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The effect of PBAT (poly(butylene adipate-co-terephthalate)) content and crystallization temperature on the crystallization and heat resistance of PLLA/PDLA blends are studied. The PBAT/PLLA/PDLA blends with different PBAT content were prepared by melt blending. Then, differential scanning calorimetry (DSC) and Vicat softening temperature (VST) were used to investigate the semicrystallization time (t1/2), crystallinity and heat resistant of the blends. The results show that the incorporation of PBAT is benefit to the rate of crystallization and t1/2 of the blends can be reduced from 1.0 min to 0.8 min at 100 °C. After annealing at 220 °C, the degree of stereo-complex (fsc), stereocomplex crystallinity (Xc,S) and VST of PLLA/PDLA blends reaches up to 100.0%, 31.1% and 204 °C, respectively. The values of the former parameters reduce to 96.0%, 15.4% and °C 194 °C after incorporating 12% PBAT. It concludes that the crystallization under high temperature contributes to the improvement of Xc,S and heat resistance. The incorporation of PBAT into PLLA/PDLA promotes the crystallization rate, while it reduces the heat resistance of the blends [ABSTRACT FROM AUTHOR]

The raw material of polylactide (PLA) is lactic acid obtained by biological fermentation. PLA is the most promising degradable polymer to replace traditional plastics to address the pollution problems caused by their non-degradability. However, the application of PLA is hindered by its low softening temperature, easy hydrolysis, and poor toughness. Herein, the ternary composites with PLLA, PDLA and Poly (butylene adipate- co -terephthalate) (PBAT) were prepared by melt blending to balance its thermal stability, hydrolysis, and toughness. The effects of PBAT content (3 %, 6 %, 9 % and 12 %) and isothermal crystallization temperature on composite properties were fully investigated. The results show that the composite of stereo-complexed PLA (sc-PLA) with 6 % PBAT crystallized at 110 °C exhibits good comprehensive properties. Its vicat softening temperature (VST), mass loss rate under alkaline (pH = 12) and breaking elongation are 166 °C, 21.6 % and 4.40 %, respectively. Compared with the pure PLLA sample crystallized at same condition, the VST, mass loss rate and breaking elongation are 159 °C, 24.7 % and 3.76 % respectively, which increased by nearly 5 %, 13 % and 20 %. This indicates that this strategy is feasible to balance the heat resistance, hydrolysis resistance and toughness of PLA, while it sacrifices the tensile strength a little. This work provides a new way to modify and improve the PLA properties. Nonetheless, it is also necessary to coordinate the compatibility of PLA and PBAT. [ABSTRACT FROM AUTHOR]

One-hundred percent stereo-complexation in poly( l-lactide) (PLLA)/poly( d-lactide) (PDLA) fibers with non-equivalent molecular weights could be achieved via thermal treatment. Stereo-complexed polylactide (sc-PLA) fibers exhibited excellent hydrolysis resistance and thermal resistance. Till now, preparation of sc-PLA fibers with satisfactory qualities required both PLLA and PDLA with equivalently high molecular weights. Moreover, the high-molecular-weight PDLAs are expensive, restricting industrial-scale production and applications of sc-PLA products. In this study, equal-weight mixtures of low-molecular-weight PDLA (L-PDLA) and high-molecular-weight PLLA (H-PLLA) were melt spun into sc-PLA fibers and then completely stereo-complexed via thermal treatment. The hydrolysis resistance of L3/D1 fibers [PLLA ( M = 3.0 × 10)/PDLA ( M = 1.0 × 10)] was similar to that of L3/D3 fibers [PLLA ( M = 3.0 × 10)/PDLA ( M = 3.2 × 10)], but much higher than that of L3 fibers [PLLA ( M = 3.0 × 10)]. Melting temperature and softening temperature of L3/D1 fibers (223 and 126 °C) were also similar to those of L3/D3 fibers (224 and 131 °C), but higher than that of L3 fibers (172 and 72 °C). Utilizing H-PLLA and L-PDLA to prepare sc-PLA fibers with excellent performance is conducive to the wide industrial application of sc-PLA. [ABSTRACT FROM AUTHOR]

The combination of crystallization, transparency, and strength is still a challenge for broadening the application of polylactic acid (PLA) films, while it is also difficult to balance. In this work, the long aliphatic chains of octadecylamine (ODA) were grafted onto the surface of cellulose nanocrystal (CNC) by tannic acid oxidation self-polymerization and Michael addition/Schiff base reaction between polytannic acid and ODA. Furthermore, the ODA grafted CNC (g-CNC) was used as green reinforcement for the PLA matrix and a series of PLA/g-CNC nanocomposite films were prepared by the casting method. The DSC, WAXD, POM, UV–vis and stretching test were employed to examine the effect of g-CNC on the properties of the as-prepared PLA/g-CNC nanocomposite films. It shows that the g-CNC is effective to improve the melt crystallization rate of PLA from 11 min to 7.3 min. Most importantly, the crystal size of the PLA spherulites was significantly reduced due to the well dispersion in the amorphous PLA matrix, which would effectively improve the transmittance of the PLA films and synchronously realize the combination of crystallization (62 %) and transparency (80.6 %). Moreover, the improved crystallization could also enhance the heat deformation performance of the PLA films since the heat resistance is closely associated with the crystallinity. Besides, the grafted ODA long chains improve the compatibility between CNC and PLA, leading to the reinforcement of PLA matrix, where the tensile strength reaches 65.05 MPa from 44.31 MPa. Compared with the pristine CNC, the addition of g-CNC makes more comprehensive improvement in the properties of the PLA films. [ABSTRACT FROM AUTHOR]

A clean and cost-effective method for 100% stereo-complexation in polylactide (PLA) fibers with molecular weight (MW) as high as 6 × 10 5 demonstrates good potential for industrial-scale continuous manufacture. Polylactide, a widely recognized biodegradable and renewable biopolymer, has a negligible share of plastic markets due to its poor hydrolytic and thermal resistance. Stereo-complexation is effective in overcoming these challenges. However, current stereo-complexation approaches usually require solvents and/or external nucleation reagents, and are expensive and complicated. Moreover, high-MW PLAs favored for developing durable products are difficult to be stereo-complexed. In this research, enantiomeric PLAs both with MW up to 6 × 10 5 were completely stereo-complexed via a facile thermal treatment on pilot-scale devices. Neither solvent nor nucleation agent was used. For poly(L-lactide) (PLLA) fibers with MW of 6 × 10 5 , percentage retention of MW and percentage retention of tensile strength after hydrolysis under simulated textile dyeing condition increased from 39% to 93% and from 20% to 89%, respectively, after complete stereo-complexation. The melting point, softening point and percentage retention of MW after hydrolysis of stereo-complexed PLA (sc-PLA) fibers were up to 51 °C, up to 59 °C and up to 183% higher than that of PLLA fibers with the same MW, respectively. The mechanism of thorough stereo-complexation in high-MW PLA fibers was proposed and verified. It is promising to use this approach to broaden industrial applications of renewable and degradable biopolymers for sustainable development of material industries. [ABSTRACT FROM AUTHOR]

A facile and clean technology for stereo-complexation of polylactides (PLAs) shows potential to be readily incorporated into continuous industrial processes for manufacture of films, fibers and other plastic products. Using this approach, complete stereo-complexation of high-molecular-weight PLAs could be achieved via simple thermal treatment, rendering the production of durable PLA commodities inexpensive and industrially scalable. Currently, due to their high susceptibility to water and heat, PLA products have restricted industrial applications, and cannot compete with their petroleum-derived counterparts. Stereo-complexation of poly( l -lactic acid) (PLLA) and poly( d -lactic acid) (PDLA) could effectively decrease water and heat sensitivity of common PLLA products. However, many stereo-complexation processes required harmful solvents or nucleating agents, and thus, were costly, complicated, and had low potential for short-term industrialization. Moreover, complete stereo-complexation was mostly achieved for PLAs with weight-average molecular weight lower than 1 × 10 5 . In this research, PLLA and PDLA both with viscosity-average molecular weight of 3 × 10 5 were completely stereo-complexed (sc) via simple thermal treatment. Comparing to PLLA fibers, sc-PLA fibers had softening points 60 °C higher, and their thermal and hydrolytic stability significantly enhanced. Relationship among temperature of thermal treatment, degree of stereo-complexation and performance properties of sc-PLA fibers were also established. This clean technology makes possible industrial-scale production of commercializable biobased plastics. [ABSTRACT FROM AUTHOR]