The influence of matrix crystallinity,filler grain size and modification on properties of PLA/calcium carbonate composites

Thermal and mechanical properties of polylactide (PLA) composites with different grades of calcium carbonate, 40 nm and 90 nm nanoparticles, and also with submicron particles, unmodified and modified with calcium stearate or stearic acid, obtained by melt mixing, were compared. Films with amorphous and crystalline matrices were prepared and examined.T_g of PLA in the composites remained unaffected whereas its cold crystallization was enhanced by the fillers and predominantly depended on filler content. Filling decreased thermal stability of the materials but their 5% weight loss temperatures well exceeded 250 °C, evidencing stability in the temperature range of PLA processing. The amorphous nanocomposites with modified nanoparticles exhibited improved drawability and toughness without a significant decrease of tensile strength; nearly two-fold increase of the elongation at break and tensile toughness was achieved at 5 wt% content of the modified nanofiller. Lack of surface modification of the filler, larger grain size with an average of 0.9 μm, and matrix crystallinity had a detrimental effect on the drawability. However, the presence of nanofillers and crystallinity improved tensile modulus of the materials by up to 15% compared to neat amorphous PLA.     

Antimicrobial,mechanical, barrier,and thermal properties of bio‐based poly (butylene adipate‐co‐terephthalate) (PBAT)/Ag2O nanocomposite films for packaging application

Bio‐based nanocomposites of poly (butylene adipate‐co‐terephthalate) (PBAT)/silver oxide (Ag₂O) were prepared by the composite film casting method using chloroform as the solvent. The prepared Ag₂O at different ratios (1, 3, 5, 7, and 10 wt%) is incorporated in the PBAT. The PBAT nanocomposite films were subjected to structural, thermal, mechanical, barrier, and antimicrobial properties. The electron micrographs indicated uniform distribution of Ag₂O in the PBAT matrix. However, the images indicated agglomeration of Ag₂O particles at 10 wt% loading. The thermal stability of the nanocomposite films increased with Ag₂O content. The tensile strength and elongation of the composite films were found to be higher than those of PBAT and increased with Ag₂O content up to 7 wt%. The PBAT‐based nanocomposite films showed the lower oxygen and water vapor permeability when compared to the PBAT film. Antimicrobial studies were performed against two food pathogenic bacteria, namely, Klebsiella pneumonia and Staphylococcus aureus.     

Evaluation of PLA content in PLA/PBAT blends using TGA

The thermogravimetric analysis (TGA) was used to evaluate the polylactide (PLA) content in PLA/poly(butylene adipate-co-terephthalate) (PLA/PBAT) blends. The TGA curves of PLA/PBAT blends containing magnesium oxide (MgO) can clearly show two-step weight loss profiles because PLA can be selectively depolymerized in PLA/PBAT blends under the catalysis of MgO, and thus the PLA content can be determined according to the TGA curve for the blends. The detection scope of this method is especially applicable to the PLA content in the range of 10–90 wt% in PLA/PBAT blends at a heating rate 10 °C·min⁻¹. The measurement reliability was evaluated by parallel experiments. When the PLA content was 20, 50 and 80 wt%, the standard deviation (STDEV) and the absolute error for the measurements were less than 2.0 wt% and ±1.0 wt%, respectively, which indicated that the method is sufficiently reliable.     

ZnO nanoparticles as chain elasticity reducer and structural elasticity enhancer: Correlating the degradating role and localization of ZnO with the morphological and mechanical properties of PLA/PP/ZnO nanocomposite

The main purpose of this study was to investigate the effect of zinc oxide (ZnO) nanoparticles on the morphological, mechanical, thermal, and rheological properties of PLA/PP blend. In this regard, nanocomposites containing 1, 3, and 5 wt% of ZnO nanoparticles were prepared by melt mixing. In addition, three different mixing procedures were adopted to study their effects on the microstructure of nanocomposites. The rheological behaviors demonstrated a higher elasticity and less compatibility for two phases in the case of nanocomposites containing nanoparticles in harmony with the morphological observations. Accordingly, it was correlated to the elasticity originating from the interphase, anticipated coalescence of dispersed particles as a result of degradation of PLA chains triggered by ZnO nanoparticles (ZnO‐NPs) and also agglomeration of ZnO‐NPs depending on the content of nanoparticles and chosen mixing procedure. It was also found that mixing method puts a remarkable influence on the microstructure and rheological behavior of nanocomposites. Results of mechanical characterizations and thermogravimetric analysis (TGA) also confirmed the degradation induced by ZnO nanoparticles.     

Nanoperlite effect on thermal,rheological, surface and cellular properties of poly lactic acid/nanoperlite nanocomposites for multipurpose applications

In this study, poly lactic acid (PLA) based nanocomposites containing perlite nanoparticles were prepared by melt mixing method. Various characterization techniques were employed to evaluate the performance PLA/nanoperlite nanocomposites. The nanocomposites were characterized via FTIR to investigate the functional groups and chemical structure of the nanocomposites. Thermal properties of the nanocomposites, examined by DSC, showed that the increase of nano-perlite content in the PLA matrix reduces the crystallinity and melting temperature of the nanocomposites. The rheological studies indicated that both of storage and loss modulus are increased when the nanoperlite is added up to 5 wt%. However, the modulus is reduced in samples containing more than 5 wt% nanoparticle due to their agglomeration. The in-vitro degradation studies of the nanocomposites at elevated and normal temperatures showed hydrolytic degradation around 13–15 months. The surface behavior results implied that the water contact angle values exhibit a reducing trend when the nanoperlite content increases up to 3 wt%, which can be related to the decreased crystallinity of PLA and also to the hydrophilic nature of perlite. Moreover, the adhesion of osteoblast cells and their viability on an electrospun scaffold, made of optimized sample, showed the initial implications of potential applications of the nanocomposites in bone regeneration and biomedical applications. These multipurpose nanocomposites can also be used for packaging applications.     

Design and preparation of poly(lactic acid) hydroxyapatite nanocomposites reinforced with phosphorus‐based organic additive: Thermal,combustion, and mechanical properties studies

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.     

Morphology and properties of biodegradable poly (lactic acid)/poly (butylene adipate-co-terephthalate) blends with different viscosity ratio

Phase morphology exerts a tremendous influence on the properties of polymer blends. The development of the blend morphology depends not only on the intrinsic structure of the component polymers but also on extrinsic factors such as viscosity ratio, shearing force and temperature in the melt processing. In this study, various poly (butylene adipate-co-terephthalate) (PBAT) materials with different melt viscosity were prepared, and then poly (lactic acid) (PLA)/PBAT blends with different viscosity ratio were prepared in a counter-rotating twin-screw extruder under constant processing conditions. The influence of viscosity ratio on the morphology, mechanical, thermal and rheological properties of PLA/PBAT (70/30 w/w) blends was investigated. The experimental results showed that the morphology and properties of PLA/PBAT blends strongly depended on the viscosity ratio. Finer size PBAT phase were observed for viscosity ratio less than 1 (λ < 1) compared to samples with λ > 1. It was found that the interfacial tensions of PLA and PBAT were significantly different when the viscosity ratio was changed, the lowest interfacial tensions (0.12 mN/m) was obtained when the viscosity was 0.77. Additionally, the maximal tensile strength in PLA/PBAT blends were obtained when the viscosity ratio was 0.44, while the maximal impact properties were obtained when the viscosity ratio was 1.95.     

The morphological,mechanical, rheological,and thermal properties of PLA/PBAT blown films with chain extender

Biodegradable poly(lactic acid) (PLA)/poly(butylene adipate‐co‐terephthalate) (PBAT) blends and films were prepared using melt blending and blowing films technique in the presence of chain extender‐Joncryl ADR 4370F. The ADR contains epoxy functional groups and used as a compatibilizer. The morphological, mechanical, rheological, thermal, and crystalline properties of the PLA/PBAT/ADR blown films were studied. Scanning electron microscopy micrographs of the films revealed more ductile deformation with increasing PBAT content. The addition of PBAT enhanced the toughness of the PLA film. Tensile tests indicated that the elongation at break increased from 20.5% to 334.6% in the machine direction and from 7.1% to 715.9% in the transverse direction. The Young modulus increased from 2690.5 to 395.6 MPa in the machine direction and from 2623.5 to 154.0 MPa in the transverse direction. The sealing strength of 40/60/0.15 PLA/PBAT/ADR film was the highest among all the samples up to 9.4 N 15 mm⁻¹. These findings gave important implications for designing and manufacturing polymer packaging materials.     

Simultaneously toughening and reinforcing poly(lactic acid)/thermoplastic polyurethane blend via enhancing interfacial adhesion by hydrophobic silica nanoparticles

This work focuses on satisfactorily toughening and reinforcing poly(lactic acid)/thermoplastic polyurethane (PLA/TPU) blend with low TPU content (10 wt%) using appropriate amounts of hydrophobic silica nanoparticles (SiO₂) via simple melt mixing. Both thermodynamic prediction and transmission electron microscopy micrographs demonstrate that most SiO₂ nanoparticles distribute at interfaces between the PLA and TPU phases. This improves interfacial adhesion between the phases, which is attributed to good bonding strength between the PLA and SiO₂ via hydrophobic interaction and formation of hydrogen bonds between the TPU and SiO₂. The PLA/TPU (90/10) ternary blend nanocomposite with 2 wt% SiO₂ exhibits obviously high impact strength (about 5.0 and 12.6 times that of the corresponding blend and PLA, respectively) and higher tensile strength than the blend and even the PLA. Crazing is the main reason for improved impact toughnesses of the blend nanocomposites. This work provides a simple and effective strategy to endow PLA/elastomer blends with optimum strength–toughness balance by adding appropriate amounts of nanoparticles.     

Melt‐blending of unmodified and modified cellulose nanocrystals with reduced graphene oxide into PLA matrix for biomedical application

In this article, we successfully fabricated the bionanocomposites using cellulose nanocrystals (CNCs) and reduced graphene oxide (rGO) reinforced into biodegradable polylactic acid (PLA) matrix through melt‐mixing method. Due to the affinity difference between hydrophilic CNC and hydrophobic PLA, the surface modification of CNC was employed using quaternary ammonium salts (CTAB) as a surfactant. The nanocomposites were developed using different blend ratios of CNC/modified CNC (1, 2, and 3) wt% and (0.5 wt%) rGO into the polymer matrix. The morphology of CNC, q‐CNC (modified CNC), and nanocomposites were inspected by atomic force microscopy (AFM) and field emission scanning electron microscopy (FESEM). It is demonstrated from tensile tests that, the nanocomposite with 1 wt% CNC and rGO showed maximum tensile strength compared with PLA and its nanocomposites. Moreover, the nanocomposite with 1 wt% CNC and rGO was also having maximum thermal stability. From cytotoxicity evaluation, it is observed that all the nanocomposites are nontoxic and cytocompatible to HEK293 cells. In addition to this, the nanocomposite with q‐CNC showed enhanced barrier properties compared with PLA and PLA/CNC/rGO nanocomposite. The results obtained from different characterizations showed that the incorporation of surfactant onto CNC improved the dispersion in PLA but at the same time deteriorated the PLA matrix.     

Compatibilisation effect of PP-g-MA copolymer on iPP/SiO2 nanocomposites prepared by melt mixing

In the present study, a series of iPP/SiO₂ nanocomposites, containing 1, 2.5, 5, 7.5, 10 and 15 wt% SiO₂ nanoparticles, were prepared by melt mixing in a twin screw co-rotating extruder. Poly(propylene-g-maleic anhydride) copolymer (PP-g-MA) containing 0.6 wt% maleic anhydride content was added to all nanocomposites at three different concentrations, 1, 2.5 and 5 wt%, based on silica content. Mechanical properties such as tensile strength at break and Young’s modulus were found to increase and to be mainly affected by the content of silica nanoparticles as well as by the copolymer content. For the tensile strength at break as well as for yield point, a maximum was observed, corresponding to the samples containing 2.5-5 wt% SiO₂. At higher concentrations, large nanosilica agglomerates are formed that have as a result a decrease in tensile strength. Young’s modulus increases almost linearly on the addition of SiO₂, and takes values up to 60% higher than that of neat iPP. Higher concentrations of PP-g-MA resulted in a further enhancement of mechanical properties due to silica agglomerate reduction. This finding was verified from SEM and TEM micrographs. Evidently the surface silica hydroxyl groups of SiO₂ nanoparticles react with maleic anhydride groups of PP-g-MA and lead to a finer dispersion of individual SiO₂ nanoparticles in the iPP matrix. The enhanced adhesion in the interface of the two materials, as a result of the mentioned reaction, has been studied and proved by using several equations. The increased Vicat point of all nanocomposites, by increasing the PP-g-MA content, can also be mentioned as a positive effect.     

Synergistic effect of nucleation and compatibilization on the polylactide and poly(butylene adipate-<Emphasis Type="Italic">co</Emphasis>-terephthalate) blend films

Polylactide (PLA) films blended with 10 wt% poly(butylene adipate-co-terephthalate) (PBAT) were prepared by using a twin screw extruder in the presence of the nucleating agent of titanium dioxide (TiO₂) and the compatibilizers of toluene diisocyanate (TDI) and PLA-grafted-maleic anhydride (PLA-g-MA). The synergistic effect of the nucleation and compatibilization on the properties and crystallization behavior of the PLA/PBAT (PLB) films was explored. The results showed that the addition of TiO₂ significantly enhanced the tensile strength and the impact tensile resistance of the PLB films while slightly decreased its thermal stability. In addition, the compatibilizers of TDI and PLA-g-MA in the system not only affected the crystallinity and cold crystallization process of the PLB films, but also increased the mechanical properties of them due to the improvement of the interfacial interaction between PLA and PBAT revealed by the morphological measurement. The synergistic effects of the nucleating agent and the compatibilizer afforded the blend films with increased tensile strength and impact tensile toughness, improved cold crystallization property and χ _c.     

Functional Nanocomposite Films of Poly(Lactic Acid) with Well-Dispersed Chitin Nanocrystals Achieved Using a Dispersing Agent and Liquid-Assisted Extrusion Process

The development of bio-based nanocomposites is of high scientific and industrial interest, since they offer excellent advantages in creating functional materials. However, dispersion and distribution of the nanomaterials inside the polymer matrix is a key challenge to achieve high-performance functional nanocomposites. In this context, for better dispersion, biobased triethyl citrate (TEC) as a dispersing agent in a liquid-assisted extrusion process was used to prepare the nanocomposites of poly (lactic acid) (PLA) and chitin nanocrystals (ChNCs). The aim was to identify the effect of the TEC content on the dispersion of ChNCs in the PLA matrix and the manufacturing of a functional nanocomposite. The nanocomposite film’s optical properties; microstructure; migration of the additive and nanocomposites’ thermal, mechanical and rheological properties, all influenced by the ChNC dispersion, were studied. The microscopy study confirmed that the dispersion of the ChNCs was improved with the increasing TEC content, and the best dispersion was found in the nanocomposite prepared with 15 wt% TEC. Additionally, the nanocomposite with the highest TEC content (15 wt%) resembled the mechanical properties of commonly used polymers like polyethylene and polypropylene. The addition of ChNCs in PLA-TEC15 enhanced the melt viscosity, as well as melt strength, of the polymer and demonstrated antibacterial activity.     

Properties of immiscible and ethylene-butyl acrylate-glycidyl methacrylate terpolymer compatibilized poly (lactic acid) and polypropylene blends

Poly(lactic acid) (PLA) and polypropylene (PP) blends of various proportions were prepared by melt-compounding. The miscibility, phase morphology, thermal behavior, and mechanical and rheological properties of the blends were investigated. The blends were immiscible systems with two typical morphologies, spherical droplet and co-continuous, and could be obtained at various compositions. Complex viscosity, storage modulus and loss modulus depend on the PP content. Thermal degradation of all blends led to two weight losses, for PLA and PP. The incorporation of PP improved the thermal stability of the blend. The effect of compatibilizer (ethylene-butyl acrylate-glycidyl methacrylate terpolymer, EBA-GMA) on the morphology and mechanical properties of 70/30 w/w PLA/PP blends was investigated. The tensile strength of these blends reached a maximum for 2.5 wt% EBA-GMA, and impact strength increased with increasing EBA-GMA content, suggesting that EBA-GMA is an effective compatibilizer for PLA/PP blends.     

Melt processing of maleic anhydride grafted poly(lactic acid) and its compatibilizing effect on poly(lactic acid)/poly(butylene adipate-<Emphasis Type="Italic">co</Emphasis>-terephthalate) blend and their composite

Poly(lactic acid) (PLA)/poly(butylene adipate-co-terephthalate) (PBAT) blends were prepared using melt processing. The effects of maleic anhydride grafted PLA (PLA-g-MA) and calcium carbonate (CaCO₃) content on mechanical, thermal, and morphological properties of the blends were investigated. PLA-g-MA was synthesized by varying monomer and initiator contents using a reactive melt-grafting process. Tensile properties of PLA/PBAT blend were enhanced with adding 2 phr of PLA-g-MA. SEM micrographs exhibited the improvement of interfacial adhesion between PLA and PBAT in the compatibilized blend. Moreover, thermal stability of the blends improved with presence of PLA-g-MA. With increasing CaCO₃ content, Young’s modulus of the composites increased.     

Investigation of the electrical properties of XLPE/SiC nanocomposites

The interface between nanoparticles and the polymer matrix, which dominates the electrical properties of nanocomposites, can effectively improve the DC breakdown and suppress space charge accumulation in nanocomposites. To research the interface characteristics, XLPE/SiC nanocomposites with concentrations of 1 wt%, 3 wt% and 5 wt% were prepared. The DC breakdown, dielectric properties and space charge behavior were examined using pulsed electro-acoustic (PEA) equipment and a dielectric analyzer. The test results show that the nanocomposites with concentrations of 1 wt% and 3 wt% have higher DC breakdown field strength than neat XLPE. In contrast, there is a lower DC breakdown strength at a concentration of 5 wt%, possibly due to the agglomeration of nanoparticles. Nanoparticle doping increases the real and imaginary permittivities over those of neat XLPE. Furthermore, with increasing concentration, a larger increase in the permittivity amplitude was observed. Based on the space charge behavior, all nanocomposites could suppress space charge accumulation, but the nanocomposite with a concentration of 1 wt% exhibited the best effect. Meanwhile, heterocharge accumulation near electrodes was observed in neat XLPE and the nanocomposite with a concentration of 5 wt%. In contrast, homocharge accumulation near electrodes was observed in the nanocomposite with a concentration of 3 wt%. This phenomenon may be due to different amounts of shallow traps in nanocomposites with different concentrations, which might lead to differing electron or hole mobility.     

On the use of plant cellulose nanowhiskers to enhance the barrier properties of polylactic acid

Polylactic acid (PLA) nanocomposites were prepared using cellulose nanowhiskers (CNW) as a reinforcing element in order to asses the value of this filler to reduce the gas and vapour permeability of the biopolyester matrix. The nanocomposites were prepared by incorporating 1, 2, 3 and 5 wt% of the CNW into the PLA matrix by a chloroform solution casting method. The morphology, thermal and mechanical behaviour and permeability of the films were investigated. The CNW prepared by acid hydrolysis of highly purified alpha cellulose microfibers, resulted in nanofibers of 60–160 nm in length and of 10–20 nm in thickness. The results indicated that the nanofiller was well dispersed in the PLA matrix, did not impair the thermal stability of this but induced the formation of some crystallinity, most likely transcrystallinity. CNW prepared by freeze drying exhibited in the nanocomposites better morphology and properties than their solvent exchanged counterparts. Interestingly, the water permeability of nanocomposites of PLA decreased with the addition of CNW prepared by freeze drying by up to 82% and the oxygen permeability by up to 90%. Optimum barrier enhancement was found for composites containing loadings of CNW below 3 wt%. Typical modelling of barrier and mechanical properties failed to describe the behaviour of the composites and appropriate discussion regarding this aspect was also carried out. From the results, CNW exhibit novel significant potential in coatings, membranes and food agrobased packaging applications.     

Physico-Mechanical Properties of Biodegradable Rubber Toughened Polymers

Summary: In this study, blends of poly(lactic acid) (PLA) with poly(butylene adipate-co-terephthalate) (PBAT) were studied for their mechanical and thermal properties as a function of the PBAT content. Tensile testing, impact testing, differential scanning calorimetry (DSC), dynamic mechanical analysis (DMTA) and scanning electron microscopy (SEM) were used to characterize the blends. It was observed that PLA/PBAT blends maintained quite high modulus and tensile strength compared to pure PLA. Small amounts of PBAT improved the elongation at break and the impact resistance showing a debonding effect typical of rubber toughened systems.     

Influence of chemical surface modification of cellulose nanowhiskers on thermal,mechanical, and barrier properties of poly(lactide) based bionanocomposites

In the aim of producing fully organic bionanocomposite based on poly(lactide) (PLA), cellulose nanowhiskers (CNW) were grafted by n-octadecyl-isocyanate (CNW-ICN) applying an in situ surface grafting method. The compatibilizing effect of the long aliphatic grafted chain was investigated by thermal, mechanical and permeability analysis of solvent cast nanocomposite films. The grafted CNW-ICN could be successfully dispersed in the polymer matrix. The gained compatibility brought about a nucleating effect, decreasing the half time of isothermal crystallization from 25 min for the neat PLA to 8.4 min for the nanocomposite including 2.5 wt% CNW-ICN, e.g., tensile strength was improved by 10 MPa for the same 2.5 wt% CNW-ICN/PLA composite. Mechanical reinforcement was also effective in the rubbery state of PLA and increased the tensile modulus of the rubbery plateau providing thereby thermal resistance to the polymer. Oxygen barrier properties did not change significantly upon the inclusion of CNW-ICN, even when the quantity of CNW-ICN was increased to 15 wt%. More interestingly, the water vapour permeability of the CNW-ICN nanocomposite was always lower than the one of ungrafted CNW composites, which led to the conclusion that the hydrophobic surface graft and improved compatibility could counteract the effect of inclusion of hydrophilic structures in the matrix on water vapour transport. In conclusion, the surface grafting of CNW with isocyanates might be an easy and versatile tool for designing fully organic bionanocomposites with tailored properties.     

Chemical modification of poly(lactic acid) and its use as matrix in poly(lactic acid) poly(butylene adipate-co-terephthalate) blends

Poly(lactic acid), PLA, was chemically modified with maleic anhydride (MA) by reactive extrusion. The effect of this modification on molar mass (MM) and acidity was assessed by means of size-exclusion chromatography (SEC) and titration, respectively. PLA MM decreased in the presence of MA solely and of MA and peroxide. Reduction in MM was monitored by the increase in acidity. PLA blends containing poly(butylene adipate-co-terephthalate) (PBAT) were prepared through different mixing protocols, PLA/PBAT, PLA-g-MA/PBAT and PLA/PBAT/MA/peroxide (PLA/PBAT in situ). SEC results and rheological properties revealed reduction in MM and viscosity of the modified blends. PLA/PBAT presented increase in MM and bimodal MM distribution. The calculated interfacial tension was significantly lower for the modified blends, despite the lower average particle area of PLA/PBAT. Surprisingly, the modified blends presented higher yield strength than that predicted by the rule of mixtures, which might indicate interfacial reactions.