Xuechuan Wang

Synthesis of amino-terminated hyperbranched polymers and their application in microfiber synthetic leather base dyeing

In the current study, amino-terminated hyperbranched polymers (NH2-HBP) were synthesized by Michael addition reaction in which N, N’-methylene bisacrylamide (MBA) and diethylene triamine (DETA) were used as raw materials, and water was used as a solvent. Reaction temperature, raw material ratio, and reaction time were optimized via single-factor experiments in which the production rate and primary amino content were used as indexes. The results showed that the mol ratio of MBA to DETA was 1:1.1, the temperature was 70°C, and reaction time was 24 h. Under this condition, the primary amino content of NH2-HBP was 2.83 mmol/g, and the yield was 91.16%. The NH2-HBP structure was characterized by Fourier transform infrared spectroscopy and nuclear magnetic resonance. Moreover, the relative molecular mass distribution of NH2-HBP was also determined by gel permeation chromatography. As an active substance, NH2-HBP was grafted onto the polyamide microfiber synthetic leather used in clothes, and organic phosphine was used as a cross-linking agent. The change in dye uptake, surface chroma, and resistance to dry-rub and wet-rub fastness properties was discussed. When the NH2-HBP dosage was 5.5%, the dye uptake improved from 56.89% to 94.85% (an increase of almost 61%). The surface chroma also deepened, the dry-rub fastness improved from 3.0 to 4.5, and the wet-rub fastness improved from 2.5 to 3.5.

Effects of Crystallization Temperature and Blend Ratio on the Crystal Structure of Poly(butylene adipate) in the Poly(butylene adipate)/Poly(butylene succinate) Blends

The effects of crystallization temperature and blend ratio on the polymorphic crystal structures of poly(butylene adipate) (PBA) in poly(butylene succinate) (PBS)/poly(butylene adipate) (PBS/PBA) blends were studied by means of differential scanning calorimetry (DSC), wide-angle X-ray diffraction (XRD) and atomic force microscopy (AFM). It was revealed that the polymorphism of PBA can be regulated by the blend ratio even in a non-isothermal crystallization process. The results demonstrate that high temperature favors flat-on α crystals, while low temperature contributes to edge-on β crystals. It was also found that the effect of blend ratio on the crystallization mechanism of PBA is well coincident with that of the crystallization temperature. The increment of PBS content in the PBS/PBA blend gives rise to more β-form crystals of PBA. For those PBS/PBA blends with low PBA content, the interlamellar phase segregation of PBA makes its molecular chains so difficult to diffuse from one isolated microdomain to another that high crystallization temperature and sufficiently long crystallization time will be required if the PBA α-type crystals are targeted.

Crystallization kinetics and morphology of poly(vinylidene fluoride)/poly(ethylene adipate) blends

The miscibility, isothermal crystallization kinetics and morphology of the poly(vinylidene fluoride) (PVDF)/poly(ethylene adipate) (PEA) blends have been studied by differential scanning calorimetry (DSC), optical microscopy (OM) and scanning electron microscopy (SEM). A depression of the equilibrium melting point of PVDF was observed. From the melting point data of PVDF, a negative but quite small value of the interaction parameter χPVDF-PEA is derived using the Flory-Huggins equation, implying that PVDF shows miscibility with PEA to some extent. Nonisothermal and isothermal crystallization kinetics suggest that the crystallization rate of PVDF decreases with increasing the amount of PEA, and a contrary trend was found when PEA crystallizes with the increase of the amount of PVDF. It was further disclosed that the blend ratio and crystallization temperature affect the texture of PVDF spherulites greatly, which determines the subsequent crystallization of PEA. At high temperatures, e.g. 150 °C, the band spacing of PVDF spherulites increases with the addition of PEA content and the spherulitic structure becomes more open. In this case, spherulitic crystallization of PEA is not observed for all blend compositions. At low temperatures, e.g. 130 °C, for the PEA-rich blends, the interpenetrated structures are eventually formed by the penetration of the spherulites of PEA growing within the pre-existing PVDF spherulites.

Crystallization of poly(ethylene adipate) within γ-phase poly(vinylidene fluoride) matrix

The effects of PEA on the γ-phase PVDF crystal structure and the crystallization of PEA within the pre-existing γ-phase PVDF spherulites have been investigated by optical microscopy (OM), infrared spectroscopy (IR) and scanning electron microscopy (SEM). The results demonstrate that the γ-phase PVDF spherulites consist of the lamellae exhibiting a highly curved scroll-like morphology and develop preferentially in PEA-rich blend. With increasing PEA concentration, the scroll diameter increases and the scrolls are better separated from each other. PEA crystallizes first in the interspherulitic region and transcrystalline layer develops. Subsequently, the transcrystalline layer of PEA continues to grow within the γ-phase PVDF spherulites, e.g., in the region between the scrolls, until impinging on other PEA transcrystalline layers or spherulites. The crystallization kinetics results indicate that the growth rate of PEA crystals in the intraspherulitic region of γ-phase PVDF shows a positive correlation with content of PEA, but a negative one with the crystallization temperature of γ-phase PVDF.

Effects of crystallization condition of poly(ethylene succinate) on the crystallization of poly(ethylene oxide) in their blends

The effects of the crystallization temperatures of poly(ethylene succinate) (PES) on the crystallization behavior of poly(ethylene oxide) (PEO) in their blends were investigated by means of differential scanning calorimetry, atomic force microscopy, and laser confocal fluorescent microscopy. It was found that confined and fractional crystallization of PEO takes place in the PES/PEO blends at all blend ratios if PES is crystallized at higher crystallization temperatures. And morphological observation gives a direct evidence of the different location distribution of PEO, resulting in the confined and fractional crystallization behavior.

Improving moisture absorbent and transfer abilities by modifying superfine fiber synthetic leather base with collagen-chrome tannins

The superfine fiber synthetic leather base (SFSLB) is composed of the two components of nylon fibers and polyurethane. SFSLB has excellent performance, especially in terms of mechanical properties. However, compared with native leather, SFSLB has a hot feeling due to its poor moisture absorbent and transfer abilities. So our study proposed a method of grafting collagen-chrome tannins (C-CrT) on nylon fiber in the SFSLB for improving the moisture absorbent and transfer abilities. A three-step surface modification was developed, involving washing pretreatment, sulfuric acid hydrolysis and grafting of C-CrT on SFSLB. The dosage of sulfuric acid and chrome tannins, bath ratio, reaction temperature and the time for collagen permeation and chrome tannin cross-linking were optimized via single-factor experiments. Their efficiency was determined by measuring static water-vapor transmission rate (SWVT) and liquid wicking rate. The results showed that the dosage of sulfuric acid was 15% and chrome tannins was 5%, the bath ratio was 1500%, the reaction temperature was 60℃ and the time for collagen permeation and chrome tannin cross-linking was 3 hours. Under this condition, the SWVT of modified SFSLB was 986 g/m2 · 24 h, and the liquid wicking rate was 1.323 mm/s. Compared with untreated SFSLB, the SWVT and liquid wicking rate of modified SFSLB were improved by 90.35% and 344%, respectively. The static state contact angle, scanning electron microscopy and X-ray photoelectron spectroscopy were used for the determination of sample surface performance, morphology and chemical composition, and states before and after treatment, respectively.

Study on the improvement of water vapor permeability and moisture absorption of microfiber synthetic leather base by collagen

The microfiber synthetic leather base pretreated by sulfuric acid was modified by collagen in which the organic phosphine FP was used as a cross-linking agent, for the purpose of increasing the active groups and improving its properties. Compared with the pretreated base, it was found that the amino content in the modified base was two times and the carboxyl content was three times. The water vapor permeability of the modified base increased by 65% and the moisture absorption increased by 181%. It was further found that the tensile strength of the modified base was 19.06 N/mm2, the elongation at break was 54% and the tear strength was 112.34 N/mm. The test results of Fourier transform infrared spectroscopy, scanning electron microscopy, atomic force microscopy, thermogravimetric analysis and water contact angle showed that the collagen molecules had evenly cross-linked with fiber. The modified base microfiber dispersion was greatly increased, the hydrophility was enhanced and the relative average roughness was decreased. Moreover, modification by collagen also affected the thermal properties of the base.

Epitaxial Crystallization Behavior of Poly(butylene adipate) on Orientated Poly(butylene succinate) Substrate

The crystallization behavior of poly(butylene adipate) (PBA) in the sheared PBS/PBA blend, as well as on highly orientated poly(butylene succinate) (PBS) substrate, was studied by means of DSC, POM, Raman microscopy, and XRD. The results showed that the pre-existing orientated PBS crystals exhibit a very strong nucleation ability toward PBA as reflected by the increased crystallization temperature and the occurrence of heteroepitaxy and transcrystallization of PBA on the PBS substrate. The epitaxial crystallization of PBA on the PBS substrate results in the formation of α-form PBA crystals in any crystallization conditions.

Modification of PA/PU superfine non-woven fiber for “breath” property using collagen and vegetable tannins

Unfigured sea-island superfine fiber PA/PU non-woven (USFSLB) is used to mimic leather’s microstructure as the base of artificial leather. USFSLB has many characteristics and advantages resembling those of natural leather. However, compared with natural leather, the wearing comfort of artificial leather is inferior due to its poor moisture adsorption and permeability. In this work, a “two-step” method of chemical treatment is proposed, in which collagen/chromium-vegetable tannin (C-CrT) is immobilized on nylon fiber of USFSLB to improve its moisture adsorption and permeability (“breath” property). The two-step surface modification involved sulfuric acid hydrolysis and modifying the C-CrT on nylon fiber. Compared with the pristine USFSLB, the tensile strength, the elongation at break, the anti-static performance, the thickness, and the uniformity of C-CrT-treated USFSLB were improved at different levels. Importantly, the C-CrT-treated USFSLB showed excellent moisture adsorption and permeability, especially the liquid wicking rate (LWR) improved by 344%. The self-assembly mechanism of collagen/chromium-vegetable tannin (C-CrT) modified on nylon fibers was analyzed and discussed.

Properties of polymers as a nanoscale material for fibers in leather

Hyperbranched polymers, an innovative class of nano-polymers, could enhance the properties of fibers owning to their unique structures. In this study, the ester compound (HPAE) of 3-(bis(2-hydroxyethyl)amino)propionic acid and pentaerythritol was treated with undecylenic acid to obtain novel hyperbranched multiterminal alkenyl polymers (HPAE-UAs). The sizes of the HPAE-UAs could be controlled conveniently from 400 to 1300 nm by adjusting the capped fraction of the hydroxyl groups with undecylenic acids. The molecular structures of HPAE-UAs were characterized by means of FT-IR and 1H-NMR. Then, the effect of the HPAE-UAs on the structures, thermal, and mechanical properties of the wet blue leather were investigated. TEM and SEM demonstrated that the spacing between fibers was enlarged. The thermogravimetric analysis showed that the residual volume of leather could reach up to 30.3 % at about 500 °C. Furthermore, the shrinkage temperature increased to 89.4 °C. It was found that the HPAE-UAs used in leather could improve the thermal performance, physical and mechanical properties. All of these results indicate that HPAE-UAs can be used as a fatliquor with retanning in leather process.