Toughening of polylactide by tailoring phase-morphology with P[CL-co-LA] random copolyesters as biodegradable impact modifiers

Innovative Poly(lactic Acid) Blends: Exploring the Impact of the Diverse Chemical Architectures from Itaconic Acid

Environment-friendly polymer blends of poly(lactic acid) (PLA) and itaconic acid (IA), poly(itaconic acid) (PIA), poly(itaconic acid)-co-poly(methyl itaconate) (Cop-IA), and net-poly(itaconic acid)-ν-triethylene glycol dimethacrylate (Net-IA) were performed via melt blending. The compositions studied were 0.1, 1, 3, and 10 wt% of the diverse chemical architectures. The research aims to study and understand the effect of IA and its different architectures on the mechanical, rheological, and thermal properties of PLA. The PLA/IA, PLA/PIA, PLA/Cop-IA, and PLA/Net-IA blends were characterized by dynamic mechanical thermal analysis, rotational rheometer (RR), thermogravimetric analysis, differential scanning calorimetry, X-ray diffraction, and scanning electron microscopy. The complex viscosity, storage module, and loss module for the RR properties were observed in the following order: PLA/Cop-IA, PLA/Net-IA, and PLA/PIA > PLA > PLA/IA. Thermal stability improved with increasing concentrations of Cop-IA and Net-IA. In the same way, the mechanical properties were enhanced. In addition, the micrographs illustrated the formation of fibrillar structures for all blends. The crystallinity degree displayed higher values for the blends that contain Net-IA > Cop-IA than IA > PIA. Therefore, IA and its architectures can influence these studied properties, which have potential applications in disposable food packing.

Morphology and Performance Relationship Studies on Poly(3-hydroxybutyrate-co-3-hydroxyvalerate)/Poly(butylene adipate-co-terephthalate)-Based Biodegradable Blends

Biodegradable poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV)/poly(butylene adipate-co-terephthalate) (PBAT) blends hold great potential for use in sustainable packaging applications for their advanced performance. Understanding the structure-property relationship in the blends at various proportions is significantly important for their future application, which is addressed in this work. The study found that the inherent brittleness of PHBV can only be modified with the addition of 50 wt % PBAT, where co-continuous structures formed in the blend as revealed by scanning electron microscopy (SEM) analysis. The elongation at break (%) of the blends increased from 3.81 (30% PBAT) to 138.5% (50% PBAT) and 345.3% (70 wt % PBAT), respectively. The fibrous structures of the PBAT formed during breaking are beneficial for energy dissipation, which greatly increased the toughness of the blends. Both the SEM observation and glass-transition temperature study by dynamic mechanical analysis indicated that the PHBV and PBAT are naturally immiscible. However, by simply mixing the two polymers with different composition ratios, the properties including melt flow index, heat deflection temperature, and mechanical properties can be tailored for different processing methods and applications. Our research work herein illustrates the fundamental structure-property relationship in this popular blend of PHBV/PBAT, aiming to guide the future modification direction in improving their properties and realizing their commercial applications in different scenarios.

Toughening Poly(l-lactide) Blends: Effectiveness of Sequence-Controlled Six-Arm Star-Branched Block Copolymers of Poly(l-lactide) and Poly(ε-caprolactone)

Well-defined six-arm star-branched bio-degradable block copolymers of l-lactide and ε-caprolactone were prepared using controlled ring-opening polymerization and a sequential monomer addition method using dipentaerythritol as the initiator core and organocatalysts at low temperatures in solution. Sequence of enchainment was changed by reversing the order of monomer addition giving, either, a crystalline PLA block or an amorphous PCL block as the outer segment. Well-defined six-arm poly(ε-caprolactone-b-l-lactide, 6s-PCL-b-PLA) block copolymers were obtained with a range of segment molecular weights. However, in the case of six-arm poly(l-lactide-b-ε-caprolactone, 6s-PLA-b-PCL), disruption of the block structure was observed on account of competing transesterification reactions accompanying a chain-growth reaction. Such sequence-controlled block copolymers showed interesting phase morphologies, as evidenced by differential scanning calorimetry (DSC) studies. 6s-PCL-b-PLA showed two glass-transition temperatures and two melting temperatures characteristic of the amorphous and crystalline blocks. 6s-PCL-b-PLA and 6s-PLA-b-PCL with different segment chain lengths were solution blended (10 wt %) with a commercially sourced PLA. All the blends were highly transparent. The structure and properties of the blend were examined by DSC, measurement of mechanical properties, and scanning electron microscopy. The results show that a phase-separated 6s-PCL-b-PLA copolymer results in two- to three-fold improvement in tensile toughness without the loss of modulus. A possible hypothesis for the mechanism of tensile toughness in the blend has been proposed.

Silane-Functionalized Sheep Wool Fibers from Dairy Industry Waste for the Development of Plasticized PLA Composites with Maleinized Linseed Oil for Injection-Molded Parts

Poly(lactic acid) (PLA) was plasticized with maleinized linseed oil (MLO) and further reinforced with sheep wool fibers recovered from the dairy industry. The wool fibers were firstly functionalized with 1 and 2.5 phr of tris(2-methoxyethoxy)(vinyl) (TVS) silane coupling agent and were further used in 1, 5, and 10 phr to reinforce the PLA/MLO matrix. Then, the composite materials were processed by extrusion, followed by injection-molding processes. The mechanical, thermal, microstructural, and surface properties were assessed. While the addition of untreated wool fibers to the plasticized PLA/MLO matrix caused a general decrease in the mechanical properties, the TVS treatment was able to slightly compensate for such mechanical losses. Additionally, a shift in cold crystallization and a decrease in the degree of crystallization were observed due to the fiber silane modification. The microstructural analysis confirmed enhanced interaction between silane-modified fibers and the polymeric matrix. The inclusion of the fiber into the PLA/MLO matrix made the obtained material more hydrophobic, while the yellowish color of the material increased with the fiber content.

Super tough poly(lactic acid) blends: a comprehensive review

Poly(lactic acid) or poly(lactide) (PLA) is a renewable, bio-based, and biodegradable aliphatic thermoplastic polyester that is considered a promising alternative to petrochemical-derived polymers in a wide range of commodity and engineering applications. However, PLA is inherently brittle, with less than 10% elongation at break and a relatively poor impact strength, which limit its use in some specific areas. Therefore, enhancing the toughness of PLA has been widely explored in academic and industrial fields over the last two decades. This work aims to summarize and organize the current development in super tough PLA fabricated via polymer blending. The miscibility and compatibility of PLA-based blends, and the methods and approaches for compatibilized PLA blends are briefly discussed. Recent advances in PLA modified with various polymers for improving the toughness of PLA are also summarized and elucidated systematically in this review. Various polymers used in toughening PLA are discussed and organized: elastomers, such as petroleum-based traditional polyurethanes (PUs), bio-based elastomers, and biodegradable polyester elastomers; glycidyl ester compatibilizers and their copolymers/elastomers, such as poly(ethylene-co-glycidyl methacrylate) (EGMA), poly(ethylene-n-butylene-acrylate-co-glycidyl methacrylate) (EBA-GMA); rubber; petroleum-based traditional plastics, such as PE and PP; and various biodegradable polymers, such as poly(butylene adipate-co-terephthalate) (PBAT), polycaprolactone (PCL), poly(butylene succinate) (PBS), and natural macromolecules, especially starch. The high tensile toughness and high impact strength of PLA-based blends are briefly outlined, while the super tough PLA-based blends with impact strength exceeding 50 kJ m⁻² are elucidated in detail. The toughening strategies and approaches of PLA based super tough blends are summarized and analyzed. The relationship of the properties of PLA-based blends and their morphological parameters, including particle size, interparticle distance, and phase morphologies, are presented.

PLA is a renewable, bio-based, and biodegradable aliphatic thermoplastic polyester that is considered a promising alternative to petrochemical-derived polymers in a wide range of commodity and engineering applications.

A versatile strategy for the synthesis and mechanical property manipulation of networked biodegradable polymeric materials composed of well-defined alternating hard and soft domains

Networked materials composed of well-defined alternating domains of two types of biodegradable polymers, hard poly(l-lactide) and soft poly(ε-caprolactone), were successfully synthesized.

Mechanical properties and heat resistance of stereocomplex polylactide/copolyester blend films prepared by in situ melt blending followed with compression molding

This work focuses on the process to obtain high heat-resistant stereocomplex polylactide (scPLA)/copolyester blend films by in situ melt blending of high molecular-weight poly(L-lactide) (PLLA), low molecular-weight poly(D-lactide) (PDLA) and copolyester followed with compression molding. A copolyester of poly(ε-caprolactone-co-L-lactide) was used as a film former. Stereocomplexation, mechanical properties and heat resistance of the scPLA/copolyester blend films were investigated by differential scanning calorimetry (DSC), tensile testing and dynamic mechanical analysis (DMA), respectively. The PDLA fractions enhanced stereocomplexation and heat resistance of the blend films while the copolyester fraction reduced film brittleness. Dimensional stability to heat of blend films was also determined and was accorded to their DMA results. It was concluded that the high heat-resistant and less brittle scPLA films could be prepared using 70/30 (w/w) PLLA/PDLA with 20 wt% copolyester through melt blending before compression molding. This film showed similar stress at break and heat resistance to those of polypropylene film but with lower strain at break.

Preparation and properties of flexible poly(lactic acid) blend foams

High-performance poly(lactic acid) (PLA) foam has been recognized as a promising material because of its biodegradability. However, low flexibility and foamability of PLAs has limited its use in different fields. In this study, a blend-toughening technology was used to toughen PLA and prepare flexible foams. The mechanical properties of PLA blends were evaluated, and the cellular structure of these foaming blends was characterized. The results show that the blending components significantly affected the overall mechanical properties and foaming behavior of PLA. The toughness of PLA was enhanced by adding poly(butylene adipate- co-terephthalate) (PBAT) and rigid particles. The rheological behavior of PLA was also affected by adding PBAT. Therefore, the cellular structure of the PLA foams was affected. A constitutive model was also used to fit the experimental results of the compression property of the PLA foam.

Toughening of Poly(L-lactide) with Blends of Poly(ε-caprolactone-co-L-lactide) in the Presence of Chain Extender

A poly(ε-caprolactone-co-L-lactide) copolyester was synthesized and employed to toughen poly(L-lactide) (PLLA) by reactive melt blending in the presence of an epoxy-based chain extender. The effects of chain extension reaction and copolyester content on properties of PLLA-based blends were studied. The chain extension reaction reduced crystallinity and melt flow index of PLLA/copolyester blends. Meanwhile the copolyester blending improved the crystallinities of the chain-extended PLLA up to 20 wt% copolyester. The phase compatibility between PLLA matrix and dispersed copolyester phases was enhanced by the chain extension reaction. The impact strength of chain-extended PLLA increased with the contents of copolyester and chain extender.

Recent Advances in Nanocomposites Based on Aliphatic Polyesters: Design, Synthesis, and Applications in Regenerative Medicine

In the last decade, biopolymer matrices reinforced with nanofillers have attracted great research efforts thanks to the synergistic characteristics derived from the combination of these two components. In this framework, this review focuses on the fundamental principles and recent progress in the field of aliphatic polyester-based nanocomposites for regenerative medicine applications. Traditional and emerging polymer nanocomposites are described in terms of polymer matrix properties and synthesis methods, used nanofillers, and nanocomposite processing and properties. Special attention has been paid to the most recent nanocomposite systems developed by combining alternative copolymerization strategies with specific nanoparticles. Thermal, electrical, biodegradation, and surface properties have been illustrated and correlated with the nanoparticle kind, content, and shape. Finally, cell-polymer (nanocomposite) interactions have been described by reviewing analysis methodologies such as primary and stem cell viability, adhesion, morphology, and differentiation processes.

Grafting Modification of the Reactive Core-Shell Particles to Enhance the Toughening Ability of Polylactide

In order to overcome the brittleness of polylactide (PLA), reactive core-shell particles (RCS) with polybutadiene as core and methyl methacrylate-co-styrene-co-glycidyl methacrylate as shell were prepared to toughen PLA. Tert-dodecyl mercaptan (TDDM) was used as chain transfer agent to modify the grafting properties (such as grafting degree, shell thickness, internal and external grafting) of the core-shell particles. The introduction of TDDM decreased the grafting degree, shell thickness and the T_g of the core phase. When the content of TDDM was lower than 1.15%, the RCS particles dispersed in the PLA matrix uniformly-otherwise, agglomeration took place. The addition of RCS particles induced a higher cold crystallization temperature and a lower melting temperature of PLA which indicated the decreased crystallization ability of PLA. Dynamic mechanical analysis (DMA) results proved the good miscibility between PLA and the RCS particles and the increase of TDDM in RCS induced higher storage modulus of PLA/RCS blends. Suitable TDDM addition improved the toughening ability of RCS particles for PLA. In the present research, PLA/RCS-T4 (RCS-T4: the reactive core-shell particles with 0.76 wt % TDDM addition) blends displayed much better impact strength than other blends due to the easier cavitation/debonding ability and good dispersion morphology of the RCS-T4 particles. When the RCS-T4 content was 25 wt %, the impact strength of PLA/RCS-T4 blend reached 768 J/m, which was more than 25 times that of the pure PLA.

Investigation of Thermal and Thermomechanical Properties of Biodegradable PLA/PBSA Composites Processed via Supercritical Fluid-Assisted Foam Injection Molding

Bio-based polymer foams have been gaining immense attention in recent years due to their positive contribution towards reducing the global carbon footprint, lightweighting, and enhancing sustainability. Currently, polylactic acid (PLA) remains the most abundant commercially consumed biopolymer, but suffers from major drawbacks such as slow crystallization rate and poor melt processability. However, blending of PLA with a secondary polymer would enhance the crystallization rate and the thermal properties based on their compatibility. This study investigates the physical and compatibilized blends of PLA/poly (butylene succinate-co-adipate) (PBSA) processed via supercritical fluid-assisted (ScF) injection molding technology using nitrogen (N₂) as a facile physical blowing agent. Furthermore, this study aims at understanding the effect of blending and ScF foaming of PLA/PBSA on crystallinity, melting, and viscoelastic behavior. Results show that compatibilization, upon addition of triphenyl phosphite (TPP), led to an increase in molecular weight and a shift in melting temperature. Additionally, the glass transition temperature (T_g) obtained from the tanδ curve was observed to be in agreement with the T_g value predicted by the Gordon–Taylor equation, further confirming the compatibility of PLA and PBSA. The compatibilization of ScF-foamed PLA–PBSA was found to have an increased crystallinity and storage modulus compared to their physically foamed counterparts.

Toward "Green" Hybrid Materials: Core-Shell Particles with Enhanced Impact Energy Absorbing Ability

Restrained properties of "green" degradable products drive the creation of materials with innovative structures and retained eco-attributes. Herein, we introduce the creation of impact modifiers in the form of core-shell (CS) particles toward the creation of "green" composite materials. Particles with CS structure constituted of PLA stereocomplex (PLASC) and a rubbery phase of poly(ε-caprolactone-co-d,l-lactide) (P[CL-co-LA]) were successfully achieved by spray droplet atomization. A synergistic association of the soft P[CL-co-LA] and hard PLASC domains in the core-shell structure induced unique thermo-mechanical effects on the PLA-based composites. The core-shell particles enhanced the crystallization of PLA matrices by acting as nucleating agents. The core-shell particles functioned efficiently as impact modifiers with minimal effect on the composites stiffness and strength. These findings provide a new platform for scalable design of polymeric-based structures to be used in the creation of advanced degradable materials.

New transparent poly(l-lactide acid) films as high-performance bio-based nanocomposites

A new tri-POSS-end-capped poly(lactic acid) bio-nanocomposite forms transparent films with significantly enhanced gas barrier properties and improved mechanical performance.

Polylactide/Poly(ω-hydroxytetradecanoic acid) Reactive Blending: A Green Renewable Approach to Improving Polylactide Properties

A green manufacturing technique, reactive extrusion (REx), was employed to improve the mechanical properties of polylactide (PLA). To achieve this goal, a fully biosourced PLA based polymer blend was conceived by incorporating small quantities of poly(ω-hydroxytetradecanoic acid) (PC14). PLA/PC14 blends were compatibilized by transesterification reactions promoted by 200 ppm titanium tetrabutoxide (Ti(OBu)4) during REx. REx for 15 min at 150 rpm and 200 °C resulted in enhanced blend mechanical properties while minimizing losses in PLA molecular weight. SEM analysis of the resulting compatibilized phase-separated blends showed good adhesion between dispersed PC14 phases within the continuous PLA phase. Direct evidence for in situ synthesis of PLA-b-PC14 copolymers was obtained by HMBC and HSQC NMR experiments. The size of the dispersed phase was tuned by the screw speed to "tailor" the blend morphology. In the presence of 200 ppm Ti(OBu)4, inclusion of only 5% PC14 increased the elongation at break of PLA from 3 to 140% with only a slight decrease in the tensile modulus (3200 to 2900 MPa). Furthermore, PLA's impact strength was increased by 2.4× that of neat PLA for 20% PC14 blends prepared by REx. Blends of PLA and PC14 are expected to expand the potential uses of PLA-based materials.

Biodegradable polylactide based materials with improved crystallinity, mechanical properties and rheological behaviour by introducing a long-chain branched copolymer

Herein we developed a novel strategy for preparing biodegradable PLA based materials with improved crystallinity, mechanical properties and rheological behaviour by introducing a long-chain branched block copolymer of PLA and PCL.

Toughening of amorphous poly(propylene carbonate) by rubbery CO2-based polyurethane: transition from brittle to ductile

CO₂-based polyurethane was synthesized to toughen poly(propylene carbonate) (PPC), leading to a transition in the fracture behavior of PPC from brittle to ductile.

Poly(lactide-co-trimethylene carbonate) and polylactide/polytrimethylene carbonate blown films

In this work, poly(lactide-co-trimethylene carbonate) and polylactide/polytrimethylene carbonate films are prepared using a film blowing method. The process parameters, including temperature and screw speed, are studied, and the structures and properties of the P(LA-TMC) and PLA/PTMC films are investigated. The scanning electron microscope (SEM) images show that upon improving the content of TMC and PTMC, the lamellar structures of the films are obviously changed. With increasing TMC monomer or PTMC contents, the elongation at the break is improved, and the maximum is up to 525%. The water vapor permeability (WVP) results demonstrate that the WVP of the PLA/PTMC film increased with the increase in the PTMC content, whereas the WVP of the P(LA-TMC) film decreased. Thermogravimetric (TG) measurements reveal that the decomposition temperatures of the P(LA-TMC) and PLA/PTMC films decrease with increases in the TMC and PTMC contents, respectively, but the processing temperature is significantly lower than the initial decomposition temperature. P(LA-TMC) or PLA/PTMC film can extend the shelf life of apples, for instance, like commercial LDPE film used in fruit packaging in supermarkets.