Oil-Based and Bio-Derived Thermoplastic Polymer Blends and Composites 259
Table 8.13Thermal properties of neat high-density
polyethylene (HDPE) in comparison to HDPE with
20–30–40–50–60 wt% of wood.
Samples (numbers
represent ratios) Tm(∘C)
횫Cp
(J g−^1 ∘C−^1 ) X(%)
HDPE 100 138.2 16.8 74.7
HDPE 80/Wood 20 142.0 14.0 76.6
HDPE 70/Wood 30 143.3 22.0 78.1
HDPE 60/Wood 40 140.0 10.0 78.5
HDPE 50/Wood 50 143.4 6.0 79.0
HDPE 40/Wood 60 140.9 4.0 86.1
Taziet al. 2014 [58]. Reproduced with permission of
John Wiley and Sons.
Important analyses were also conducted on the thermal stability of WPCs. Taziet al.
[58] studied the effect of wood and MAPE percentages on thermo-physical properties.
They found that the addition of wood fillers and coupling agent (MAPE) to the polymer
matrix resulted in an increase of the melting temperature of HDPE up to value higher
than 141∘C; the same phenomenon was reported in the literature. Table 8.13 sums up
their results.
Heat capacity (ΔCp) decreases while the filler amount increases: wood fillers obstacle
molecular chains mobility close to melting temperature. Moreover, wood fillers acted as
nucleating agents, increasing crystallinity of the matrix, from 60% to 85%.
In order to improve wood-like effect, nailing and screwing properties and to reduce
density, foam-like structure could be produced in WPC materials [59]. The most
common ways to obtain foam are thermal decomposition of chemical blowing agents
(CBAs), volatilization of physical agents (low boiling liquids), expansion of dissolved
gas in a polymer and addition of gas-filled microspheres into a polymer system.
The principles of a foam production are based on bubble nucleation, growth and
stabilization.
Important properties of CBAs are a decomposition temperature suitable for the
chosen polymer matrix, avoiding fast reaction during decomposition, easy agent mix
and dispersion in the polymer, high gas yield and non-tool corrosivity. Exothermic
and endothermic blowing agents [60] were studied by Mengeloglu and Matuana in
PVC (70 wt%)/WF composite (30 wt%) [61]: they compared modified azocarbonamide
(exothermic agent) and sodium bicarbonate (endothermic agent). Speaking about
density, no big differences were noticed between the two CBAs; both of them provided
lower densities compared to PVC/WF composite without CBAs. The average cell size
instead was affected by the CBA type in particular azocarbonamide allowed obtaining
lower cell size than sodium bicarbonate one. Some results are displayed in Figure 8.17
and Table 8.14.
Many parameters affected WPC foam properties, and Yoonet al. [62] studied the
influence of N 2 amount (physical blowing agent), injection speed, weight reduction and
mold temperature. Shrinkage of WPC foam seems to be affected by N 2 amount, weight
reduction and mold temperature, while WPC foam deformation was influenced by
