and face layers whereas, the core layer is made of C. glauca praticles only. In addition, the MOR and IB strength of boards were not significantly different from those made out of flax shives only (fig. 1). However, MOE was significantly higher than that of flaxboard. Furthermore mixing of flax shives at the above indicated level resulted in an increase of 29.3%, 57.3% and 44.2% in MOR, MOE and IB strength, respectively, relative to the control.
It is apparent from the result of dimensional stability that the lowest value for thickness swelling after 2- hour water-soak test was obtained when flas shives are mixed in the face and back layers and the core is made from C. glauca particles (Fig.2) . However, no significant difference was found among the particleboard made with different percentages of flax shives (i.e. 50%, 75% and 100%). With regard to TS after 24-hour water-soak test, the lowest value was obtained when flax shives are mixed in the face and back layers only, but the differences between the different mixtures in those layers and the control (100% C.glauca particles) were not significant.
Water absorption after each of the two periods of water soak test was the lowest when the face and back layers of particleboard consisted of 75% flax shives and the core is made of C. glauca , particles only. However, the difference between boards made with the different percentages of flax shives in those layers were not significant (Fig. 3).
It is evident from the above results that strength properties of particleboard made of 75% of flax shives in the face and back layers and the core from C. glauca particles, only gave higher values than those obtained with other percentages of flax shives or made entirely of C. glauca particles. The thickness swelling and water absorption were reduced at the above indicatd level and location of flax shives.
Mixing casuarina particles with flax shivea in the face and back layers, causes reduction of the density of the board and hence increases the bonding quality which in can improve the properties of the board. Other studies (Gertjejansen et al. 1973, Vital et al. 1374, Coleman III andBiblis 1976, Kelly 1977, and Wojcik et al . 1989) have also demonstrated the advantages achieved by mixing wood species.
Accordingly, mixing wood particles with other lignocellulosic particles, is a good mean for improving the quality of casuarina
preticleboards produced in Egypt.
CONCLUSION
Based on the results of the present study, the following conclusions can be made
1. Mixing flax- shives with casuarina particles improve the strength and dimensional stability properties of particleboard.
2. Strength porperties of particleboard made of 75% flax shives in the face and back layers and the core from C. glauca particles only gave higher values than those obtained with other percentages of flax shives or made entirely of C. glauca particles.
3. The thickness swelling and water absorption were reduced at the above indicated level and location of flax shives.
REFERENCES
American Society for Testing and Materials- 1978. Standard methods of evaluating theproperties of wood—base fiber and particle panel materials. ASTM D 1037-78 Philadelphia. Pa. USA.
Coleman III, G.E. andE.J. Biblis. 1976. Properties of particleboard from Southern yellow pine and cottonwood mixtures. Forest Prod. J. 26(1); 48-51.
El-Osta, M.L.M.; M.M. Megahed, andM.M. El-morshedy 1988. Properties of particleboard from windbreak trees. Alex. J. Agric . Res. 16 (4) : 46-59.
Gretjejansen, B.R. ; M. Hyvarinen; J. Haygreen. and D. French, 1973. Physical properties of phenolic-bonded wafertype particleboard from mixtures of aspen, paper birch and tamarack, Forest Prod. J. 23 (6): 24-28.
Kelly, M.W. 1977. Critical literature review of relationships between processing parameters and physical properties of particleboard. USDA For . Serv. , Gen. .
Tech. Rep. FPL-10. For. Prod. Lab. Madison. Wis.
Kelly, U.W. and E.W. Price. 1985. Effect of species and panel density on durability
of structural flakeboard. Forest Prod. J. 35(2) ; 39-44.
Vital, B.R.; W.F. Lehmann; and R.S. Boone. 1974. How species and board densities affect properties of exotic hardwood particleboards. Foest. Prod. J. 24(12); 37-45.
Wojcik, U.K.; P.B. Blankenhorn; and R.E. Labosky Jr. 1989. Comparison of red maple
(Acer rubrum L.) and aspen (Poplus grandidentata Michk) 3-layer flakeboards. Wood and Fiber Sci. 21(3) : 306-312.
1 This research was partly supported by the Ford Foundation under Grant Number 860-0710.
▲ Download complete version of the paper including figures and tables. Click Here ▲ Top
|
