Environmental Engineering Reference
In-Depth Information
is an option to use renewable resources and to reduce waste. Thermoplastic starch
(TPS), polyhydroxyalkanoates (PHAs), polylactides and their blends are promising
candidates for such replacement and are subject to many researches. Polylactic acid
(PLA) has been intensively investigated in past years. This biodegradable polyester,
which can be used in many applications from packaging to biocompatible materi-
als, has a thermoplastic behavior combined with high mechanical performance, good
appearance and low toxicity (Jamshidian et al. 2010 ). Due to its similar characteristics
to other polymers such as polyethylene terephthalate (PET), high impact polystyrene
(HIPS), and polyvinylchloride (PVC), the PLA is proposed as a substitute for these
synthetic polymers.
This work presents the modeling and the simulation of the PLA processing in
a single screw extruder. The model is based on the momentum equation coupled
with the energy equation through physical parameters considering the rheological
behavior of the PLA reported by Jacobsen et al. ( 2000 ) and Mehta et al. ( 2005 ).
2Development
A single screw extruder consists of one screw rotating in a closely fitting barrel; the
transport mechanism is based on friction between the polymer and the walls of the
channel as shown in Fig. 1 . The material enters through the feed throat (feed hopper)
and comes into contact with the screw and in the final part of the barrel there is a die
which gives the final product its profile.
The governing equations describing this problem, with the assumption of constant
density, are the continuity equation:
∇· ʽ =
0
,
(1)
the momentum equation:
D
Dt =−∇
ˁ
p
+∇· = +
f
,
(2)
Fig. 1 Single screw extruder
 
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