Abstract
Poly(lactic acid)/triacetine plasticized cellulose acetate (PLA/pCA) blends were prepared by extrusion at two different temperatures and tetrabutylammonium tetraphenyl borate (TBATPB) was added as a transesterification catalyst to reactively promote the formation of PLA-CA copolymer during the reactive extrusion. The occurrence of chain scission in the PLA phase and branching/crosslinking in the CA phase in the presence of TBATPB, resulting also in a darkening of the material, were demonstrated by studying torque measurements and by performing proper thermogravimetric tests on CA with the different additives. Tensile and impact tests onto the blends prepared at the lower temperature showed better properties than the ones obtained at a higher temperature. Then, the mechanical properties of PLA/plasticized cellulose acetate (pCA) blends prepared at the lower temperature were investigated as a function of the content of plasticized CA in the blend. A range of compositions was observed where blends exhibited improved impact properties with respect to pure PLA without a significant decrease in their elastic modulus. The study of the phase morphology of the blends revealed that the occurrence of reactive compatibilization did not significantly affect the phase distribution. In general, fibrillar CA particles were formed in the PLA matrix during extrusion, thus allowing the preparation of CA fibre reinforced composites. The trend of morphology as a function of the composition and processing conditions was then discussed by considering the evolution of phase morphology in immiscible polymer blends.
Highlights
Polylactide (PLA), a polymer derived from lactic acid (2-hydroxy propionic acid), is currently proposed in many applications because it can be obtained from renewable agricultural sources [1,2], its production consumes carbon dioxide [3], it provides significant energy savings [4], it is recyclable and compostable [5], it can promote the growth of agricultural activities and its physical and mechanical properties can be modulated by properly designing the polymer architecture [6,7]
The Poly(lactic acid)/triacetine plasticized cellulose acetate (PLA/plasticized cellulose acetate (pCA)) blends that were eventually pre-mixed with the tetrabutylammonium tetra-phenylborate (TBATPB) in powder, were extruded in a MiniLab II HaakeTM Rheomex CTW 5 conical twin-screw extruder (Thermo Fisher Scientific, Waltham, MA, USA) at 230 ◦ C and at 197 ◦ C
In order to study the effect of extrusion temperature and TBATPB transesterification catalyst on the PLA/pCA blends extrusion, four preliminary blends with a content of PLA of 75% by weight were prepared (Table 1)
Summary
Polylactide (PLA), a polymer derived from lactic acid (2-hydroxy propionic acid), is currently proposed in many applications because it can be obtained from renewable agricultural sources [1,2], its production consumes carbon dioxide [3], it provides significant energy savings [4], it is recyclable and compostable [5], it can promote the growth of agricultural activities and its physical and mechanical properties can be modulated by properly designing the polymer architecture [6,7]. The applicability of this method requires better control of the processing rheology necessary for the final application, and the effect on impact properties is very limited Another approach followed for improving the mechanical resistance at high temperatures is the preparation of composites or nano-composites in which proper fibres or particulate fillers can reinforce the PLA matrix. Wang et al [45] grafted maleic anhydride on PLA in solution, achieving a functionalization degree of 1.13 wt% After purification, they used pure PLA, or the grafted PLA for comparison, to prepare PLA/cellulose acetate blends of various compositions with PLA as the main component in a discontinuous mixer at 160 ◦ C, below the melting temperature of CA. The trend of morphology as a function of the composition and processing conditions is discussed, with the aim of providing a correlation with final properties
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