Effect of maleic anhydride grafted poly(lactic acid) on rheological behaviors and mechanical performance of poly(lactic acid)/poly(ethylene glycol) (PLA/PEG) blends

A series of polylactic acid (PLA)/polyethylene glycol (PEG) blends was prepared by melt blending using PEG as a plasticizer to address the disadvantages of PLA brittleness. PEG can weaken the intermolecular chain interactions of PLA and improve its processing properties. PLA-grafted maleic anhydride (GPLA) was reactively blended with PLA/PEG to obtain a high tenacity PLA/PEG/GPLA blend. GPLA was prepared by melt grafting using diisopropyl peroxide as the initiator and maleic anhydride as the graft. The effects of different PEG molecular weights (1000–10 000 g mol⁻¹) on the properties of PLA/PEG/GPLA blends were investigated. GPLA reacted with PEG1000 (M_w = 1000 g mol⁻¹) to form short PLA branched chains and reacted with {"type":"entrez-protein","attrs":{"text":"PEG10000","term_id":"1256949604","term_text":"PEG10000"}}PEG10000 (M_w = 10 000 g mol⁻¹) to form a small number of PLA branched chains, which was unconducive to increasing the intermolecular chain entanglement. The branched PLA formed by the reaction between PEG6000 (M_w = 6000 g mol⁻¹) and GPLA had a remarkable effect on increasing intermolecular chain entanglement. The complex viscosity, modulus, and melt strength values of PLA/PEG6000/GPLA blends were relatively large. The elongation at break of the blends reached 526.9%, and the tensile strength was 30.91 MPa. It provides an effective way to prepare PLA materials with excellent comprehensive properties.

Preparation of PLA/PEG/GPLA blends with high toughness by reactive blending of PLA grafted maleic anhydride (GPLA).     

Tuning the compatibility to achieve toughened biobased poly(lactic acid)/poly(butylene terephthalate) blends

A series of sustainable biobased polymer blends from poly(lactic acid) (PLA) and poly(butylene terephthalate) (PBT) were fabricated and characterized. These blends are engineered to achieve optimal mechanical properties and toughness with a reactive epoxidized styrene-acrylic copolymer (ESAC) compatibilizer, and an ethylene-n-butyl-acrylate-co-glycidyl methacrylate (EBA-GMA) elastomer-based compatibilizer. The results showed that the tensile strength, modulus, flexural strength and modulus of the PBT increase, while the elongation at break and notched impact strength decrease after blending with the biopolymer PLA. The full co-continuity of PLA in PBT was confirmed at a 50/50 wt% blend ratio. The droplet size of the PLA was reduced and the distinct phases of the blends were gradually diminished with the increasing content of the ESAC compatibilizer. The increase in the complex viscosity of the blends was due to the formation of PLA-g-PBT copolymers in the blend after addition of reactive compatibilizers. The incorporation of both compatibilizers in the blends led to superior notched impact strength in comparison to only a single compatibilizer used in the blends. The synergistic effect of both compatibilizers effectively reduces the PLA droplet size and improves the dispersion of PLA in PBT as evidenced by atomic force microscopy (AFM) topography observations. The high toughness of the blends corresponds to the formation of effective EBA-GMA structures and enhanced interfacial compatibilization due to the synergistic effect of the compatibilizers.

Novel toughened biobased polymer blends from poly(lactic acid) and poly(butylene terephthalate) were developed by judicious compatibilization.     

In situ formation of PLA-grafted alkoxysilanes for toughening a biodegradable PLA stereocomplex thin film

Poly(lactide) (PLA) has received tremendous attention recently from researchers and industrialists due to its ability to solve environmental problems related to plastic pollution. However, PLA''s brittleness, poor thermal stability, low elongation at break, and poor melt processing prevent its use in a broader spectrum of applications. Herein, we produced a very tough and thermally more stable PLA stereocomplex by simply mixing PLA with organoalkoxysilane. The stereocomplex PLA/silane (sc-PLA–silane) composite was prepared by simple mixing of three types of organoalkoxysilanes in sc-PLA followed by in situ formation of a silane-based rubbery core with a cross-linked PLA shell. Mechanical and thermal properties were improved by stereocomplexation of PLA with a small amount (1–5 wt%) of PLA-grafted silanes. The addition of organoalkoxysilane with different functional groups resulted in a plasticizer of rubbery silica-PLA core–shell gel through in situ condensation and grafting of long PLA chains at the interface between the stereocomplex and silane particles. The results revealed that the toughness of sc-PLA was improved dramatically with only a small addition (only 2.5%) of 3-(triethoxysilyl)propyl isocyanate (ICPTES). The morphology and mechanical and thermal properties of the toughened stereocomplex films were characterized. The results revealed that elongation at break was increased from 16% to 120%, while other mechanical properties such as tensile strength and modulus were retained. Surface analysis confirmed that this toughness was achieved by formation of a silica-PLA core–shell gel. The mechanical properties of PLA were improved without any significant reduction in modulus and tensile strength using this simple methodology.

Current work provides a synergistic approach to prepare super tough PLA without any significant loss of its excellent intrinsic mechanical properties.     

Accelerated biodegradation of PLA/PHB-blended nonwovens by a microbial community

In this study, the accelerated biodegradation of PLA/PHB (polylactic acid/polyhydroxybutyrate)-blended nonwovens was investigated in the presence of a microbial community. The PLA/PHB-blended nonwovens were buried in natural soil for 56 days, with soil samples collected for subsequent bacterial community domestication. The tensile strength and elongation at break of the PLA/PHB-blended nonwovens as well as the CO₂ generated by the Gen III and natural soil communities were determined to assess the degradation rates of the polymer samples. After incubation for 15 days with the Gen III soil bacterial suspension, the surfaces and fibrous structure of nonwovens and the fibers within the nonwovens exhibited distinct changes. In addition, the amount of EvCO₂ reached 566.79 mg, the tensile strength decreased from 10.95 ± 0.7 to 2.57 ± 0.31 MPa, a loss of 77%, and the elongation at break changed from 5.32 ± 0.45 to 7.07 ± 1.04%. The 16S rRNA pyrosequencing results showed that Proteobacteria and Firmicutes were the 2 most important bacterial phyla in the Gen III community, accounting for 80.4 and 19.4% of the total classified sequences, respectively. The results of this study demonstrate that compared to a natural soil microbial community, the domesticated strains in the Gen III community, especially members of the phyla Proteobacteria and Firmicutes, are useful in accelerating the degradation of PLA/PHB-blended nonwovens.

Accelerated biodegradation of PLA–PHB blends by domesticated Proteobacteria and Firmicutes strains.     

Influence of Moringa oleifera biodiesel–diesel–hexanol and biodiesel–diesel–ethanol blends on compression ignition engine performance,combustion and emission characteristics

In the current work, the influences of Moringa oleifera biodiesel–diesel–hexanol and Moringa oleifera biodiesel–diesel–ethanol blends on compression ignition engine characteristics were experimentally investigated. Experiments were conducted on a diesel engine at 0%, 25%, 50%, 75% and 100% load conditions run at a constant speed of 1500 rpm. The results revealed that B90-D5-H5 acquired the lowest BSFC and maximum BTE of 0.375 kg kW⁻¹ h⁻¹ and 28.8%, respectively, and B100 had the highest BSFC of 0.425 kg kW⁻¹ h⁻¹. B90-D5-H5 had the highest cylinder peak pressure of 74 bar at 4°CA aTDC. The maximum heat release rate (HRR) and longer ignition delay (ID) period of 44 J per °CA and 14.4°CA, respectively, were attained in the B90-D5-H5 blend. At 100% load condition, the lowest amount of carbon monoxide (CO) of 0.32% vol. was acquired in the B80-D5-E15 blend. The maximum nitric oxide (NO) emission of 1090 ppm was also acquired in the B80-D5-E15 blend. B100 had the lowest NO of 846 ppm; B80-D5-E15 had the lowest unburned hydrocarbon (UBHC) emission of 34 ppm at 100% load and the lowest smoke opacity of 34%. Biodiesel–diesel–alcohol blends improve engine performance and decrease emissions compared to the conventional diesel. The utilization of biodiesel–diesel–alcohol blends reduces the consumption of diesel. Hence, ethanol and hexanol are recommended as potential alternative additives in biodiesel–diesel blends to improve engine performance and reduce emissions.

In the current work, the influences of Moringa oleifera biodiesel–diesel–hexanol and Moringa oleifera biodiesel–diesel–ethanol blends on compression ignition engine characteristics were experimentally investigated.     

Bio-based,biodegradable and amorphous polyurethanes with shape memory behavior at body temperature

In this work, a series of bio-based, biodegradable and amorphous shape memory polyurethanes were synthesized by a two-step pre-polymerization process from polylactide (PLA) diol, polycaprolactone (PCL) diol and diphenylmethane diisocyanate-50 (MDI-50). The ratio of PLA diol to PCL diol was adjusted to investigate their thermal and mechanical properties. These bio-based shape memory polyurethanes (bio-PUs) showed a glass transition temperature (T_g) value in the range of −10.7–32.5 °C, which can be adjusted to be close to body temperature. The tensile strength and elongation of the bio-PUs could be tuned in the range from 1.7 MPa to 12.9 MPa and from 767.5% to 1345.7%, respectively. Through a series of shape memory tests, these bio-PUs exhibited good shape memory behavior at body temperature. Among them, PU with 2 : 1 as the PLA/PCL ratio showed the best shape recovery behavior with a shape recovery rate higher than 98% and could fully reach the original shape state in 15 s at 37 °C. Therefore, these shape memory bio-PUs are promising for applications in smart biomedical devices.

A series of bio-based, biodegradable and amorphous polyurethanes with shape memory behavior at body temperature were synthesized.     

Polyester-based polyurethanes derived from alcoholysis of polylactide as toughening agents for blends with shape-memory properties

A process for sizing down and functionalizing commercial polylactide (PLA) resin is developed by alcoholysis with 1,4-butanediol (BDO) and propylene glycol (PG) to medium-sized PLA-based diols, with lower cost than a bottom-up synthesis process. These are subsequently used as polyols in preparing polyurethanes (PU) by reacting with 1,6-diisocyanatohexane (HDI). The PLA-based PU has an excellent elongation at break of 487%. The products are suitable as toughening agents for brittle PLA resin due to their highly elastic properties and high compatibility with PLA. The PU products are blended with PLA resin at various compositions, and their physical and mechanical properties and shape recovery are examined. The tensile tests showed enhancements in elongation at break up to 160% with low modulus. The fracture morphology and FTIR results confirm that the blends show strong interfacial interaction and adhesion between the PLA-based PU disperse phase and the PLA matrix. The PLA/PU blends exhibit a high shape recovery efficiency, and their recovery mechanisms are identified. These flexible PLA/PU blends are promising for various applications where bio-compatibility/degradability and high ductility are required, especially as filaments for 3D bio-printing.

A process for sizing down and functionalizing polylactide (PLA) is developed by alcoholysis. These are used as polyols in preparing PLA-based polyurethanes for toughening of brittle PLA. The blends exhibit improved mechanical properties with a high shape recovery efficiency.     

Effect of stereocomplex crystal and flexible segments on the crystallization and tensile behavior of poly(l-lactide)

The effects of poly(ethylene glycol) (PEG) and/or poly(d-lactide) (PDLA) blocks on the crystallization and mechanical properties of poly(l-lactide) (PLLA) were investigated systematically via differential scanning calorimetry (DSC), polarized optical microscopy (POM), wide-angle X-ray diffraction (WAXD) and tensile testing. The structural evolution during uniaxial stretching of the obtained blends above the glass transition temperature was studied by in situ WAXD. It was observed that the stereocomplex (SC) crystals promoted the nucleation of PLLA homocrystals (α/α′ crystal), and flexible PEG blocks could enhance the spherulitic growth rate. The PLLA/PDLA–PEG–PDLA had a higher elongation at break than that of PLLA/PDLA without significant loss in tensile strength and stiffness. In situ WAXD showed that the PLLA/PDLA–PEG–PDLA crystallized faster during stretching. It was shown that the incorporation of SC crystals and flexible PEG blocks could not only accelerate the crystallization but also improve the toughness of PLLA.

Effect of stereocomplex crystal and PEG segments in blends on the crystallization and tensile behavior of PLLA.     

Effects of synthesised polyaniline (PAni) contents on the anti-static properties of PAni-based polylactic acid (PLA) films

An anti-static polymer film was prepared using biodegradable poly(lactic acid) as a matrix and polyaniline (PAni) as an anti-static agent. It is aimed to be applied in packaging applications to dissipate the accumulated charges. The anti-static properties of PLA films were investigated with various PAni contents ranging from 0% to 20% through ex situ polymerisation by the solution casting method. PAni was synthesised in the solution form through chemical oxidation at 0 °C. The synthesis of PAni was confirmed by Fourier transform infrared (FTIR) spectroscopy and ultraviolet-visible (UV-Vis) absorption spectroscopy. The mechanical and anti-static properties of the samples were characterised using a Universal Testing Machine (UTM) and a resistivity meter, respectively. The experimental results indicated that incorporation of PAni into PLA films affected the morphology, anti-static and mechanical properties of the samples. PLA/PAni showed a compact surface with a porous structure, reflecting the interfacial interaction between PLA and PAni in the presence of a plasticiser. It was discovered and compared with other compositions, PLA with 15% PAni exhibited excellent anti-static performance with 2.45 × 10¹⁰ ohm/sq surface resistivity and the highest tensile strength, elongation at break and modulus of 29.3 ± 2.4 MPa, 60.1 ± 1.6% and 1364.0 ± 85.2 MPa respectively. Hence, PAni is a good candidate to be used in PLA/PAni systems by giving a suitable surface resistivity that can potentially be applied in anti-static packaging applications.

An anti-static polymer film was prepared using biodegradable poly(lactic acid) as a matrix and polyaniline (PAni) as an anti-static agent to eliminate accumulated static charges.     

Multiblock copolymers of PPC with oligomeric PBS: with low brittle–toughness transition temperature

In order to decrease the brittle–toughness transition temperature and increase the mechanical strength of poly(propylene carbonate) (PPC), a series of multiblock copolymers of poly(propylene carbonate)-multiblock-poly(butylene succinate) (PPC-mb-PBS) are designed and synthesized. ¹H-NMR, DOSY and GPC results demonstrate the successful synthesis of PPC-mb-PBSs with designed multiblock sequence. The thermal, crystalline and mechanical properties of these PPC-mb-PBSs are evaluated by DSC, TGA, POM, tensile and tearing testing. Experiment results demonstrate that crystallinity, thermal and mechanical properties of PPC-mb-PBSs can be readily modulated by changing the composition and block length of PPC and PBS moieties. It is found that all the prepared PPC-mb-PBSs are semi-crystalline polymers with a melting temperature at 93–109 °C and a T_g at around −40 °C. Both crystallization rate and crystallinity of the multiblock copolymers increase with increasing both PBS content and PBS block length. As a consequent, the tensile strength increases with increasing PBS/PPC block ratios at room and lower temperatures. In conclusion, the amorphous PBS phase in the block copolymers acts as soft segment, endowing PPC-mb-PBS copolymers with much better flexibility than PPC at low temperature of 273 K when PPC segments are frozen.

In present work, biodegradable multiblock copolymers from oligomeric PPC and PBS with low brittle–toughness transition temperature and superior mechanical properties was synthesized, making it more potential candidate as packaging materials.     

Novel tunable super-tough materials from biodegradable polymer blends: nano-structuring through reactive extrusion

Structuring blends on sub-micrometer scales, especially nano-scales, has a higher potential for improving their thermomechanical properties. Here, we propose a design strategy to fabricate compatible nano-blends by manipulating the reactions between two biodegradable polymers, e.g. polybutylene succinate (PBS) and polybutylene adipate terephthalate (PBAT), with extremely low free radical contents through reactive extrusion processing. Observed by transmission electron microscopy (TEM) and atomic force microscopy (AFM), it is found that PBAT is tightly surrounded by large amounts of PBS–PBAT co-polymers and dispersed in a PBS matrix with a particle size of less than 100 nm. We show how impact strength and polymer moduli can be improved simultaneously by decreasing the small amount of dispersed phase into nano-scale (droplet or lamina structures). With 5 wt% PBAT content in the PBS–PBAT blend, the notched impact strength of PBS is increased 1200% and the Young''s modulus is increased 15%. Through in situ rheological monitoring and Fourier-transform infrared spectroscopy (FTIR) studies, the reason why nano-blends can be formed in such a low amount of peroxide is illustrated. Our investigation most significantly indicates the transformation of the partially compatible PBS–PBAT micro-blend into a fully compatible PBS–PBAT through nano-structuring. This work addresses the importance of reaction rate and mechanism in favoring the formation of co-polymers rather than homo-polymer crosslinking or self-decomposition in polymer blend modification via reactive extrusion design.

From micro to nano, super-tough PBS with high impact strength is fabricated.     

Novel sustainable materials from waste plastics: compatibilized blend from discarded bale wrap and plastic bottles

This work studies a novel sustainable polymeric material made from a reactive blend of two agri-food waste plastics, with the new material showing strong promise for value-added industrial uses. Discarded bale wrap destined for landfill that was originally made from linear low density polyethylene (LLDPE) and used polyethylene terephthalate (PET)-based plastic bottles were melt mixed in a twin-screw extruder. The miscibility of such recycled LLDPE (rLLDPE) in recycled PET (rPET) is enhanced by the incorporation of a compatibilizer and the PET molecular architecture is maintained using a chain extender, which governs its melt strength. Microscopic analysis of the blends with the compatibilizer and chain extender confirms the enhanced interaction of rPET and rLLDPE chains and the formation of co-continuous morphologies. The efficient interaction of a soft phase (rLLDPE) with a hard phase (rPET) leads to prolonged fracture propagation by an appropriate impact energy transfer mechanism, which ultimately enhances the impact resistance and elongation at break of the resulting blend. The incorporation of a compatibilizer and chain extender in the rPET/rLLDPE blend makes it a toughened blend (with 60 J m⁻¹ notched Izod impact strength) with ∼80% elongation at break in comparison to ∼3% for the blend without a compatibilizer or chain extender. Around ∼36% enhancement is observed in the tensile strength without affecting the tensile and flexural modulus in comparison to the blend without a compatibilizer or chain extender. Applications of the developed materials can extend from rigid packaging applications to the production of filaments for 3D printing.

This work studies a novel sustainable polymeric material made from a reactive blend of two agri-food waste plastics, with the new material showing strong promise for value-added industrial uses.     

An environmentally sustainable plasticizer toughened polylactide

Cardanol (CD), derived from renewable natural cashew nutshell liquid, has been used as a new plasticizer for polylactide (PLA), to create blends which retain the environmentally friendly features of PLA. The differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA) and scanning electron microscopy (SEM) results all reveal that PLA and CD show good miscibility at low CD content. CD significantly decreased the glass transition temperature and enhanced the crystallization ability of PLA, demonstrating good plasticizing efficiency with PLA. At 10 wt% CD, ultimate elongation and impact toughness increased to 472% and 9.4 kJ m⁻², respectively, which represented improvements of 31-fold and 2.6-fold over the corresponding measurements for neat PLA. The plasticization effect of CD was also demonstrated by the decreased melt complex viscosity and shear storage modulus at lower CD content for the blends when compared with neat PLA. Thus, the investigated CD presents an interesting candidate for a PLA plasticizer, meeting “double green” criteria. No cytotoxicity was found for the blends and hence they may be suitable for biomedical applications.

Cardanol, derived from renewable resources, exhibits good plasticizing efficiency for PLA, meeting “double green” criteria.     

Polylactic acid based Janus membranes with asymmetric wettability for directional moisture transport with enhanced UV protective capabilities

Efficient directional moisture transport can remove excess sweat away from the human body and keep the body dry; fully utilizing this functionality to improve the wearing experience is urgently needed in the area of functional textiles. Herein, a facile strategy is used to design an eco-friendly and biodegradable PLA membrane with enhanced directional moisture transport and UV protection abilities. The PLA-based Janus membrane with asymmetric wettability is fabricated via sol–gel and electrospinning methods. Titanium dioxide nanoparticles (TiO₂) were anchored onto the surface of the PLA fabric during the TiO₂ sol–gel fabrication process using polydopamine, forming superhydrophilic TiO₂@PDA–PLA. Then a thin PLA fibrous membrane layer showing hydrophobicity was electrospun onto this (PLA-E). The Janus PLA-E/TiO₂@PDA–PLA membrane was successfully fabricated. Due to the asymmetric wettability and anchored TiO₂, the PLA-E/TiO₂@PDA–PLA Janus membrane exhibits efficient directional moisture transport and excellent UV protection abilities, and this work may provide a new pathway for fabricating multifunctional personal protective materials and have attractive potential applications in the future.

The PLA-E/TiO₂@PDA–PLA Janus membrane with asymmetric wettability exhibits efficient directional moisture transport and excellent UV protective capacity.     

Preparation and properties of a novel poly(lactic-acid)-based thermoplastic vulcanizate from both experiments and simulations

A novel bio-based thermoplastic vulcanizate (TPV) material consisting of poly(lactic acid) (PLA) and a novel polymeric slide ring material (SeRM) was fabricated via isocyanate-induced dynamic vulcanization. The microscopic morphology, thermal properties, biocompatibility, and mechanical properties of the SeRM/PLA TPV material were comprehensively investigated, in turn by transmission electron microscopy, differential scanning calorimetry, in vitro cytotoxicity test, electron tension machine, and molecular dynamics simulations. Phase inversion in TPV was observed during the dynamic vulcanization, and TEM images showed that SeRM particles that were dispersed in PLA continuous phase had an average diameter of 1–4 μm. Results also indicated that an optimum phase inversion morphology was obtained at the SeRM/PLA blending ratio of 70/30 w/w. Glass transition temperature of PLA was found to be slightly decreased, owing to the improvement in interface compatibility by chemically bonding the PCL side chains (of SeRM molecules) and PLA chains. The tensile strength and elongation at break of TPVs were approximately 14.7 MPa and 164%, respectively, at SeRM/PLA blending ratio of 70/30, owing to the unique sliding effect of SeRM molecules when subjected to deformations. Cytotoxicity test results proved that the bio-based TPVs were fully non-toxic to L929 cells. In such aspects we believe that the bio-based TPV can be a promising material in the biomedical applications as an alternative of traditional commodity plastics.

A novel bio-based thermoplastic vulcanizate (TPV) material consisting of poly(lactic acid) (PLA) and a novel polymeric slide ring material (SeRM) was fabricated via isocyanate-induced dynamic vulcanization.     

Construction of a ternary system: a strategy for the rapid formation of porous poly(lactic acid) fibers

Combining electrospinning technology with nonsolvent induced phase separation (ESP-NIPS), 10 wt% poly(lactic acid) (PLA) spinning solutions are prepared by using chloroform as a good solvent and absolute ethanol as a nonsolvent. The “PLA/CHCl₃/C₂H₅OH” ternary system is constituted to realize the rapid preparation of porous-structured PLA fibers. The morphologies, thermal properties and crystalline structures of the obtained fibers are characterized and the rapid forming mechanism of PLA porous fibers is investigated and discussed. The interaction parameters between the substances of the “PLA/CHCl₃/C₂H₅OH” ternary system, binodal line, spinodal line and critical point are obtained by theoretical calculation and experiment, and the “PLA/CHCl₃/C₂H₅OH” ternary phase diagram model is established. The results show that, when the mass ratio of chloroform/ethanol is around 75/25, the rapid “in situ” formation of the PLA fibers can be realized with porous structures within 5–10 s. The establishment of a “nonsolvent-solvent–polymer” ternary phase diagram model has laid a theoretical foundation for the rapid formation of polymer porous fibers by ESP-NIPS. The ESP-NIPS for the porous PLA fibers preparation provides a new resolution for the rapid formation of porous polymer materials, which is vital to further expand the application of electrospun fibers in emergency situations such as isolation, protection, insulation and flame retardant usage.

Combining electrospinning technology with ESP-NIPS, using chloroform as a solvent and absolute ethanol as a nonsolvent, poly(lactic acid) porous fibres are prepared within 5–10 s. This preparation provides a new resolution for the rapid formation of porous polymer materials.     

Novel compatibilized nylon-based ternary blends with polypropylene and poly(lactic acid): morphology evolution and rheological behaviour

In this paper, the interaction between nylon 6 (PA6), polypropylene (PP) and poly(lactic acid) (PLA) is reported. To improve the compatibility between these immiscible polymers, a reactive compatibilization approach was used through extrusion with maleic anhydride grafted polypropylene (PP-g-MA). To further improve the compatibility of the phases, PLA was selected as a semi-polar polymer and a low molecular weight was used to assure a good droplet dispersion. All the blends were twin-screw extruded in the melt at different compositions. The morphologies of binary and ternary blends were investigated using microscopic techniques by means of scanning electron microscopy (SEM) and atomic force microscopy (AFM). The PP-g-MA grafting process was observed to have a dramatic effect on the compatibility of both the binary and ternary blends and while a drastic reduction of the PP dispersed phases particle size was observed, the affinity between PLA and PP was also highlighted. The surface tension of the homopolymers and the interfacial tension of the pairs of polymers were measured to characterize the interaction at their interfaces. The interaction of PA6/PLA appeared preferable to PLA/PP, explaining the thinner dispersion obtained for PLA phase. The morphologies observed were compared to the predictions of spreading coefficient and minimum free energy models. While both models predicted the encapsulation of PP by the PLA phase, disagreeing with the morphological results, the rheological measurement gave an explanation for this phase separation. Using rheology measurements, the interaction between the phases was further investigated and the viscosity ratios were measured for the different pairs of polymers, stressing the high interaction between PA6 and PLA with and without compatibilizer. The droplet size of the dispersed phases appeared to substantially influence the chain relaxations in the melt.

Excellent sub-micrometric dispersions in ternary blends were reached by blending a semi-polar PLA at low viscosity in PA6/PP formulations.     

Regulation of polylactic acid using irradiation and preparation of PLA–SiO2–ZnO melt-blown nonwovens for antibacterial and air filtration

Since the COVID-19 pandemic, polypropylene melt-blown nonwovens (MBs) have been widely used in disposable medical surgical masks and medical protective clothing, seriously threatening the environment. As a bio-based biodegradable polymer, polylactic acid (PLA) has attracted great attention in fabricating MBs. However, there are still issues with the undesirable spinnability of PLA and the limited filtration and antibacterial performance of PLA MBs. Herein, a high-efficiency, low-resistance, and antibacterial PLA filter is fabricated by melt-blown spinning and electret postprocessing technology. The irradiation technique is used to tune PLA chain structure, improving its spinnability. Further, silica (SiO₂) nanoparticles are added to enhance the charge storage stability of PLA MBs. With a constant airflow rate of 32 L min⁻¹, the PLA-based MBs exhibit a high particulate filtration efficiency of 94.8 ± 1.5%, an ultralow pressure drop of 14.1 ± 1.8 Pa, and an adequate bacterial filtration efficiency of 98 ± 1.2%, meeting the medical protective equipment standard. In addition, the zinc oxide (ZnO) masterbatches are doped into the blend and the antibacterial rate of PLA-based MBs against Escherichia coli and Staphylococcus aureus is higher than 99%. This successful preparation and modification method paves the way for the large-scale production of PLA MBs as promising candidates for high-efficacy and antibacterial filters.

PLA MBs with high filtration efficiency and antibacterial activity were prepared by reducing viscosity by irradiation and blending ZnO and SiO₂.     

Morphological and mechanical properties of biodegradable poly(glycolic acid)/poly(butylene adipate-co-terephthalate) blends with in situ compatibilization

In the present work, the biodegradable blends of poly(glycolic acid) (PGA) and poly(butylene adipate-co-terephthalate) (PBAT) with in situ compatibilization using 4,4′-methylenebis(phenyl isocyanate) (MDI) were prepared. The combined results of FTIR, DSC, SEM, DSC, POM, TGA and rheology demonstrated that the MDI was successfully reacted with PGA/PBAT, the complex viscosity and storage moduli (G′) of the blends were increased. Melt elasticity and viscosity of the blends were also increased on increasing the concentration of PBAT. SEM results indicated that the compatibility was improved by in situ compatibilization. Due to the apparent differences in melting temperature (T_m) between PGA and PBAT, the morphology of the dispersed phase evolved from a spherical structure to in situ microfiber when the content of PBAT was up to 60% during injection molding. The interfacial adhesion between PGA and PBAT was strengthened, consequently, the impact strength of the blend was sharply increased from 9.0 kJ m⁻² to 22.2 kJ m⁻². On account of the chain extension effect, the crystallinity, crystallization temperature and crystallization size were decreased, which was also of benefit for the improvement of toughness. Meanwhile, the thermal stability of the PGA was improved through blending with PBAT. A novel biodegradable blending material with enhanced toughness and thermal stability was prepared.

A novel biodegradable poly(glycolic acid)/poly(butylene adipate-co-terephthalate) (PGA/PBAT) material with enhanced toughness through in situ compatibilization was prepared.     

Waste brewed tea leaf derived cellulose nanofiber reinforced fully bio-based waterborne polyester nanocomposite as an environmentally benign material

Bio-resources have carved a unique niche for the ever-increasing thrust of the global scientific community to impart green credentials to various research outputs along with the demands for advanced materials. In this milieu, the authors wish to fabricate a fully bio-based waterborne polyester nanocomposite as an advanced material using different bio-based reactants and cellulose nanofibers as the nanomaterial. Three different compositions of the nanocomposite were prepared at different loadings of cellulose nanofibers (0.25, 0.5 and 1 weight%) which were isolated from waste brewed green tea leaves. The structural attributes of the nanocomposites were evaluated by Fourier transform infrared spectroscopic, X-ray diffraction, scanning electron microscopic and transmission electron microscopic studies. The nanocomposites were further cured with glycerol based epoxy and fatty acid based poly(amido amine) as the hardener to obtain the respective thermosets. The significant improvements in mechanical properties including tensile strength (13.71–22.33 MPa), elongation at break (128–290%), toughness (15.65–45.18 MJ m⁻³) and scratch hardness (8 to >10 kg) were observed for the thermosetting nanocomposites and the thermogravimetric analysis supports their high thermostability (234–265 °C). Further, the thermosetting nanocomposites were found to be highly biodegradable by Bacillus subtilis and Pseudomonas aeruginosa bacterial strains, hemocompatible with the erythrocytes present in RBCs and showed antioxidant properties. Thus, this nanocomposite could be used as a promising eco-friendly material for different related applications.

A fully bio-based waterborne polyester/cellulose nanofiber nanocomposite was fabricated by an environmentally benign route as a safe and biodegradable material.