Effects of pulping conditions and processing variables on the performance of kenaf medium density fibre board
Kenaf, Hibiscus cannabinus L., is a environmentally friendly crop which is recognized as one of the potential lignocellulosic material to replace wood in different kinds of wood based products. Kenaf has excellent properties for pulp and paper, medium density fibre board (MDF), and other composit...
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| Format: | Thesis |
| Language: | English |
| Published: |
2014
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| Subjects: | |
| Online Access: | http://psasir.upm.edu.my/id/eprint/76083/1/IPTPH%202014%208%20IR.pdf |
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| Summary: | Kenaf, Hibiscus cannabinus L., is a environmentally friendly crop which is recognized
as one of the potential lignocellulosic material to replace wood in different kinds of
wood based products. Kenaf has excellent properties for pulp and paper, medium
density fibre board (MDF), and other composites, as it has a low density, little abrasion
during processing, high filling levels, and high specific mechanical properties. The
kenaf stem is composed of an outer layer (bast) and a core which either by chemicals
and/or by enzymatic retting it is easy to separate. The bast constitutes 25 to 40% of the
stem dry weight and shows a dense structure. Alternatively, the core is wood-like and
makes up the remaining 60 to 75% of the stem. Both portions are greatly different ties in
terms of anatomy, physical and chemical content.
Studies concerning the production of medium density fibre board (MDF) with kenaf as
an alternative fibrous material have been carried out as an attempt to provide a
sustainable and viable destination for this lignocellulosic material. This work aimed to
evaluate the properties of kenaf fibres at different refining conditions and to produce
kenaf MDF of acceptable strength. In this dissertation, MDF was prepared from kenaf
and rubber wood and their mixture. The parameters of preparation and the resulting
intermediate products as well as the final products, MDF, were characterized and
compared at each experimental step.
The investigation of fibre dimensions based on pulping of bast and core fibre resulted in
different behavior of the two classes of fibre. There are significant variations in all
aspects of fibre morphology of bast fibre at different pulping temperatures and pulping
time, and a significant interaction was detected between both parameters. The bast fibre
produced longer and thinner fibre, compared to the core fibre, thus yielding fibre of
higher aspect ratio. The changes in fibre morphology were clear when the pulped
temperature increased. The core fibre exhibited significant variations in fibre length,
fibre width, and wall thickness in all parameters. The lumen diameter and aspect ratio fibre width, and wall thickness in all parameters. The lumen diameter and aspect ratio
were not significantly affected by differences in pulping temperature, pulping time, and
the interaction between both parameters. The fibre width was reduced at an increasing
pulping temperature and time, but lumen diameter was not significantly affected. The
aspect ratio also decreased with increasing pulping temperature and time. The length of
core fibre decreased with increasing pulping temperature and pulping time. The fibre
width shows constant reduction as the pulping condition become more severe.
Consequently the Runkel ratio was decreased also. The pH value of both fibres was
reduced as the temperature increased; core fibre was more acidic (pH= 3.8) compared to
bast fibre (pH= 4.5). It is evident from results that bast fibre is more resistant to acid and
displayed greater acid buffering capacity compared to core fibre.
The investigation of the effect of refining pressure (6 and 8) and resin content (10, 12,
14 %) on physical (WA and TS), and mechanical (MOE, MOR, IB) properties MDF
made from a mixture of biomass kenaf (Hibiscus cannabinus L.) stem and rubberwood
showed thermo-mechanical refining and resin content were influential in the increment
of physical and mechanical properties of the MDF. For 8 bar of refining pressure with
14% resin content, the MDF recorded optimum WA of 83.12%, TS of 20.2%, MOR of
25.3 MPa, MOE of 3450 MPa and IB of 0.51 MPa [density 700 (kg/m3)].
Response surface methodology was used to establish the optimum process variables
(resin content, and pressure) for effect on board properties. By using response surface
and contour plots, the optimum set of operating variables can be obtained graphically, in
order to achieve the desired board properties. Therefore, it was recommended that the
board properties increase when the resin content and pressure increased. It can be
inferred that any parameters, individually, had a positive effect on the increase of board
properties. The main effects of parameters are in following order: main effect of resin
content> pressure. |
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