thermal property, mechanical strength, and stability even
after water absorption have been fabricated from the
solvent-free, thermoplasticization method. The superior
supramolecular interactions are attributed to the hydrogen
bonding, re-enforced by the interactions between the
hydroxyl groups of the wheat straw with the chlorine atoms
in the supramolecular inducer. The strong hydrogen bonding, however, could considerably be lowered as a result of
the supramolecular interactions between the inducers and
the wheat straw powders (Dong et al. 2019). The nanoTiO 2 adopted frothed wheat straw fiber/polypropylenehierarchical (F-WSFs/PP) composites have been fabricated
via hot-extrusion technique. The TiO 2 -KH550 modified
F-WSFs/PP composites have exhibited excellent mechanical
strengths and UV-protective properties (Wang et al. 2020).
The biocomposites of nanocrystalline cellulose (NCC) from
the rice straw and chitosan (CS) have been developed using
acid hydrolysis-ultrasonic and blending-casting technique.
The NCC/CS biocomposite interfaces show the rod-like
structure attained from the higher ultrasonic power at constant acid hydrolysis conditions. Larger interfacial compatibility of the NCC/CS biocomposites with excellent ductility
is accomplished at 5% NCC. The optimum distribution of
the NCC exerts electrostatic interactions, and strong hydrogen bonding between the NCC and the CS, resulting in
higher thermal stability (Xu et al. 2018). The rice straw
biomass has been utilized to separate the cellulose nanofibers
with different oxidation degree. The bleached rice fibers are
derived from the rice straw biomass undergoing the
bleaching processes and chemical extraction. The oxidation
of rice fibers is facilitated by the radical (TEMPO)
2,2,6,6-tetramethylpiperidine 1-oxyl to remove the rice cellulose nanofibers. The reinforcement capacity of the rice
nanofibers is achieved by casting the nanocomposite films
with poly(vinyl alcohol), to achieve the critical tensile
strength of the films (Alcántara and González 2020). Green
composites based on rice straw (RS) have been fabricated by
utilizing benzylation techniques and soda-pulping. The RS
products include the benzylated RS pulp, untreated RS, RS
pulp, and pulping liquor along with the benzylated RS,
which are integrated into the starch (thermoplastic) via a
twin-screw extrusion procedure. The RS pulp with the cellulosic microfibers has increased the tensile strength of the
plasticized starch much greater than the untreated RS. The
thermoplasticization process considerably enhanced the
toughness of the plasticized starch/RS biocomposites due to
the improved phase miscibility (Shoja et al. 2020).
The groundnut shell (GNS) and rice husk (RH) have been
utilized to make hybrid polypropylene (PP) biocomposites
for green building materials. The rice husk morphology with
low aspect ratio is excellent to be developed into composites
having good flexural and tensile strength (maximum value of
37.6 MPa and 15.6 MPa, respectively). The thermal conductivity of the composites range from 0.156 to 0.270
W/mK and the highest sound absorption coefficient is 0.48.
The flame retardation property of the composites is equivalent to the market gypsum derived ceiling tiles, but the
composite water absorption is 85% less than the gypsum
tiles (Guna et al. 2020). Biosilica, from the teff straw, has
been blended with alginate and chitosan to produce
alginate-biosilica (AlgBS) and chitosan-biosilica (ChiBS)
for use as sorbents. The pyridine removal efficacy is influenced by the pyridine concentration, biocomposite dosage,
pH, temperature, and contact time. The maximum removal
efficiency for early pyridine concentration of 50 mg/L for
ChiBS and AlgBS is 90 and 96%, respectively (Bageru and
Srivastava 2019). A novel biocomposite has been produced
by combining poly(vinyl alcohol), graphene oxide, and
chitosan, for application in wound dressing. It also exhibits
anti-inflammatory and antimicrobial properties, with the
ability to promote cell proliferation (Chen et al. 2020). The
biomass bioconversion into biocomposites and high-value
bioproducts meet the sustainability goals of the industries on
“reduce, recycle, and reuse” of wastes. However, the challenges remain for a large-scale implementation within a
more economically viable integrated bio-refinery set-up
(Abdullah and Hussein 2020).
6 Conclusion and Future Perspectives
Straw biomass as a lignocellulosic agricultural residue possesses tremendous potential as feedstock for bioconversion
into valuable products. The bioconversion of organic matters
into bioenergy or bioproducts can be achieved through
eco-friendly and biological methods, in combination with
light physical and chemical pretreatment methods along with
technologies based on enzymatic hydrolysis, fermentation,
and anaerobic digestion. However, the major challenges are
to meet the goals of sustainable development for
community-based, eco-friendly, and cost-effective processes.
Thereby, substantial effort is needed to address the
scaling-up of an integrated bio-refinery for the bioconversion
of straw biomass into bioproducts especially in terms of the
selection of the plant location to be close to the energy grids
and the market needs. The diverse applications on the use of
biomaterials and biocomposites should be explored further
especially in the construction sector, infrastructure building,
pharmaceutical, and biomedical segments, to attain the full
potential of the bioproducts derived from the straw biomass.
Bioconversion of Straw Biomass into Bioproducts
379
after water absorption have been fabricated from the
solvent-free, thermoplasticization method. The superior
supramolecular interactions are attributed to the hydrogen
bonding, re-enforced by the interactions between the
hydroxyl groups of the wheat straw with the chlorine atoms
in the supramolecular inducer. The strong hydrogen bonding, however, could considerably be lowered as a result of
the supramolecular interactions between the inducers and
the wheat straw powders (Dong et al. 2019). The nanoTiO 2 adopted frothed wheat straw fiber/polypropylenehierarchical (F-WSFs/PP) composites have been fabricated
via hot-extrusion technique. The TiO 2 -KH550 modified
F-WSFs/PP composites have exhibited excellent mechanical
strengths and UV-protective properties (Wang et al. 2020).
The biocomposites of nanocrystalline cellulose (NCC) from
the rice straw and chitosan (CS) have been developed using
acid hydrolysis-ultrasonic and blending-casting technique.
The NCC/CS biocomposite interfaces show the rod-like
structure attained from the higher ultrasonic power at constant acid hydrolysis conditions. Larger interfacial compatibility of the NCC/CS biocomposites with excellent ductility
is accomplished at 5% NCC. The optimum distribution of
the NCC exerts electrostatic interactions, and strong hydrogen bonding between the NCC and the CS, resulting in
higher thermal stability (Xu et al. 2018). The rice straw
biomass has been utilized to separate the cellulose nanofibers
with different oxidation degree. The bleached rice fibers are
derived from the rice straw biomass undergoing the
bleaching processes and chemical extraction. The oxidation
of rice fibers is facilitated by the radical (TEMPO)
2,2,6,6-tetramethylpiperidine 1-oxyl to remove the rice cellulose nanofibers. The reinforcement capacity of the rice
nanofibers is achieved by casting the nanocomposite films
with poly(vinyl alcohol), to achieve the critical tensile
strength of the films (Alcántara and González 2020). Green
composites based on rice straw (RS) have been fabricated by
utilizing benzylation techniques and soda-pulping. The RS
products include the benzylated RS pulp, untreated RS, RS
pulp, and pulping liquor along with the benzylated RS,
which are integrated into the starch (thermoplastic) via a
twin-screw extrusion procedure. The RS pulp with the cellulosic microfibers has increased the tensile strength of the
plasticized starch much greater than the untreated RS. The
thermoplasticization process considerably enhanced the
toughness of the plasticized starch/RS biocomposites due to
the improved phase miscibility (Shoja et al. 2020).
The groundnut shell (GNS) and rice husk (RH) have been
utilized to make hybrid polypropylene (PP) biocomposites
for green building materials. The rice husk morphology with
low aspect ratio is excellent to be developed into composites
having good flexural and tensile strength (maximum value of
37.6 MPa and 15.6 MPa, respectively). The thermal conductivity of the composites range from 0.156 to 0.270
W/mK and the highest sound absorption coefficient is 0.48.
The flame retardation property of the composites is equivalent to the market gypsum derived ceiling tiles, but the
composite water absorption is 85% less than the gypsum
tiles (Guna et al. 2020). Biosilica, from the teff straw, has
been blended with alginate and chitosan to produce
alginate-biosilica (AlgBS) and chitosan-biosilica (ChiBS)
for use as sorbents. The pyridine removal efficacy is influenced by the pyridine concentration, biocomposite dosage,
pH, temperature, and contact time. The maximum removal
efficiency for early pyridine concentration of 50 mg/L for
ChiBS and AlgBS is 90 and 96%, respectively (Bageru and
Srivastava 2019). A novel biocomposite has been produced
by combining poly(vinyl alcohol), graphene oxide, and
chitosan, for application in wound dressing. It also exhibits
anti-inflammatory and antimicrobial properties, with the
ability to promote cell proliferation (Chen et al. 2020). The
biomass bioconversion into biocomposites and high-value
bioproducts meet the sustainability goals of the industries on
“reduce, recycle, and reuse” of wastes. However, the challenges remain for a large-scale implementation within a
more economically viable integrated bio-refinery set-up
(Abdullah and Hussein 2020).
6 Conclusion and Future Perspectives
Straw biomass as a lignocellulosic agricultural residue possesses tremendous potential as feedstock for bioconversion
into valuable products. The bioconversion of organic matters
into bioenergy or bioproducts can be achieved through
eco-friendly and biological methods, in combination with
light physical and chemical pretreatment methods along with
technologies based on enzymatic hydrolysis, fermentation,
and anaerobic digestion. However, the major challenges are
to meet the goals of sustainable development for
community-based, eco-friendly, and cost-effective processes.
Thereby, substantial effort is needed to address the
scaling-up of an integrated bio-refinery for the bioconversion
of straw biomass into bioproducts especially in terms of the
selection of the plant location to be close to the energy grids
and the market needs. The diverse applications on the use of
biomaterials and biocomposites should be explored further
especially in the construction sector, infrastructure building,
pharmaceutical, and biomedical segments, to attain the full
potential of the bioproducts derived from the straw biomass.
Bioconversion of Straw Biomass into Bioproducts
379