Neat PLLA Research Articles

Effect of γ-irradiation and antimicrobial agent on properties of poly(L-lactide) active films

Data on irradiation of poly(L-lactide) (PLLA) based active packaging is still limited. Therefore, effect of γ-irradiation on neat PLLA and active packaging with oligohexamethylene guanidine hydrochloride (OHMG·HCl) has been studied. Combined use of irradiation and active packaging technology is promising approach to maintain food safety and prolong shelf life. It has been found that regardless of the OHMG·HCl content PLLA undergoes chain scission during irradiation and this process becomes less pronounced at doses higher than 50 kGy. Slight racemization of PLLA during exposure has been observed using polarimetry and 13C NMR spectroscopy. Mechanical properties of films have been examined. Biocide addition led to a 30% decrease in films elongation at break. Irradiation either caused elongation decrease. Dose of 50 kGy and higher made PLLA active films brittle. Multiple melting behavior of irradiated PLLA has been analyzed by differential scanning calorimetry. Fraction of crystals with higher melting temperature rose with dose. Possible reason for this phenomenon is formation of α′ form with less ordered chain packaging that recrystallizes during heating. The biocide addition has not affected this process. Furthermore, in vitro antimicrobial test has shown efficacy of films with 2 wt.% of OHMG·HCl against gram-negative, gram-positive bacteria and fungi.

Enhanced rheological, crystallization, mechanical, and heat resistance performance of poly(L‐lactide)/basalt fibers composites via in situ formation of stereocomplex polylactide crystals

AbstractDue to its favorable mechanical strength, transparency, and biocompatibility, polylactic acid (PLA) has considerable potential as a biodegradable material. Nevertheless, developing high‐performance PLA composites through environmentally friendly and cost‐effective methods remains a significant challenge. In this study, the composites comprising poly(L‐lactide) (PLLA), basalt fibers (BFs), and poly(D‐lactide) (PDLA) are prepared through facile melt blending. The in situ formed stereocomplex polylactide (SC‐PLA) crystals improve the crystallization ability and rheological behavior of PLLA/BF/PDLA composites. Upon adding 5 wt% PDLA, BFs are nicely dispersed in PLLA matrix because of increased shear intensity. The synergistic effect of BFs and SC‐PLA crystals enhances the mechanical, thermomechanical, and heat resistance properties of PLLA. In particular, PLLA/BF/10%PDLA composites exhibit a Vicat Softening Temperature (VST) of 155.5°C, increasing by approximately 100°C over neat PLLA. Annealing treatment increases the Young's modulus, thermomechanical properties, and VST of samples while reducing their tensile strength. Interestingly, the tensile strength of the annealed PLLA/BF/10%PDLA composites is 50.2 MPa, twice that of the annealed neat PLLA due to the introduction of SC‐PLA crystals. Simultaneously improving the rheological, mechanical, and heat resistance performance of PLLA opens possibilities for expanding its potential applications in the industrial field.

Surface modification of titanium implants via PLLA/HA fibrous composite coating to improve piezoelectric properties

Titanium (Ti)-based implants are among the most advantageous biomaterials in both orthopedic and dental applications, owing to their excellent properties and biocompatibility. However, their bioinert surface poses challenges to osteointegrity, raising concerns about implant loosening. The present study examines the effect of surface modification of Ti by applying a bioactive piezoelectric fibrous coating comprised of electrospun poly(L-lactide) (PLLA) as a biodegradable piezopolymer and varying amounts of hydroxyapatite (HA) filler (5−20 wt%) as an osteoconductive piezoceramic. According to SEM micrographs, adding HA increased the fiber diameter, porosity, and pore size of the fibrous structure. Furthermore, peeling test of the fibrous coating demonstrated that applying a polydopamine (PDA) coating before electrospinning onto the Ti substrate effectively enhanced the adhesion strength of the coating. Additionally, the PLLA/HA composite coating exhibited increased piezoelectric properties, with piezoresponse rising from 2.41 ± 0.192 mV/N (5 wt% HA) to 5.42 ± 0.192 mV/N (20 wt% HA). Similarly, PLLA/HA coatings showed superior apatite-forming ability in simulated body fluid (SBF) at 7 and 28 days, with significantly higher calcium-phosphate deposition and a Ca/P ratio close to natural bone, surpassing the neat PLLA coating and bare Ti substrate. Finally, testing with MG-63 cell lines indicated that fibrous composite coatings enhance cell support, demonstrating optimal alkaline phosphatase (ALP) secretion levels and positive cell attachment. Consequently, the surface-modified Ti with fibrous PLLA/HA coating emerges as a promising strategy for the clinical treatment of bone defects.

Fabricating high-performance biomedical PLLA/PVDF blend micro bone screws through in situ structuring of oriented PVDF submicron fibers in microinjection molding

Poly(l-lactide) (PLLA) is regarded as a polymer with excellent biocompatibility, but its inherent brittleness property greatly restricts its application in the biomedical engineering field. Blending PLLA with other polymers is one of the sufficiently viable methods of property improvement. In this paper, the Poly(l-lactide) (PLLA)/Polyvinylidene fluoride (PVDF) blend was first prepared by melt-compounding, and then microinjection molded into the blend micro bone screw with high strength and toughness. The experimental results show that the PVDF dispersed phases could in situ form the highly oriented fibers with shish-kebab structures under the effect of strong shear stress field of microinjection molding along flow direction. These parallelly aligning PVDF fibers could simultaneously realize the significant enhancement in both toughness and strength of the micro bone screw. Specifically, in the bending test the blend micro bone screw with oriented PVDF fibers can withstand the compression displacement of nearly 2 mm, while the neat PLLA one would break within only 0.5 mm displacement. In addition, a bending recovery phenomenon was observed in the load-displacement curve of the blend, demonstrating the mechanical transition from brittle fracture to ductile fracture. Moreover, with addition of 30 % PVDF, the elongation at break increases from 7.8 % to 57.8 %, while the tensile strength increases from 60.9 MPa to 74.3 MPa. The PLLA/PVDF micro screws possess better toughness and excellent biocompatibility compared to pure PLLA products. They also exhibit great potential for stimulating the proliferation of cells through piezoelectric output, opening up new possibilities for the development of next-generation fracture fixation materials.

PLLA/(MWCNTs-ZnO)@PDA composite with NIR-light induced shape memory effect, antibacterial properties and 3D printability

PLLA based shape-memory polymer composites with multifunctions have attracted growing attention in biomedical applications. Generally, a single nanofiller has the problem of insufficient functionalization and easy aggregation. Therefore, we design and fabricate polydopamine (PDA) surface modified MWCNTs-ZnO hybrid nanostructure ((MWCNTs-ZnO)@PDA). The dispersion of (MWCNTs-ZnO)@PDA in PLLA is improved in comparison with the pristine MWCNTs or ZnO. The results indicate that the (MWCNTs-ZnO)@PDA nanosystem shows a synergistic effect on the mechanical properties and photothermal properties of the composites. Comparative analysis with neat PLLA demonstrates a remarkable 17% increase in tensile strength and a 19% increase in elongation at break for PLLA/(MWCNTs-ZnO)@PDA composite. Additionally, the composites exhibit excellent NIR light-induced shape memory effects with a shape recovery ratio reaching 100%. Moreover, PLLA/(MWCNTs-ZnO)@PDA composites show favorable antibacterial activity against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). Furthermore, the polymer composites display good 3D printability, and the 3D-printed porous scaffold possesses high compressive strength and modulus. Also, the PLLA/(MCNTs-ZnO)@PDA scaffold can be compressed into a compact size and recover its original shape under NIR light irradiation. This work provides an approach to prepare novel shape-memory polymer composites with multifunctions including high strength, light-induced shape-recovery, antibacterial properties and printability.

Fabrication of antibacterial poly (L-lactic acid)/tea polyphenol blend films via reactive blending using SG copolymer

Poly (L-lactic acid) (PLLA) composite materials with both excellent antibacterial properties and mechanical properties are highly desirable for both food packaging and biomedical applications. However, a facile method to prepare transparent PLLA composite films with both excellent antibacterial and mechanical properties is still lacking. In this work, blend films based on PLLA, tea polyphenols (TP) and poly (styrene-co-glycidyl methacrylate) (SG) copolymers (PLLA/TP/SG) were prepared by melt blending using twin screw extruder. The blend films showed high transparency with a brownish color originated from tea polyphenols. Both SEM and DSC analyses confirmed that the blends are thermodynamically compatible. GPC and mechanical assessments demonstrated that the PLLA/TP binary blends exhibit reduced molecular weight and compromised mechanical properties, compared to neat PLLA. However, incorporating SG copolymer resulted in increased molecular weight and improved mechanical properties for the PLLA/TP/SG blends. The FT-IR spectra exhibited a shift to lower wavenumber for the absorption peak associated with the benzene ring on TPs after blending with PLLA and SG, indicating the occurrence of transesterification between PLLA and TP. Plate coating studies revealed that the PLLA/TP/SG blends with TP incorporation at 5 wt% exhibited a bacteriostatic rate of 99.99 % against Staphylococcus aureus and Escherichia coli. Overall, our study reveals that the PLLA/TP/SG blend films exhibit excellent antibacterial properties coupled with good mechanical properties, rendering them a promising candidate for antibacterial packaging materials.

Towards ductile and high barrier poly(L-lactic acid) ultra-thin packaging film by regulating chain structures for efficient preservation of cherry tomatoes

The irreconcilable paradox between barrier performance and ductility is a “stumbling block” restricting the development of poly(L-lactic acid) (PLLA) films in the packaging industry. In this work, we reported the fabrication of an ultra-thin PLLA-based film with barrier properties and ductility by adjusting the polarity and conformational behavior of the polymer chains. Firstly, a novel unsaturated poly(L-lactic acid-co-butyrate itaconate) P(LA-BI) copolymer containing CC double bonds was synthesized using melt polycondensation. The results reveal that the addition of 60 % of P(LA-BI) enables PLLA film to achieve an elongation at a break of 83.6 % due to P(LA-BI) containing partially branched structures, which resulted in the polymer chains being arranged more in a high-energy gg conformer. Meanwhile, because of the large number of CO polar groups in P(LA-BI), PLLA/P(LA-BI)60 film show CO2 and O2 permeability coefficients (CDP and OP) of 1.8 and 0.45 × 10−8 g·m·m−2·h−1·Pa−1 respectively, which means that it has excellent gas barrier properties. Moreover, PLLA/P(LA-BI)60 film shows a 33.3 % increase in CO2/O2 ratio and an excellent ultraviolet (UV) barrier performance compared to neat PLLA. Preservation results suggested that the CO2 and O2 levels within the package could be regulated by varying the amount of P(LA-BI) added. Among them, PLLA/P(LA-BI)40 film generated a more desirable CO2 and O2 atmosphere for cherry tomatoes preservation, which was reflected by the delaying of senescence, discoloration, and decay, inhibition of oxidative cell damage through reduced malondialdehyde production, and maintenance of nutritional and flavor substances in cherry tomatoes. This PLLA-based film offers the advantages of operational simplicity, environmental friendliness, and inexpensive cost, making it great promising for food preservation and other applications requiring barrier properties and ductility.

Studies on the effect of polylactide in-situ grafting during melt processing on poly(ʟ-lactide)/graphene oxide composite films

The present work tried to solve the compatibility and dispersion problems of industrial grade graphene oxide (GO) mixing with polylactide (PLA) by melt processing for practical application. PLA was grafted on the GO using the silane coupling agent (KH560) as “bridge” by in-situ melting reaction to improve the compatibility. For better compatibility and dispersion, poly(ᴅ-lactide) (PDLA) was grafted on GO (D-G) to form stereocomplex crystallites with poly(ʟ-lactide) (PLLA) to enhance the interaction between GO and PLLA matrix. By biaxial stretching, the PLLA and GO composite films were prepared. Results show that GO was seriously aggregated in the film containing GO without PLA grafting (PLLA/L/G0.05) and the average size of aggregated GO was about 19.5 μm. PLA grafting decreased the aggregated GO size, so that the films containing L-G or D-G presented better dispersion. The film containing 5 % D-G (PLLA/D-G0.05) exhibited the smallest average size of aggregated GO, about 12.7 μm. Compared with neat PLLA film, PLLA/L/G0.05 film presented worse tensile properties due to serious aggregation of GO. While, PLLA/D-G0.05 film presented the best tensile performance that tensile strength and elongation at break reached 120 MPa and 107 %, respectively.

Toughening Polylactide Stereocomplex by Injection Molding with Thermoplastic Starch and Chain Extender.

The high cost, low heat resistance, and brittleness of poly(L-lactide) (PLLA) is a significant drawback that inhibits its diffusion into many industrial applications. These weaknesses were solved by forming a polylactide stereocomplex (ST) and blending it with thermoplastic starch (TPS). We blended poly (L-lactide)(PLLA), up to 30% thermoplastic starch, and a chain extender (2%) in an internal mixer, which was then hand-mixed with poly (D-lactide)(PDLA) and injection molded to form specimens, in order to study mechanical, thermal, and crystallization behavior. Differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (XRD) demonstrated that the stereocomplex structures were still formed despite the added TPS and showed melting points ~55 °C higher than neat PLLA. Furthermore, stereocomplex crystallinity decreased with the increased TPS content. Dynamic mechanical analysis revealed that ST improved PLLA heat resistance, and tensile testing suggested that the TPS improved the elongation-at-break of ST. Moreover, the chain extender reduced the degradation of ST/TPS blends and generally improved ST/TPS composites' mechanical properties.

Effect of Biobased SiO2 on the Morphological, Thermal, Mechanical, Rheological, and Permeability Properties of PLLA/PEG/SiO2 Biocomposites

Nowadays, companies and researchers are concerned about the negative consequences of using synthetic polymers and direct their efforts to create new alternatives such as biocomposites. This study investigated the effect of biobased SiO2 on the properties of poly(L-lactic acid)/SiO2 (PLLA/SiO2) and poly(L-lactic acid)/SiO2/poly(ethylene glycol) (PLLA/SiO2/PEG) composites. The SiO2 was obtained from rice husk incineration and mixed with PLLA at various concentrations (5, 10, and 15 wt.%) via melt extrusion before compression molding. Furthermore, PLLA/SiO2/PEG composites with various PEG concentrations (0, 3, 5, and 10 wt.%) with 10 wt.% SiO2 were produced. The sample morphology was studied by scanning electron microscopy (SEM) to analyze the dispersion/adhesion of SiO2 in the polymer matrix and differential scanning calorimetry (DSC) was used under isothermal and non-isothermal conditions to study the thermal properties of the samples, which was complemented by thermal stability study using thermogravimetric analysis (TGA). Rheological analysis was performed to investigate the viscoelastic behavior of the composites in the melt state. At the same time, tensile mechanical properties were obtained at room temperature to determine their properties in the solid state. DSC and X-ray diffraction analysis (XRD) were combined to determine the crystalline state of the samples. Finally, gas permeation measurements were performed using a variable pressure (constant volume) method to analyze the permeability of different gases (CO2, CH4, O2, and H2). The results showed that SiO2 decreased the PLLA chain mobility, slowing the crystallization process and lowering the gas permeability while increasing Young’s modulus, thermal stability, and viscosity. However, PEG addition increased the crystallization rate compared to the neat PLLA (+40%), and its elongation at break (+26%), leading to more flexible/ductile samples. Due to improved silica dispersion and PLLA chain mobility, the material’s viscosity and gas permeability (+50%) were also improved with PEG addition. This research uses material considered as waste to improve the properties of PLA, obtaining a material with the potential to be used for packaging.

Nonisothermal crystallization of poly(L‐lactic acid) promoted by polyols

AbstractThe inherent weak crystallization capacity has an impact on the processability and serviceability of poly(lactic acid) (PLA) and limits its application. D‐mannitol (DM) and xylitol (Xy), acting as a nucleation accelerant, were melt‐blended with poly(L‐lactic acid) (PLLA) and the nonisothermal crystallization behavior was investigated. At 1% dosage, the crystallization temperatures of polyol‐modified PLLAs are 10–15°C higher than those of neat PLLA in the cooling rate range of 5–20°C. The theoretical half‐time of crystallization (t1/2) of the Jeziorny model remains constant over the cooling rate range of 10–20°C min−1, in contrast to the greatly reduced t1/2 reported for heterogeneous nucleating agents. Xy is more effective than DM in promoting crystallization. It increases the crystallinity of PLLA to ~40% within the 1%–5% dosage; and the activation energy of nonisothermal crystallization calculated by the Friendman method follows the order of magnitude: neat PLLA ˃ PLLA/DM ˃ PLLA/Xy. Polyols promote the crystallization of PLLA by a mechanism different from heterogeneous nucleation, providing an efficient and biosafety approach to improve the performance of PLA.

Fabrication and design of poly(l‐lactic acid) membrane for passive MAP packaging of Brassica chinensis L

PLDx L copolymers were synthesized from physically stable rigid poly(l-lactic acid) (PLLA) and a few different molecular weights of polydimethylsiloxane (PDMS) to increase the O2 and CO2 permeabilities of PLLA films and make them acceptable for packaging highly respirable products. The effect of PDMS on the morphology, mechanical properties, and gas permeability of PLDx L was investigated. Copolymers showed approximately 10 times the fracture strain and 1.7 times the CO2 and O2 permeabilities of neat PLLA. Additionally, PLDx L maintained an increased CO2 /O2 perm-selectivity consistent between 5 and 40°C. Passive modified atmosphere packaging of Brassica chinensis L was developed to assess the membrane's impact on headspace gas inside the package. The results showed that poly(amide)/poly(ethylene) packaging with 48cm2 PLD1.8 L membrane as a breathing window can provide 50g B. chinensis L. with a healthy atmosphere of 3%-8% O2 and 5%-8% CO2 between 6 and 22 days. Vegetables packaged in PLD1.8 L had the lower respiration rate, lower nitrite contents, and less proliferation of microorganisms. Moreover, a suitable atmosphere kept vegetables with higher ascorbic acid and a good appearance after more than 2 weeks of storage at 5°C. PRACTICAL APPLICATION: The permeability of the PLLA-based membrane can be adjusted for the breathable window membrane of sealed fresh products. In the future, several types of film could be developed to match the respiratory and metabolic characteristics of different kinds of products. Such PLLA-based specialized membranes can refine the fresh-keeping function and be more attractive to the customer.

Construction of fully biodegradable poly(L-lactic acid)/poly(D-lactic acid)-poly(lactide-co-caprolactone) block polymer films: Viscoelasticity, processability and flexibility

Development of biodegradable polymer films is essential for sustainable energy conservation and ecological protection. In this work, to improve the processability and toughness of poly(lactic acid) (PLA) films, poly(lactide-co-caprolactone) (PLCL) segments were introduced into poly(L-lactic acid) (PLLA)/poly(D-lactic acid) (PDLA) chains via chain branching reactions during reactive processing, and fully biodegradable/flexible PLLA/D-PLCL block polymer with long-chain branches and stereocomplex (SC) crystalline structure was prepared. Compared with neat PLLA, PLLA/D-PLCL exhibited much higher complex viscosity/storage modulus, lower tanδ values in terminal region and obvious strain-hardening behavior. Through biaxial drawing, PLLA/D-PLCL films were prepared, which showed improved uniformity and non-preferred orientation. With increasing draw ratio, the total crystallinity (Xc) and Xc for SC crystal both increased. By introduction of PDLA, the two phases of PLLA and PLCL penetrated and entangled with each other, and the phase structure transformed from “sea-island” structure to “co-continuous network” structure, which was beneficial for exerting the toughening effect of flexible PLCL molecules on PLA matrix. The tensile strength and elongation at break of PLLA/D-PLCL films increased from 51.87 MPa and 28.22 % of neat PLLA film to 70.82 MPa and 148.28 %. This work provided a new strategy for developing fully biodegradable polymer films with high performance.

Effects of PDLA molecular weight on the crystallization behaviors and rheological properties of asymmetric PDLA/PLLA blends

The molecular weight of poly(d-lactide) (PDLA) and poly(l-lactide) (PLLA) affects the performance of their blends by controlling the formation and characteristics of stereocomplex (SC) crystals. In this work, the crystallization behaviors and rheological properties of asymmetric PDLA/PLLA (5/95, w/w) blends were carefully investigated considering the molecular weight of PDLA (Mn(PDLA) = 1.5 × 103–18.7 × 103 g/mol) when the molecular weight of PLLA was selected as 5.0 × 104 g/mol. The results revealed that PDLA holding too low or too high Mn(PDLA) was unfavorable to the formation of SC crystallites owing to their weak interaction or difficult diffusion in the PLLA matrix, and the optimal Mn(PDLA) was ca.5.4 × 103 g/mol. Given this optimal Mn(PDLA), the composite viscosity and tensile viscosity of the obtained PDLA/PLLA blend were increased by 2–3 orders of magnitude and 10 times compared with neat PLLA, respectively, due to the formation of SC crystals with a high content (ΔHm-SC of 26.0 J/g). Besides, this PDLA/PLLA blend showed a fast crystallization rate and strong solid-like viscoelastic behavior. This work revealed the regular correspondence between Mn(PDLA) and the performance of asymmetric PDLA/PLLA blends.

Polylactide/poly[(R)‐3‐hydroxybutyrate] (PHB) blend fibers with superior heat‐resistance: Effect ofPHBon crystallization

AbstractBlending low content of poly[(R)‐3‐hydroxybutyrate‐co‐4‐hydroxybutyrate] (P34HB ≤8 wt %) with poly(L‐lactide) (PLLA) has proven effective in enhancing heat resistance of PLLA fibers. Unfortunately, the enhancement is relatively limited with boiling water shrinkage of PLLA/P34HB blend fibers reduced to 9.9% at most. In this study, a series of PLLA/poly[(R)‐3‐hydroxybutyrate] (PHB) blend fibers with low PHB content (≤8 wt %) was prepared with sound spinnability. Surprisingly, the PLLA/PHB blend fibers showed much lower boiling water shrinkage than the PLLA/P34HB blend fibers with the same blend ratio. In particular, the boiling water shrinkage was dropped from ca. 80% for neat PLLA fibers to 9.9% for the PLA/P34HB blend fibers and further to 3.8% for the PLA/PHB blend fibers with 8 wt % P34HB or PHB added. Such an exceptionally improved heat resistance of the PLLA/PHB blend fibers could be closely related to an increase in crystallinity (Xc,PLLA) of the PLLA phase. Specifically, the mobility of the PLLA segments was promoted in the presence of PHB, along with notably improved orientation of the PLLA phase in the PLLA/PHB blend fibers. More importantly, investigation on crystallization behaviors revealed that the PHB phase served as an effective nucleating agent to accelerate the overall crystallization of PLLA. By contrast, the P34HB phase only acted as spherulite growth‐accelerating and/or nucleation‐assisting agents. These findings help provide a facile and effective strategy to improve heat resistance of PLLA fibers more significantly.

Fabrication of outstanding mechanical performance engineered poly (lactic acid)/thermoplastic poly(ester)urethane in-situ nanofiber composites with a large-scale industrial innovation methodology

As one of the most promising biodegradable materials, poly(lactic acid) (PLA) is seriously restricted by its notorious brittleness and weak heat distortion resistance. Hitherto, the possibility of effectively toughening PLA while simultaneously maintaining high strength and stiffness has hardly been realized on an industrial scale. In this work, an innovative industrial methodology was applied to manufacture high-performance engineered (95-x) poly(l-lactic acid)/5poly(d-lactic acid)/xthermoplastic poly(ester)urethane ((95-x)L/5D/xT) nanofiber composites. The in-situ formed TPU nanofibers (TNFs) combined with sterocomplex crystals (SCs) generating synergistic effects significantly improve the crystallization behavior and elasticity of melt. The compatibility between PLA matrix and TNFs in (95-x)L/5D/xT nanofiber composites was significantly reinforced by constructing bundle structures. The bundle structure is composed of rigid PLA hybrid crystals tightly bundled with a handle of oriented TNFs with good interfacial compatibility, bundle structures interlink with each other forming 3D strengthening-toughening bundle structures contributing to the mechanical performance. The notched Izod impact strength of 80L/5D/15T and 75L/5D/20T nanofiber composites prodigiously increase to 74.8 and 98.7 kJ/m2, which is 27.7 and 35.6 times higher than that of neat PLLA. Meanwhile, the nanofiber composites can maintain balanced tensile yield strength, good Young's modulus, and obtain advantaged heat distortion resistance of 1132 MPa at 100 °C. Compared with reported PLA/elastomer blends, neat biodegradable plastics, general-purpose and engineering plastics, the efficient industrial-scale manufactured 80L/5D/15T and 75L/5D/20T nanofiber composites possessing outstanding mechanical performance of super toughness, balanced strength, good Young’s modulus and advantaged heat distortion resistance. It has immense potential to substitute non-degradable petroleum-based engineering plastics as structural materials in harsh environments, thereby reducing CO2 emissions and reducing pollution caused by discarded non-degradable petroleum-based plastics.

Characterization of Polymer Composites between Stereocomplex Polylactide Blends with Poly (methyl methacrylate)

Polylactide stereocomplex (ST) of poly(L-lactide) (PLLA) and poly(D-lactide) (PDLA) (PLLA:PDLA 50:50) was blended with poly(methyl methacrylate) (PMMA) 10 – 50 wt.%. The materials were dissolved in chloroform at room temperature and the films were then cast. Differential scanning calorimetry showed a stereocomplex melting peak at 208 °C – 50 °C higher than that for neat PLLA or PDLA - confirming the polylactide stereocomplex crystallites. The PMMA content ratio of 10 – 50 wt.% in the stereocomplex showed almost complete stereocomplex crystallites. A peak at about 908 cm-1 in Fourier transform infrared spectra further confirmed the stereocomplex crystallites which indicated that PMMA could blend and efficiently bond with the stereocomplex. The X-ray diffraction analysis showed that the stereocomplex crystallinity became smaller when PMMA was added. Morphology from scanning electron microscopy revealed that phases separated in the ST/PMMA blend when the amount of PMMA was increased. Adding PMMA to stereocomplex films led to an increased elongation at break which peaked at 30 % added PMMA. Increased PMMA also led to the improved thermal stability of the stereocomplex. These properties and higher toughness are also needed in common applications, in particular films for packaging and protection of manufactured products.

Constructing synergistically strengthening-toughening 3D network bundle structures by stereocomplex crystals for manufacturing high-performance thermoplastic polyurethane nanofibers reinforced poly(lactic acid) composites

As one of the most promising biodegradable materials, poly(lactic acid) (PLA) is seriously restricted by its notorious inherent brittleness and weak heat distortion resistance. In this work, a novel and simple methodology is proposed using an eccentric rotor extruder (ERE) with a predominantly elongational flow field to manufacture high-performance engineered poly(L-lactic acid)/poly(D-lactic acid)/thermoplastic polyurethane nanofiber composites on an industrial scale. The oriented tough TPU nanofibers (TNFs), rigid integrated PLA hybrid crystals and their good interface compatibility produce a strengthening-toughening bundle structure. When the PDLA content reached 3 wt%, the bundle structures interlinked with each other to form a strengthening-toughening 3D network. This resulted in a high-performance engineered 80L/5D/15T nanofiber composite with super toughness of 74.1 kJ/m2, high strength of 47.3 MPa and superior Young's modulus of 1378 MPa, which are 28.6 times, 85% and 92.7%, respectively, compared with neat PLLA. Compared with those published literatures, the 80L/5D/15T nanofiber composite not only possesses super toughness (more than 28 times) but also maintains good strength (maintain 85%), additionally good heat distortion resistance was also obtained. The performance of 80L/5D/15T nanofiber composite was significantly superior in comparison with biodegradable plastics as well as petroleum-based non-degradable general-purpose plastics and engineering plastics, demonstrating its enormous potential as a substitute structural material in harsh environments. It is believed that the novel and industrial scale methodology opens new perspectives for manufacturing other high-performance engineered biodegradable materials.

Biobased Symmetrical Fatty Amides for High Heat Deflection Temperature of Poly(l-lactide)-Based Materials

In this paper, we report the synthesis and the use of fatty bis-amides as nucleating agents for poly(l-lactide) (PLLA) to enhance its crystallization kinetics and its heat deflection temperature using short processing times. Bis-amides were synthesized in bulk from C18 fatty acid derivatives such as stearic acid, 12-hydroxystearic acid, oleic acid, or ricinoleic acid and a series of linear aliphatic diamines (C4, C6, C10, and C12) using a thermal process. The bis-amides were then mixed with neat PLLA through an extrusion process at different loadings (0.1, 0.5, 0.8, and 1 wt %) and the resulting materials were obtained by injection-molding. High degrees of crystallinity (>50%) could be achieved through short isothermal crystallization times such as 25 s at 110 °C and led to improved measured heat deflection temperatures nearing 120 °C in the best-case scenario. Such performance was achieved using the bis-amide obtained from the C4 diamine and stearic acid, which displayed the highest melting point of all the considered nucleating agents.

Using Cellulose-graft-Poly(L-lactide) Copolymers as Effective Compatibilizers for the Preparation of Cellulose/Poly(L-lactide) Composites with Enhanced Interfacial Compatibility.

Cellulose-grafte-poly(L-lactide) (C-g-PLLA) copolymers synthesized in a CO2-switchable solvent are proposed for use as effective compatibilizers for the preparation of cellulose–PLLA composites with enhanced interfacial compatibility. The effect of the molar substitution (MSPLLA) of the grafted PLLA side chain in the C-g-PLLA copolymer and the feeding amount of this copolymer on the mechanical and thermal properties and hydrophilicity of the composites was investigated. The composites had a largely increased impact strength with the incorporation of the compatibilizer. With the increasing of MSPLLA and the feeding amount of the copolymer, the resulting composites had an increased impact strength. When 5 wt% C-g-PLLA with MSPLLA of 4.46 was used as a compatibilizer, the obtained composite containing 20 wt% cellulose presented an impact strength equal to that obtained for the neat PLLA. The composites had a slightly decreased melting temperature and thermal decomposition temperature, but increased hydrophilicity due to the incorporation of the compatibilizer. This work suggests an effective method to improve the interfacial compatibility between cellulose and PLLA for the fabrication of fully bio-based composites with high performance.