Citation
Abba, Hammajam A.
(2018)
Characterization of millet husk-filled high density polyethylene and polylactic acid composites.
Doctoral thesis, Universiti Putra Malaysia.
Abstract
The millet husk fiber (MHF) is an agricultural byproduct from millet
(pennisetum glaucum). Currently, the use of thermoplastic composites
produced from polymers filled with natural fibers has attracted the attention of
many researchers globally. The main objective of this investigation was to
study the potential of this agro waste as filler for thermoplastic composites as
a substitute to synthetic fibers and other natural fibers. The fibers were treated
with sodium hydroxide (NaOH) and pulverized to 250 μm. Fiber loadings of 10
%, 20 % 30 % and 40 % by weight were employed throughout the formulation.
Test samples were prepared through melt blend technique followed by
compression molding process. The mechanical properties; tensile, flexural
and impact test specimens were specified according to ASTM standards and
tested using universal testing machine (UTM). The thermal properties were
characterized by using thermogravimetric analyzer (TGA).The microstructure
observations of fractured surfaces of composites were studied by using
scanning electron microscope (SEM).The investigation of water absorption in
sea and rain water was determined. The biodegradability was carried out via
soil burial technique in municipal and oxisol soils.
Tensile strength of untreated fiber millet husk powder (MHP) filled high density
polyethylene (HDPE) and MHP filled poly lactic acid (PLA) composites
decreased with increased fiber loading but slightly improved for treated fibers
composites. While the tensile modulus of both treated and untreated fibers
composites increased by increasing the fiber loadings. Flexural strength of the
MHP-HDPE treated fiber composites increased as loading increased, while
MHP-PLA composites decreased as loading increased. PLA composites
exhibit better flexural properties for treated fiber composites. The flexural modulus for both treated and untreated fiber composites of MHP-PLA and
MHP-HDPE increased as fiber loadings increases. The impact properties of
treated and untreated fibers MHP-HDPE, MHP-PLA, composites drastically
decreased as fiber loading increased. Water absorption increased as fiber
loading increased. Composites immersed in sea water uptake at higher rate
compare to those immersed in rain water. Thermal degradations of untreated
and treated fiber composites show slight difference in terms of weight loss,
while decomposition rate varies as the fiber loading increased.
Biodegradability in municipal soil showed higher rate of degradation compared
to oxisol soil. The degradation level for treated and untreated fiber composites
differs slightly in both types of soil. MHP-PLA composites degrade faster in
both municipal and oxisol soil compare to MHP-HDPE composites. The fiber
treatment has little impact on their biodegradability rates. In view of all the
findings, it was appropriate to conclude that millet husk fiber filled
thermoplastic is a promising composite.
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