Abstract
Stereocomplex poly(lactide) (PLA) was obtained by solution blending of linear PLLA and PDLA-PEG-PDLA. Effects of the L/D ratios, PEG block, and PDLA block on stereocomplexation of the blends are systemically discussed. The full stereocomplex PLA can be acquired by solution blending when L/D ratios are in the range of 7/3–5/5. The experiment results demonstrated that the stereocomplex degree of PLLA/PDLA-PEG-PDLA prepared by melt blending was closely related to the PEG block and PDLA block. POM results indicated that the blends with high L/D ratio showed large disordered spherulites, and the typical Maltese cross pattern was observed as the L/D ratios decreased. The results of PEG block on the stereocomplexation of PLLA/PDLA-PEG-PDLA revealed that the PEG blocks possessed two sides: accelerating agent for the mobility of polymer chains and decreasing nucleation capacity due to their diluting effect. The effect of PDLA block on the stereocomplexation of the blends was also well investigated. The results showed that the crystallization of sc-crystallites and hc-crystallites in the PLLA/PDLA-PEG4k-PDLA blends with different PDLA blocks presents an obvious competition relationship, and this is not beneficial to the formation of sc-crystallites with increasing PDLA block. The melting behavior of PLLA/PDLA-PEG4k-PDLA with different PDLA blocks after isothermal crystallization showed that the blends could achieve full stereocomplex when the crystallization temperature exceeded 160 °C, and a crystallite with high perfection could be formed as the crystallization temperature increased. This study systemically investigated the effects of the L/D ratios, PEG block, PDLA block, and crystallization conditions on stereocomplex crystallization of PLLA/PDLA-PEG-PDLA blends, which can provide potential approaches to control the microstructure and physical performances of PLLA/PDLA-PEG-PDLA blends.
Highlights
Poly(lactide) (PLA) as a biodegradable thermoplastics polyester [1,2] has attracted the widespread attention of many researchers and is considered to be a sustainable alternative to petrochemical-derived products [3]
This study systemically investigated the effects of the L/D ratios, Polyethylene glycol (PEG) block, PDLA block, and crystallization conditions on stereocomplex crystallization of PLLA/PDLA-PEG-PDLA blends, which can provide potential approaches to control the microstructure and physical performances of PLLA/PDLA-PEG-PDLA blends
Pan et al [16] and Tsuji et al [17] demonstrated that stereocomplexation and homocrystallization are a competitive relationship in PLLA/PDLA blends or PLLA-b-PDLA copolymers, so it is difficult to have the formation of a full stereocomplex due to limitation of memory to re-form stereocomplexation of PLA in the melt processing, especially for high-molecular weight PLLA or PDLA
Summary
Poly(lactide) (PLA) as a biodegradable thermoplastics polyester [1,2] has attracted the widespread attention of many researchers and is considered to be a sustainable alternative to petrochemical-derived products [3]. Sc-PLA presents a fast crystallization rate, as well as excellent mechanical properties, degradation characteristics and heat distortion temperature compared to those of PLLA or PDLA [15]. It is quite important to find effective technology for the stable formation of sc-PLA while maintaining its superior properties Many methods, such as nanocomposite technology [21,22], physical blending with flexible polymer [22], as well as copolymer with a soft segment [23,24], have been used to improve the stereocomplex degree. On PEG-PLLA block copolymer as compatibilizer of PLLA have been reported, revealing that the blend presents excellent properties due to softening of the PEG block It is worth combining the flexible PEG and stereocomplex technology to manipulate the crystallization behavior of PLA.
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