Polylactide (PLA), a biobased polymer, has a short elongation at break and low impact strength, which restricted its broad application as a commodity polymer. In this paper, super-tough polylactide/crosslinked polyurethane (PLA/CPU) binary blends with CPU dispersed in the PLA matrix were prepared by reactive blending of PLA with poly(ethylene glycol) (PEG) and polymeric methylene diphenylene diisocyanate (PMDI). The in situ polymerization of PEG and PMDI in the PLA matrix formed CPU, and the interfacial compatibilization between PLA and CPU phases occurred by the reaction of NCO groups with terminal hydroxyl groups of PLA, which was confirmed by Fourier transform infrared spectroscopy. The results of a tensile test and a notched Izod impact test suggest that the elongation at break and impact strength were increased to more than 20 and 30 times those of neat PLA, respectively. The effects of PEG molecular weight (namely soft segment length of CPU) and CPU content on the phase morphology and impact strength of PLA/CPU blends were investigated systematically. The optimum CPU particle size for high impact toughness was identified to be 0.7–1.0 μm when the soft segment length and the content of CPU were in the ranges of 1000–2000 g mol−1 and 20–30 wt%, respectively. The compatibility between the dispersed CPU and PLA matrix was studied by dynamic mechanical analysis through the change in glass transition temperatures of PLA and CPU components. The results suggest that the compatibility increased with increasing soft segment length and content of CPU, which was mainly due to the increased plasticization effect. With improved toughness, the PLA/CPU blends could be used as substitutes for some traditional petroleum-based polymers.

To obtain an excellent comprehensive performance of poly(ethylene succinate) (PES), we have synthesized a series of poly(ethylene succinate) (PES) urethane ionenes (PESUIs) with various content of urethane ionic group by the chain extension reaction of dihydroxyl-terminated poly(ethylene succinate) and diethanolamine hydrochloride with hexamethylene diisocyanate as a chain extender, and we systematically investigated the composition dependence of the physico-chemical properties of PESUI through a series of characteristic techniques. The results of thermal and crystallization behaviors suggest that the incorporation of urethane ionic group slightly affects the glass transition temperature, melting temperature, and thermal stability, and significantly accelerates the crystallization rate of PES without changing the crystallization mechanism. The fastest crystallization rate was reached with the incorporation of 4 mol% urethane ionic groups. Spherulitic morphology observation indicates that nucleation density significantly increased, while spherulitic growth rate gradually decreased with increase in urethane ionic group content. Both complex viscosity and storage modulus initially increased and then decreased with increase in urethane ionic group content, and their maximum values were observed for the sample with 4 mol% of urethane ionic group. Mechanical properties slightly varied with urethane ionic group content.

Super-tough poly(L-lactide)/crosslinked polyurethane (PLLA/CPU) blends with a CPU phase dispersed in the PLLA matrix were prepared by reactive blending of PLLA with poly(ethylene glycol) (PEG), glycerol, and 4,4′-methylenediphenyl diisocyanate (MDI). The gel fraction increased while the swelling ratio decreased with increasing glycerol content. FT-IR analysis suggests that interfacial compatibilization between PLLA and CPU occurred via reaction between the hydroxyl group of PLLA and the isocyanate group of MDI. The elongation at break and notched impact strength of PLLA/CPU blends were increased by up to 38 and 21 times those of neat PLLA. The morphology of PLLA/CPU blends plays an important role in notched impact strength and can be controlled by adjusting the content of glycerol. The size of the dispersed CPU phase increased gradually while the notched impact strength increased first and then decreased with increasing glycerol content. Therefore, the notched impact strength can be easily tailored by the content of glycerol of CPU. The optimum size for high impact strength was found to be ∼0.7 μm, which was obtained for the blends with glycerol content in the range of 5 to 10 wt% on the basis of PEG weight. In addition, the effect of glycerol content on the compatibility and rheological properties of PLLA/CPU blends was also investigated.

Biodegradable thermoplastic poly(ester urethane) (PEU) elastomers containing poly(diethylene glycol succinate) (PDGS) and poly(butylene succinate) (PBS) were synthesized by chain extension of dihydroxyl terminated PDGS and PBS precursors with 4,4′-methylenediphenyl diisocyanate as a chain extender. The structure, molecular weight, and physical properties of the PEUs were investigated by 1H NMR, GPC, DSC, WAXD, DMA, and tensile tests. The results suggest that the compositions affect the physical properties more significantly than the segment lengths. The PEU containing 28.2 wt % PBS showed the best mechanical properties with ultimate strength and elongation at break of 41 MPa and 1503%, respectively. Both the storage modulus and Young’s modulus increased significantly with increasing PBS segment content, which was reasonably ascribed to the increasing degree of crystallinity. The hysteresis value increased with PBS segment content while it decreased slightly with lengths of both hard and soft segments, which were also attributed to the different crystallization behaviors of the PEUs.

A fully biobased and supertough thermoplastic vulcanizate (TPV) consisting of polylactide (PLA) and a biobased vulcanized unsaturated aliphatic polyester elastomer (UPE) was fabricated via peroxide-induced dynamic vulcanization. Interfacial compatibilization between PLA and UPE took place during dynamic vulcanization, which was confirmed by gel measurement and NMR analysis. After vulcanization, the TPV exhibited a quasi cocontinuous morphology with vulcanized UPE compactly dispersed in PLA matrix, which was different from the pristine PLA/UPE blend, exhibiting typically phase-separated morphology with unvulcanized UPE droplets discretely dispersed in matrix. The TPV showed significantly improved tensile and impact toughness with values up to about 99.3 MJ/m3 and 586.6 J/m, respectively, compared to those of 3.2 MJ/m3 and 16.8 J/m for neat PLA, respectively. The toughening mechanisms under tensile and impact tests were investigated and deduced as massive shear yielding of the PLA matrix triggered by internal cavitation of VUPE. The fully biobased supertough PLA vulcanizate could serve as a promising alternative to traditional commodity plastics.

Poly(butylene succinate-co-diethylene glycol succinate) (P(BS-co-DEGS)) random copolymer was synthesized and characterized in a previous paper [ Ind. Eng. Chem. Res. 2012, 51, 12258−12265]. In this paper, we focus on the isothermal crystallization behaviors of P(BS-co-DEGS). The isothermal crystallization kinetics, spherulitic morphology, and growth kinetics of P(BS-co-DEGS) were investigated by differential scanning calorimetry and polarized optical microscopy and compared with those of neat poly(butylene succinate) (PBS). The results suggest that the crystallization rate of P(BS-co-DEGS) was much slower than that of neat PBS and decreased with increase of DEGS content, while the crystallization mechanism remain unchanged. P(BS-co-DEGS) showed banded morphology, and the band spacing decreased with increase of DEGS content at a given supercooling. The spherulitic growth rate of P(BS-co-DEGS) decreased with increase in DEGS content. A transition from crystallization regime II to crystallization regime III occurred for all samples, and the transition shifted to lower temperatures with increase in DEGS content.

A series of poly(butylene terephthalate)-poly(butylene succinate) (PBT-PBS) copolyesters were synthesized by the melt chain-extension reaction of dihydroxyl terminated PBT (HO-PBT-OH) and PBS (HO-PBS-OH) prepolymers using toluene-2,4-diisoyanate (TDI) as a chain extender. Transesterification between PBT and PBS during the chain-extension reaction has been investigated in detail. Both random and block PBT-PBS copolymers can be synthesized by changing the prepolymers' molecular weights at a given reaction time and temperature. The chemical structures and sequence distributions of the copolyesters were analyzed by proton nuclear magnetic resonance (1H-NMR) spectroscopy. The thermal transition behaviours of copolyesters with different sequence distribution were characterized by differential scanning calorimeter (DSC). The number-average molecular weight (Mn) of HO-PBT-OH played a dominant role in the sequence distribution of the resulting copolyesters. The degree of randomness of the copolymer was around 1 when Mn of HO-PBT-OH was 5000 g mol−1 regardless of that of HO-PBS-OH, it decreased to less than 1 when Mn of HO-PBT-OH was more than 10000 g mol−1, and it gradually decreased with the increase in Mn of HO-PBS-OH. The copolyesters with different degrees of randomness showed different thermal transition and crystallization behaviours.

Novel urethane ionic groups were incorporated into biodegradable poly(ethylene succinate) (PES) by chain extension reaction of PES diol (HO–PES–OH) and diethanolamine hydrochloride (DEAH) using hexamethylene diisocyanate (HDI) as a chain extender. The synthesized polymer was a novel segmented poly(ester urethane) ionomer (PESI) in which the soft segments were formed by reaction of HO–PES–OH with HDI and the hard segments that contained ionic groups were derived from reaction of DEAH with HDI. The crystallization rate of PESI was dramatically accelerated when 3 mol % urethane ionic groups were incorporated. However, the crystallization mechanism did not change. The significant acceleration in crystallization rate was attributed to the improved nucleation efficiency by incorporation of the urethane ionic group, because PESI showed significantly enhanced nucleation density but slightly slowed spherurlitic growth rate in comparison with PES which was synthesized by chain extension reaction of HO–PES–OH with HDI. The increased nucleation efficiency was ascribed to the aggregation of hard segments of PESI induced by the ionic interactions.

A series of biodegradable double crystalline poly(ethylene succinate)-b-poly(butylene succinate) (PES-b-PBS) multiblock copolymers with various PES and PBS block lengths were successfully synthesized by chain-extension reaction of dihydroxylated poly(ethylene succinate) (HO-PES-OH) and poly(butylene succinate) (HO-PBS-OH) using 1,6-hexamethylene diisocyanate (HDI) as a chain-extender. The compositions and structures were characterized by proton nuclear magnetic resonance spectroscopy (1H NMR). The miscibility of amorphous phase and crystallization behaviors of the two blocks were investigated by standard differential scanning calorimetry (DSC), temperature modulated DSC (TMDSC), polarized light optical microscopy (POM), and wide-angle X-ray diffraction (WAXD). When the block length of PBS and PES were less than 4710 g mol−1, the amorphous phases of the two blocks were miscible. As the block length increased to more than 5430 g mol−1, the amorphous phases of the two blocks changed to be partially miscible, and the miscibility decreased with further increasing the block lengths. The crystallizability of both PBS and PES blocks increased with an increase in size of their blocks. POM observation showed that the copolymers displayed banded spherulitic morphologies, and the crystallization of PES happened in confined space after crystallization of PBS blocks. WAXD analysis suggested that the crystals of the copolymers were composed of crystals of both PES and PBS blocks.

Biodegradable multiblock copolymers poly(butylene succinate-b-poly(ethylene glycol) succinate) (P(BS-b-PEGS)) were prepared by direct polycondensation. The thermal and crystallization behavior of P(BS-b-PEGS) with weight fraction of PEGS component from 6 to 26 wt % were comparatively investigated with those of neat poly(butylene succinate) (PBS) by wide-angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), and polarized optical microscopy (POM). P(BS-b-PEGS) showed the same crystal structure as neat PBS, but the degree of crystallinity of copolymers was lower than that of neat PBS and decreased with increase in PEGS content. The isothermal crystallization kinetics study suggests that incorporation of PEGS component did not change the crystallization mechanism, but reduced the crystallization rate of the samples, and that increasing crystallization temperature decreased the crystallization rate of all the samples. The spherulites of neat PBS and P(BS-b-PEGS) showed banded morphologies. The spherulitic growth rate of the samples also decreased with increase of PEGS content and crystallization temperature. A transition from crystallization regime II to III occurred for all the samples, and the transition shifted to lower temperatures with increase in PEGS content.

Diethylene glycol was incorporated into poly(butylene succinate) (PBS) to form biodegradable poly(butylene succinate-co-diethylene glycol succinate) (P(BS-co-DEGS)) copolymer through a two-step procedure of esterification and polycondensation from succinic acid with 1,4-butanediol and diethylene glycol. The chemical structure of P(BS-co-DEGS) was confirmed by proton nuclear magnetic resonance spectroscopy (1H NMR). The effect of incorporated DEGS content on the molecular weight, thermal properties, crystallization behaviors, and hydrophilicity of the copolymers was investigated by gel permeation chromatography (GPC), differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), thermogravimetry analysis (TGA), and water contact angle. The mechanical properties and hydrolytic degradation behaviors of P(BS-co-DEGS) were also studied. The results suggest that with an increase of DEGS content, the crystallizability and degree of crystallinity of the copolymers decreased, while the crystal structure kept unchanged; the thermal stability of the copolymers hardly changed, while the hydrophilicity and hydrolytic degradation rate increased. The tensile modulus decreased, but the elongation at break increased and the tensile strength increased first and then decreased with an increase of DEGS.

Poly(l-lactic acid) (PLLA) is regarded as one of the most promising biobased and biodegradable polymers. However, its application was restricted due to the brittle nature. In the present study, PLLA was blended with a novel biodegradable flexible multiblock copolymer, poly(butylene succinate-b-ethylene succinate) (PBES) to produce new biodegradable materials. PLLA/PBES blends with different composition were prepared by solution blending and casting method with chloroform as a mutual solvent. Miscibility, crystallization behavior, and mechanical properties of the blends were investigated by differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), and tensile tests. The results indicated that PLLA and PBES showed limited miscibility in the amorphous phase. The crystallization rate of PLLA was accelerated with the increase of PBES in the blends while the crystallization mechanism did not change. The results of tensile tests suggest that the blends showed longer elongation at break than neat PLLA. The elongation at break of PLLA was obtained to be 10%, and those of PLLA/PBES 80/20, 60/40, 40/60 and 20/80 were 29, 110, 442, and 455%, respectively.Highlights► The blend of PLLA and PBES showed limited miscibility. ► The crystallization rate of PLLA was accelerated by blending with PBES. ► The crystal structures of PLLA and PBES did not change.

Biodegradable blend of poly(butylene succinate) (PBS) and poly(ethylene succinate) (PES) was prepared by solution blending and casting method with chloroform as a mutual solvent. Miscibility of the blends was investigated by differential scanning calorimetry (DSC). The results indicated that PBS and PES were partially miscible. Crystallization kinetics, crystalline morphology and crystal structure of the blends were studied by DSC, polarized optical microscope (POM), and wide-angle X-ray diffraction (WAXD), respectively. Nonisothermal and isothermal crystallization kinetics suggested that the crystallizability of PBS in the blends decreased first and then increased with increase in PES content, and that of PES increased steadily with increase in PBS content. POM observation illustrated that the rich component formed a continuous phase and the other formed a dispersed phase. The results of WAXD indicated that the crystal structures of PBS and PES were almost unchanged before and after blending, since the positions of characteristic diffraction peaks of both components remain almost unchanged.Graphical abstractCrystallization rate of PBS in the blends decreased first and then increased with increase in PES content, and that of PES increased steadily with increase in PBS content. The rich component formed a continuous phase and the other formed a dispersed phase of the blend. Crystal structures of PBS and PES were almost unchanged after blending with each other.Highlights► PBS/PES blend systems are partially miscible. ► Blending did not change the crystallization mechanisms of PBS and PES not affects the crystallization rates. ► The rich component formed the continuous phase while the poor component formed the dispersed phase of the blends. ► Crystal structures of PBS and PES were almost unchanged after blending with each other.

Chitin is the second most abundant semicrystalline polysaccharide. Like cellulose, the amorphous domains of chitin can also be removed under certain conditions such as acidolysis to give rise to crystallites in nanoscale, which are the so-called chitin nanocrystals or chitin whiskers (CHWs). CHW together with other organic nanoparticles such as cellulose whisker (CW) and starch nanocrystal show many advantages over traditional inorganic nanoparticles such as easy availability, nontoxicity, biodegradability, low density, and easy modification. They have been widely used as substitutes for inorganic nanoparticles in reinforcing polymer nanocomposites. The research and development of CHW related areas are much slower than those of CW. However, CHWs are still of strategic importance in the resource scarcity periods because of their abundant availability and special properties. During the past decade, increasing studies have been done on preparation of CHWs and their application in reinforcing polymer nanocomposites. Some other applications such as being used as feedstock to prepare chitosan nanoscaffolds have also been investigated. This Article is to review the recent development on CHW related studies.

Poly(butylene succinate) (PBS) was blended with thermoplastic starch (TPS) to improve the mechanical properties and reduce water absorption of the resulting starch-based plastics. In order to enhance the miscibility between TPS and PBS, reactive PBS (RPBS) with terminal NCO group was synthesized first and then blended with TPS. The mechanical properties of the TPS were greatly improved after blending with RPBS, the tensile strength was increased to 10 times more than TPS even only 10 wt% RPBS was introduced. The water absorption of the blend was significantly reduced with increasing RPBS content. SEM results suggest RPBS to be uniformly distributed in the TPS matrix, and the size of the RPBS phase was decreased with reducing intrinsic viscosity of RPBS. The study of contact angle indicated that the hydrophobicity of the blend was largely enhanced toward TPS. With improved mechanical properties and reduced water absorption, the materials could find more extensive applications.

Miscibility and crystallization behaviors of poly(butylenes succinate) (PBS) and poly(l-lactic acid) (PLLA) segments in their multiblock copoly(ester urethane) were investigated by differential scanning calorimetry (DSC), polarized optical microscopy (POM), and wide-angle X-ray diffraction (WAXD). The single glass transition and depressed crystallization temperatures of PEUs with different compositions suggest that PBS and PLLA segments are miscible in amorphous phase of PEUs. Nonisothermal crystallization kinetics of PEUs was studied by Avrami and Mo methods; both results suggest that the crystallization rates of PEUs decreased with increasing weight fraction of PLLA segments. POM results indicate that banded spherulites were formed for PEUs when PLLA segments were introduced, and the band spacing increased with weight fraction of PLLA segments. The investigation of WAXD demonstrated the crystal structure of PEUs was the same as that of PBS, suggesting the crystallization of PEUs arose from PBS segments, and PLLA segments were unable to crystallize in PEUs.

Poly (l-lactic acid) (PLLA) is a biobased polymer, and poly(trimethylene terephthalate) (PTT) is a semibiobased polymer. However, PLLA is biodegradable, and PTT is not. In this paper, their copolymers (PTHT−PLLA) are synthesized via chain-extension reaction of hydroxyl terminated poly(trimethylene-co-hexamethylene terephthalate) (PTHT−OH) and hydroxyl terminated poly(l-lactic acid) (PLLA−OH) using toluene-2,4-diisocyanate (TDI) as a chain extender. The structures and molecular weights of PTHT−OH, PLLA−OH, and PTHT−PLLA were characterized by Fourier transform infrared (FTIR) spectroscopy, proton nuclear magnetic resonance (1H NMR), and gel permeation chromatography (GPC). The thermal, crystalline, and mechanical properties of PTHT−PLLA were further studied by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), and tensile testing. The resulting PTHT−PLLA copolyesters went through a two-stage thermal decomposition behavior and showed two glass transition temperatures. The tensile testing results showed that PTHT−PLLA copolyesters have excellent flexibility with a strain of more than 300%, which is much higher than that of PLLA. The copolyesters are expected to have a better biodegradability than PTT.

Miscibility and crystallization behaviors of poly(ethylene succinate)/poly(p-dioxanone) (PES/PPDO) blends were investigated by differential scanning calorimetry (DSC), polarized optical microscopy (POM), and wide-angle X-ray diffraction (WAXD). PES/PPDO blends are completely miscible as proved by the single grass transition temperature (Tg) dependence of composition and decreasing crystallization temperature of the blends in comparison with the respective component. POM observation suggests that simultaneous crystallization of PES and PPDO components in the blends took place, spherulites of one component can crystallize inside the spherulites of the other component, and the unique interpenetrated crystalline morphology has been formed for the blends in the full composition range. Isothermal crystallization kinetics of the blends was studied by DSC and the data were analyzed by the Avrami equation. The results suggest that the crystallization mechanisms of the blends were unchanged but the overall crystallization rates were slowed down compared with neat PES and neat PPDO. WAXD results indicate that the crystal structures of PES and PPDO did not change in the blends.