Trace properties of () non-chain-extended and () chain-extended blend films with various PLLA-PEG-PLLA/PDLA-PEG-PDLA ratios. Storage modulus from DMA of (top) non-chain-extended and (bottom) chain-extended films with various PLLA-PEG-PLLA/PDLA-PEG-PDLA ratios.
- Biodegradable polymers
- Classification of biodegradable polymers
- Poly(lactic acid)
- Stereocomplex polylactides
- Research objectives
- Expected results obtained from the research
- Scopes of research
- Research Place
scPLA showed higher heat resistance than PLLA and PDLA (Sun et al., 2011). To synthesize PLLA-b-PEG-b-PLLA and PDLA-b-PEG-b-PDLA triblock copolymers with controlled molecular weight.
Block copolymers of poly(ethylene glycol) and polylactide
As shown in Table 2, the melting temperature (Tm) and glass transition temperature (Tg) of the PLLA blocks decreased as the feed ratio and molecular weight of PEG increased. To avoid the migration of PEG from the plastic resulting in lower mechanical properties of packaging films and contamination of food, high molecular weight PLLA-PEG-PLLA triblock copolymers with different lengths of the PLLA segment were synthesized by copolymerization.
Stereocomplexation of PLLA/PDLA blends
- Effect of PLLA/PDLA blend ratio on stereocomplexation
- Effect of M.W. of PLLA and PDLA on sterecomplexation
- Effect of stereocomplexation on mechanical properties
- Effect of stereocomplex on thermal stability
It can be seen that scPLA exhibited higher tensile strength and elongation at break than PLLA and PDLA. It can be seen that scPLA showed higher thermal stability at 250°C and 260°C than PLLA and PDLA.
Stereocomplexation of PLLA/PDLA-PEG-PDLA blends
- Effect of PEG block length on stereocomplexation
- Effect of PDLA block length on stereocomplexation
The effect of PEG PDLA-PEG-PDLA block length on stereocomplexation was investigated using PLLA with M.W. The effect of PDLA block length PDLA-PEG-PDLA on stereocomplexation was investigated using PLL with M.W.
Stereocomplexation of PLLA-PEG-PLLA/PDLA-PEG-PDLA blends
17 shows the DSC curves of 50/50 (w/w) PLLA-PEG-PLLA/PDLA-PEG-PDLA blends obtained in the cooling and subsequent heating scans. DSC curves of PLLA/PDLA mixtures of similar molecular weight are included in Fig. The acceleration effects of PEG on PLLA/PDLA crystallization are attributed to the enhanced chain diffusion and mobility (Wei et al., 2014).
DSC curves of PLLA-PEG-PLLA/PDLA-PEG-PDLA and PLLA/PDLA blends: (A) cooling scans from the melting state (250 °C); (B) Subsequent heating scans after cooling. As the length of the PEG center block increases, the tensile strengths and moduli of PLLA-PEG-PLLAs, PLLA-PEG-PLLA/PDLA-PEG-PDLA blends decrease and their elongation at break increases, because the flexible PEG segments promote elongation at break. the smoothness of PLLA, PDLA crystallites under mechanical deformation (Nijenhuis et al., 1996). The PLLA/PDLA and PLLA-PEG-PLLA/PDLA-PEG-PDLA blends exhibit higher tensile strength and elongation at break than the corresponding PLLA and PLLA-PEG-PLLA.
The kink elongation of PLLA-PEG-PLLA with a PEG20k midblock increases 4-10-fold after stereocomplexation with the corresponding PDLA-PEG-PDLA. The increased strength of the enantiomeric mixtures arises from the greater strength and compact chain packing in the SC; this is consistent with the results of PLLA/PDLA blend (Tsuji & Ikada, 1999) and stereocomplex thermoplastic elastomers (Chang et al., 2015; Huang et al., 2016; Huang et al., 2014). Tensile stress versus strain curves for solution cast films of (A) PLLA-PEG-PLLA and (B) PLLA-PEG-PLLA/PDLA-PEG-PDLA blends (Han et al., 2016).
- Chemicals and instruments
- Chemicals
- Instruments
- Monomer preparation and characterization
- Synthesis of polylactides
- Synthesis of triblock copolymers
- Synthesis of triblock copolymers
- Characterization of polylactides
- Optical rotation property
- Diluted-solution viscometry
- Gel permeation chromatography (GPC)
- Thermogravimetric analysis (TGA)
- Differential scanning calorimetry (DSC)
- Preparation of stereocomplex polylactides
- PLLA-PEG-PLLA/PDLA blends
- PLLA-PEG-PLLA/PDLA-PEG-PDLA blends
- Characterization of scPLA
- Differential scanning calorimetry (DSC)
- X-ray diffractometry
- Tensile testing
- Thermo-mechanical properties
- Dimensional stability to heat
- Data analysis
The obtained polymers were granulated before being dried in a vacuum oven at 110 °C for 2 h to remove some unreacted DLA. The obtained copolymers were granulated before being dried in a vacuum oven at 110 °C for 2 h to remove some unreacted lactides. The stereocomplex polylactides (scPLA) of PLLA-PEG-PLLA/PDLA blends were prepared by melt mixing using an internal mixer at 200ºC for 4 minutes with a rotor speed of 100 rpm.
Stereocomplex polylactides (scPLA) of PLLA-PEG-PLLA/ PDLA-PEG-PDLA blends were fabricated by melt blending using an internal mixer at 200ºC for 4 minutes at 100 rpm rotor speed. For the heating scan, 2 - 5 mg of the sample was sealed in an aluminum pan that was melted at 250C for 2 minutes to eliminate its thermal history before being quenched to 0C and reheated from 0 to 250 C at the rate of 10 °C/min under nitrogen atmosphere to observe Tg, Tcc and Tm of homo-crystallites (Tm,hc) and stereocomplex crystallites (Tm,sc). For the cooling curves, the sample was annealed at 250C for 2.0 min to remove thermal history before cooling from 250 to 0C at a rate of 10C/min to observe the crystallization temperature (Tc) and crystallization enthalpy (Hc ).
The crystal structure of the film samples was determined by wide-angle X-ray diffractometry (XRD) at 25°C operating at 40 kV and 40 mA CuK. The degree of crystallinity was calculated from XRD (XRD-Xc) for homo-crystallites (XRD-Xc,hc) [equation (3.13)] and stereocomplex crystallites (sc-Xc,XRD) [equation (3.14)] of the film samples. . The thermomechanical properties of the film samples (mm) were measured by dynamic mechanical analysis (DMA) in tensile mode with a scan amplitude of 10 m and a scan frequency of 1 Hz from 40 to 140 °C at a heating rate of 2C/min.
Characterization of lactides
- Optical rotation property
- Thermal decomposition
Characterization of PLLA-PEG-PLLA, PDLA-PEG-PDLA and PDLA
- Optical rotation property
- Measurement of intrinsic viscosity
- Molecular weight characteristics
- Thermal decomposition
- Thermal transition properties
- Chemical structures
The Mn of PDLA was almost value with the feed Mn (5,000 g/mol) suggested that the 1-dodecanol initiator can control molecular weight of the PDLA. The PDLA showed a single step of decomposition in range 200400C, while both the PLLA-PEG-PLLA and PDLA-PEG-PDLA two-step decompositions in ranges 200300C (PLA blocks) and 300 C (PEG blocks). It should be noted that the Td,max of PLA blocks of triblock copolymers was lower than that of the PDLA.
This can be explained because the flexible PEG blocks reduced the thermal stability of the PLA blocks by reducing the intermolecular interactions between the PLA chains. This was because the PEG center blocks acted as plasticizers to improve the chain mobility of the PLA blocks. Figures 31(a), 31(b) and 31(c) respectively show the polymerization reaction of PLA-PEG-PLA, the 1H NMR spectrum of PLLA-PEG-PLLA and the 1H NMR spectrum of PDLA-PEG- PDLA.
The last methylene protons of EO units (peak f) are shown in the inset spectra in Fig. a) Ring opening polymerization reaction of PDLA and (b) 1H NMR spectrum of PDLA in CDCl3 (peak assignments as shown). a) Ring opening polymerization reaction of PLA-PEG-PLA, (b) 1H NMR spectrum of PLLA-PEG-PLLA and (c) 1H NMR spectrum of PDLA-PEG-PDLA in CDCl3 (peak assignments as shown).
![Table 12. [η] and M v of PDLA and triblock copolymers.](https://thumb-ap.123doks.com/thumbv2/filepdfco/10214254.0/60.892.121.812.205.1122/table-12-η-m-v-pdla-triblock-copolymers.webp)
Characterization of PLLA-PEG-PLLA/PDLA blends
- Thermal transition properties
- Crystalline structures
- Tensile properties
- Thermo-mechanical properties
- Dimensional stability to heat
The larger XRD-Xc,sc values were observed for the blend films with chain extension. The breaking strain of the PLLA-PEG-PLLA film was largely improved with chain extension. The stress and strain at break of the blend films with chain extension decreased with increasing PDLA ratio.
Tensile properties of () non-chain-extended blend films and () chain-extended blend films with different PLLA-PEG-PLLA/PDLA ratios ( = could not be determined). Storage modulus from DMA of (top) non-chain-extended films and (bottom) chain-extended films with different PLLA-PEG-PLLA/PDLA ratios. Both PLLA-PEG-PLLA films with and without chain extension showed the highest film elongation [Fig.
All the blend films after testing showed shorter film elongation than the PLLA-PEG-PLLA film. The heat resistance of the blend films was thus better than the PLLA-PEG-PLLA films for both the blend films with and without chain extension. Dimensional stability to heat of () non-chain-extended and () chain-extended blend films with different PLLA-PEG-PLLA/PDLA ratios ( = could not be determined).
Characterization of PLLA-PEG-PLLA/PDLA-PEG-PDLA blends
- Thermal transition properties
- Crystalline structures
- Tensile properties
- Thermo-mechanical properties
- Dimensional stability to heat
The XRD-Xc,sc of the extended chain blended films increased with the PDLA-PEG-PDLA ratio. For the non-chain-extended films, the blend films showed higher stress and strain at break than the PLLA-PEG-PLLA film. The stress and strain at break of the blend films increased with increasing PDLA-PEG-PDLA ratio.
The results showed that the stereocomplexation between PLLA-PEG-PLLA and PDLA-PEG-PDLA blended films improved their tensile properties. That it did not change significantly with the PDLA-PEG-PDLA ratio indicated that the stiffness of the PLLA-PEG-PLLA and blend films was similar. The XRD-Xc,sc of PLLA-PEG-PLLA/PDLA-PEG-PDLA mixed films without extended chain was in the range of 25%.
The increase in storage modulus during cold crystallization of the blended films was lower than that of the PLLA-PEG-PLLA film and steadily decreased as the PDLA-PEG-PDLA ratio increased. This is due to the higher XRD-Xc,sc of the extended chain blend films. Dimensional heat stability of () non-chain extended and () chain extended blend films with different PLLA-PEG-PLLA/PDLA-PEG-PDLA ratios.
Synthesis and characterization of polymers
This can be explained by the longer polylactide blocks of the triblock copolymers that improved the larger crystallites.
Preparation and characterization of polymer blends
The chain extender improved the film flexibility of both the PLLA-PEG-PLLA/PDLA and PLLA-PEG-PLLA/PDLA-PEG-PDLA blend films. Improvement of the melt flow properties and flexibility of poly(L-lactide) - b- poly(ethylene glycol) - b-poly (L-lactide) by chain extension reaction for potential use as flexible bioplastics. A comparative study on the mechanical, thermal and morphological characterization of poly(lactic acid)/epoxidized palm oil blends.
ABA-type thermoplastic elastomers composed of poly(ε-caprolactone-co-δ-valerolactone) soft midblock and polymorphic poly(lactic acid) hard endblocks. Properties of stereo multi-block polylactides obtained by chain extension of stereo tri-block polylactides consisting of poly(L-lactide) and poly(D-lactide). Polylactide fibers with improved hydrolytic and thermal stability via complete stereocomplexation of high molecular weight poly (L-lactide) of 600,000 and lower molecular weight poly (D-lactide).
Strongly accelerated crystallization of poly(lactic acid): cooperative effect of stereocomplex crystallites and polyethylene glycol. Effect of crystallization temperature on interactive crystallization behavior of poly(l-lactide)-block-poly(ethylene glycol) copolymer. Stiffening of poly(L-lactic acid) by incorporation of poly(ethylene glycol) as a middle block chain, Polymer Science, Series A.
