Surface functionalisation of bacterial cellulose as the route to produce green polylactide nanocomposites with improved properties

The effect of surface functionalisation of bacterial cellulose nanofibrils (BC) and their use as reinforcement for polylactide (PLLA) nanocomposites was investigated. BC was functionalised with various organic acids via an esterification reaction. This rendered the otherwise hydrophilic BC hydrophobic and resulted in better compatibility (interfacial adhesion) between PLLA and BC. A direct wetting method, allowing the determination of the contact angle of polymer droplets on a single BC nanofibre, was developed to quantify the interfacial adhesion between PLLA and functionalised BC. It was found that the contact angle between PLLA droplets and functionalised BC decreased with increasing chain lengths of the organic acids used to hydrophobise BC. A novel method to compound BC with PLLA based on thermally induced phase separation (TIPS) to yield a dry form of pre-extrusion composite was also developed. The mechanical properties of the surface functionalised BC reinforced PLLA nanocomposites showed significant improvements when compared to neat PLLA and BC reinforced PLLA. The thermal degradation and viscoelastic behaviour of the nanocomposites were also improved over neat PLLA.     

细菌纤维素/明胶复合多孔支架材料的制备与表征

介绍了以细菌纤维素水凝胶膜和明胶为原料制备细菌纤维素/明胶多孔复合支架的方法,并利用红外光谱、扫描电子显微镜、X射线衍射及力学性能测试对多孔复合支架进行研究。结果表明,复合多孔支架的表面孔径变大、孔隙率下降,但依然呈三维网络结构;明胶的加入使细菌纤维素的链规整度下降,结晶度变小、力学性能下降;同时,明胶能够调节细胞的响应并且促进细胞的贴附和生长,使细菌纤维素/明胶复合多孔支架更有利于细胞的粘附、增殖,更适用于生物医学领域。     

一种细菌纤维素/姜黄素复合材料的制备及表征

采用原位吸附法，将细菌纤维素（Bacterial Cellulose，BC）浸渍在不同浓度的姜黄素乙醇溶液中，经超声震荡，使BC对姜黄素吸附饱和，获得不同浓度下的BC/姜黄素复合材料。采用SEM、FTIR、XRD及水接触角测量仪等对BC/姜黄素复合材料性能进行测试表征。测试结果表明，原位吸附法成功地将姜黄素固定在BC材料中，随着姜黄素乙醇溶液浓度的提高，BC中吸附姜黄素的量增加，同时将试样置于潮湿环境下，吸附姜黄素的试样具有抗霉变特性，是一种具有应用前景的包装材料或组织工程材料。     

Energetic and economic analysis of trans-critical CO2 booster system for refrigeration in warm climatic condition

The performance of five CO₂ booster refrigeration systems is analysed and compared in this paper for supermarket application. The investigated configurations include a standard booster system, abbreviated as BC1, a booster system with parallel compressor (BC2), a booster system with flooded low temperature evaporator (BC3), a booster system with work recovery expander (BC4) and a booster with parallel compressor along with flooded low temperature evaporator and work recovery expander (BC5). Annual hourly averaged temperature variations at four prominent cities across the world are taken as case study. Simulation indicates advantage of the proposed system BC5 over BC1 configuration. Work recovery unit is found to have the highest potential in the annual energy savings in BC5, followed by parallel compressor and flooded evaporator. The maximum annual energy savings is found to be 22.16% for BC5 in New Delhi. Economic analysis reveals recovery time of less than four years for the additional investment made in BC5. The slope of recovery time is found steeper at lower tariff compared to that at higher tariff.     

竹炭聚丙烯纤维的制备及性能研究

用双螺杆挤出机制备了含3%改性竹炭聚丙烯母粒,并熔融纺丝制备了改性竹炭聚丙烯纤维。采用Mastersizer 2000激光粒度仪、TEM、SEM、FT-IR、XRD分析改性竹炭微粉的粒度分布及结构,用SEM、TG-DSC对母粒及纤维进行了表征。结果表明改性竹炭微粉的粒度为5.8μm,粒子均匀分布在聚丙烯基体中,纤维表面不光滑,直径为25～80μm;DSC结果表明竹炭粒子加入会提高PP熔点;TG结果显示竹炭粒子的加入会加速PP的分解。采用抑菌晕法和振荡摇瓶法对竹炭聚丙烯的抗菌性能进行研究,发现其对大肠杆菌具有较好的抑制效果。     

Cross-linked bacterial cellulose networks using glyoxalization

In this study, we demonstrate that bacterial cellulose (BC) networks can be cross-linked via glyoxalization. The fracture surfaces of samples show that, in the dry state, less delamination occurs for glyoxalized BC networks compared to unmodified BC networks, suggesting that covalent bond coupling between BC layers occurs during the glyoxalization process. Young's moduli of dry unmodified BC networks do not change significantly after glyoxalization. The stress and strain at failure are, however, reduced after glyoxalization. However, the wet mechanical properties of the BC networks are improved by glyoxalization. Raman spectroscopy is used to demonstrate that the stress-transfer efficiency of deformed dry and wet glyoxalized BC networks is significantly increased compared to unmodified material. This enhanced stress-transfer within the networks is shown to be a consequence of the covalent coupling induced during glyoxalization and offers a facile route for enhancing the mechanical properties of BC networks for a variety of applications.     

Short sisal fibre reinforced bacterial cellulose polylactide nanocomposites using hairy sisal fibres as reinforcement

“Hairy” bacterial cellulose coated sisal fibres were created using a simple slurry dipping process. Neat sisal fibres were coated with BC to create (i) a dense BC coating around the fibres or (ii) “hairy” fibres with BC oriented perpendicular to the fibre surface. These fibres were used to produce hierarchical sisal fibre reinforced BC polylactide (PLLA) nanocomposites. The specific surface area of the BC coated fibres increased when compared to neat sisal. Single fibre tensile tests revealed no significant difference in the tensile modulus and tensile strength of “hairy fibres”. However, when sisal fibres were coated with a dense BC layer, the mechanical fibre properties decreased. The tensile, flexural and visco-elastic properties of the hierarchical PLLA nanocomposites reinforced by both types of BC coated sisal fibres showed significant improvements over neat PLLA.     

细菌纤维素/聚乳酸互穿网络复合材料的结晶与熔融

为了研究细菌纤维素(BC)网络结构对聚乳酸(PLA)结晶与熔融过程的影响,以PLA为基体,BC为增强体,通过PLA-三氯甲烷溶液与BC-无水乙醇分散液的共混扩散制备了具有互穿网络结构的BC/PLA生物复合材料。采用SEM、偏光显微镜(POM)、DSC和莫志深(MO)模型研究了复合材料的微观形态、球晶形貌、非等温结晶动力学和熔融行为。结果表明:采用溶液共混扩散法可得到以BC为骨架、PLA缠绕其表面的互穿网络结构的复合材料。随降温速率增加,BC/PLA复合材料的结晶温度、熔融温度和相对结晶度均下降。BC可作为异相成核剂,适量添加可同时提高BC/PLA复合材料的结晶速率和相对结晶度,细化球晶尺寸。MO模型可较好地描述BC/PLA复合材料的非等温结晶动力学行为。     

天然细菌纤维素增强不饱和聚酯树脂复合材料的制备及性能

将天然纤维-细菌纤维素（BC）作为增强材料加入不饱和聚酯树脂（UPR）基体中,采用RTM工艺制备BC/UPR复合材料,并对其力学性能、吸湿性能进行了研究。通过紫外辐照方法探讨了BC/UPR复合材料的降解性能。研究结果表明:通过对细菌纤维素的表面改性,在亲水性的天然纤维和疏水性的高聚物基体之间形成了化学键结合,提高了BC/UPR复合材料的力学性能;BC纤维体积分数的增加也有助于提高力学性能, 当纤维体积分数为20%时,该复合材料拉伸强度最高可达152.9MPa; BC/UPR复合材料的吸湿过程符合Fick定律,吸湿可导致力学性能下降; BC/UPR复合材料吸收光能后,表面含氧官能团数量增加,发生一定程度的光降解。      

Improvement on the properties of polylactic acid (PLA) using bamboo charcoal particles

Bamboo charcoal (BC) derived from bamboo plants is one kind of well recognized multi-functional materials which has been used in various applications such as medical, cosmetic, food processing and health-related products. In this paper, BC particle is used as reinforcement for polylactic acid (PLA) to enhance its mechanical, thermal and optical properties. The comparison on tensile, flexural and impact properties of BC particle reinforced PLA composites (BC/PLA composites) with the content ranging from 2.5 to 10 wt.% is conducted. Experimental results indicated that the maximum tensile strength, flexural strength and ductility index (DI) of BC/PLA composites increased by 43%, 99% and 52%, respectively as compared with those of neat PLA. This phenomenon was attributed to the uniform distribution of high aspect ratio and surface area of BC particles. Further increasing the BC content to 7.5 wt.% would decrease the glass transition temperature of BC/PLA composites. The mechanical properties of BC/PLA composites were reduced as compared with a neat PLA sample when they were exposed to compost degradation. However, less reduction in these properties was found when they were subject to UV irradiation. UV–Vis spectrometer analysis supported the results of UV irradiation. Fracture surfaces of tensile test samples with and without compost degradation or UV irradiation were analysed by using scanning electron microscopy (SEM). SEM images revealed that there was a good BC particle dispersion in the composites through extrusion and injection moulding processes if the particle content was below 7.5 wt.%.     

Study of failure of EB-PVD thermal barrier coating upon near-α titanium alloy

The cracking failure of a conventional thermal barrier coating (TBC), consisting of a near-α titanium substrate, a NiCoCrAlY bond coat (BC), and a 8 wt.% yttria-stabilized zirconia ceramic layer deposited by electron beam-physical vapor deposition (EB-PVD) method, was studied by cyclic furnace testing and isothermal exposure. The scanning electron microscope, electron probe microanalysis, and microhardness indentation were used to probe the failure mechanism. It is found that due to the mismatch of the coefficient of thermal expansion, the as-deposited BC is suffered the long-term tensile creeping at room temperature. During the high-temperature exposure, the TBC locally rumples, bringing in-plane tensile stress at the shoulders, and out-of-plane tensile stress at the peak of the rumpled BC, where primal cracks are originated. During the cooling period, the ridges of substrate pulled by the local rumpling of the BC blocks the contracting of the BC, originating new cracks in planar BC, and aggravating the original cracks. Furthermore, the oxidation products pushed into the BC and the 8YSZ enlarges the TBC and cracks the substrate along the weakest diffused grain boundaries. The cracking failure related to the diffusion of the BC to the substrate is also discussed.     

Preparation and in vitro characterization of BC/PVA hydrogel composite for its potential use as artificial cornea biomaterial

In order to investigate the potential use for bacterial cellulose (BC) as a novel artificial cornea replacement, BC/poly(vinyl alcohol) (BC/PVA) hydrogel composites were synthesized by freezing-thaw method. The BC/PVA composites were characterized by UV–Vis spectrophotometer (UV–Vis), X-ray diffraction (XRD), thermogravimetric (TG) analysis, mechanical property tests and scanning electron microscope (SEM) analyses. Our results showed that the resultant BC/PVA composites exhibited desirable properties as artificial cornea replacement biomaterial including high water content, high visible light transmittance and suitable UV absorbance, increased mechanical strength and appropriate thermal properties. Results of this work revealed that the BC/PVA composites exhibited some promising characteristics as artificial cornea composite material and may be improved further for its realistic applications.     

Characterization of TEMPO-oxidized bacterial cellulose scaffolds for tissue engineering applications

Introduction of active groups on the surface of bacterial cellulose (BC) nanofibers is one of the promising routes of tailoring the performance of BC scaffolds for tissue engineering. This paper reported the introduction of aldehyde groups to BC nanofibers by 2,2,6,6-tetramethylpyperidine-1-oxy radical (TEMPO)-mediated oxidation and evaluation of the potential of the TEMPO-oxidized BC as tissue engineering scaffolds. Periodate oxidation was also conducted for comparison. Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) analyses were carried out to determine the existence of aldehyde groups on BC nanofibers and the crystallinity. In addition, properties relevant to scaffold applications such as morphology, fiber diameter, mechanical properties, and in vitro degradation were characterized. The results indicated that periodate oxidation could introduce free aldehyde to BC nanofibers and the free aldehyde groups on the TEMPO-oxidized BC tended to transfer to acetal groups. It was also found that the advantageous 3D structure of BC scaffolds remained unchanged and that no significant changes in morphology, fiber diameter, tensile structure and in vitro degradation were found after TEMPO-mediated oxidation while significant differences were observed upon periodate oxidation. The present study revealed that TEMPO-oxidation could impart BC scaffolds with new functions while did not degrade their intrinsic advantages.     

Optical nanocomposites prepared by incorporating bacterial cellulose nanofibrils into poly(3-hydroxybutyrate)

A biocompatible polymeric nanocomposite was prepared by incorporating bacterial cellulose (BC) into a poly(3-hydroxybutyrate) (PHB) matrix. The transparency of the PHB/BC nanocomposite was high due to the homogeneous nano-sized spherulite and nanofibril of PHB and BC, which are smaller than the wavelength of visible rays. The X-ray diffraction patterns of the PHB in the nanocomposite film showed peaks corresponding to the crystallized PHB. The thermal stability of PHB in the nanocomposite film has been improved. The morphology studies showed that the PHB molecules filled vacancies between BC nanofibrils. An increase in the mechanical properties was observed by incorporating the BC into the PHB matrix. This PHB/BC nanocomposite can be considered for various applications, such as display devices, tissue engineering scaffold, and food packaging, because of its improved mechanical properties along with biodegradability and biocompatibility.     

On boundary conditions for homogenization of volume elements undergoing localization

This paper presents an adaption of periodic boundary conditions (BC), which is termed tessellation BC. While periodic BC restrict strain localization zones to obey the periodicity of the microstructure, the proposed tessellation BC adjust the periodicity frame to meet the localization zone. Thereby, arbitrary developing localization zones are permitted. Still the formulation is intrinsically unsusceptible against spurious localization. Additionally, a modification of the Hough transformation is derived, which constitutes an unbiased criterion for the detection of the localization zone. The behavior of the derived formulation is demonstrated by various examples and compared with other BC. It is thereby shown that tessellation BC lead to a reasonable dependence of the effective stress on the localization direction. Furthermore, good convergence of stiffness values with increasing size of the representative volume element is shown as well as beneficial characteristics in use with strain softening material.     

Structural and electronic properties of hydrogen adsorptions on BC₃ sheet and graphene: a comparative study

We have systematically investigated the effect of hydrogen adsorption on a single BC? sheet as well as graphene using first-principles calculations. Specifically, a comparative study of the energetically favorable atomic configurations for both H-adsorbed BC? sheets and graphene at different hydrogen concentrations ranging from 1/32 to 4/32 ML and 1/8 to 1 ML was undertaken. The preferred hydrogen arrangement on the single BC? sheet and graphene was found to have the same property as that of the adsorbed H atoms on the neighboring C atoms on the opposite sides of the sheet. Moreover, at low coverage of H, the pattern of hydrogen adsorption on the BC? shows a proclivity toward formation on the same ring, contrasting their behavior on graphene where they tend to form the elongated zigzag chains instead. Lastly, both the hydrogenated BC? sheet and graphene exhibit alternation of semiconducting and metallic properties as the H concentration is increased. These results suggest the possibility of manipulating the bandgaps in a single BC? sheet and graphene by controlling the H concentrations on the BC? sheet and graphene.     

Appearance of cell-adhesion factor in osteoblast proliferation and differentiation of apatite coating titanium by blast coating method

We have already reported that the apatite coating of titanium by the blast coating (BC) method could show a higher rate of bone contact from the early stages in vivo, when compared to the pure titanium (Ti) and the apatite coating of titanium by the flame spraying (FS) method. However, the detailed mechanism by which BC resulted in satisfactory bone contact is still unknown. In the present study, we investigated the importance of various factors including cell adhesion factor in osteoblast proliferation and differentiation that could affect the osteoconductivity of the BC disks. Cell proliferation assay revealed that Saos-2 could grow fastest on BC disks, and that a spectrophotometric method using a LabAssay^TM ALP kit showed that ALP activity was increased in cells on BC disks compared to Ti disks and FS disks. In addition, higher expression of E-cadherin and Fibronectin was observed in cells on BC disks than Ti disks and FS disks by relative qPCR as well as Western blotting. These results suggested that the expression of cell-adhesion factors, proliferation and differentiation of osteoblast might be enhanced on BC disks, which might result higher osteoconductivity.     

Preparation and characterization of a novel COL/BC composite for potential tissue engineering scaffolds

This paper describes the biosynthesis of a novel collagen-bacterial cellulose (COL/BC) composite by adding collagen to the culture medium of Acetobacter xylinum. The morphology of COL/BC composite was observed by SEM and TEM and compared with pristine BC. The composite was further characterized by FTIR and XRD. It is found that the structure of BC network changes when collagen is present in the nutrient medium. Further work is underway to gain insights into the mechanisms governing the experimental phenomena.     

Bacterial cellulose/silica hybrid fabricated by mimicking biocomposites

In plants such as grasses, rice, and sugar cane, biomineralizatin occurs such that amorphous silica is drawn from soil, transferred and deposited on polysaccharide matrix. In this study, by mimicking natural biomineralization in plants, a cellulose/silica hybrid was produced using bacterial cellulose (BC). BC hydro-gel was immersed in an aqueous solution of silanol derived from tetraethoxysilane (TEOS), and silanol was then converted into silica in the BC hydro-gel matrix. By pressing the BC hydro-gels and hybrids at 120 °C and 1–2 MPa, water-free translucent sheets were obtained. In the leaves of rice plants, large silica bodies (μm order) were embedded in the polysaccharide matrix, whereas in the BC/silica hybrids, nano scale silica was embedded between the micro fibrils of the BC matrix. Reflecting this structure, the modulus of elasticity and tensile strength of dry BC/silica hybrid improved to 17 GPa at 25 °C and 185 MPa, respectively. In the case of rice plants, the modulus was 3.5 GPa at 25 °C and the tensile strength was 25–88 MPa, suggesting a weaker structure than in BC hybrid.     

细菌纤维素/聚乙烯醇双网络复合水凝胶的制备与性能研究

利用冷冻-解冻法制备了细菌纤维素（BC）/聚乙烯醇（PVA）双网络复合水凝胶,研究不同BC含量及循环周期对BC/PVA复合水凝胶力学性能和溶胀特性的影响,结果表明,随着BC含量的增多,复合水凝胶的含水率、平衡溶胀比、拉伸强度和压缩强度与普通的PVA水凝胶相比均有一定程度的提高;综合考虑,当BC含量为4%时,各项性能均达到最佳值;随着循环次数的增多,水凝胶内部的物理交联点增多,导致水凝胶的含水率下降,拉伸强度和压缩强度则有明显的上升趋势。SEM观察的结果与之前的分析是一致的。