Experimental study on structure and mechanical properties of hemp/PBTG composites with fiber contents and thermal exposures

Most materials used in daily life are polymeric materials based on petrochemistry. The used polymeric materials can cause land pollution and air pollution after landfill or incineration. In contrast, natural fiber reinforced (NFR) composites are more suitable for the environment, however the reliability in terms of the durability and weatherability of NFR composites is still lacking. Thus, NFR composites require the reliability involved with durability and weatherability. In this work, poly(butylene terephthalate-co-glutarate) (PBTG), with a chemical structure similar to biodegradable PBAT, was used as the matrix in the composites, and hemp fibers were used as the reinforcement. Hemp/PBTG composites were fabricated by stacking hemp-fiberwebs and PBTG films with various fiber contents and thermal exposure times. Characteristics of the composites, such as the morphological structure, chemical structure, tensile properties, compressive properties, flexural properties, and impact strength, were analyzed to obtain the effects of fiber volume fraction and thermal exposure. As a result, hemp/PBTG composites were hardened in proportion to fiber volume fractions, and the hardening behavior of the composites increased tensile strength and flexural strength. However, the hardened structure of the composites decreased the impact strength and compressive strength of the composites. On the other hand, the mechanical properties of hemp/PBTG composites with thermal exposure times, were governed significantly by the brittleness behavior of the resin and the increased crystallinity of hemp fibers. Thus, the hemp fibers contributed to the improvements on structural stability, tensile strength and flexural strength of the hemp/PBTG composites, and increased the thermal durability of the composites with various thermal exposures.     

Long term performance study of glass reinforced composites with different resins under marine environment

For marine structural applications which poses significant challenges to the choice of materials due to presence of corrosive seawater, polymer matrix based fiber reinforced composites are increasingly becoming the material of choice. However the performance properties of composites are greatly influenced by the moisture absorbed by the composite. In the current study, the long term performance is assessed by determining the amount of moisture absorbed and the reduction of mechanical properties over 12 months in a simulated sea-water environment at different temperatures. Three commonly used thermoset resins with different chemistry such as unsaturated polyester (USP), epoxy resin (EP) and vinylester (VE) are chosen. The effect of fiber reinforcement on the long term performance is investigated. A suitable method for manufacturing glass reinforced composite with good interfacial bonding and high volume fraction is also developed in current study. It is observed that vinylester plaques and composites absorb lesser moisture compared to USP and Epoxy systems resulting in lesser reduction in flexural strength and making the best performing among polymers studied. It is also found that sea-water diffusion into the composite follows non-Fickian behaviour and diffusion relaxation model fits well with the experimental data and corresponding model parameters are evaluated.     

A novel method to analyze the moisture liberation of textile fabrics

In this paper, a purpose-built apparatus was used to analyze the moisture liberation of textile fabrics. Fabrics were wetted and placed in an air-conditioned room to test the variation of weight and surface temperature during the process of moisture liberation. Effects of textile materials and fabric structures on the velocities of moisture liberation of fabrics were analyzed; the temperature variation and its relationship with moisture regains of fabrics in the moisture liberation were also studied. Moisture liberation velocities of polyester and silk fabrics are much higher than that of wool and cotton fabrics. For the same textile materials, knitted fabrics absorbed more water and thus took longer time to liberate the water. The surface temperature of fabrics showed three stages during moisture liberation. With the decrease of moisture regain, fabric temperature decreased gradually and jumped quickly to ambient temperature. In this way we could evaluate the moisture desorption of fabrics and develop quick-drying fabrics with imporved moisture and thermal properties.     

The study on the air volume fraction of electrospun nanofiber nonwoven mats

Electrospinning is an efficient method to produce polymer fibers with a diameter range from nanometers to a few microns using an electrically driven jet. Electrospun nanofiber nonwoven fabrics can be applied into different areas with higher air volume fraction, especially applied into textile materials with good warmth retention property. In this article, the air volume fraction in nonwoven mats made of electrospun nanofibers was verified by studying fiber volume fraction in the mats. Then the relationship between fiber volume fraction and fiber diameter was derived, and the fiber volume fraction is in direct ratio to the square of fiber radius. By experimental verification, to get electrospun PAN nanofiber nonwoven mats with high air volume fraction about 99 %, it can fix the polymer concentration on 8 %. The voltage fixed on 20 kV, the tip-to-collector distance on 15 cm. The experiment is in accordance with the theory excellently.     

Metal oxide/polymer hybrid nanofiber as flexible moisture absorbent

In order to realize flexible organic light emitting diode (OLED), it is critically important to protect moisture and oxygen penetration into the flexible device through the polymer substrates because of intrinsically poor stability of organic materials of OLED to moisture. Since complete protection of the moisture penetration is almost impossible, moisture absorbents are used inside OLED. In this study, metal oxide/polymer hybrid nanofiber with mechanical flexibility and efficient moisture absorption capability was fabricated by electrospinning. Hydrophilic poly(vinyl pyrrolidone) (PVP) or hydrophobic poly(vinylidenefluoride) (PVDF) and calcium oxide (CaO) were used as the fiber forming polymers and as the moisture absorbing particle, respectively. Polymers were first dissolved in appropriate solvents and CaO was then dispersed in the prepared polymer solutions. The hybrid solution was then electrospun, producing the hybrid nanofiber web looking like paper with thickness of about 100 µm. It was observed that all CaO particles were uniformly held by the nanofiber. It was also observed that only a small portion of the surface of CaO particles was covered by fiber since the fiber diameter was much smaller than the CaO particle size. This implied effective moisture absorption through the free surface of CaO. The hybrid nanofiber absorbed moisture very efficiently upto about 70 % of the nanofiber mass. Once moisture was absorbed by the nanofiber, it was never released even at 150 °C in vacuum for 2 hours. It is, therefore, expected that the nanofiber may be applied as the flexible thin moisture absorbent to improve stability of the flexible OLED.     

Effect of soaking corrosion on flexural properties of carbon fiber reinforced epoxy syntactic foams

The fiber-reinforced syntactic foam is a type of lightweight materials. In this paper, hollow glass microspheres/epoxy syntactic foams reinforced by carbon fibers are prepared. Carbon fibers of five mass fractions are used to obtain five types of reinforced syntactic foams. The effect of the fiber content and soaking corrosion on the flexural properties of syntactic foams are investigated. The results of soaking test show that the moisture rate in distilled water is greater than that in seawater. The flexural test results show that the flexural strength of syntactic foams increases obviously by adding fibers. The maximum value increases 25.5 % than that of composites without adding fibers when fiber-mass fraction is 5 %. Soaking corrosion reduces the flexural properties of the syntactic foams. The flexural strengths of syntactic foams immersed in water and seawater with 5 % fiber-mass fraction decrease 34.4 % and 37.5 % respectively. The main reasons of the flexural strength reduction of syntactic foams with soaking corrosion are discussed.     

Effect of mulch on soil temperature,moisture, weed infestation and yield of groundnut in northern Vietnam

Groundnut (Arachis hypogaea L.) is one of the chief foreign exchange earning crops for Vietnam. However, owing to lack of appropriate management practices, the production and the area under cultivation of groundnut have remained low. Mulches increase the soil temperature, retard the loss of soil moisture, and check the weed growth, which are the key factors contributing to the production of groundnut. On-farm trials were conducted in northern Vietnam to study the impact of mulch treatments and explore economically feasible and eco-friendly mulching options. The effect of three mulching materials (polythene, rice straw and chemical) on weed infestation, soil temperature, soil moisture and pod yield were studied. Polythene and straw mulch were effective in suppressing the weed infestation. Different mulching materials showed different effects on soil temperature. Polythene mulch increased the soil temperature by about 6 °C at 5 cm depth and by 4 °C at 10 cm depth. Mulches prevent soil water evaporation retaining soil moisture. Groundnut plants in polythene and straw mulched plots were generally tall, vigorous and reached early flowering. Use of straw as mulch provides an attractive and an environment friendly option in Vietnam, as it is one of the largest rice growing countries with the least use of rice straw. Besides, it recycles plant nutrients effectively.     

Influence of low soil nitrogen and phosphorus on gluten polymeric and monomeric protein distribution in two high quality spring wheat cultivars

The effect of low levels of nitrogen, phosphorus and a combination of the two on the distribution of polymeric and monomeric proteins in two high quality spring bread wheat cultivars was investigated for two consecutive seasons. Size exclusion-high performance liquid chromatography (SE-HPLC) was used to determine the quantity and relationships of monomeric and polymeric proteins, and their relationship with flour protein content (FPC) and SDS sedimentation volume (SDSS). The low nitrogen and combined low nitrogen and low phosphorus treatments had a much larger effect on the protein fractions than the low phosphorus treatment alone. The SDS-soluble large monomeric protein fraction and the percentage SDS-insoluble monomeric proteins, were significantly increased under low nitrogen and a combination of low nitrogen and low phosphorus treatments. The percentage SDS-insoluble large and total polymeric proteins was significantly reduced under low nitrogen and a combination of low nitrogen and phosphorus treatments. The SDS-soluble and -insoluble small polymeric proteins were significantly increased under both low nitrogen and a combination of low nitrogen and low phosphorus treatments. The low nitrogen treatment consistently caused the lowest FPC and SDSS values. Under low nitrogen conditions, there was a significant positive correlation between the SDS-soluble gliadins and SDSS, and FPC.     

Structural aspects of alkali treated sisal fiber — A SAXS investigation

The present work emphasizes the effect of alkali (NaOH) solution on macromolecular parameters of sisal fiber. The macromolecular parameters of alkali treated sisal fiber were computed along with air-dried sisal fiber by treating fiber as a non-ideal two-phase system characterized by continuous variation of electron density at the phase boundary. Small angle Xray scattering (SAXS) technique was employed to evaluate the macromolecular parameters, using correlation functions, applying the theories of Vonk, Ruland and Misra et al. The finite value of width of transition layer suggests to treat the fiber to be a non-ideal two-phased system. The evaluated macromolecular parameters are: transversal periodicity, specific inner surface, volume fractions of matter and void phases, transversal lengths in both phases, range of inhomogeneity, volume fraction of transition layer and length of coherence.     

Application of electrostatic force microscopy on characterizing an electret fiber: Effect of tip to specimen distance on phase shift

The application of Electrostatic Force Microscopy (EFM) on characterizing a corona charged polypropylene fiber by phase measurements was studied. Electrostatic force gradient images were obtained from the phase shifts with varied EFM tip bias voltages at a constant tip-to-sample distance, and with varied tip-to-sample distances at a constant tip bias voltage. Mathematical expressions were introduced to interpret the phase measurements in terms of the tip bias voltage and the tip-to-specimen distance. The phase measurements from EFM appeared feasible to provide the qualitative information of electrical properties of charged polymeric materials. The fit of mathematical expressions to the experimental measurements was discussed with regards to the effect of tip geometry on the interaction between the tip and the specimen.     

山区旱地间套种春玉米的覆盖效果研究

3年定位试验结果表明,栏肥、秸秆、地膜和杂草覆盖对山区旱地间套种春玉米具有显著的增产增效作用,增产幅度18.1%～36.4%,其中以秸秆覆盖最为明显,且以前作秸秆全部覆盖最好.栏肥、秸秆和杂草覆盖保水效果好,具增降温的双重功效,并能明显提高土壤肥力,而地膜覆盖保水抗旱效果差,又耗地力,不利于山区旱地的可持续生产。     

Winter wheat genotypes under different levels of nitrogen and water stress: Changes in grain protein composition

Hard white winter wheat with superior and consistent quality is preferable for Asian markets. This study investigated the combined influences of moisture deficit during grain-fill and N management on protein quality, dough rheological properties, and protein molecular weight distributions in soft and hard winter wheats. Genotypes were grown under an irrigation gradient and two N-fertilization levels. Grain polyphenol oxidase (PPO) activity, SDS sedimentation, and Mixograph analyses were evaluated. Flour protein composition was characterized using SE-HPLC. Moisture stress during grain-fill increased flour protein content. N fertilization increased flour protein content. No significant correlation was found between flour protein and PPO. Changes in protein composition were related to general increases in protein content, regardless if the result of reduced irrigation or increased fertilization rate. The percentage of monomeric proteins increased more than the polymeric proteins as flour protein increased. Similarly, SDS sedimentation volume increased as a function of protein content. As expected, subunit GluD1 5+10 was associated with larger sedimentation volume and higher dough strength in genotypes as compared to those with subunit GluD1 2+12. Biplot analyses showed that genotypes of similar protein quality and composition responded similarly to N and irrigation treatments.     

Estimated Glycemic Index and Dietary Fiber Content of Cookies Elaborated with Extruded Wheat Bran

The increasing demand for high-fiber products has favored the design of numerous bakery products rich in fiber such as bread, cookies, and cakes. The objective of this study was to evaluate the dietary fiber and estimated glycemic index of cookies containing extruded wheat bran. Wheat bran was subjected to extrusion process under three temperature profiles: TP1;(60, 75, 85 and 100 °C), TP2;(60, 80, 100 and 120 °C), and TP3;(60, 80, 110 and 140 °C) and three moisture contents: (15, 23, and 31 %). Cookies were elaborated using extruded wheat bran (30 %), separated into two fractions (coarse and fine). The dietary fiber content of cookies elaborated with extruded wheat bran was higher than the controls; C0 (100 % wheat flour) and C1 (30 % of no extruded bran coarse fraction) and C2 (30 % of no extruded bran fine fraction). The higher values of dietary fiber were observed on cookies from treatments 5 (TP1, 31 % moisture content and coarse fraction) and 11 (TP2, 31 % moisture content and coarse fraction). The estimated glycemic index of cookies ranged from 68.54 to 80.16. The dietary fiber content of cookies was increased and the lowest glycemic index corresponded to the cookies elaborated with extruded wheat bran. Cookie made with the treatment 11 had a better dietary fiber content and lower estimated glycemic index.     

夏玉米子粒含水率和子粒灌浆的粒位差异及其关系研究

以不同自然脱水类型玉米品种为材料,分析其花后不同部位子粒含水率变化、粒重、体积、灌浆动态以及灌浆参数,明确子粒含水率变化与灌浆动态的关系。结果表明,灌浆后期两个时间节点子粒含水率差异较大,先玉335较蠡玉16子粒含水率分别低4.27和5.49个百分点。子粒含水率、体积和粒重均存在粒位效应,两个玉米品种子粒含水率均表现为下部子粒中部子粒上部子粒,子粒体积和粒重粒位效应表现为下部子粒中部子粒上部子粒。灌浆速率粒位效应存在基因型差异,蠡玉16表现为中部子粒下部子粒上部子粒,先玉335表现为下部子粒中部子粒上部子粒。灌浆启动势均表现为上部子粒下部和中部子粒,活跃灌浆期粒位差异较大,且品种间粒位效应趋势相反,先玉335活跃灌浆期上部子粒略大于下部子粒,蠡玉16下部子粒活跃灌浆期长于中部和上部子粒。灌浆峰值出现时间不同,两个品种最大灌浆速率出现时间相差4.77 d。     

Moisture migration in a cereal composite food at high water activity: Effects of initial porosity and fat content

Water sorption isotherms and effective moisture diffusivities were determined at 20 °C for sponge cakes at high water activity as a function of their initial porosity, in the range 86 and 52% (0 g/g dry basis fat content), and of their fat content, ranging between 0 and 0.30 g/g dry basis (67% initial porosity). The equilibrium moisture values were not affected by food structure and decreased with increasing fat content. The effective moisture diffusivity decreased from 7.5 to 0.3×10⁻¹⁰ m²/s with increasing moisture content from 0.30 to 2.20 g/g dry basis. Decreasing initial porosity from 86 to 52% decreased effective moisture diffusivity by more than four orders of magnitude. This behaviour was related to differences of water transfer mechanisms, with the contribution from liquid water diffusion in the solid matrix and from vapour water diffusion in pores. Increasing fat content of 0.30 g/g dry basis in sponge cake, independently of porosity, decreased effective moisture diffusivity by more than five orders of magnitude. A predictive mathematical model was used to simulate moisture intake in two-composite food systems: sponge cakes with varying initial porosities and fat contents and an agar gel as a model of a non-rate limiting water source. Increasing the density of the structure or addition of fat in the cereal-based phase could increase shelf life of composite foods.     

Influence of the draw ratio on the mechanical properties and electrical conductivity of nanofilled thermoplastic polyurethane fibers

Electrically conducting textile fibers were produced by wet-spinning under various volume fractions using thermoplastic polyurethane (TPU) as a polymer and carbon black (CB), Ag-powder, multi-walled carbon nanotubes (MWCNTs), which are widely used as electrically conducting nanofillers. After applying the fiber to the heat drawing process at different draw ratios, the filler volume fraction, linear density, breaking to strength, and electrical conductivity according to each draw ratio and volume fraction. In addition, scanning electron microscopy (SEM) images were taken. The breaking to strength of the TPU fiber containing the nanofillers increased with increasing draw ratio. At a draw ratio of 2.5, the breaking to strength of the TPU fiber increased by 105 % for neat-TPU, 88 % for CB, 86 % for Ag-powder, and 127 % for MWCNT compared to the undrawn fiber. The breaking to strength of the TPU fiber containing CB decreased gradually with increasing volume fraction, and in case of Ag-powder, it decreased sharply owing to its specific gravity. The electrical conductivity of the TPU fiber containing CB and Ag-powder decreased with increasing draw ratio, but the electrical conductivity of the TPU fiber containing MWCNT increased rapidly after the addition of 1.34 vol. % or over. The moment when the aggregation of MWCNT occurred and its breaking to strength started to decrease was determined to be the percolation threshold of the electrical conductivity. The heat drawing process of the fiber-form material containing the anisotropic electrical conductivity nanofillers make the percolation threshold of the electrical conductivity and the maximum breaking to strength appear at a lower volume fraction. This is effective in the development of a breaking to strength and electrical conductivity.     

甘蓝型油菜“三系”杂种优势利用研究

本文叙述了优质甘蓝型油菜(B.napus)三系杂种优势利用研究的概况。在实现了甘蓝型油菜低芥酸“三系”配套的基础上,又获得了较稳定的“双低”三系材料。现有低芥酸杂交油莱在有效分枝数、单株角果数和每果粒数等因素方面,表现了一定的优势。研究表明,优质甘蓝型油菜“三系”与原有普通甘蓝型油菜“三系”一样,具有保持材料比较广泛,制种技术比较简便等特点。     

Physicochemical, Structural and Textural Properties of Tortillas from Extruded Instant Corn Flour Supplemented with Various Types of Corn Lipids

The chemical composition and the components of corn grain affect the quality of tortillas produced from extruded instant corn flour (EICF). We have studied the effects of various types of corn lipids added at several concentrations to the regular raw corn flour before processing. The structural properties of flour, the effective moisture diffusion coefficient and the weight loss during cooking of fresh masa, as well as the textural characteristics of tortillas were analysed as a function of concentration and type of corn lipid added. The concentration of added lipid ranged from 0·5 to 2% (w/w). Each type and concentration of lipid was observed to have a different effect in the quality of masas and tortillas. Commercially it is desired to have tortillas with good properties and a high yield, that is, optimum weight transformation from corn to tortilla. From our analysis, the lowest dehydration rate (lowest effective moisture diffusion coefficient) and the best physicochemical and textural characteristics of fresh masas and tortillas were obtained from flour supplemented with 0·5% (w/w) of the nonpolar lipid fraction III. The loss in starch crystallinity due to the cooking process of masa into tortilla was similar in all treatments.     

Effects of cross-linking on mechanical and physical properties of agricultural residues/recycled thermoplastics composites

Maleated graft polyolefins as cross-linking agents (CAs) are widely used to improve properties of wood thermoplastic composites made by melt extrusion process. In this study, novel CAs, free isocyanate group (NCO)-terminated urethane pre-polymers (UPs) were synthesized and used in manufacturing wheat straw (WS)/recycled polyethylene (PE) composites. The composites using polymeric diphenylmethane diisocyanate (pMDI) as a CA were also made in comparison. The relationship between composite properties and the level of CA and its content as well as the composite density and hot pressing time were investigated based on wood based board processes. The results show that the internal bonding (IB) strength, the IB after soaked in boiling water for 2 h (2hWIB), the modulus of rupture (MOR), the modulus of elasticity (MOE) and the 24 h thickness of swell after absorption of water (24hTS) of the composites are significantly improved with increased CA contents and composite densities. The optimal hot pressing time is 1.1 min/mm at 180°C. The cross-linking function is attributed to the reaction between free NCOs of CA molecules with hydroxyls of WS and the moisture in the raw materials, as well as the interaction between weak polar chain segments in the CA molecules to the non-polar PE. It is highly feasible to manufacture high quality composite using WS and recycled PE as raw materials when cross-linked with just 2.5% of UPs.     

干旱胁迫对春大豆开花期根系生理特性的影响

为明确大豆根系生理特性的变化与抗旱性的关系,在盆栽条件下,以3个抗旱性不同的大豆品种为材料,测定开花期根系相对含水率、根系活力、丙二醛含量、超氧化物歧化酶和过氧化物酶活性.结果表明:大豆根系相对含水率及根系活力随干旱胁迫程度增强而降低,抗旱品种降低程度小于不抗旱品种;根系丙二醛含量随干旱程度的增加而升高,各品种间无明显差异;抗旱品种超氧化物歧化酶活性随干旱程度的增加而升高,而不抗旱品种则表现为先升高后降低趋势;过氧化物酶活性各品种间随着干旱胁迫程度的加强均呈先升高后降低趋势,抗旱品种变化更为明显.干旱胁迫下大豆通过改变根系内部的生理变化以提高其抗旱性.