环氧化改性天然橡胶／丁腈橡胶共混物研究

用电子扫描显微镜(SEM)、差示扫描量热计(DSC)、红外光谱、强力试验机等仪器,对环氧化改性天然橡胶/丁腈胶共混物的形态与性能进行研究,并与未改性的天然橡胶/丁腈胶共混物进行对比。结果表明,天然橡胶分子引入环氧化基团后极性增大,两组分分子间的相互作用力增强,共混物相容性得到明显的改善,从而具有较理想的形态,展现出较好的力学拉伸性能,可望达到使用的要求。     

环氧化天然胶／丁腈胶共混物硫化条件的研究

采用流变仪、差示扫描量热计、强力试验机等仪器,开展环氧化天然橡胶/丁腈橡胶共混物硫化条件的研究,包括配方的选择、制备工艺、贮存时间等方面,从而确定适宜的硫化条件与工艺,并据以制备出具有一定程度共硫化的硫化胶;与环氧化橡胶、丁腈橡胶、天然橡胶/丁腈胶共混物相比,环氧化橡胶/丁腈橡胶共混物在力学与耐油性能上均有所改善,因此可以在工业上应用。     

用热重法研究天然胶乳与合成胶乳的相容性

采用热重分析法研究天然胶乳与丁腈胶乳、丁苯胶乳及环氧化天然胶乳与丁腈胶乳的共混。研究结果表明,共混胶乳的相容性可以通过其共混产物的热降解ＤＴＧ曲线来判定。      

The influence of thermal stabilization stage on the molecular structure of polyacrylonitrile fibers prior to the carbonization stage

Structural transformation from a linear chain structure to crosslinked chain structure, occuring during the thermal stabilization stage of carbon fiber manufacture, was followed through the use of infrared spectroscopy, differential scanning calorimetry (DSC), elemental analysis and gel-fraction measurements. The results obtained from the analysis of IR spectroscopy showed the gradual and continuous loss of intensity of the nitrile (C≡N) vibration at 2242 cm⁻¹ closely associated with the cyclization reactions whereas the intensity loss of the methylene (CH₂) groups vibration around 2920–2939 cm⁻¹ has been attributed to the loss of hydrogen atoms as part of the dehydrogenation reactions. The dehydrogenation index, evaluated using the absorbance ratio of A₁₄₅₂/A₁₃₆₈, also indicated the gradual loss of hydrogens in agreement with decreasing hydrogen content with progressing stabilization process. IR spectroscopy also showed the emergence of new absorption bands attributed to the formation of crosslinked ladder-like structure in the 1590–1600 cm⁻¹ region. The amount of newly formed crosslinked structure was characterized using DSC conversion index, IR conversion index and gel-fraction measurements. The results are compared and discussed in detail.     

乙酰化蛋黄果多糖及其抗氧化活性研究

蛋黄果（Lucuma nervosa A. DC）乙酰化修饰多糖的抗氧活性优于未修饰多糖,通过分析乙酰化蛋黄果多糖的乙酰化度、红外光谱和形貌特征,阐明引起抗氧活性提升的原因。试验采用超声波辅助法提取蛋黄果果肉粗多糖,用三氯乙酸法除去蛋白质得到多糖。选取3份0.50 g多糖加入20% NaOH溶液溶解,分别加入1、3、5 mL乙酸酐,得到3种取代度（0.237±0.05、0.275±0.07、0.228±0.04）的乙酰化蛋黄果果肉多糖,评价其清除DPPH自由基、OH自由基和ABTS自由基的能力。结果表明,乙酸酐添加量由少到多时,蛋黄果多糖乙酰基取代度先显著升高,后趋于平缓下降。乙酰化蛋黄果多糖的红外光谱显示了3417 cm^-1（-OH）、2950 cm^-1（-CH）处的伸缩振动和1636 cm^-1处的（-OH）转动振动,1738 cm^-1处出现酯基C=O的伸缩振动吸收峰,表明乙酰化已经成功接入。扫描电镜结果显示,未经乙酰化的蛋黄果多糖表面相对光滑平整,呈片状结构;乙酰化修饰多糖分子间交联增强,构象发生了变化,变为表面形状不规则,出现很多空隙且表面粗糙。3种乙酰化蛋黄果多糖中DHG-Ac2（3 mL醋酐）清除效果最好,在浓度1.0 mg/mL时,DPPH清除能力、ABTS自由基清除率、OH自由基清除率分别为91.37%、58.73%、56.36%,分别高于蛋黄果多糖10.0%、43.7%、25.3%。这是引入的乙酰基能活化多糖链中的异头碳,使多糖的供氢能力提升,继而提升乙酰化蛋黄果多糖的抗氧化作用。本研究为海南产蛋黄果多糖的深入开发与抗氧化应用提供了基础研究数据。     

The characterization of polyacrylonitrile fibers stabilized by electron beam irradiation

This study investigates polyacrylonitile(PAN) fibers stabilized with various doses of electron beam irradiation (EBI) ability to produce carbon fibers. Feasibility was verified by FT-IR, the percent of gel fraction, density, DSC, XRD, and mechanical measurements. FT-IR spectra showed that the intensities of the stretching C??N bonds decreased at 2,244 cm^?1 with increasing EBI dose. This de crease was related to cyclization of nitrile groups during EBI-stabilization. The degree of cyclization was determined from the gel fraction and density tests. The gel content and density of PAN fibers stabilized by EBI increased with an increase in the EBI dose. Thermal properties were characterized by differential scanning calorimetry (DSC) and thermally activated reactions. DSC curves showed that EBI treatment influenced the quantity of released heat and the exothermic position at low temperature over a wide temperature range. The strongest diffraction peak from the PAN precursor fiber arose from the (100) plane; its stabilization index (SI) was evaluated by X-ray diffraction. The X-ray results showed that the peak intensity decreases gradually with increasing EBI dose. In addition, tensile strength decreased the EBI stabilization level.     

The Effect of Substituent,Degree of Acetylation and Positioning of the Cationic Charge on the Antibacterial Activity of Quaternary Chitosan Derivatives

A series of water-soluble cationic chitosan derivatives were prepared by chemoselective functionalization at the amino group of five different parent chitosans having varying degrees of acetylation and molecular weight. The quaternary moieties were introduced at different alkyl spacer lengths from the polymer backbone (C-0, C-2 and C-6) with the aid of 3,6-di-O-tert-butyldimethylsilyl protection of the chitosan backbone, thus allowing full (100%) substitution of the free amino groups. All of the derivatives were characterized using ¹H-NMR, ¹H-¹H COSY and FT-IR spectroscopy, while molecular weight was determined by GPC. Antibacterial activity was investigated against Gram positive S. aureus and Gram negative E. coli. The relationship between structure and activity/toxicity was defined, considering the effect of the cationic group’s structure and its distance from the polymer backbone, as well as the degree of acetylation within a molecular weight range of 7–23 kDa for the final compounds. The N,N,N-trimethyl chitosan with 100% quaternization showed the highest antibacterial activity with moderate cytotoxicity, while increasing the spacer length reduced the activity. Trimethylammoniumyl quaternary ammonium moieties contributed more to activity than 1-pyridiniumyl moieties. In general, no trend in the antibacterial activity of the compounds with increasing molecular weight or degree of acetylation up to 34% was observed.     

Characterization of conductive poly(acrylonitrile-<Emphasis Type="Italic">co</Emphasis>-vinyl acetate) composites: Matrix polymerization of pyrrole derivatives

In this study, poly(acrylonitrile-co-vinyl acetate) (P(AN-co-VAc)) composite films were prepared by chemical polymerization of pyrrole(Py), N-methyl pyrrole (NMPy) and N-phenyl pyrrole (NPhPy) with cerium(IV) [Ce(IV)] on P(AN-co-VAc) matrix. An increase was observed in the absorbances of CN ring stretching vibration (1451 cm⁻¹) by introducing pyrrole (Py) derivatives on P(AN-co-VAc) matrix. The nitrile (CN) and carbonyl (C=O) groups played a significant role on the interactions with cationic sites of Py derivatives. Conductivity was increased in the presence of carbonyl (C=O) groups due to their additional negative charges on P(AN-co-VAc) matrix compared to PAN. Poly(N-Phenyl Pyrrole) (PNPhPy) exhibited higher dielectric constant and AC conductivity in the frequency range between the 10⁻²–10⁷ Hz. The TGA results exhibited shifts of peak to higher temperatures by the presence of Py derivatives by increasing the weight loss %.     

基因HAT1在小麦生理型雄性不育系中的表达分析

组蛋白乙酰转移酶（HAT）在生物生殖发育中对染色体的结构修饰和基因的表达调控发挥着重要作用。为探讨组蛋白乙酰化与小麦生理型雄性不育的关系,利用实时荧光定量技术,分析了化学杀雄剂SQ 1诱导的生理型雄性不育小麦花药各发育时期组蛋白乙酰转移酶基因HAT1的表达水平。结果表明,与同期可育花药相比,生理型雄性不育小麦花药的HAT1基因表达水平在单核期显著升高,二核期变化趋势基本相同,三核期显著降低。DNA Ladder显示,不育花药在单核期出现明显的DNA片段化,比正常花药提前凋亡。这表明SQ 1诱导的小麦生理型雄性不育可能与HAT1基因表达异常和花药细胞提前凋亡有关。     

Effect of different carbohydrates on the functional properties of black rice glutelin (BRG) modified by the maillard reaction

The objective of this study was to investigate the effects of the glycosylation of BRG on its structures and functional properties. The glycosylation of BRG was achieved via Maillard reactions with four carbohydrates, including arabinose (AN), sodium alginate (SA), maltodextrin (MD), and lactose (LT), and the corresponding conjugates were named BRG-AN, BRG-SA, BRG-MD, and BRG-LT, respectively. The formation of the BRG conjugates was confirmed by changes in the BRG amino groups, conjugation degree, as well as molecular weight. BRG-AN and BRG-MD presented a significantly higher conjugation degree and lower amino group levels compared to the other two conjugates. Circular dichroism (CD) analysis indicated that all the conjugated BRG displayed markedly decreased levels of β-sheets and increased levels of α-helixes. However, only BRG-AN increased significantly in irregular loops. Results from the Fourier Transform Infrared Spectroscopy (FTIR) analysis indicated that the most apparent changes in the structures of BRG conjugates were evident as absorption peaks at 3389 cm⁻¹, 1528 cm⁻¹, 1230 cm⁻¹, and 953–1180 cm⁻¹. After glycosylation, the solubility, emulsion activity index (EAI), and emulsion stability index (ESI) of BRG were significantly improved. After glycosylation of the BRG, induced by Maillard reactions with four carbohydrates, the denaturation temperature (T_d) and enthalpy (ΔH) change values increased substantially from 90.16 °C to 124.28 °C and 11.01 J/g to 18.43 J/g, respectively. The results indicated that BRG-AN exhibited better solubility, EAI, and ESI than the other BRG conjugates.     

Effect of the nixtamalization with calcium carbonate on the indigestible carbohydrate content and starch digestibility of corn tortilla

There is a growing interest for an environment-friendly nixtamalization process. Nixtamalization with calcium salts generates a minimum level of polluting residues. The effect of a nixtamalization process with calcium carbonate (NCC) on the indigestible carbohydrate content and starch digestibility of tortillas was evaluated. Traditional and NCC tortillas showed lower moisture content than commercial tortillas. Similar protein, ash, and carbohydrate content were found for the three tortillas, but NCC tortillas showed the highest lipid content. The NCC tortilla had the highest dietary fiber content, with the highest insoluble dietary fiber level. Fresh and stored (96 h) NCC and traditional tortillas showed similar resistant starch content. Fresh traditional tortilla showed the highest slowly digestible starch (SDS), but upon storage the rapidly digestible starch (RDS) content of NCC tortilla decreased. Fresh traditional and NCC tortillas had lower predicted glycemic index (pGI) than commercial tortillas, and upon storage, the three tortillas presented lower pGI values than their fresh counterparts. Consumption of tortillas produced with the NCC can produce positive effects in the human health.     

Strawboard from vapor phase acetylation of wheat straw☆

Commercial ground wheat straw was used in a central composite response surface experimental design to examine four acetylating process variables: reaction temperature, reaction time, initial moisture content of straw, and the vapor flow rate of chemical reagent. The response variable was acetyl content determined as a function of straw weight gain. Diphenylmethyane diisocyante was used as a binder to prepare board samples with a hot press. Equilibrium moisture content (EMC) was determined at 65 and 90% RH at 27°C, and dimensional stability was determined using a humidity cycle of 30–90% RH at 27°C. ASTM D1037-93 standard method for a 3-point flex test was used to measure mechanical properties. The microstructures of both treated and untreated wheat straw and boards were observed with a scanning electron microscope. The vapor phase acetylation system used acetylated ground wheat straw to a 24% weight gain (dry weight basis). A mathematical model (R²=0.97) was developed to predict the weight gain as a function of the four acetylation processing variables. The maximum reduction in all strawboard properties occurred at the highest weight gain (24%). The strawboard EMC decreased (30% maximum reduction) as weight gain increased at both 65 and 90% RH. The strawboard dimensional stability increased as the weight gain increased (maximum reductions of 80% in thickness swell and 50% in linear expansion). The initial mechanical properties of the strawboards decreased as the weight gain increased (maximum reductions of 64% in strength and 48% in stiffness). The density of the strawboards decreased as the weight gain increased (23% maximum reduction). SEM micrographs showed no physical evidence of structural damage to cell walls from the acetylation.     

菠萝叶纤维制备纳米纤维素晶体的研究

菠萝叶纤维经过氢氧化钠预处理、硫酸水解制备得到纳米纤维素晶体（NCC）,再用扫描电镜（SEM）、傅立叶转换红外光谱仪（FTIR）、热重（TG）分析仪和X-射线衍射分析仪（XRD）对其结构和性能进行表征和分析。结果表明,NCC晶体颗粒尺寸为30~50 nm;红外光谱证明非纤维素部分有效去除;NCC晶型仍属于纤维素I,结晶度从75.9％提高到87.5％;比起原纤维,NCC的降解温度明显降低。     

Effects of the nitrile group substitution on the gas separation properties of aromatic polyamide membranes

The effects of nitrile group substitution onto aromatic polyamide backbone on the gas permeability and permselectivity of the polymers are examined. The gas permeability of aromatic polyamides increase with increasing the content of nitrile group substitution, whereas the permselectivity decreases with increasing the nitrile group contents. The effects of chain linrearity on the permeability and permselectivity are also examined. The non-linearity of the polymers increases the permeability. These behaviors are interpreted in terms of chain packing and crystallinity of the aromatic polyamides.     

Correlating the fineness and residual gum content of degummed hemp fibres

It is well known residual gum exists in degummed or retted hemp fibres. Gum removal results in improvement in fibre fineness and the properties of the resultant hemp yarns. However, it is not known what correlation if any exists between the residual gum content in retted hemp fibres and the fibre fineness, described in terms of fibre width in this paper. This study examined the mean width and coefficient of variation (CV) of fibre width of seventeen chemically retted hemp samples with reference to residual gum content. The mean and CV of fibre width were obtained from an Optical fibre diameter analyser (OFDA 100). The linear regression analysis results show that the mean fibre width is directly proportional to the residual gum content. A slightly weaker linear correlation also exists between the coefficient of variation of fibre width and the residual gum content. The strong linear co-relation between the mean of fibre width and the residual gum content is a significant outcome, since testing for fibre width using the OFDA is a much simpler and quicker process than testing the residual gum content. Scanning Electron Microscopy (SEM) reinforces the OFDA findings. SEM micrographs show a flat ribbon like fibre cross-section hence the term “fibre width” is used instead of fibre diameter. Spectral differences in the untreated dry decorticated skin samples and chemically treated and subsequently carded samples indicate delignification. The peaks at 1370 cm⁻¹, 1325 cm⁻¹, 1733 cm⁻¹, and 1600 cm⁻¹ attributed to lignin in the untreated samples are missing from the spectra of the treated samples. The spectra of the treated samples are more amine-dominated with some of the OH character lost.     

Inhibition of acetyl cholinesterase by solanaceous glycoalkaloids and alkaloids

Seven solanaceous glycoalkaloids (α-chaconine, β₂-chaconine, α-solanine, dehydrocommersonine, commersonine, demissine and tomatine) and three alkaloids (solanidine, tomatidine and demissidine) were tested for their ability to inhibit acetyl cholinesterase in anin vitro system. Glycoalkaloids at concentrations of 33–41 parts per million (ppm) gave cholinesterase inhibition ranging from 4.2 to 26.8%. All three alkaloids had lower anticholinesterase (4.2 to 15.4%) than the seven glycoalkaloids, except for tomatine. Two well-known cholinesterase inhibitors, carbaryl, a carbamate insecticide and Guthion, an organophosphate insecticide, were also tested for comparison. It required only 1 to 2 ppm of the insecticides to give the same average percent inhibition as was observed with the glycoalkaloids at concentrations of 33–35 ppm.     

A Study of Combining Elastin in the Chitosan Electrospinning to Increase the Mechanical Strength and Bioactivity

While electrospun chitosan membranes modified to retain nanofibrous morphology have shown promise for use in guided bone regeneration applications in in vitro and in vivo studies, their mechanical tear strengths are lower than commercial collagen membranes. Elastin, a natural component of the extracellular matrix, is a protein with extensive elastic property. This work examined the incorporation of elastin into electrospun chitosan membranes to improve their mechanical tear strengths and to further mimic the native extracellular composition for guided bone regeneration (GBR) applications. In this work, hydrolyzed elastin (ES12, Elastin Products Company, USA) was added to a chitosan spinning solution from 0 to 4 wt% of chitosan. The chitosan–elastin (CE) membranes were examined for fiber morphology using SEM, hydrophobicity using water contact angle measurements, the mechanical tear strength under simulated surgical tacking, and compositions using Fourier-transform infrared spectroscopy (FTIR) and post-spinning protein extraction. In vitro experiments were conducted to evaluate the degradation in a lysozyme solution based on the mass loss and growth of fibroblastic cells. Chitosan membranes with elastin showed significantly thicker fiber diameters, lower water contact angles, up to 33% faster degradation rates, and up to seven times higher mechanical strengths than the chitosan membrane. The FTIR spectra showed stronger amide peaks at 1535 cm⁻¹ and 1655 cm⁻¹ in membranes with higher concentrated elastin, indicating the incorporation of elastin into electrospun fibers. The bicinchoninic acid (BCA) assay demonstrated an increase in protein concentration in proportion to the amount of elastin added to the CE membranes. In addition, all the CE membranes showed in vitro biocompatibility with the fibroblasts.     

Evaluation of antioxidant activity of methanolic extract from peanut hulls in fried potato chips

Antioxidant activity of methanolic extract from peanut hulls (MEPH) was evaluated in fried potato chips during storage at 25 ^°C and 45 ^°C. Free fatty acids (FFA) and peroxide values (POV) were used as criteria to assess MEPH as an antioxidant. After six months storage at 45 ^°C potato chips treated with 1200 and 1600 ppm of MEPH showed lower values of FFA (0.083, 0.080%) and POV (30.0, 29.0 mEq/kg) than the control samples (FFA 0.377%, and POV 180 mEq/kg). Potato chips treated with BHA and BHT showed POVs of 29.0 and 25.0 mEq/kg whereas FFA values were 0.0086 and 0.074%, respectively, after six months storage at 45 ^°C. These results illustrate that MEPH, at various concentrations, exhibited very strong antioxidant activity which was almost equal to synthetic antioxidants (BHA & BHT). Subjective evaluation studies also showed that potato chips treated with 1200–1600 ppm MEPH after six months storage at 45 ^°C, were organoleptically acceptable.     

Chitosan–starch composite film: preparation and characterization

Chitosan film has potential applications in agriculture, food, and pharmacy. However, films made only from chitosan lack water resistance and have poor mechanical properties. Forming miscible, biodegradable composite film from chitosan with other hydrophilic biopolymers is an alternative. The objective of this study was to prepare chitosan/starch composite films by combining chitosan (deacetylated degree, 90%) solution and two thermally gelatinized cornstarches (waxy starch and regular starch with 25% amylose). The film’s tensile strength (TS), elongation-at-break (E), and water vapor transmission rate (WVTR) were investigated. The possible interactions between the two major components were evaluated by X-ray diffraction and Fourier-transform infrared spectroscopy (FTIR). Regardless of starch type, both the TS and E of the composite films first increased and then decreased with starch addition. Composite film made with regular starch showed higher TS and E than those with waxy starch. The addition of starch decreased WVTRs of the composite films. The introduction of gelatinized starch suppressed the crystalline peaks of chitosan film. The amino group band of chitosan molecule in the FTIR spectrum shifted from 1578 cm⁻¹ in the chitosan film to 1584 cm⁻¹ in composite films. These results indicated that there was a molecular miscibility between these two components.     

Effect of co-monomer ratio in ABS and wood content on processing and properties in wood/ABS composites

Acrylonitrile-Butadiene-Styrene copolymers (ABS) reinforced with wood flour were investigated for rheological, mechanical and thermal properties. Three grades of commercial ABS resin (high flow (HF-ABS), medium impact (MI-ABS) and super high impact (SI-ABS) grades) were characterized using H-NMR and elemental analysis for the determination of co-monomer content. Wood flour from Para rubber trees treated with N-2 (aminoethyl)-3-(aminopropyl) trimethoxy silane was blended with ABS in the melt blending process using a twin-screw extruder. Wood flour contents used in this work were 0.0 %, 9.1 %, and 33.3 % wt. The composites with higher acrylonitrile contents showed higher melt viscosity especially at the low shear rate. Carreau’s model was used for curve-fitting. The extrudate swell ratio of the composites tended to increase at the shear rate of 10–500 s⁻¹ and then decreased dramatically once the shear rate were further applied. Neat ABS and wood/ABS composites with higher butadiene content illustrated a higher swelling ratio. The neat MI-ABS and composites showed the highest ultimate tensile strength and modulus due to the butadiene content effect. As the wood flour loading was increased, the tensile modulus of all ABS composites increased with the sacrifice of the tensile strength of composites. The elongation at break and impact strength were noticeably the highest for wood/SI-ABS composites among all because of the effect of rubbery butadiene content. Thermal stability of plastic in 9.1 % wood in HF-ABS composites was improved compared with the neat HF-ABS due to the low acrylonitrile content.