الفهرس 
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Abstract
This work targets the investigation of the potentiality of using
sorghum stalks (SS) as reinforcements for high density polyethylene
(HDPE), especially for outdoor applications.
Characterisation of sorghum stalks was performed taking into
consideration morphological, thermal, chemical, and mechanical
properties, to study the potentiality of their use as a polymer
reinforcing material. Optical and scanning electron microscopy was
used to investigate the morphology of sorghum stalks, and relate
mechanical properties to structure. Sorghum stalks have been divided
into three equal regions: bottom, middle, and top, and each region was
individually studied. The thermal degradation behaviour has been
studied using static and dynamic thermogravimetric analysis. The
results of this study show that it is not recommended to subject the
fibres to elevated temperatures (>200°C) for time periods exceeding
10 min. Tensile testing was used to evaluate the mechanical properties
of fibres. The highest tensile strength of 280 N/mm
was found at the
middle region of the sorghum stalk rind (SSR), while the tensile
strength of the pith was found to be about 1.5 N/mm
v
2
.
After compounding SSR with HDPE and MAPE, number-
2
weighted distributions for fibre length and aspect ratio were built
showing a right skewed distribution with large number of small
particles. The obtained fibre length and aspect ratio distributions were
fitted by a two-parameter Weibull model.
With respect to the composite, mechanical properties in
tension and bending were evaluated for different compositions of SSR
and maleic anhydride polyethylene (MAPE) as a coupling agent.
Compared to pure HDPE, 20wt% SSR/3wt% MAPE composition
showed an increase of about 14%, 71%, and 156% in tensile strength,
bending strength, and flexural modulus, respectively. 40wt%
SSR/0wt% MAPE composition showed an increase about of 346% in
flexural modulus.
The resistance to the deteriorating effect of service conditions
as in outdoor applications was also studied. Specimens immersed in
distilled water, showed a maximum increase in weight by 6.88% at
40wt% SSR/0wt% MAPE composition. After saturation, specimens
were tested in bending to compare results with un-aged specimens. A
reduction in strength and modulus was found. The mechanical
properties in bending of ultraviolet exposed specimens were
compared to un-aged and to pure HDPE specimens. There is no
significant reduction in mechanical properties compared to unexposed
specimens.