Once mechanical behavior of TPS films was studied, the feasibility
to develop packaging bags for food products was evaluated.
Thus, films thermo-sealing capacity was studied in first instance.
TPS films and composites containing talc nanoparticles were able to
be thermo-sealed obtaining a good quality seal. This could be
attributed to the disappearance of the interface between both individual
layers, due to their high molecular interaction, allowing to
form a new homogenous layer (Cho et al., 2007). TPS films thermosealing
resistance, which determines package integrity, was studied
by tensile tests. Fig. 2 shows tested specimen’s photographs of TPS
films and its bionanocomposite containing 5% w/w talc particles, as
well as the corresponding stress-strain curves. Talc addition
modified the failure mode of TPS films. Break near the seal was
detected for TPS films while adhesive-cohesive failure was found
for films with talc nanoparticles (Fig. 2A and B). Stress-strain curves
shown in Fig. 2C were in agreement with the observed failure
modes (López et al., 2011). TPS film’s failure mode revealed that the
corresponding juncture was resistant enough to bear the applied tensile stress failing thereby the material film before the seal.
Maximum tensile resistance was 1.6 0.3 MPa, being this value
closer to the maximum strength of TPS films determined by the
aforementioned tensile test (Table 1). The fact that both values
were similar regardless different crosshead speed used in tensile
tests is an indicative that TPS films material failed before the seal.
On the other hand, film juncture of TPS composite with 5% w/w talc
nanoparticles failed before material breakage. This result is in
accordance with TPS matrix reinforcement by talc addition,
demonstrated through tensile and quasi-static tests (Fig. 1 and
Table 1). For these composite films the involved energy to cause
adhesive-cohesive seal failure was 19.1 1.7 J/m. Moreover, average
thermo-sealing resistance of composite films was 1.7 0.1 MPa.
The fact that this value resulted significantly lower than the
maximum tensile strength obtained by tensile tests (Table 1)
demonstrates that seal was less resistant than film material. In
addition, talc incorporation to TPS matrix increased the resistance
around 11% to cause specimen failure, regardless the breakage
mode. SEM observations of the seal zone of tested specimens were
carried out in order to analyze if failure of TPS films with 5% w/w
talc corresponded to an adhesive or a cohesive mode. Fig. 3 presents
SEM micrographs corresponding to both films which were in
contact before tensile tests. Fig. 3A and B are like specular images
between them. When seal was opened, part of the material corresponding
to one of the films was pulled out, causing a cohesive
failure mode. Resulting hollows due to the material pulling are
indicated with arrows in Fig. 3A. On the other hand, in Fig. 3B are
marked the remaining material which corresponds to the hollows
observed in its specular image. The fact that thermo-sealed TPS
films with talc particles presented a cohesive failure indicates that
packaging bags based on this kind of bionanocomposites could be
easily opened by the peeling off method.