Blown film stability for low, medium, and high molecular weight polylactic acid and their tensile properties

Abstract

Three poly (lactic acid) (PLA) resins with molecular weight (Mw) equal to 55 (3251D), 125 (L105) and 163 (LX175) kg/mol were characterized in terms of capillary viscosity, mechanical and thermal properties and used to produce blown films. The effect of temperature, extrusion rate, stretching (TUR) and blow-up (BUR) ratios were evaluated to determine the optimum processing conditions for blown films based on the bubble stability and to determine their final tensile properties. As expected, the processing temperature was the most critical parameter on the film stability. The lower Mw PLA showed limited processing stability. Stable conditions were found at higher temperature (200°C) for higher Mw. These results correlate with the PLA viscosity (melt strength). Finally, the PLA film tensile strength (TS) strongly depended on their processability. For example, 3251D and L105 required high stretching (TUR = 3.4 and 7) for maximum TS (30 and 64 MPa) with a low blow-up ratio (BUR = 1.02–1.15). However, a moderate increase in BUR (10% at TUR = 3) led to a substantial drop in TS (from 29 MPa to 21 MPa for PLA 3251D and 44 MPa–34 MPa for L105). Overall, LX175 was the most interesting resin with 49 MPa TS which was independent of the BUR and TUR used in this investigation.

Properties of polylactic acid blends with potato thermoplastic starch using maleated polyethylene as a compatibilizer

“…Weight loss due to thermal degradation was recorded in the 30–600°C range. PLA degradation occurs in a single step as reported for different PLA grades, 43 whereas TPS and the blends show multiple degradation stages due to their complex formulation.…”

“…grades, 43 whereas TPS and the blends show multiple degradation stages due to their complex formulation. PLA was the most stable material with an initial degradation between 293 and 300 C and a maximum degradation rate (DTGA) at 372 C. For the blends, the first step occurs at 100-126 C corresponding to the loss of weakly bound water and low molecular weight compounds.…”

Characterization of PLA Sheets Prepared by Stretching under Different Conditions: Influence of Reprocessing and Establishing Optimal Conditions

“…These data correlate well with the values for switch overpressure recorded during the injection molding process, which varied from about 599–633 bar for the unprocessed materials (L105 and Opt series) to 492–539 for the extruded ones (SD and LD samples). The reduced viscosity of the polymer is an indication of its degradation; to minimize this effect, chain extenders, isocyanates, and other additives are being studied as a means to increase the recyclability of PLA products [ 9 , 33 ]. The start of the degradation can be observed in the yellowish color observed for the injection-molded samples, and is tabulated as yellow index in Section 3.9 .…”

“…However, these works were mainly focused on obtaining films and are not particularly aligned with blow molding or thermoforming, as they usually start from an extruded film rather than injection-molded samples. A recent study by Licea-Saucedo et al [ 33 ] included an analysis of blow-molding of different PLA grades, and found that temperature influences, to a great extent, the mechanical properties of the obtained films; instabilities were also encountered during the process. They found a high dependency between the temperature and the processability; the tensile strength of the films was independent of the stretching and blow-up ratios for PLA LX175, with an average value of 49 MPa.…”