Correction: Trans crystallization behavior and strong reinforcement effect of cellulose nanocrystals on reinforced poly(butylene succinate) nanocomposites

Correction for ‘Trans crystallization behavior and strong reinforcement effect of cellulose nanocrystals on reinforced poly(butylene succinate) nanocomposites’ by Taeho Kim et al., RSC Adv., 2018, 8, 15389–15398.

Fig. 1(b) shown in the published article was incorrect and the revised figure and legend are shown below. In addition, a sentence of text “The CNCs consisted of multi-stacked crystals with a layer spacing of approximately 9 Å due to strong hydrogen bonding and cross linkage between nanocrystals” should be removed from the second paragraph of the Results and discussion section.Open in a separate windowFig. 1Morphology of CNCs: (a) TEM, (b) AFM images.The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers.     

Surface modification of cellulose nanocrystals with different acid anhydrides for improved dispersion in poly(butylene succinate)

Hydrophilic cellulose nanocrystals (CNC) are typically poorly dispersed in non-polar polymer matrices and, hence, a method for the surface modification of CNC is developed for improving this dispersion. This method included an esterification reaction with acetic anhydride, butyric anhydride, and caproic anhydride. The particle size distribution (range of sizes: 80–310 nm) of CNC was determined. The SEM-EDAX indicated that (i) the structure of CNC was maintained even after incorporation of the acid anhydride and (ii) the carbon C content of modified-CNC was higher than that of pure CNC. The chemical structure of modified-CNC was identified via FT-IR and ¹³C NMR spectroscopy. The contact angle of CNC and modified-CNC with water and methylene iodide was measured. The surface energy of modified-CNC was lower than that of pure CNC. Thermal-property measurements indicated that the initial decomposition temperature (based on 5 wt%) of the modified-CNC was slightly higher than that of CNC. Poly(butylene succinate) (PBS) composites were obtained by mixing modified-CNC into a PBS matrix via simple melt blending of a double screw. The PBS/modified-CNC composites were investigated via DSC and XRD. Tensile testing indicated that the tensile modulus improved gradually with increasing modified-CNC content, whereas the elongation at fracture decreased.

The hydrophobic CNC was dispersed in PBS to become a high dispersity and mechanical property and thermal stability PBS/modified-CNC composite.     

Temperature dependence of the rigid amorphous fraction of poly(butylene succinate)

In this contribution the temperature evolution of the constrained or rigid amorphous fraction (RAF) of biodegradable and biocompatible poly(butylene succinate) (PBS) was quantified, after detailed thermodynamic characterization by differential scanning calorimetry and X-ray diffraction analysis. At the glass transition temperature, around −40 °C, the rigid amorphous fraction in PBS is about 0.25. It decreases with increasing temperature and becomes zero in proximity of 25 °C. Thus, at room temperature and at the human body temperature, all the amorphous fraction is mobile. This information is important for the development of PBS products for various applications, including biomedical applications, since physical properties of the rigid amorphous fraction, for example mechanical and permeability properties, are different from those of the mobile amorphous fraction.

At room temperature and at the human body temperature, all the amorphous fraction is mobile in poly(butylene succinate).     

Effects on the crystallization behavior and biocompatibility of poly(LLA-ran-PDO-ran-GA) with poly(d-lactide) as nucleating agents

The blends of poly(l-lactide acid-p-dioxanone-glycolide) (PLPG) with poly(d-lactide) (PDLA) (PLPG/PDLA) were prepared by a solution-casting method. The effects of PDLA on the properties of the PLPG were studied. DSC and WAXD results confirmed that PLA stereocomplex (sc-PLA) crystals were formed by blending PLLA segments in PLPG with PDLA, and the melting endotherm for both PLLA and sc-PLA relied on PDLA content. The non-isothermal crystallization results indicated that the crystallization process was remarkably accelerated by the addition of PDLA. Meanwhile, the results of isothermal crystallization indicated that the half-time of crystallization decreased with the increase of PDLA content. Besides, the enzymatic degradation behavior of the samples showed that with the increase of PDLA content, the mass loss gradually decreased. Furthermore, TGA and DTG results indicated that the thermal degradation of the samples was a complex process. Moreover, the biocompatibility of the samples was tested by cell culture and using CCK-8 and live/dead staining. Results showed that the samples possessed lower cytotoxicity. Therefore, the PLPG/PDLA blends are promising candidate materials in biomedical applications.

Sc-PLA crystals in the PLPG/PDLA blends were formed by hydrogen bond between PDLA and PLLA segments, which enhance the crystallization ability of PLLA in the PLPG matrix by decreasing the activation free energy.     

Influence of poly(lactide) stereocomplexes as nucleating agents on the crystallization behavior of poly(lactide)s

The influence of the addition of linear and four-arm poly(lactide) (PLA) stereocomplexes (scPLAs) on the non-isothermal and isothermal crystallization behavior of poly(l-lactide) (PLLA) and poly(d-lactide) (PDLA) from the molten state was investigated. The linear PLAs and four-arm PLA with a similar chain length for each arm were synthesized by ring-opening polymerization. The linear and four-arm scPLAs were then prepared by solution blending and characterized by ¹H-NMR, FTIR, and WAXD analysis. Various mass ratios of the scPLAs were subsequently added to PLLA and PDLA as nucleating agents and specimens were prepared by solution casting. The isothermal and non-isothermal crystallization behavior of the specimens was examined by differential scanning calorimetry and polarized optical microscopy. The SC crystallites effectively promoted the nucleation of the PLAs, thereby increasing the general crystallization rate of the matrix. A 10% content of stereocomplex nucleating agent increased the crystallization rate of PDLA and PLLA by more than 55% and 70%, respectively. Compared with the linear scPLA, the four-arm scPLA more strongly promoted crystallization at higher temperatures. This might be because the greater degree of branching and larger steric hindrance of the four-arm scPLA led to the formation of defective SC crystallites, which was more beneficial for adsorption of the matrix on the crystal surface and permitted the nucleation and growth at higher temperatures. These results demonstrate that scPLAs can potentially be used as nucleating agents to improve the performance and transparency of PLA films.

The influence of the addition of linear and four-arm poly(lactide) stereocomplexes on the crystallization behavior of poly(l-lactide) and poly(d-lactide) from the molten state was investigated.     

The effect of MDI on the structure and mechanical properties of poly(lactic acid) and poly(butylene adipate-co-butylene terephthalate) blends

In this work, poly(lactic acid) and poly(butylene adipate-co-terephthalate) (PLA/PBAT 50/50) were melt-blended in the presence of 4,4′-methylene diphenyl diisocyanate (MDI) which acted as a reactive chain extender. The mechanical properties, phase morphology, thermal behavior and crystalline structure of the blends were investigated. Fourier transform infrared measurements revealed that some remarkable chemical interaction had taken place between the two polymers and MDI. Upon increasing the content of MDI, the blends showed increased tensile strength and elongation at break. With the addition of 0–2 wt% MDI, the impact strength of PLA/PBAT-MDI blends increased from 7.0 kJ m⁻² to 70.0 kJ m⁻². A large shift towards each other in terms of the glass transition temperature was observed by DMA and DSC analysis. SEM micrographs showed not only a reduction in the PBAT phase size but also a significant increase in interfacial adhesion between the PLA and PBAT phases with increasing of MDI. Furthermore, the toughening mechanism of the oriented samples was confirmed by wide-angle X-ray diffraction (WAXD) and small-angle X-ray scattering (SAXS) images; it was possible for the smaller crystallites of blends to form during the course of chain extension.

The FTIR spectrum of the PLA (a) and the PBAT (b) reacted with MDI.     

The effects of different inorganic salts on the structure and properties of ionic liquid plasticized starch/poly(butylene succinate) blends

1-Butyl-3-methylimidazole chloride ([BMIM]Cl) plasticized starch/poly(butylene succinate) (PBS) blends containing inorganic salts with different cations were prepared by a Haake mixer. The compatibility, thermal behaviors including crystallinity, crystallization temperature and melting temperature, thermal stability, and mechanical properties of these blends were systematically investigated by Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and X-ray diffraction (XRD). The results showed that the inorganic salts could interact strongly with [BMIM]Cl plasticized starch/PBS blends to improve their mechanical properties, while the thermal stability of the [BMIM]Cl plasticized starch/PBS blends was simultaneously reduced. The SEM results suggested that the compatibility of [BMIM]Cl plasticized starch and PBS was significantly improved with increasing inorganic salt content. Furthermore, by incorporating inorganic salts, the melting enthalpy (ΔH_m), crystallinity (X_c), and cold crystallization temperature (T_cc) of the blends were decreased.

1-Butyl-3-methylimidazole chloride ([BMIM]Cl) plasticized starch/poly(butylene succinate) (PBS) blends containing inorganic salts with different cations were prepared by a Haake mixer.     

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.     

Spent coffee waste as a renewable source for the production of sustainable poly(butylene succinate) biocomposites from a circular economy perspective

Turning waste products into useable resources is a necessity for the sustainable future of our planet. Such is the case with popular beverage coffee that produces solid waste in the form of spent coffee grounds (SCG). There is an opportunity to use SCG material as a cheap, sustainable, and biodegradable polymer filler that is received as waste from espresso machines. There have been relatively many studies that prove the concept of various agricultural and forestry waste, which can be integrated into modern green materials. Building upon this concept, we have selected a promising polyester poly(butylene succinate) (PBS) as a matrix owing to its bio-based and biodegradable nature. High loadings of SCG from 20 to 60 wt% were tested for optimal composition performance. Tensile, dynamic mechanical, thermal, and structural properties of the composites were examined, while their biodegradation in composting conditions was also analyzed. SCG filler showed different performance from various cellulose fiber-based composites, and properties significantly varied depending on loading. Compared to neat PBS, biodegradation occurred twice as fast for composite materials with high SGC loadings.

Spent coffee waste from espresso machines was used as a renewable filler for the melt processing of sustainable poly(butylene succinate) biocomposites with enhanced exploitation properties.     

Effects of poly(ethylene glycol)-grafted graphene on the electrical properties of poly(lactic acid) nanocomposites

Maleic anhydride was reacted with the armchair edges of graphene nanosheets (GN) via Diels–Alder reaction. Then, polyethylene glycol (PEG) was grafted onto the GN in the presence of anhydride groups through an esterification reaction. The PEG-grafted GN (PEG-g-GN) was characterised via FTIR analysis, thermogravimetric analysis, scanning electron microscopy, Raman spectroscopy and contact angle measurements, proving that PEG was successfully grafted onto the GN surface. The results indicated that PEG-g-GN possessed high electrical conductivity and was dispersed in polylactic acid (PLA). The composites were fabricated by using PEG-g-GN and GN as the conductive agent in the PLA matrix. Owing to the function of PEG molecular chains, PEG-g-GN can be uniformly dispersed in the PLA matrix and improve the tensile strength of composites to 59.46 MPa and conductivity to 9.69 × 10⁻⁴ S cm⁻¹ at a PEG-g-GN content of 1 wt%.

PEG-grafted GN has been synthesized and the effects of modification on the PLA composite conductivity, mechanical properties are investigated.     

Enhanced osteogenesis of mesenchymal stem cells on electrospun cellulose nanocrystals/poly(ε-caprolactone) nanofibers on graphene oxide substrates

Cellulose nanocrystals (CNCs) have received a great amount of attention to the production of micro/nano-platforms for tissue engineering applications. CNCs were extracted from rice husk biomass and characterized by different spectroscopic techniques. The biocompatibility of the extracted CNCs was revealed by the WST-1 assay technique in the presence of human mesenchymal stem cells (hMSCs) after different time intervals. An improvement in the mechanical properties was observed in the fabricated scaffolds (PCL/CNC) compared to PCL scaffolds. Graphene oxide (GO)-coated (PCL/CNC) electrospun scaffolds (GPC) were prepared by the deposition of PCL/CNC composite nanofibers on the surface of GO for tissue engineering. Notably, better cell proliferation and differentiation were observed in the presence of the fabricated scaffolds. This enhancement of the properties of the fabricated scaffolds was due to the presence of conductive GO moieties which facilitated the cellular response. Therefore, the fabricated materials have the potential to be used as a biomaterial for enhanced cell proliferation and osteogenic differentiation.

Cellulose nanocrystals (CNCs) have received a great amount of attention to the production of micro/nano-platforms for tissue engineering applications.     

Rheological behavior,crystallization properties,and foaming performance of chain-extended poly (lactic acid) by functionalized epoxy

The inherently linear poly (lactic acid) suffers unsatisfying foaming behavior due to its low melt strength and poor crystallization properties. To overcome this drawback, a random terpolymer of ethylene, acrylic ester and glycidyl methacrylate (EGMA) was employed to improve the rheological behavior, crystallization properties, and foaming performance of poly (lactic acid) (PLA) through a chain extension reaction. The branched/micro-crosslinked structure formed by the chain extension reaction between EGMA and PLA effectively improved the dynamic rheological properties of PLA. As the content of EGMA increased from 0 wt% to 20 wt%, the crystal nucleation and crystal growth rate of various PLA samples have been significantly accelerated, resulting in a larger number and smaller size of spherulites, and the crystallinity of various PLA samples increased from 7.9% to 38.54%. The cell size of various PLA foams decreased from 53.5 to 22.0 μm and the cell density increased from 3.5 × 10⁶ cells per cm³ to 2.5 × 10⁷ cells per cm³, meanwhile, the cellular morphology of PLA foam was obviously improved. Moreover, the actual weight loss of PLA foams reached 26.1%, which is higher than the theoretical weight loss.

The branched/micro-crosslinked structure formed by chain extension reaction between EGMA and PLA improved the rheological behavior and crystallization properties of PLA, which ameliorated the foaming performance of various PLA samples.     

Introduction of stereocomplex crystallites of PLA for the solid and microcellular poly(lactide)/poly(butylene adipate-co-terephthalate) blends

Solid and microcellular poly(l-lactide)/poly(butylene adipate-co-terephthalate) (PLLA/PBAT) blends with or without poly(d-lactide) (PDLA) were prepared via melt blending and batch foaming process with supercritical carbon dioxide, respectively. The introduction of PDLA on the rheological properties, crystallization behavior and dynamic mechanical properties of the PLLA matrix were investigated. The formed PLA stereocomplex between PLLA and PDLA enhanced the storage modulus and complex viscosity of PLLA/PBAT blends efficiently. Interestingly, the addition of 5 wt% or 10 wt% PDLA in the PLLA/PBAT blends was unfavorable for the PLLA crystallization behavior. The potential reason can be sc-PLA crystallites acting as the physical crosslinking points, which constrained the molecular mobility of the PLLA matrix and even blocked the nucleating effect of PBAT domains. Both the enhanced melt strength and decreased crystallinity of the PLLA matrix are favorable for the cell nucleation and growth and the gas adsorption, respectively. The designed partially foaming of PLLA/PBAT with or without PDLA was carried out to investigate the foaming mechanism. The final cell morphology of PLLA/PBAT foams exhibited typical open-cell structure mainly attributed to the soft immiscible PBAT phase as separated domains. With further addition of PDLA in the PLLA/PBAT blends, the microcellular morphology exhibited decreased average cell size and increased cell density. The sc-PLA crystallites networks in the PLLA matrix acted as cell nucleating agents, which meanwhile resisted the force of cell growth and then prevented the cell collapse.

The introduced PLA stereocomplex could enhance the melting strength of PLLA/PBAT blends efficiently. The microcellular morphology of PLLA/PBAT foams with PDLA exhibited decreased average cell size and increased cell density.     

Melting centrifugally spun ultrafine poly butylene adipate-co-terephthalate (PBAT) fiber and hydrophilic modification

This paper demonstrates that melt centrifugal spinning could be used to effectively fabricate degradable poly (butylene adipate-co-terephthalate) (PBAT) fibers with uniform fiber diameter. The hydrophobic PBAT fibers were modified into hydrophilic fibers using the hyperbranched polyesters (HBP) with three-dimensional molecular chain structures and a large number of functional groups at the chain ends. The structures and properties of the obtained fibers were characterized with SEM, XRD, DSC, contact angle, and tensile strength analyses. Results indicate that fibers with uniform diameters can be conveniently fabricated by designing a spinneret. The obtained fibers showed no apparent change in crystallization compared to PBAT pellets, while the thermal stability and mechanical properties of PBAT/HBP fibers were dependent on the HBP ratio in fibers. More importantly, the obtained fibers gradually changed from hydrophobic to super-hydrophilic with increasing HBP content in fibers up to 30%. The modified hydrophilic PBAT/HBP presents a greatly significant potential for application in biomedical fields.

The PBAT fibers were fabricated by using our own designed melting centrifugal spinning setup, and followed by improving the fiber wettability with hyperbranched polyesters (HBP).     

Blends of poly(butylene adipate-co-terephthalate) (PBAT) and stereocomplex polylactide with improved rheological and mechanical properties

Biodegradable blends of poly(butylene adipate-co-terephthalate) (PBAT) and stereocomplex polylactide (sc-PLA) were prepared herein via a melt blending method at various sc-PLA loadings. Wide-angle X-ray diffraction and differential scanning calorimetry results verified that complete stereocomplex polylactide crystallites in the PBAT could be achieved. Scanning electron microscopy observation indicated that sc-PLA was dispersed in the PBAT matrix as spherical particles; the dispersed size of the sc-PLA did not display a pronounced increase once the content of sc-crystallites reached a critical gel point. As solid fillers, sc-PLA could reinforce the PBAT matrix in a relatively wider temperature region and accelerate the non-isothermal crystallization of PBAT. The properties of PBAT were greatly improved after blending with sc-PLA, particularly when a percolation network structure of spherical filler had formed in the blends. In addition, all the blends showed higher yield stresses and moduli than those of the neat PBAT but exhibited reduction in elongations in tensile mechanical tests. These results would be interesting to the industrial polymer materials community, and may be of significant use and importance for the wider practical application of PBAT.

Schematic representation of formed solid sc-PLA in the PBAT melting during melt processing.     

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.     

Structural design of polyurethane/poly(butylene succinate)/polycaprolactone compounds via a multilayer-assembled strategy: achieving tunable triple-shape memory performances

Shape memory polymeric materials composed of thermoplastic polyurethane (TPU), poly(butylene succinate) (PBS), and polycaprolactone (PCL) were prepared through layer-multiplying co-extrusion of blends. With the two well-separated melting transitions respectively from PCL and PBS, the multicomponent compounds realized triple-shape memory effect. By tailoring the structure of the individual layer, the multilayer systems with designable phase morphology were fabricated, which developed tunable shape memory performances. Particularly, the multi-continuous structure containing alternating layers of TPU and the co-continuous PBS/PCL blend presented the optimal shape fixity and recovery ratios, whose minimum value can reach 84%. It was revealed that the high phase continuity along the deformation direction and the strong interfacial shearing effect promoted the ability to fix the temporary shapes and recover them to the permanent state. In addition, the multi-continuous structure maximized the synergy of the components in mechanical properties, resulting in an excellent balance of tensile strength and ductility. The present strategy for morphology control of multicomponent structures provides a promising method to fabricate outstanding triple-shape memory polymers with optimal mechanical properties.

Novel strategy for structural design of multicomponent systems via layer-multiplying co-extrusion: achieving tunable triple-shape memory performances of polyurethane/poly(butylene succinate)/polycaprolactone compounds.     

Morphology and crystallization behavior of poly(3-hydroxybutyrate-co-3-hydroxyvalerate)/polyhedral oligomeric silsesquioxane hybrids

Poly(3-hydroxybutyrate-co-3-hydroxyvalerate)/polyhedral oligomeric silsesquioxane (PHBV/POSS) hybrids with different POSS contents of 5, 10, 15, 20, 25 and 30 wt% were prepared by solution casting. The composition, crystallization and melting behavior, crystal structure, spherulite morphology, surface morphology, and tensile properties of PHBV/POSS hybrids were characterized by EDS, DSC, FTIR, XRD, HSPOM, AFM and a tensile testing machine. The results showed that POSS was well dispersed in the PHBV matrix. PHBV and POSS crystals coexisted in the hybrids. The crystallinity of pure PHBV was larger than that of PHBV/POSS hybrids. POSS restricted the crystallization of PHBV in PHBV/POSS hybrids. With the increase of POSS content, the crystallinity of PHBV/POSS hybrids decreased from 56.8 (pure PHBV) to 33.6% (PHBV/POSS hybrid with 30 wt%). However, the introduction of POSS did not affect the spherulite morphology of PHBV. The Avrami equation was used to describe the isothermal crystallization kinetics of PHBV/POSS hybrids. The results showed that as the crystallization temperature increased, the crystallization rate became slow. In addition, POSS can improve the tensile properties of PHBV.

Polyhedral oligomeric silsesquioxane (POSS) changed the crystallization behavior of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and improved the mechanical properties of PHBV.