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Highlights: [•] Binary ionic liquid system was built as a powerful solvent for dissolving chitosan. [•] Regenerated chitosan fibers were prepared by dry-wet spinning technique especially. [•] Tensile strength of the prepared chitosan fibers reaches up to 2.1cN/dtex [•] This fiber is stronger than existing fibers prepared from acetic acid solution. [ABSTRACT FROM AUTHOR]

Abstract: In this study, glycine hydrochloride (Gly·HCl) is confirmed to be a promising solvent for dissolving native chitosan and preparing regenerated chitosan membrane. As compared with the chitosan membrane prepared from traditional acetic acid, the membrane prepared from Gly·HCl by dry technique shows excellent tensile strength and initial modulus, i.e. 103.8MPa and 3.2GPa, respectively, which is superior to any chitosan membrane and most chitosan blend membranes reported in literatures. Besides, scanning electron microscopy (SEM), wide-angle X-ray diffraction (WAXD) and Fourier transform infrared spectroscopy (FT-IR) were used to visualize the difference between the two kind of regenerated chitosan membranes. The SEM results show that the membrane prepared from Gly·HCl by dry technique presents a novel structure, which ensures its high tenacity. Furthermore, the chitosan microporous membranes were also prepared using PEG as porogen. [Copyright &y& Elsevier]

Abstract: A binary system consisting of acidic ionic liquid glycine hydrochloride (Gly·HCl) and neutral ionic liquid 1-butyl-3-methylimidazolium chloride ([Bmim]Cl) is proposed to be cosolvent for chitosan and cellulose, the spinning solution of chitosan/cellulose can be prepared in one step. The regenerated chitosan/cellulose composite fiber with 9.4wt.% chitosan was prepared through dry–wet spinning process. SEM shows that the chitosan is scattered on the surface and interior of the composite fiber. WAXD shows that the degree crystallization of the composite fibers is far less than that of raw materials. The result of elemental analysis (EA) indicates that there is little weight loss of chitosan during the spinning process. Moreover, the prepared composite fiber presents good thermal stability, i.e. its T onset is 305.1°C, and excellent mechanical property, i.e. its tensile strength is 4.63cN/dtex. All the results show that Gly·HCl/[Bmim]Cl binary system is a promising solvent for the preparation of chitosan/cellulose composite fiber. [Copyright &y& Elsevier]

Poly (lactic acid), a promising biodegradable polymer, is restricted by poor heat resistance, which is determined by the crystallization. It is important to expound the relationship between crystal structure and thermal, mechanical performance. Several PLA specimens were prepared by fully crystallized at different temperature (100 °C, 110 °C, 115 °C, 120 °C, and 130 °C) from melt state. The morphology, crystallization behaviors, thermal and mechanical properties were evaluated by polarizing optical microscope (POM), wide-angle X-ray diffraction (WAXD), differential scanning calorimeter (DSC), dynamic mechanical analysis (DMA), and Vicat softening temperature (VST), respectively. It was found that the PLA crystal shows the characterization of spherulite and many nuclei are generated at low temperature (100 °C and 110 °C). The nuclei gradually decrease and the spherulites grow as the crystallization temperature increases. Compared with the amorphous PLA specimens, the tensile strength of crystallized samples gradually decreases from 29.4 MPa to 25.8 MPa and the VST is improved from 51.6 °C to 64.9 °C. It confirms that the crystallization is an effective way to enhance the heat resistance. However, when the temperature reaches 130 °C, the crystalline and amorphous region aggregate, forming the distinct two phases, which leads to a decrease in VST (53.2 °C). Meanwhile, the spherulites become irregular, larger, and imperfect at high temperature, resulting in the further deterioration of mechanical performance. In addition, the molecular dynamics was further used to simulate the structural evolution during the crystallization and reveals the mechanism behind the relationship. Image 1 • The relationship between PLA crystal structure, morphology, and its thermal, mechanical performance is investigated. • Molecular dynamics was used to visualize and reveal the mechanism behind the relationship. • Excessive crystallization temperature forms the imperfect crystal and leads to the decrease of performances. [ABSTRACT FROM AUTHOR]

• Industrial-scale continuous PAN fibers to carbon fibers were prepared. • Stabilization behaviors of PAN fibers under different atmosphere are investigated. • Graphite layers are associated with cross-linking structures of PAN oxidative fibers. • Low-oxygen has negative influence on tensile modulus of carbon fibers. Understanding and regulating the oxidative stabilization behavior of polyacrylonitrile (PAN) precursor fibers are critical subjects of high-performance carbon fiber production technologies. Here, we performed continuous stabilization and carbonization of PAN fibers at industrial carbon fiber production lines in different locales (different oxygen partial pressure in atmosphere), and investigated the microstructural evolution of the fibers with a systematically analysis at different stages. Influence of oxygen partial pressure in oxidative stabilization atmosphere on tensile modulus of the obtained carbon fibers was obvious. Oxygen diffused into PAN fibers during oxidative stabilization, more homogeneous and crosslinked structures generated under higher oxygen partial pressure atmosphere, and gave the stabilized fibers lower skin-core ratio. The graphite layers gradually generated in the subsequent carbonization stages, and the gathered graphite layers transformed into graphite microcrystalline, the wide-angle x-ray diffraction (WAXD) demonstrated that higher oxygen partial pressure conditions contributed to the generation of higher crystallite preferred orientation and bigger crystallite size, Raman spectroscopy also confirmed the obtained carbon fibers with higher oxygen partial pressure conditions possessed more ordered graphite structures. Thus, relatively higher oxygen partial pressure in air gave the stabilized fibers more crosslinked structures, and contributed to the formation of high-performance carbon fibers. [ABSTRACT FROM AUTHOR]

To reduce carbon dioxide emissions, the development of sustainable bio-based polyamides with performance advantages has become the focus of widespread attention. 1,5-Pentanediamine (PDA) is a renewable monomer produced by decarboxylation of lysine, which can be used as a sustainable alternative to traditional petroleum-based diamines and play a crucial role in the synthesis of bio-based polyamides. Herein, a series of bio-based aliphatic polyamides (PA5X) synthesized from PDA and aliphatic diacids with different methylene groups were successfully prepared via melt polycondensation. Their chemical structures were characterized, and the effects of diacid chain length on crystallization behavior, memory effect, and thermo-mechanical properties were emphatically investigated. The results show that the melting and crystallization temperatures of PA5X decrease with increasing diacid chain length. Meanwhile, the PA5X exhibits high thermal stability, with T d,5 % exceeding 380 °C. Unlike the even-even polyamide, the crystalline form of PA5X is γ -form, and the crystallization behavior and spherulitic morphology change significantly with diacid chain length, which is attributed to the complex entanglement effects. More particularly, the correlation between the diacid chain length and the melt memory effect is explored. PA56 with shorter methylene groups exhibits stronger melt memory effects due to the memory effects being directly affected by segmental chain interactions. Moreover, PA5X exhibits comparable or even superior tensile strength and ductility compared with hexamethylenediamine-based polyamide (PA6X) and reported fully bio-based PA11. This work provides a comprehensive investigation into the structure-property relationship of the bio-based polyamide PA5X, demonstrating great potential for application in high-performance eco-friendly materials. [Display omitted] • Bio-based polyamides were synthesized based on renewable 1,5-Pentanediamine (PDA) and various aliphatic diacids. • The physical properties of polyamides can be effectively modulated by altering the diacid chain length. • Compared to even-even polyamides, these polyamides exhibit comparable or even superior thermal and mechanical properties. [ABSTRACT FROM AUTHOR]

With bio-renewable and environmentally friendly nature, biobased polyamides have emerged as attractive alternatives to traditional petroleum-derived polymers. However, poor thermal and mechanical performance, high costs, and limited scalability significantly hinder their practical applications. Herein, a series of biobased copolyamides PA6/PA56 (CoPAs) were successfully synthesized from caprolactam, adipic acid, and the lysine-derived biobased monomers 1,5-pentanediamine. The copolyamides were characterized by gel permeation chromatography (GPC), nuclear magnetic resonance spectroscopy (1H NMR), wide-angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), thermogravimetric analysis (TGA), rheological analysis, mechanical testing, and scanning electron microscopy (SEM). The result shows the α to γ transition in the crystalline form of the copolyamides with comonomer loading. The melting temperature, crystallization temperature, and crystallinity gradually decrease due to the introduction of the odd-even structure, causing deviation in amide positions and reducing hydrogen bond formation between molecular chains. Furthermore, variable-temperature infrared (VTIR) analysis and density functional theory (DFT) calculations further confirm a decrease in intermolecular forces. Importantly, the mobility of the molecular chains in the amorphous region is significantly improved, endowing the copolyamides with sufficient degrees of freedom to cope with externally applied strains. Moreover, significant entanglement facilitates effective stress transfer during stretching. As a result, the synthesized copolyamides achieve a high strength of 51 MPa and a remarkable toughness of 199 MJ/m3, without sacrificing thermal stability and processing properties. These biobased CoPAs show great potential and prospects in the field of high-performance thermoplastic materials, films, and textiles. [Display omitted] • Hydrogen bonding decreased with the introduction of the odd-even structure. • The massive entanglements formed within the copolyamides effectively transferred the stress. • The mechanical properties of biobased copolyamides were remarkably enhanced. [ABSTRACT FROM AUTHOR]

• GTs were used to prepare CS/GTs composite fiber by blended solution spinning. • CS/GTs fiber has higher dry and wet breaking strength. • Higher breaking strength was due to ionic cross-linking between chitosan and GTs. • CS/GTs fiber has significantly higher antimicrobial and fluorescent properties. Natural extracts gallnut tannins (GTs) were used as functional components to prepare chitosan/gallnut tannins (CS/GTs) composite fiber by blended solution spinning. Chitosan fiber has great potential to be used as absorbent suture and dressing due to its good biocompatibility. However, the weak mechanical properties limited its application. Chitosan and GTs were blended in aqueous solution of acetic acid to spin the composite fiber. The results indicated that CS/GTs fiber can be easily prepared due to the appropriate rheology characteristics for blended solution. Compared with pure chitosan fiber, CS/GTs fiber with 10% GTs showed lower hydrophilicity and higher dry, wet breaking strength by more than 40% due to ionic cross-linking between chitosan and GTs. The bacterial reduction to Staphylococcus aureus increased from 49.0 to 99.7% and about double green and red fluorescent intensity were observed for CS/GTs fiber. GTs have great potentiality in improving the properties of chitosan fiber. [ABSTRACT FROM AUTHOR]

Poly(L -lactide) (PLA) is the most important biobased polymer and is widely used in various fields. However, its application is still greatly limited by the distinct disadvantage such as poor thermal resistance. In this study, in order to improve the thermal properties, crosslinked PLA with high crystallinity (44 %) and high gel content (91 %) is prepared by the UV irradiation of its semicrystalline films by the loading of certain photoinitiators and curing agents. The structure and properties of the obtained films are systematically investigated with NMR, DSC, DMA, TG and WAXD. It is found that the crosslinking of the semicrystalline PLA film is more difficult than that of the amorphous in the absence of crosslinker. However, the combinations of 2phr photoinitiator such as 4,4′-dichloro benzophenone (DCB) and 2 phr crosslinker of 1,3,5-triallylisocyanurate (TAIC) can effectively trigger the crosslinking and high gel content up to 91 % can be achieved. Corresponding to the high density crosslinking, an increase of the glass transition temperature from 66.6 °C to 75.5 °C is observed for crystallized PLA, indicating an obvious improvement in thermal resistance. More interestingly, it is found that this crosslinked PLA with high crystallinity and high gel content still possesses high crystallizability. [Display omitted] • The combination of photoinitiator and curing agents is efficient to promote the crosslinking of crystallized PLA. • PLA with high crystallinity (44 %) and high gel content (91 %) was prepared by UV irradiation. • The resulting PLA films presents improved thermal resistance and good crystallizability. [ABSTRACT FROM AUTHOR]

A clean and cost-effective method for 100% stereo-complexation in polylactide (PLA) fibers with molecular weight (MW) as high as 6 × 10 5 demonstrates good potential for industrial-scale continuous manufacture. Polylactide, a widely recognized biodegradable and renewable biopolymer, has a negligible share of plastic markets due to its poor hydrolytic and thermal resistance. Stereo-complexation is effective in overcoming these challenges. However, current stereo-complexation approaches usually require solvents and/or external nucleation reagents, and are expensive and complicated. Moreover, high-MW PLAs favored for developing durable products are difficult to be stereo-complexed. In this research, enantiomeric PLAs both with MW up to 6 × 10 5 were completely stereo-complexed via a facile thermal treatment on pilot-scale devices. Neither solvent nor nucleation agent was used. For poly(L-lactide) (PLLA) fibers with MW of 6 × 10 5 , percentage retention of MW and percentage retention of tensile strength after hydrolysis under simulated textile dyeing condition increased from 39% to 93% and from 20% to 89%, respectively, after complete stereo-complexation. The melting point, softening point and percentage retention of MW after hydrolysis of stereo-complexed PLA (sc-PLA) fibers were up to 51 °C, up to 59 °C and up to 183% higher than that of PLLA fibers with the same MW, respectively. The mechanism of thorough stereo-complexation in high-MW PLA fibers was proposed and verified. It is promising to use this approach to broaden industrial applications of renewable and degradable biopolymers for sustainable development of material industries. [ABSTRACT FROM AUTHOR]

[Display omitted] • The isodimorphism of biobased PA6/PA56 was studied by the thermodynamic model. • The polymorphic crystallization behavior of PA6-type crystals is influenced by the content of 56 units. • The inclusion of 6 units in the crystal led to lower defect excess free energy (ε). A series of semi-crystalline bio-based copolyamides PA6 x 56 y were synthesized via melt polycondensation from caprolactam (6 units) and bio-based Pentamethylene adipamide units (56 units). DSC results show that the melting and crystallization temperature depend on the comonomers composition, and exhibit isodimorphic behavior. Combined with the analysis of WAXD, it is found that the 56 units are more tend to be excluded from rather than incorporated into the PA6 crystals. However, it does not imply a complete exclusion. Unexpectedly, there is a significant relationship between the content of 56 units on the polymorphic crystallization behavior of PA6-type crystals. Moreover, the pseudo-eutectic point appears when 56 units content is 30 mol %, and the spherulite morphology exhibits a strong correlation with the pseudo-eutectic point. In addition, the excess free energy of defects (ε) is calculated by applying the Wending-Suter model, and it is found that the ε -value caused by the insertion of 56 units into the crystal formed by PA6 is higher than that of 6 units into a crystal formed by PA56. Therefore, 6 units are more easily inserted into crystals formed by PA56, i.e., 6 units have better compatibility with PA56 crystals. In summary, this work reveals the involved mechanisms of comonomer units in the crystallization process and provides a potential strategy to guide the development of high-performance copolymers in the future. [ABSTRACT FROM AUTHOR]

In this research, solutions of styrene-butadiene-styrene block copolymer (SBS) in 2-ethoxyethyl methacrylate (EOEMA) were used to prepare strippable films via rapid visible-light curing, where the mixture of camphorquinone (CQ), diphenylsilane (DPS) and diphenyliodonium hexafluorophosphate (Iod) was employed as the photoinitiating system, LED@405 nm, sunlight or household LED panel light as the light source and no any solvent was involved. The double bond conversion for pure EOEMA under LED@405 nm was firstly monitored by real-time FTIR and it reached 72% within 300 s. The rapid-curing of SBS/EOEMA solutions were systematically investigated and it was found that the solution with 16 wt% SBS became completely dried at the presence of 2.16 mol% crosslinker and 3.6 wt% photoinitiating system after 240 s irradiation under LED@405 nm. The tensile strength, elongation at break and glass transition temperature of the resultant strippable film were determined to be about 4.4 ± 0.5 MPa, 130 ± 11.2% and 6.9 °C, respectively, by mechanical properties testing and DSC measurements. Also, the decontamination efficiencies (DE) of household LED panel light/sunlight cured-strippable film for uranium nitrate on stainless steel, glass, and ceramic surface were evaluated to be higher than 90%. These results indicate that this rapid-curing strippable films would be a good candidate material for large-scale radioactive decontamination. [ABSTRACT FROM AUTHOR]

Without additional matrix or reinforcement, compression molded composites from waste polypropylene (PP) carpets/nylon (PA) carpets or PP carpets/polyester (PET) carpets have higher mechanical properties and sound absorption than traditional jute/PP composites. Large amount of carpets have been discarded every year, leading to waste of petro-based materials and serious environmental pollution. Fabrication of composites from discarded carpets via compression molding could save petroleum resources and alleviate environmental pressure. In this research, the compression molded composites from waste PP/PA carpets or PP/PET carpets showed good mechanical properties, sound absorption and water stability. Compared to the jute/PP composites, nylon 6,6 (PA66)/PP carpet composites had 37% and 9% higher flexural strength and impact resistance, as well as 45% and 10% higher sound absorption and water stability, indicating their potential for transportation and construction industries. [ABSTRACT FROM AUTHOR]

PA56 is a newly commercialized bio-based polyamide with excellent thermal, mechanical and processing properties. However, its hydrogen bonds and crystalline structures are not well investigated yet. In this study, PA56 films with γ form and α-like form crystalline phases were successfully prepared by melt-crystallization and solution casting, respectively. The hydrogen bond and crystalline structure were systematically studied with solid-state 13C NMR, variable temperature-FTIR and dynamic oscillatory rheological tests. 13C NMR and variable temperature-FTIR results indicate that the hydrogen bond strength of PA56 in α-like form crystal is higher than that in γ-form, while both are lower than that of PA66 in α-form. The chemical shifts of carbons in diamine units are highly dependent on the crystalline forms due to the molecular chain of PA56 adopts different conformations in γ-form and α-like form. The curve-fitting of variable temperature-FTIR spectra reveals that the melt crystallization results in γ-form regardless of the crystal form before melt. Dynamic oscillatory rheological tests demonstrate that the stronger hydrogen bond interactions endow α-like form of PA56 a higher dynamic storage modulus and complex viscosity than γ-form. [Display omitted] • The hydrogen bond strength and crystalline structure of PA56 were investigated. • The hydrogen bond strength of PA56 in α-like form is highe than that in γ form. • Melt crystallization results in γ-form regardless of the crystal form before melt. • The relationship between crystal structure and rheology property was clarified. [ABSTRACT FROM AUTHOR]