Biomedical Engineering Reference
In-Depth Information
Figure 9.
Fragment lengths of raw and lignin treated cotton fibers in a polypropylene matrix
determined by the single fiber fragmentation test (standard deviations are given as error bars).
Modified Process Parameters
In the general outline it is obvious that the mechanical composite characteristics of the
composites produced by compression moulding technique CP-1 were not improved as
much as possible. This was mainly caused by the suboptimal process parameters used
in the study. A previous study (Graupner et al., 2009) has shown tensile strength values
more than twice as high for 40 mass% Lyocell 1.3 fiber reinforced PLA produced us-
ing other process parameters (3 hr pre-drying at 105°C in a forced air oven, 20 min.
compression molding at 180°C). According to a model given by Moser for stereo-
scopic, randomly oriented fiber layers (Moser, 1992) a theoretical Young´s modulus
of 7,105 N/mm² could be calculated for 40 mass% Lyocell 1.3 fiber reinforced PLA.
In the previous study a value of 6,784 N/mm² could be achieved while in the present
study a value of only 4,142 N/mm² was measured. The aim of the changed processing
parameters was a reduction of cycle time and process complexity. So, the pre-drying
step which was used in the previous work was changed into a 10 min pre-heating
step in the open press at 180°C and the press time was reduced from 20 to 10 min
(compression moulding technique CP-1). Our results prove that these processing pa-
rameters affect the mechanical composite characteristics negatively (compare chapter
Influence of the semi-finished product and Lignin treatment).
A clear improvement of the mechanical characteristics with regard to tensile and
impact characteristics of multilayer web reinforced PLA composites was achieved
by using modified process parameters (compression moulding technique CP-2). In
comparison to the processing technique CP-1 a pre-drying step was inserted (2 hr at
105°C) and the compression molding time in the hot press was reduced to 5 min. The
cooling of the composites occurred in a cold press for 5 min at 25°C.
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