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3 PVA/BC Bionancomposite Films with Particle Size Effect
3.1 Introduction
The morphology of bamboo charcoals (BCs) generally demonstrates a wide range
of internal pore distribution from less than 1 nm to 1 µm [1]. The walls of basic
units within BCs, known as parenchyma, are very rough despite their smooth outer
surfaces, which makes entire particles quite hard. With a large number of roughly
walled pores inside BCs, polymeric chains tend to easily penetrate into internal BC
pores [2] to form strong mechanical bonding in addition to the existing hydrogen
bonding of pores. Hence, mechanical properties of resulting bionanocomposites can
be improved accordingly owing to effective interfacial bonding between nanofillers
and polymer matrices. Nevertheless, the selection of polymer matrices also plays
a leading role in the manufacture of bionanocomposites in addition to the inclusion of BCs. Polymeric behaviour in a porous medium is associated with capillary
forces so that polymeric chains can be further prevented from entering into internal
pores [2]. According to the Laplace theory [2, 3], the strength of capillary forces
depends on surface chemistry and physical properties of polymers. When hydrophilic
media are selected, applied positive capillary pressures drive polymeric chains into
BC pores to form both effective mechanical and chemical bondings, which is the
reason why PVA as a base polymeric material has been chosen in this study. On
the contrary, the surfaces of hydrophobic media generate negative capillary pressures to hinder the penetration of polymeric chains into BC pores, leading to phase
separation in a bionanocomposite system. Such a mechanism can be interpreted
as typical debonding effect widely observed in polymer/BC composites such as
polylactic acid (PLA)/BC composites [4], ultrahigh molecular-weight polyethylene
(UHMWPE)/BC composites [5] and polyaniline (PANI)/BC composites [6].
3.2 BC Particle Characterisation
3.2.1 BC Composition and Surface Area
BCs generally comprise the elements of carbon, oxygen, hydrogen, nitrogen and
small quantities of ash [7]. Since the carbon content is a function of many material
processing parameters such as pyrolysis temperature, moisture content and composition of biomass [8], it is regarded as a key factor to determine the charcoal quality. As
seen from Table 3.1, the carbon content of NBCs appears to be relatively high when
compared with that of MBCs (i.e. 84.18% vs. 80.04%), which is in good accordance
with previous results obtained by Li et al. [7]. As such, BCs can be considered as
good carbon-based fillers for effective reinforcements in bionanocomposite systems.
Oxygen, hydrogen and nitrogen contents for both NBCs and MBCs (O%: 5–10%,
H%: 2.2–2.5% and N%: 0.5–0.7%) become less pronounced accordingly.
3 PVA/BC Bionancomposite Films with Particle Size Effect
3.1 Introduction
The morphology of bamboo charcoals (BCs) generally demonstrates a wide range
of internal pore distribution from less than 1 nm to 1 µm [1]. The walls of basic
units within BCs, known as parenchyma, are very rough despite their smooth outer
surfaces, which makes entire particles quite hard. With a large number of roughly
walled pores inside BCs, polymeric chains tend to easily penetrate into internal BC
pores [2] to form strong mechanical bonding in addition to the existing hydrogen
bonding of pores. Hence, mechanical properties of resulting bionanocomposites can
be improved accordingly owing to effective interfacial bonding between nanofillers
and polymer matrices. Nevertheless, the selection of polymer matrices also plays
a leading role in the manufacture of bionanocomposites in addition to the inclusion of BCs. Polymeric behaviour in a porous medium is associated with capillary
forces so that polymeric chains can be further prevented from entering into internal
pores [2]. According to the Laplace theory [2, 3], the strength of capillary forces
depends on surface chemistry and physical properties of polymers. When hydrophilic
media are selected, applied positive capillary pressures drive polymeric chains into
BC pores to form both effective mechanical and chemical bondings, which is the
reason why PVA as a base polymeric material has been chosen in this study. On
the contrary, the surfaces of hydrophobic media generate negative capillary pressures to hinder the penetration of polymeric chains into BC pores, leading to phase
separation in a bionanocomposite system. Such a mechanism can be interpreted
as typical debonding effect widely observed in polymer/BC composites such as
polylactic acid (PLA)/BC composites [4], ultrahigh molecular-weight polyethylene
(UHMWPE)/BC composites [5] and polyaniline (PANI)/BC composites [6].
3.2 BC Particle Characterisation
3.2.1 BC Composition and Surface Area
BCs generally comprise the elements of carbon, oxygen, hydrogen, nitrogen and
small quantities of ash [7]. Since the carbon content is a function of many material
processing parameters such as pyrolysis temperature, moisture content and composition of biomass [8], it is regarded as a key factor to determine the charcoal quality. As
seen from Table 3.1, the carbon content of NBCs appears to be relatively high when
compared with that of MBCs (i.e. 84.18% vs. 80.04%), which is in good accordance
with previous results obtained by Li et al. [7]. As such, BCs can be considered as
good carbon-based fillers for effective reinforcements in bionanocomposite systems.
Oxygen, hydrogen and nitrogen contents for both NBCs and MBCs (O%: 5–10%,
H%: 2.2–2.5% and N%: 0.5–0.7%) become less pronounced accordingly.