Polylactic acid with improved heat deflection temperatures and self-healing properties for durable goods applications.

The heat-resistant agent N-(4-carboxyphenyl) maleimide–alt–styrene (PCS) was used to modify polylactic acid (PLA) in order to improve the thermostability of PLA. The heat deflection temperature (HDT), thermodegradation, crystallization behavior and thermomechanical property were analyzed. The HDT of PLA added with PCS increased by about 10°C, and after heat treatment, the improvement of HDT was more significant. The thermal degradation behavior of PLA before and after modification hardly changed. The crystallinity ( Xc), crystallization rate ( 1/t1/2) and crystallization temperature ( Tc) of the composite material were significantly improved, but the crystalline structure did not change. The crystallinity of the composite material was twice that of pure PLA, the crystallization rate increased by about 30% and the crystallization temperature went up more than 10°C. The storage modulus ( E’) of PLA was improved by PCS due to enhancing its crystallinity. The thermostability of PLA was significant improved after PCS is added.

The disadvantages of the poor mechanical properties of polylactic acid (PLA) limit its ability to be used in a wide number of applications. Melt blending of PLA and thermoplastic polyester elastomer (TPEE) has been performed in an effort to toughen the PLA without significant losses in modulus and ultimate tensile strength. In order to enhance the compatibility of PLA and TPEE, a diisocyanate compound was used as a reactive modifier. The thermal and mechanical properties, miscibility and phase morphologies of the blends were investigated. A blend of PLA and TPEE with a modifier does not lead to an important drop in tensile strength and modulus whereas the elongation at break is characterized by a significant increase (above 300%), compared with that of neat PLA and PLA/TPEE. The blends of PLA/TPEE/Modifier were found by thermal and fractured surface analysis to be an immiscible system with the addition of a modifier. However, the relative ductility of PLA/TPEE/Modifier is 34 times higher than that of neat PLA. The brittle fracture of neat PLA was transformed into a ductile fracture by the addition of a modifier.

This study deals with the modification of a predominantly amorphous poly(lactic acid) (PLA) by blending it with a semi-crystalline biopolymer, polyhydroxybutyrate-co-valerate (PHBV), which has a high crystallinity. The blends with different concentrations of PLA and PHBV were compounded with spent coffee grounds (SCGs) and processed by injection moulding. The structural, thermal and mechanical properties of the produced samples were investigated. Particular attention was paid to the effect of the presence of SCG and the concentration of PHBV in the blend on the crystallization kinetics and the heat deflection temperature (HDT). For equimolar blends, only a slight increase in HDT (about 5 °C) was observed, but the addition of PHBV suppressed the cold crystallization of PLA, which otherwise negatively affects the dimensional stability of injection moulded parts. A similar effect, but to a lesser extent, was achieved by adding SCG to the PLA matrix. Thus, it is clear that the material structures of PLA/PHBV blends and composites help to minimize additional shrinkage of the parts and increase their dimensional stability. Due to the co-continuous structure of the symmetric PLA/PHBV blends and the increase in the degree of crystallinity from 36 to 47% by annealing the produced samples, the heat deflection temperature increased from 65 up to 90 °C.

The work investigated the effect of carbon nanotubes (CNTs) on the properties of polylactic acid. It was found that the addition of CNTs does not alter the chemical structure of the polymer, but substantially influences its crystallinity, thermophysical, conductive and mechanical characteristics. Analysis of structural features showed the absence of new chemical bonds, but structural ordering of the matrix and changes in morphology were recorded. It is shown that the degree of crystallinity and melting temperature increase with a CNT content of up to 0.6%, and decrease when this value is exceeded. The electrical conductivity increases significantly after reaching the percolation threshold (0.5%), which indicates the formation of a conductive network. The mechanical properties show a nonlinear dependence with a minimum at a content of 0.5% CNT due to the agglomeration of nanotubes. The results obtained indicate the need to optimize the composition of the composite to achieve the desired characteristics.

In this research, the effect of the atomic radius of silica nanoparticles (SiO2) on the tensile and thermal properties of polylactic acid (PLA) based nanocomposites was analyzed. Different nanocomposite samples were made using PLA matrix with three atomic radius ranges of 15–20 nm, 20–30 nm, and 50–70 nm, and three-volume percentages (1, 2, and 3%) SiO2 nanoparticles. First, to observe the state of dispersion of SiO2 nanoparticles in the fabricated samples, photographs were taken with the field emission scanning electron microscope (FESEM) and the platinum coating method. FESEM images showed that 15–20 nm and 20–30 nm nanoparticles were better dispersed in the PLA matrix than 50–70 nm due to their smaller size. Then experimental tests were performed on the samples and parameters of modulus of elasticity, tensile strength, and heat deflection temperature (HDT) were measured. The results of the experiments showed that 15–20 nm SiO2 nanoparticles caused a 1% decrease in modulus of elasticity, a 2% decrease in tensile strength, and a 3.5% increase in HDT temperature. 20–30 nm SiO2 nanoparticles increased the modulus of elasticity by 8.8%, tensile strength by 1.8%, and HDT temperature by 1%. 50–70 nm SiO2 nanoparticles also caused a 3.3% increase in modulus of elasticity, a 1.1% increase in tensile strength, and a 4% increase in HDT temperature. The results showed that besides the volume fraction, the size of the reinforcing nanoparticles is also an effective factor in the mechanical properties of PLA nanocomposites.

Wood plastic composites (WPCs) offer a means to reduce the carbon footprint by incorporating natural fibers to enhance the mechanical properties. However, there is limited information on the mechanical properties of these materials under hostile conditions. This study evaluated composites of polypropylene (PP), polystyrene (PS), and polylactic acid (PLA) processed via extrusion and injection molding. Tests were conducted on tensile and flexural strength and modulus, heat deflection temperature (HDT), and creep analysis under varying relative humidity conditions (10% and 90%) and water immersion, followed by freeze—thaw cycles. The addition of fibers generally improved the mechanical properties but increased water absorption. HDT and creep were dependent on the crystallinity of the composites. PLA and PS demonstrated a superior overall performance, except for their impact properties, where PP was slightly better than PLA.

Microcrystalline cellulose chemically modified by 3-isocyanatopropyl triethoxysilane (K-MCC) was incorporated as reinforcement into a polylactic acid (PLA) matrix to prepare PLA/K-MCC composites by melt blending. X-ray diffraction showed that PLA's crystalline structure was not affected by the added K-MCC, but its degree of crystallinity increased somewhat. Differential scanning calorimetry indicated that, when 5 wt-%K-MCC was added to PLA, the crystallisation of PLA improved greatly, and the degree of crystallinity reached a maximum of 39.4%, which exceeded that of pure PLA. Mechanical testing revealed that the tensile strength, modulus and heat distortion temperature of PLA also increased significantly after modified MCC was added, and the optimum mechanical properties of the composite were obtained. Dynamic rheological tests revealed shear thinning behaviour in the PLA/K-MCC composites. With increasing shear rate, more obvious shear thinning was observed because of more homogeneous dispersion of K-MCC with fewer hydroxyl groups in the PLA matrix.

Generally, poly(ethylene glycol) (PEG) is added to poly(lactic acid) (PLA) to reduce brittleness and improve mechanical properties. However, shape memory properties of PEG/PLA blends suffered due to the blend’s incompatibility. To enhance shape memory abilities of the blends, 0.45% maleic anhydride-grafted poly(lactic acid) (PLA-g-MA) was used as a compatibilizer. Thermal and mechanical properties, morphologies, microstructures, and shape memory properties of the blends containing different PLA-g-MA contents were investigated. The compatibilized blend with 2 wt% PLA-g-MA exhibited enhanced tensile modulus, strength, and elongation at break, as well as a lower glass transition temperature and degree of crystallinity than the uncompatibilized blend. Results revealed that PLA-g-MA improved interfacial adhesion between phases and promoted chain entanglement. Shape fixity performance of the compatibilized blends were comparable to that of neat PLA. The compatibilized blend containing 2 wt% PLA-g-MA possessed the best shape fixity and recovery performance. Although a high recovery temperature was expected to enhance the recovery of the PEG/PLA blends, the compatibilized blends can be recovered to their original shape at a lower temperature than the PLA. This study illustrated the possibility of optimizing PLA properties to meet requirements necessary for biomedical applications.

In this study, polylactic acid (PLA) films were prepared via twin screw extruder attached with blown film die. The research consisted of two parts. The first part concentrates on studying the effect of types and loading of plasticizer, in which they were used to increase the flexibility of PLA, on thermal, mechanical and gas barrier properties of plasticized PLA blown films. From DSC and DMA results, 5 wt% of all plasticizers were compatible with PLA and it affected degree of crystallinity of PLA increased. In addition, tensile tests indicated that polypropylene glycol, PPG(1200) at 5 wt% was a suitable plasticizer for PLA which can be observed from an increase in elongation at break approximately 45 times. The second part focuses on the effect of surfactant types and organoclay loading on properties of PLA/clay nanocomposite blown films. From XRD result, interlayer spacing of organoclay increased compared with that of pristine clay. Furthermore, film of PLA/montmorillonite modified by trimethyl tallow quaternary ammonium chloride (PLA/MMT/M₃T films) showed better clay dispersion and higher transmittance of light than film of PLA/montmorillonite modified by tallow bis(2-hydroxyethyl) amine (PLA/MMT/HT(OH)₂ films). Furthermore, from DSC and DMA results, PLA/MMT/HT(OH)₂ films gave higher degree of crystallinity than PLA/MMT/M₃T films. For mechanical properties, PLA/MMT/M₃T films exhibited higher elongation at break than PLA/MMT/HT(OH)₂ films and 3 wt% of organoclay showed optimum properties when added into with plasticized PLA. In addition, PLA/MMT/HT(OH)₂ films showed higher water vapor permeation (6.19 %) but lower oxygen permeation (7.94 %) compared to PLA/MMT/M₃T films.

A new phosphorus‐based organic additive (PDA) was designed and successfully synthesized using a three‐component reaction for improvement of the thermal and combustion resistance of polylactic acid (PLA). For compensate for mechanical properties of PLA, hydroxyapatite nanoparticles was modified via in situ surface modification with PDA and was used for preparation of PLA nanocomposites. The structure and morphology as well as thermal, combustion, and mechanical properties of the all PLA systems were investigated. The X‐ray diffraction (XRD) and field‐emission scanning electron microscopy (FE‐SEM) results indicated that the presence of PDA as surface modifier has been necessary for a desirable dispersion of hydroxyapatite (HA) nanoparticles in the PLA matrix. The thermal, combustion, and mechanical properties of the PLA system films were investigated using thermogravimetric analysis (TGA), microscale combustion calorimeter (MCC), and tensile test, respectively. The initial decomposition temperature and char residue of PLA containing 6 mass% of PDA along with 2 mass% HA nanoparticles were increased 20°C and 12% respectively, compared with that of the neat PLA. The peak of heat release rate was decreased from 566 W/g for the neat PLA to 412 W/g for PLA containing 2 mass% of PDA along with 6 mass% HA nanoparticles. By incorporation of only 2 mass% HA nanoparticles and 6 mass% of PDA, the tensile strength was obtained 51 MPa higher than that of the neat PLA.

In this research, green composites were produced by reinforcing 30% hemp fiber by weight for the purpose of improving the properties of polylactic acid (PLA) polymer. Surface treatments such as alkali (NaOH) and silane (APTES), different modification methods such as poly (butylene succinate) (PBS) and thermoplastic polyurethane (TPU) blend processes, maleic anhydride (MA) coupling were all employed to improve fiber-matrix interfacial adhesion. Extrusion and injection molding were used to create PLA bio-composites, and their thermal, mechanical, and degrading characteristics were examined. The glass transition and crystallization temperature generally reduced, while the melting temperature and degree of crystallinity increased, according to Differential Scanning Calorimetry (DSC). Reinforcement of hemp fiber increased the tensile strength of all bio-composites. Compared to pure PLA, the tensile strength of N-H/PLA (alkali-treated hemp/PLA) is 54.3%, P-H/PLA (PBS-untreated hemp/PLA) is 24.69% improved the T-H/PLA (TPU-untreated hemp/PLA) had the best elongation at break value due to the TPU polymer’s flexibility. The N-H/PLA bio-composite showed the lowest soil degradability after neat PLA. The S-H/PLA (silane-treated hemp/PLA) offers the highest weight loss value. The FTIR spectra of APTES-treated hemp fibers did not change significantly. The N-H/PLA had the lowest water absorption, while the M-H/PLA (MA- untreated hemp/PLA) had the greatest.

Polylactic acid (PLA) is a hydrolytically degradable aliphatic polyester, and water vapor permeability may have a significant influence on the rate of degradation. A method is devised to use bags prepared from PLA films and filled with molecular sieves to determine the water vapor permeability in the polymer, its copolymers with caprolactone, and blends with polyethylene glycol. The “solution-diffusion” model is used to determine the permeability parameters. These include the solubility coefficient,S, a measure of the equilibrium water concentration available for hydrolysis and the diffusion coefficient,D, which characterizes the rate of water vapor diffusion into the film under specific conditions. Values ofS andD at 50‡C and 90% relative humidity ranged from 400 × 10-6 to 1000 × 10-6 cm3 (STP)/(cm3 Pa) and 0.20 × 10-6 to 1.0 × 10-6 cm2/s, respectively. TheS andD coefficients were also measured at 20 and 40‡C and compared to those of other polymers. The degree of crystallinity was found to have little influence on the measured permeability parameters. The heat of sorption, δHS, and the activation energy of diffusion, ED, were used to show that the permeability process is best described by the “water cluster” model for hydrophobic polymers. Finally, the diffusion coefficient is used to compare the rate of water diffusion to the rate of water consumption by ester hydrolysis. Results indicate that hydrolytic degradation of PLA is reaction-controlled.

Polyethylene glycol enhanced antibacterial activity of EDTA and ethyl maltol blended PLA against Staphylococcus aureus for biodegradable active packaging

The inherent brittleness of PLA is a major challenge for its use in various applications. In this study, the effect of incorporation of halloysite nanotube (HNT) and polyethylene glycol (PEG) on mechanical and thermal properties of polylactic acid (PLA) was investigated. Various concentrations of PEG-600 and HNT were used with PLA, and films were prepared by solvent casting method. Mechanical, morphological, and thermal properties of these composite films were investigated to study the effect of PEG and HNT on the properties of PLA. Addition of PEG increased elongation at break, but reduced the tensile strength. However, addition of HNT in PLA/PEG compensated the fall in tensile strength. Addition of 3 wt% HNT into PLA blend involving 5 wt% PEG increased its elongation at break by 640% and tensile strength by 22%, while no significant change in Young’s modulus was observed. Dynamic mechanical thermal analysis (DMTA) showed significant improvement in storage modulus of PLA/PEG/HNT films in the rubbery region. Glass transition temperature decreased for the PEG-plasticized films, while the crystallinity improved as compared to neat PLA. Thermal stability of PLA/PEG/HNT films was higher than those of PLA, PLA/PEG, and PLA/HNT films. The degree of crystallinity obtained using X-ray diffraction analysis showed good agreement with that determined from differential scanning calorimetry (DSC).

In our research, the effect of D‐lactide content in injection‐molded and annealed poly(lactic acid) (PLA) was investigated for crystallinity as well as crystalline forms (less‐ordered α′ and more‐ordered α crystalline forms) and thus on the mechanical, heat deflection temperature (HDT), and creep properties. Three different PLA grades 3052D, 3001D, and 3100HP were investigated with D‐lactide contents of 4%, 1.4%, and 0.5%, respectively. The injection‐molded PLA specimens were then postproduction annealed in a heat chamber at 80–140 °C for 1 h to develop various crystallinities and various ratios of α′ and α crystal forms. It was demonstrated that not only annealing but also the D‐lactide content significantly influences the crystallization, crystal structure, and accordingly properties of PLA like notched Charpy impact strength, HDT, and creep characteristics. Higher HDT, impact properties, and creep resistance could be reached by using PLA with lower D‐lactide content with a certain annealing temperature range to develop definite crystal structures. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47103.