Viscoelastic properties of plasticized PVC reinforced with cellulose whiskers

New nanocomposites are processed with a plasticized poly(vinyl chloride) matrix reinforced by cellulose whiskers whose characteristics are a high aspect ratio and a large interface area. Dynamic mechanical analysis performed on samples reinforced with a filler fraction of up to 12.4 vol % gives the viscoelastic properties of the composite above and below its glass transition temperature. Different theoretical predictions are proposed to describe this behavior, but none of them is found wholly satisfactory for describing the reinforcing effect of these fillers. A model based on the Halpin–Kardos equation, with the assumption of an immobilized phase around the whiskers, is developed to account for significant decrease in the modulus drop, on passing above the glass transition temperature. The small discrepancy between this model and the experimental modulus measured in the rubber plateau is discussed as a possible effect of a percolating whisker network whose crosslinks are assured by chains adsorbed onto the whisker surface. Swelling experiments support this hypothesis. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 1797–1808, 1999     

Preparation and properties of transparent cellulose hydrogels

Highly transparent cellulose hydrogels with physical crosslinkage were prepared from nonaqueous organic cellulose solutions and viscose by coagulating and regenerating cellulose in an aqueous solution containing a water‐miscible organic solvent. Nonaqueous organic cellulose solutions used were LiCl/dimethylacetamide, paraformaldehyde/dimethyl sulfoxide, and triethylammonium chloride/dimethyl sulfoxide. Preparation conditions and physical properties of the transparent cellulose hydrogels were studied. The transparency of the cellulose hydrogels depended on the composition of the aqueous solution containing the organic solvent. Furthermore, transparent cellulose hydrogels from viscose showed high tensile strength. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3020–3025, 2003     

Robust hydrogel of regenerated cellulose by chemical crosslinking coupled with polyacrylamide network

Regenerated cellulose/polyacrylamide (RC/PAAm) double network (DN) hydrogels are composed of cellulose crosslinked by epichlorohydrin (ECH) and chemical-crosslinked PAAm. The prepared RC/PAAm DN hydrogels present enhanced strength, good shape recovery property, excellent energy dissipation properties, decreased equilibrium water content, and low equilibrium swelling ratio (SR). The compressive strength and modulus of RC/PAAm hydrogel are about 4.3 and 11.5 times compared to that of RC hydrogel, respectively. Intriguingly, the chemical crosslinking between ECH and cellulose chains could increase the distance between cellulose chains. Consequently, the increasing molar ratio of ECH to glucose leads to larger SRs and decreased mechanical strength of the hydrogels. Additionally, higher PAAm contents lead to more densely crosslinked networks, and thus decreasing the SRs and improving the mechanical strength of the hydrogels. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47811.     

pH sensitive phosphate crosslinked films of starch-carboxymethyl cellulose

This work aims to develop hydrogel films of starch and carboxymethyl cellulose (CMC) crosslinked with sodium trimetaphosphate (STMP) and to characterize some of their properties. Starch and STMP (S/T), starch and CMC (S/C), and mixed (S/T/C) films were prepared by casting. The degree of substitution, morphology, swelling degree, FTIR, mechanical properties, and sorption isotherms were studied. Reticulated samples (S/T and S/T/C) showed the same degree of substitution (0.050 ± 0.001). All films presented homogeneous morphology, but the mixed film showed greater roughness. Crosslinking increased the swelling capacity of the mixed hydrogel at pH 7, although it remained decreased concerning the S/T hydrogel. However, this property was sensitive to pH variations. The mixed film (S/T/C) showed greater mechanical resistance. The casting process was efficient to produce hydrogel films of starch/CMC crosslinked with STMP and the general results demonstrated the advantages of the mixed hydrogel.     

Thermal and mechanical properties of polypropylene nanocomposite materials reinforced with cellulose nano whiskers

We use polypropylene (PP, an apolar polymer) and cellulose nano whiskers (CNW, a polar material) to produce nano polymer composites with enhanced mechanical and thermal properties. To improve compatibility, maleic anhydride grafted PP has also been used as a coupling agent. To enhance the uniform distribution of CNW in the composite, the matrix polymer is dissolved in toluene, and sonification and magnetic stirring are applied. Good film transparency indicates uniform CNW dispersion, but CNW domains in the composite film observed under an scanning electron microscope may indicate slight agglomeration of CNW in the composite film. The tensile strength of the composite compared with neat PP improves by 70–80% with the addition of CNW. The crystallinity has also been improved by about 50% in the CNW reinforced samples. As the content of CNW increases, the composite exhibits higher thermal degradation temperature, higher hydrophilicity, and higher thermal conductivity. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Development of bacterial cellulose nanowhiskers reinforced EVOH composites by electrospinning

In the current study, hybrid electrospun ethylene vinyl alcohol (EVOH) fibers reinforced with bacterial cellulose nanowhiskers (BCNW) were developed and characterized. Additionally, electrospinning was suggested as a method for the incorporation of well‐dispersed BCNW into an EVOH matrix by melt compounding. With the aim of maximizing the BCNW's loading in the electrospun fibers, an optimized method was applied for generating fibers from solutions containing up to 40 wt % BCNW. As demonstrated by FTIR spectroscopy, it was possible to incorporate BCNW concentrations up to ～ 24 wt %, although a complete incorporation of the nanofiller into the fibers was only achieved with solutions containing up to 20 wt % of the filler, DSC analyses suggested that the incorporation of the nanofiller reduced the crystallinity of the as‐obtained EVOH fibers and produced an increase in the glass transition temperature of these during the second heating run. Thermogravimetric analyses showed that even though EVOH protects the nanowhiskers from thermal degradation, the electrospun hybrid fibers present a relatively lower thermal stability than the pure EVOH fibers. FTIR analyses of the samples subjected to different thermal treatments confirmed that the stiffening effect observed by DSC only occurs after melting of the EVOH phase and is cooperative with a partial acid chemical development in the BCNW, which promotes strong chemical interactions between the polymeric matrix and the nanofiller. Finally, the hybrid electrospun fibers were incorporated into pure EVOH by melt compounding to produce composite films. This methodology showed higher stability and dispersion of the BCNW than direct addition of the freeze‐dried nanofiller to EVOH. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Preparation and properties of bacterial cellulose/graphene oxide composite films using dyeing method

In this study, bacterial cellulose (BC) hydrogels were cultured from a kombucha SCOBY starter. The scanning electron microscopy (SEM) results indicated that the dried BC exhibited an interpenetrating fibrous mat. The BC films harvested for 5, 10, and 15 days were 15–19, 14.4–24, and 30–31 μm thick, respectively. Then, BC/graphene oxide (GO) composite films were prepared via the exhaust dyeing method. GO sheets penetrated the BC matrix, resulting in the formation of a BC/GO composite, as revealed by the SEM analysis results. The mechanical properties of the composite films were investigated. Compared with virgin BC, the tensile strength of the composite films was higher, while the %E at break was lower, resulting in a significant increase in the Young's modulus. The X-ray diffraction results indicated that an increase in the dyeing time (0.5–2 h) gradually induced cellulose crystalline conformation, which in turn affected the swelling ability, mechanical properties, and electrical properties of the BC/GO composite films. After the reduction of GO to reduced GO (rGO), flexible conductive BC/rGO films were obtained, as confirmed by their resistivity values. Thus, flexible conductive composite films with excellent mechanical properties were successfully fabricated.     

Drawing of self‐reinforced cellulose films

Self‐reinforced cellulose films were prepared by incomplete dissolution of commercial microcrystalline cellulose in LiCl/DMAc solvent and subsequent coagulation of regenerated cellulose in the presence of undissolved microcrystalline cellulose. By drawing in wet conditions and subsequent drying, preferred orientation was introduced into the self‐reinforced cellulose films, resulting in significantly improved tensile strength of up to 430 MPa and modulus of elasticity of up to 33 GPa. A linear relationship was observed between applied draw, and the orientation of cellulose in the films, and the measured elastic modulus and tensile strength, respectively. The optically transparent drawn films significantly surpass the strength and modulus of elasticity of current all‐bio‐based planar materials and may therefore present a bio‐degradable alternative to nonbio‐based materials with similar performance. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2703–2708, 2007     

Effect of different modified lignins on the properties of xylan composite hydrogels

To improve the mechanical properties of hemicellulose hydrogel, a green, adjustable mechanical property, high swelling ratio (SR) composite hydrogel was successfully prepared by using modified lignin as a reinforcing agent. The structure and characteristics of the composite hydrogels were investigated by TGA, FTIR, SEM, rheological analysis, and SR. It can be found that the modified lignin could significantly improve the mechanical properties of the composite hydrogels. The maximum compressive stress of unmodified lignin hydrogel was 61.72 kPa and the compressive deformation was 75%. Compared with the unmodified lignin hydrogel, the mechanical properties were significantly improved, with the maximum compressive stress of the modified lignin hydrogel was 145.2 kPa and the compressive deformation was up to 90%. After adding modified lignin, the SR of the as-prepared hydrogel was up to 155.17 g/g, which was much higher than that of unmodified lignin hydrogel (105.79 g/g). The composite hydrogel had good antioxidant properties, and the free radical removal rate can reach 85.3%, which is twice as much as that without the modified lignin. With cost-effective lignin as a reinforcing agent, the as-prepared hemicellulose hydrogel with adjustable mechanical properties is favorable for great application potential.     

Solubility of bacterial cellulose and its structural properties

Based on experiments conducted, it has been found that bacterial cellulose, like spruce cellulose, is soluble in an aqueous NaOH solution with the concentration of 8.5% at a temperature of −5°C if the polymerization degree of the cellulose does not exceed 400. When 1% of urea is added to the NaOH solution, the solubility of cellulose increases; and, in this solvent, bacterial cellulose may be dissolved so long as its polymerization degree is below 560. The results of these experiments are of great practical importance since they point to the possibility of the preparation of cellulose spinning solutions suitable for fiber formation. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:1871–1876, 1998     

BC/PAM双网络水凝胶的制备及性能研究

为了改善细菌纤维素(BC)的物理及机械性能,扩大其在医用材料及功能材料等领域的应用,以细菌纤维素为基体,丙烯酰胺(AM)为单体,N,N-亚甲基双丙烯酰胺(MBA)为交联剂,采用自由基聚合的方法在BC骨架中引入聚丙烯酰胺(PAM)网络,获得BC/PAM双网络水凝胶。采用扫描电镜(SEM)、热重分析(TGA)对其形态结构及热稳定性进行研究,同时分别研究了单体和交联剂浓度对复合材料的溶胀、保水以及机械性能的影响。结果发现,随着单体和交联剂浓度的增加,BC/PAM水凝胶的溶胀和保水性均获得一定程度的改善。另外,增加单体浓度,复合材料的杨氏模量明显上升,形态结构更加致密,热稳定性显著提高。     

Polypropylene reinforced with nanocrystalline cellulose: Coupling agent optimization

Five different grades of maleic anhydride polypropylene (MAPP) having different molecular weight and acid value (AV) were used as coupler in PP‐nanocrystalline cellulose (NCC) composites. The main objective was to study the effect of MAPP structure (Mw, AV) and filler/coupler (F/C) ratio on mechanical properties in order to find optimum mechanical properties in tension, flexion, and impact. Results showed that both Mw and AV have direct effect on mechanical properties and a balance between both must be achieved to get the best performance. However, regardless of MAPP structure, optimum improvement was obtained for F/C = 7.5/1. Shear rheological data showed that at high MAPP content, MAPP acts as lubricant. DSC and AFM analysis showed small reduction in the size of PP crystals in the presence of NCC. Rheological data under large amplitude oscillatory shear showed that the nanocomposites used here are under percolation. Using these analyses, possible reinforcement mechanisms were investigated. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42438.     

生物基细菌纤维素/膨润土无机凝胶复合材料的制备

通过向以水稀释3倍体积的玉米芯水解液中加入膨润土无机凝胶,利用木醋杆菌原位发酵技术制得细菌纤维素/膨润土无机凝胶复合材料,并对其微观形貌进行表征,对发酵液的pH、产量、糖转化率和持水量进行了测试。结果表明:扫描电子显微镜照片显示膨润土无机凝胶吸附于细菌纤维素的表面和孔内;发酵液的pH随膨润土无机凝胶添加量的增大而上升并最终保持在8左右;产量随膨润土无机凝胶添加量的增大而增大;糖转化率随膨润土无机凝胶添加量的增大而减小;复合材料的持水量随着膨润土无机凝胶添加量的增大而减小。     

Aramid nanofiber reinforced nitrile rubber assisted by cellulose nanocrystals

A fiber-reinforced rubber composite was prepared by mixing aramid nanofibers (ANF) suspension and nitrile rubber (NBR) latex. The effects of ANF content and corresponding surface modification on the microstructure, vulcanization performance, processing and mechanical properties of composite materials, were systematically investigated. We found that, compared with commonly used short-cut aramid fibers, ANF fillers tend to form a stronger filling network within NBR matrix, resulting in a pronounced Payne effect. By improving the interfacial adhesion via dopamine (DA) coating onto ANF surface, the tensile strength can be further enhanced as expected. Besides, to eliminate the detriment of mechanical performance due to residual sodium polyacrylate in the course of flocculation, cellulose nanocrystal (CNC) was adopted to serve as a thickener during solution mixing. The incorporation of CNC can significantly improve the mechanical properties, which identifies a synergistic reinforcement effect arising from the cooperation of two types of fillers.     

细菌纤维素纳米晶稳定液体石蜡Pickering乳液的制备

采用生物法合成了高纯度的细菌纤维素(BC),通过浓硫酸水解制得细菌纤维素纳米晶(BCN)。以液体石蜡为油相,BCN为固体乳化剂,在超声作用下制得O/W型Pickering乳液。通过SEM,TEM,FT-IR,XRD,接触角测量仪及激光粒度和Zeta电位分析仪对BC及BCN进行了表征。考察了BCN质量浓度、水相p H和离子强度对Pickering乳液稳定性的影响。结果表明,BC在浓硫酸水解过程中发生了氧化反应,其水解主要发生在无定型区,使所得BCN的结晶指数高达97%。BCN悬浮液的粒径和Zeta电位值分别为462.5 nm和-40.8 m V,其三相接触角为95.7°,具有良好的乳化性能。在超声乳化作用下制得的乳液粒径大小为8.6~17.3μm。通过调控水相p H能够改变BCN表面电荷密度,从而改变乳液的稳定性,随着水相p H的增大,乳液相体积分数增大,乳液稳定性增强。随着Na Cl浓度的增大,乳液的稳定性降低,乳液相体积分数减小。此外,SEM的观测结果表明,BCN在稳定Pickering乳液过程中呈现纤维线条和聚集体颗粒2种形态。     

细菌纤维素硫酸酯的制备及吸附Cu~(2+)的研究

以细菌纤维素为原料,合成细菌纤维素硫酸酯,用于吸附去除水中的Cu2+。采用红外光谱仪对细菌纤维素硫酸酯的结构进行了分析,探讨了反应时间、温度、H2SO4浓度等因素对交换容量的影响,在优化条件下交换容量为2.87mmol·g-1,并对其吸附Cu2+的性能进行了研究。结果表明,细菌纤维素硫酸酯对Cu2+有强的吸附能力,且易于再生。     

Zinc sulfide nanoparticles template by bacterial cellulose and their optical properties

Spherical zinc sulfide (ZnS) nanoparticles dispersed on bacterial cellulose (BC) nanofibers homogeneously were successfully fabricated through in situ precipitation method using BC as template and explored the formation mechanism. The structure and properties were characterized by Fourier transform infrared, X‐ray diffractometer, FESEM, and so on. The results demonstrated that the nanoparticles were sphalerite structure ZnS and the size increased with the increase of the zinc precursor concentrations. Moreover, a high photocatalytic activity (92%) for degradation of methyl orange was observed and the photoluminescence spectra of the nanocomposites exhibited a blue emission band centered at 468 nm. The flexible BC membrane carried of ZnS nanoparticles might be a promising candidate in the application fields of fluorescence and photo‐catalysis. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40874.     

pH‐ and thermal characteristics of graft hydrogels based on chitosan and poly(dimethylsiloxane)

Graft copolymerization of epoxy‐terminated poly(dimethylsiloxane) (PDMS) onto chitosan was reacted without using a catalyst. pH‐sensitive hydrogels were obtained that are based on two different components: a natural polymer and a synthetic polymer. These PDMS substitutents provide the basis for hydrophobic interactions that contribute to the formation of hydrogels. Various graft hydrogels were prepared from different weight ratios of chitosan and PDMS. Swelling behavior of these hydrogels was studied by immersion of the gels in various buffer solution. Photocrosslinked hydrogels exhibited a high equilibrium water content (EWC). Particularly, the sample CP31 of the highest chitosan–PDMS weight ratio showed the highest EWC in time‐dependent, temperature‐dependent, and pH‐dependent swelling behavior. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2661–2666, 2002     

Bacterial nanocellulose‐reinforced arabinoxylan films

There is an increasing interest in substituting today's films for food packaging applications with films based on renewable resources. For this purpose, rye arabinoxylans, unmodified and enzymatically debranched, were studied for the preparation of neat films and composite films reinforced with bacterial cellulose (BC). Mixing in a homogenizer produced optically transparent, uniform films. Physical and mechanical characteristics of such films are here reported. Debranching of the arabinoxylan caused an increase in its crystallinity of 20%. Debranching as well as reinforcement with BC resulted in a decrease of the moisture sorption of the films. The debranching also resulted in a reduced breaking strain while the reinforcement with BC increased stiffness and strength of the films. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

离子液体法制备再生细菌纤维素纤维

以离子液体(氯化1-甲基-3-正丁基咪唑)溶解高聚合度细菌纤维素(BC),采用湿法纺丝制备再生细菌纤维素(RBC)初生纤维;通过红外光谱分析(FTIR)、广角X射线衍射(WAXD)分析、热失重(TG)分析、扫描电镜( SEM)、单丝强度拉伸等表征了RBC初生纤维的结构和性能.结果表明:该溶剂体系通过10 h的快速搅拌溶...