PLLA Blends Research Articles

Crystallization Studies on the Stereocomplexation of Poly(ʟ‐lactide) / 4‐Armed Poly(ϵ‐caprolactone‐co‐d,ʟ‐lactide)‐ block‐poly(d‐lactide) Blends

AbstractA series of four‐armed poly(ϵ‐caprolactone‐co‐d,ʟ‐lactide)‐block‐poly(d‐lactide) (4a‐CDL‐D) copolymers with different poly(d‐lactide) (PDLA) block lengths (Mn,PDLA) were synthesized via ring opening polymerization using pentaerythritol as initiator. They were blended with poly(ʟ‐lactide) (PLLA) to improve its crystallization rate and mechanical properties. It was found that the crystallization of PLLA in the PLLA/4a‐CDL‐D blend was affected differently when Mn,PDLA changed. In the PLLA/4a‐CDL blend without PDLA blocks, the crystallization was retarded obviously because of the dilution effect of 4a‐CDL on PLLA crystallization. Interestingly, a crystallization acceleration effect was found when Mn,PDLA was 0.5k although no stereocomplex (SC) crystallites existed. When Mn,PDLA was 1k or higher (1.5k and 2k), SC crystallites could be formed in the PLLA/4a‐CDL‐D blends. However, when Mn,PDLA was 1k or 1.5 k, the formation of SC crystallites was difficult and they showed weaker acceleration effect on PLLA crystallization. While when Mn,PDLA was 2k, the crystallization of PLLA was accelerated markedly due to the significant increase of nucleation sites. At last, these blends had longer elongation at breaks than neat‐PLLA. This work provided a novel method for the acceleration of PLLA crystallization by adjusting the PDLA chain length in PLLA blends.

Designing of reactive micro-crosslinked PBAT as the efficient biodegradable toughener for PLLA

Melt blending with biodegradable poly (butylene adipate-co-terephthalate) (PBAT) represents a facile strategy to toughen poly (l-lactide) (PLLA). Unfortunately, the toughening efficiency of PBAT is far from the practical requirements regardless of significant efforts to strengthen interface between PLLA and PBAT phases. Herein, two reactive micro-crosslinked PBAT tougheners (RMBTs) via simple reactive processing of PBAT/glycidyl methacrylate (GMA)/dicumyl peroxide (DCP) with or without PLLA-inclusions have been designed to break the toughening restriction of PBAT for PLLA. The results indicate that the RMBT without PLLA increases the toughness of the final PLLA blends in comparison to pristine PBAT. Intriguingly, further enhancements can be achieved by using the RMBT incorporating PLLA moieties. The notched impact strength of the PLLA-incorporated RMBT toughed PLLA is as high as 52.3 kJ/m2 at 30% PBAT content, which is 600% higher than the pristine PBAT toughed PLLA, while the tensile strength keeps almost the same value of about 44.4 MPa. The collaborative enhancement is not only attributed to the micro-crosslinking and reactive group grafting modification, but also ascribed to sub-inclusion of rigid PLLA chains in the PBAT phase. The comprehensive mechanical properties of the fully biodegradable PLLA blends are even higher than those of the commercially available polycarbonate/acrylonitrile-butadiene-styrene (PC/ABS) blends. The high toughening efficiency of the reactive micro-crosslinked PBAT would evoke new inspiration in the field of industrial manufacture of fully degradable PLLA blends with high stiffness-toughness balance.

Frustrated crystallization behavior under hierarchical confinement in electrospun fibers of poly(styrene)/poly(ethylene oxide)/poly(l‐lactide) ternary mixtures

AbstractThe crystallization behavior of binary crystalline mixtures composed of poly(ethylene oxide) (PEO) and poly(l‐lactide) (PLLA) was investigated in the electrospun nanofibers fabricated by the ternary blends of polystyrene (PS), PEO, and PLLA. The weight fraction of PEO/PLLA mixture was kept at ≤0.2 such that PS formed the matrix phase. The preferred mixing of PEO and PLLA resulted in the formation of mixed PEO/PLLA dispersed domains in the PS matrix. The small diameter of the electrospun nanofibers restricted the size of dispersed domain. During cooling from melt, PLLA crystallized first resulting in crystallization induced phase separation and entrapment of PEO within the intracrystalline regions of PLLA crystals. Hence, whereas the PLLA crystallized within the soft PS matrix, the crystallization of PEO occurred within the hierarchical confinement imposed by the PLLA crystals as well as the glassy PS matrix. Interestingly, it was found that the confinement favored the formation of α crystals phase in PLLA even at very low crystallization temperatures. Furthermore, due to plausible entrapment of PEO segments within the PLLA crystals, significant depression in PLLA melting temperature was observed. Moreover, the PEO melting temperature also depressed by more than 30°C due to the frustrated crystallization within the hierarchical confinement.

In-situ reactive compatiblization modified poly(l-lactic acid) and poly (butylene adipate-co-terephthalate) blends with improved toughening and thermal characteristics

Triglycidyl isocyanurate (TGIC) with multifunctional epoxy is used for reactive compatibilization of Poly (l-lactic acid) (PLLA)/Poly (butylene adipate-co-terephthalate) (PBAT) blends. Interfacial tension, FTIR and SEM results show that TGIC has greater affinity and stronger reactivity with PBAT. The mixing sequence of PLLA/PBAT/TGIC blends has a significant impact on the compatibility. The TGIC and PBAT are reactive blended first, followed by the PLLA, which is most advantageous to produce a substantial amounts of branched copolymers PLLA-g-PBAT at the interface for the (PBAT/4%T) /PLLA blend. The considerable improvement of interfacial compatibility and the thickening of interfacial layer promote the stress transfer from the matrix to the dispersed PBAT phase. In comparison to PLLA/PBAT blend, the breaking elongation of (PBAT/4%T)/PLLA blend is raised by 25.6 times up to 164.2 % and the tensile strength is enhanced up to 32.1 MPa. The present work offers valuable perspectives on how to encourage the efficient application of reactive compatibilizers with epoxy groups in polyester blends.

PLLA grafting draws GO from PGA phase to the interface in PLLA/PGA bone scaffold owing enhanced interfacial interaction

The interfacial interaction between poly (l-lactic acid) (PLLA) and poly (glycolic acid) (PGA) is poor although the blending of PLLA and PGA may combine the advantages of both, which seriously affects the mechanical properties of PLLA/PGA bone scaffold. In this study, PLLA chains were grafted onto graphene oxide (GO) by ring-opening polymerization reaction, and the modified GO was used as nanofiller to increase the interfacial interaction for PLLA/PGA scaffold fabricated by selective laser sintering (SLS). The result indicated that GO grafted with PLLA chains reduced the interfacial tension between GO and PLLA from 24.09 mN/m to 3.74 mN/m, thus drawing GO from PGA phase to the interface between PLLA and PGA. The GO at the interface hindered the coalescence of PGA phase through the repulsive forces and facilitated the breakup of the PGA phase, which increased the contact surface area between PLLA and PGA, and thereby enhancing the interfacial interaction. Consequently, the tensile and compressive strength of the PLLA/PGA scaffold containing 1 wt% the PLLA-grafted GO, on which L-LA ring-opening polymerized for 24 h, were increased by 44.64% and 69.65%, respectively, compared with PLLA/PGA scaffold. Besides, the cell adhesion and fluorescence experiments demonstrated that the bone scaffold had good cytocompatibility for cell adhesion, migration and proliferation.

Polylactide cocrystals and gels

AbstractSynthetic biodegradable polyesters have emerged as an alternative to conventional petroleum‐derived polymers for a diverse range of applications. Among these, polylactides are the most commercially successful biodegradable polymers. The presence of stereoregular chains makes poly(l‐lactide) (PLLA) and poly(d‐lactide) (PDLA) semicrystalline. The blending of enantiomeric PLLA and PDLA resulted in the stereocomplex formation due to non‐covalent interactions of enantiomeric chains. PLLA exhibits different crystalline forms depending on the crystallization conditions with different chain conformations, as well as different chain packing structures. PLLA and its blend with PDLA are known to form cocrystals with certain solvents. This review focuses mainly on the recent progress in understanding the cocrystal formation, polymorphic phase transitions of these cocrystals, gelation mechanism and stereocomplex formation in blend gels of polylactides.

Extraordinary toughness and heat resistance enhancement of biodegradable PLA/PBS blends through the formation of a small amount of interface-localized stereocomplex crystallites during melt blending

Simultaneously improving the toughness and heat resistance of poly(l-lactide) (PLLA) is significant for expanding biodegradable materials' application range. In this work, reactive compatibilizers containing PBS and PLLA (PBS-St-GMA-PLLA (SGL)) or poly(d-lactide) (PBS-St-GMA-PDLA (SGD)) were synthesized and incorporated in blends of commercial PLLA and PBS as compatibilizers. The in situ formation of stereocomplex (SC) crystallites of PLA at the interface of PLLA and PBS was successfully achieved through simple melt blending. The effects of SC crystallites, amount of compatibilizers on morphology, crystallization behavior, mechanical properties, heat resistance and degradability properties of PLLA/PBS blends were studied. Morphological evolution showed that SGL and SGD significantly improved the compatibility of PLLA/PBS blends. After incorporating 5% SGD, the elongation at break and notched impact strength of PLLA/PBS blends with SC crystallites reached 273% and 34 kJ/m2, respectively, 12 and 5 times than that of pristine PLLA/PBS blends. As compared with PLLA/PBS/SGL blends that cannot form SC crystallites, the tensile strength of the blends was effectively improved by the presence of SC crystallites, ascribing to improved interfacial compatibility and remarkable acceleration in matrix crystallization kinetics of PLLA. Consequently, the blends containing 5% SGD exhibited excellent heat resistance (E′80°C > 680 MPa) after brief annealing, which far exceeded the PLLA or PLLA/PBS blends. This work may provide a feasible way to prepare PLLA-based materials with excellent comprehensive properties by the formation of SC crystallites.

Controlling stereocomplex crystal morphology in poly(lactide) through chain alignment

The incorporation of poly(d-lactide) (PDLA) to form stereocomplex crystallites (SCs) within a poly(l-lactide) (PLLA) matrix is among the most effective strategies in overcoming PLLA's numerous drawbacks. However, high concentrations of PDLA (>3 wt%) are required to improve PLLA's crystallization kinetics and melt strength, which is undesirable owing to PDLA's high cost. In this study, we use chain alignment as a levier to tune stereocomplex superstructure morphology to overcome these limitations. Herein, PLLA/PDLA blends were manufactured using an environmentally friendly and low-cost single step spunbond fibrillation process, yielding microfibers stretched to diameters of 5–20 μm. During this stretching process, PLLA and PDLA chains are aligned along the flow direction. SCs subsequently formed in situ upon heating, dramatically improving crystallization kinetics, melt elasticity, and tensile performance compared with neat PLLA and non-stretched blend analogues, even with low PDLA content (<3 wt%). These improvements were attributed to topological variations in SC superstructures caused by alignment of PLLA and PDLA chains. The application of chain alignment in tuning SC superstructure morphology is ubiquitous in fibrillation processes.

Melt and nucleation reinforcement for stereocomplex crystallites in poly(ʟ-lactide)/lignin-grafted-poly(ᴅ-lactide) blend

Lignin-grafted-poly (ᴅ-lactide) (LGPD) with two different poly (ᴅ-lactide) (PDLA) block lengths (1100 and 2000 Da), denoted as LGPDL and LGPDH respectively, were synthesized by ring opening polymerization using dodecylated lignin as initiator. They were then blended with poly(ʟ-lactide) (PLLA) to improve its crystallization, mechanical properties and UV-absorbance properties. It was found that stereocomplex (SC) crystallites could be formed in both PLLA/LGPD blends, and the crystallization rate of PLLA/LGPDH was faster than that of PLLA/LGPDL because of the longer PDLA block length. Both in the non-isothermal and isothermal crystallization process, the crystallization of PLLA in the PLLA/LGPDH blend was the fastest when the ratio of LGPDH was 3%. SC crystallites in the PLLA/LGPDH blends also showed broader melting ranges and higher final melting temperatures comparing to the blends of PLLA and 4-armed PDLA (4a-PDLA), whose number of PDLA arms and molecular weight was similar to LGPDH. These results proved that the lignin structure grafted by the PDLA arms could affect the state of SC crystallites and their acceleration effect on the crystallization of PLLA in the blend. The degradation behavior showed that the degradation rate of the LGPDH-5% blend in the final stage of degradation (about 24 h) was the slowest comparing to other blends. Besides, the PLLA/LGPD blends had better tensile strength and UV-absorbance properties than neat PLLA.

Electrospun Methacrylated Gelatin/Poly(L-Lactic Acid) Nanofibrous Hydrogel Scaffolds for Potential Wound Dressing Application.

Electrospun nanofiber mats have attracted intense attention as advanced wound dressing materials. The objective of this study was to fabricate methacrylated gelatin (MeGel)/poly(L-lactic acid) (PLLA) hybrid nanofiber mats with an extracellular matrix (ECM) mimicking nanofibrous structure and hydrogel-like properties for potential use as wound dressing materials. MeGel was first synthesized via the methacryloyl substitution of gelatin (Gel), a series of MeGel and PLLA blends with various mass ratios were electrospun into nanofiber mats, and a UV crosslinking process was subsequently utilized to stabilize the MeGel components in the nanofibers. All the as-crosslinked nanofiber mats exhibited smooth and bead-free fiber morphologies. The MeGel-containing and crosslinked nanofiber mats presented significantly improved hydrophilic properties (water contact angle = 0°; 100% wettability) compared to the pure PLLA nanofiber mats (~127°). The swelling ratio of crosslinked nanofiber mats notably increased with the increase of MeGel (143.6 ± 7.4% for PLLA mats vs. 875.0 ± 17.1% for crosslinked 1:1 MeGel/PLLA mats vs. 1135.2 ± 16.0% for crosslinked MeGel mats). The UV crosslinking process was demonstrated to significantly improve the structural stability and mechanical properties of MeGel/PLLA nanofiber mats. The Young’s modulus and ultimate strength of the crosslinked nanofiber mats were demonstrated to obviously decrease when more MeGel was introduced in both dry and wet conditions. The biological tests showed that all the crosslinked nanofiber mats presented great biocompatibility, but the crosslinked nanofiber mats with more MeGel were able to notably promote the attachment, growth, and proliferation of human dermal fibroblasts. Overall, this study demonstrates that our MeGel/PLLA blend nanofiber mats are attractive candidates for wound dressing material research and application.

An efficient way to change surface properties of poly(l-lactic acid) by synthesis of polycaprolactone grafted fluoropolyacrylate

Macromolecules with fluoroalkyl group are promising as anti-fouling materials. In the work, a series of polycaprolactone grafted poly(octafluoropentyl methacrylate-co-hydroxyethyl methacrylate)s (PCL-PFHs) were synthesized as additives to change the surface properties of poly(l-lactic acid) (PLLA). The synthesized products were characterized with 1HNMR and GPC. PCL-PFH and PLLA were immiscible in blend, but PCL-PFH microparticles could immerse uniformly in PLLA substrate. The molar ratio of [OFPA]/[HEMA] in PFH and blend ratio of PCL-PFH/PLLA played a key role in changing the surface properties of PLLA blend. When the molar ratio and blend ratio were 4/1 and 10/90 respectively, the surface tension of PLLA blend lowered to 19.57 mN m−1, and it inhibited BSA adhesion effectively during protein adsorption process. At the same time, PLLA blend presented good hydrolytic stability. PCL-PFH also toughened PLLA, and the tensile strength and elongation at a break were 37.0 MPa and 126.1%. Then this work would built a new bridge between PLLA materials and biomedical engineering.

Entirely environment-friendly polylactide composites with outstanding heat resistance and superior mechanical performance fabricated by spunbond technology: Exploring the role of nanofibrillated stereocomplex polylactide crystals

This study aims at investigating the manufacturing and characterization of all-polylactide composites prepared by melt spunbond spinning technology. To do so, a series of asymmetric stereocomplex polylactide (SC-PLA) blends (PLLA 95 wt%/PDLA 5 wt%) was melt spun. To examine the impact of molecular structure of PDLA, the blends of linear PLLA, and low and high molecular weight as well as branched PDLAs, were subjected to a single step spunbond process. DSC thermograms of the samples showed two melting temperatures at around 170 °C and 210 °C, which were attributed to the melting of homo and stereocomplex crystals, respectively. The samples were spun at 190 °C, between the homo and stereocomplex crystals' melting temperatures, and at 230 °C, above the stereocomplex crystals' melting temperature. Morphology images showed the formation of fibers in the range of 40–50 μm. Shear rheological measurements revealed that the spun SC-PLA samples had a substantially higher viscosity and storage modulus in the low frequency region, and higher shear thinning behavior, compared to the non-spun samples. Extensional rheology measurements also showed that the spun samples demonstrated strain hardening behavior. Substantial enhancement of rheological properties was noted for the samples containing the branched and high molecular weight PDLA spun at 230 °C. After etching, the spun samples at 190 °C exhibited small spherical crystals with diameters in the range of 80–90 nm, whereas comparatively thin fibers in the size range of 60–70 nm were observed for the samples spun at 230 °C. Remarkable enhancements up to 100% and 60% was noted for the tensile modulus and strength, respectively, of the spun SC-PLA samples. The spun fibers also demonstrated a considerable reduction in boiling water and hot air shrinkage. The distinctive role of nanofibrillated stereocomplex crystals as a rheology modifier and a crystallization nucleating agent makes PLA more sustainable and paves the way for the fabricated all-PLA composites in applications requiring high heat resistance and superior mechanical performance. The present study unequivocally indicates a huge potential for the sustainable entirely all-PLA products manufactured by fiber in fiber and, indeed, unfolds unknown opportunities for PLA-based merchandises in future.

Antiflaming poly(L‐lactide) by synthesizing polyurethane with phosphorus and nitrogen

AbstractA novel polyurethane containing phosphorus and nitrogen (PU) was synthesized and characterized with 1H‐NMR, FTIR, and GPC. It was served as flame retardant to blend with poly(L‐lactide) (PLLA) through solution casting technique. PU particle dispersed in PLLA substrate irregularly and improved the crystallinity of PLLA. The initial decomposition temperature of PLLA composite was significantly lower, but char residue increased. Flame retardancy and mechanical properties of PU/PLLA blends were evaluated. When the blend ratio of PU/PLLA was 10 wt%, LOI was 26.8%, and UL94 test reached V‐2 grade. The inflaming retarding mechanism was outlined. The tensile strength of PLLA blend was 42.8 MPa, while its elongation at break was only 2%. By adjusting PU and adding compatilizer, the balance between flame retardancy and good mechanical properties of PLLA would be controlled.

Stereocomplex Crystallization Induced Significant Improvement in Transparency and Stiffness–Toughness Performance of Core‐Shell Rubber Nanoparticles Toughened Poly(l‐lactide) Blends

AbstractToughening modification of poly(l‐lactide) (PLLA) with rubber particles is often realized at the cost of transparency, mechanical strength, and modulus because high rubber loadings are generally required for toughening. In this work, a promising strategy to simultaneously improve the transparency and stiffness–toughness performance of poly(butyl acrylate)‐poly(methyl methacrylate) (BAMMA) core‐shell rubber nanoparticles toughened PLLA blends by utilizing the stereocomplex (SC) crystallization between PLLA and poly(d‐lactide) (PDLA) is devised. The results reveal that the construction of SC crystallites in PLLA matrix via melt‐mixing PLLA/BAMMA blends with PDLA can prevent BAMMA nanoparticles from aggregation and promote them to form network‐like structure at lower contents. As a result, not only higher toughening efficiency with less rubber contents but also superior transparency is achieved in the PLLA/PDLA/BAMMA blends as compared with the PLLA/BAMMA ones where large aggregated BAMMA clusters are formed. Moreover, the outstanding reinforcement of SC crystallites network for PLLA can impart an enhanced tensile strength and modulus to PLLA/PDLA/BAMMA blends, thus improving the stiffness–toughness performance of PLLA/PDLA/BAMMA blends to a higher degree. This work demonstrates that SC crystallization is a promising solution to solve the contradiction between transparency and mechanical properties and then obtain superior comprehensive performances in rubber toughened PLLA blends.

Physico chemical and phase separation characterization of high molecular PLLA blended with low molecular PCL obtained from solvent cast processes

Blends of PLLA and PCL yielded by solvent casting usually exhibit phase separation and crystallization behavior which have a strong impact on their suitability for certain biomedical applications such as degradable coatings or drug carriers. Therefore, it is important to understand the underlying mechanisms. In this study, high-molecular biodegradable semi-crystalline poly(L-lactide) (PLLA) (Mw = 320 kDa) was blended with low-molecular biodegradable semi-crystalline poly(ε-caprolactone) (PCL) (Mw = 40 kDa) in various combinations (10, 50 and 90 wt.% PCL) by solvent casting. The yielded blends were subjected to annealing at 40 °C, 80 °C and 200 °C and cooled down slowly to maintain thermodynamic equilibrium. Scanning electron microscopy, atomic force microscopy, Raman images and differential scanning calorimetry were used to investigate the structure, morphology and thermal properties of the solvent cast PLLA/PCL blends. It was shown that the physico-chemical properties of PLLA/PCL blends prepared by solvent casting differ substantially compared to those accessed by melt manufacturing processes. In summary, the blends showed a complex phase separation behavior, which is completely dependent on the method of preparation and the adjusted temperature during production process.

Effect of thermal annealing on crystal structure and properties of PLLA/PCL blend

As far as we know, to enhance the toughness of poly(L-lactide) (PLLA) without compromising its inherent biodegradability, melt blending PLLA with flexible biodegradable polymers is the most effective and universal method. However, most of research results show a slight improvement in impact toughness due to the amorphous PLLA matrix. In other words, effective impact toughness can be achieved only if PLLA blend is in a highly crystalline state. In this work, blend of PLLA with 20 wt% PCL was prepared and then samples made by injection molding were applied to thermal annealing at different temperatures for 2 h to increase the crystallinity of PLLA matrix. The results show that the crystallinity of PLLA/PCL blend annealing at 80 °C is exceeding 40% and impact strength of the samples increases from 5.92 KJ/m2 of unannealed neat PLLA to 26.81 KJ/m2. At the same time, the thermal properties are also improved by a large margin.

Organic solvent-free fabrication of mesoporous polymer monolith from miscible PLLA/PMMA blend

The fabrication of monoliths by environment-friendly methods without organic solvents remains a challenging task. In this study, we successfully produced mesoporous polymer monoliths by selective hydrolysis degradation of miscible poly(-L-lactic acid) (PLLA)/poly(methyl methacrylate) (PMMA) blends without any organic solvents. 50 to 90 wt% of PLLA blend ratios were tested. We found that freeze-dried was effective to prevent a shrinkage of monoliths. With increaser of PLLA weight fraction, porosity, mode pore diameter, and pore geometry could be controlled from 17 to 52%, 7.1–32 nm, and mainly cylindrical to spherical, respectively. Further, a comprehensive model based on volume balance and surface area equivalence successfully predicted mode pore size. The reported organic solvent-free fabrication of mesoporous polymer monoliths might enable tunable mesopore properties through only changing mechanical blending of miscible polymers.

Electrospun membranes of low molecular weight di-stereoblock poly(lactic acid)s with high thermal stability and solvent resistance via low temperature sintering

Electrospinning is a highly efficient mild method to obtain stereocomplex poly(lactic acid) fibers from blends of high molecular weight (MW) poly(L-lactic acid) (PLLA) and poly(D-lactic acid) (PDLA). However, high MW PLAs are expensive and proved difficult to avoid homocrystallites which weaken the performances. Here, di-stereoblock poly(lactic acid)s (di-sb-PLAs) with low MW of 104 g mol−1 were synthesized and electrospun into membranes. The stereocomplex (sc) crystallites were induced by sintering the amorphous as-spun membranes at 200 °C, and further improved by applying 1 MPa pressure which promoted the segment migration across fiber intersections and welded the fibers by forming new sc crystallites. Due to more readily crystallize at molecular level than the blend of PLLA and PDLA, the sintered di-sb-PLA membranes exhibited higher thermal stability, better tensile strength, and were more stable during multiple cycles of selective separating solvent and water mixtures. Increasing MW of di-sb-PLA positively affected the membrane properties and inhibited dramatical embrittlement that occurred in sintered membrane of PLLA and PDLA blend.

Highly toughened and heat resistant poly(l-lactide)/poly(ε-caprolactone) blends via engineering balance between kinetics and thermodynamics of phasic morphology with stereocomplex crystallite

Enhancing matrix crystallization via forming stereocomplex (SC) crystallite has been considered as an effect way to improve the impact toughness and heat resistance of poly(l-lactide) (PLLA) when blending with other polymers. However, the roles of some of the key parameters, such as the kinetics of morphology evolution in blends, remain, yet, unclear, causing the troubles of the reproducibility of toughening PLLA by enhancing matrix crystallization and the stability in end-use applications (particularly in relative high temperature ranges). Herein, we provide a facile way to improve the toughness and heat resistance of PLLA via engineering the balance between the kinetics and thermodynamics of the dispersed phasic morphology in PLLA blends using PLLA/poly(ε-caprolactone) (PCL) (PLLA/PCL, 80/20 w/w) as an example, by adding a small amount of poly(d-lactide) (PDLA, ≤ 1% w/w). The few PDLA chains naturally interact with PLLA matrix chains, and co-crystallize to form SC crystallites, yielding high crystalline PPLA matrix but in controllable crystallization kinetics and increase of melting viscosity. As such, the coalescence or arrest of dispersed PCL phase is tailored via the tempo- and thermo-dimensional balance manipulation of thermal annealing (thermodynamics) and injecting moulding (quenching, dynamics), that relies on the PDLA content. The ease, with which highly impact toughened and heat-resistant PLLA materials were obtained by optimizing and matching the PDLA content and processing parameters including temperature and time, points to new directions in designing toughened PLLA with an economic manner.

Role of lubricant with a plasticizer to change the glass transition temperature as a result improving the mechanical properties of poly(lactic acid) PLLA

Poly (lactic acid) (PLLA) is the best important bioplastics derived from renewable resources like blackstrap molasses (sugar beet, date palm and sugar cane). PLLA is brittle and has a low elongation at break, which hinders its applications in the industry. One method to solve this problem is to improve its mechanical properties by adding plasticizers. The PLLA blends were prepared at first by solution blending as a solvent casting method and then melting using a hydraulic hot press. PLLA was blended with a plasticizer (GMS/TA) to obtain a higher ductile of PLLA. The addition of lubricant and plasticizer (GMS/TA) leads to reduce the glass transition temperature (Tg), melting point (Tm), and the cold crystallization temperature (Tcc) in PLLA blends. The mechanical properties of PLLA have been investigated. The results indicated compatibility between PLLA and additives. The elongation at the break of the PLLA blend is stretched 270% with a tensile strength of 16 MPa. The addition of lubricant with the plasticizer leads to sliding the chain of PLLA, which causes to increase the strain. The physical blending has been demonstrated to be an effective technique to obtain an environmentally friendly PLLA blend with good mechanical properties, therefore it can be used in the food packaging sector.