Microbial trans‐glutaminase enhances the physical and mechanical properties of depigmented wool

This study investigates the effects of enzymatic treatment with microbial trans‐glutaminase (m‐TGase) on the physical and mechanical properties of the depigmented wool yarns. Coarse pigmented wool yarns were treated with iron (II) followed by depigmentation with both oxidative and oxidative‐reductive chemicals. The depigmented wool yarns were then treated with m‐TGase to reduce the negative effects of the harsh chemicals. Diverse features of the wool yarns, including: tensile strength, elongation, color, diameter, moisture content, alkali solubility, and weight reduction, were measured before and after bleaching and enzymatic treatments. The treatment with the oxidative and reductive agents led to reduced tensile strength and elongation, and increased lightness, alkali solubility, and moisture content of the yarns. In contrast, the enzymatic treatment by m‐TGases cross‐linked the proteins of wool fibers via reaction between glutamine and lysine isodipeptide remediated the wool yarns. This improved the tensile strength and elongation and decreased the alkali solubility and moisture content. Fourier transform infrared spectroscopy (FTIR) was used to follow the chemical changes in wool fibres during depigmentation and enzymatic treatments.     

Study of water sorption on modified Agave fibres

Polymer composite materials are usually reinforced by synthetic matter such as carbon or glass fibres. However, owing to their good mechanical properties and low density, natural fibres are now increasingly being considered as reinforcement. With the aim of a new natural fibre based composite, various chemical treatments have been performed on Agave (Americana L.) fibres in order to improve their compatibility with the polymer matrix and to reduce their affinity for water. The effect of these treatments on the fibre water sorption power has been investigated by means of a micro-balance. Equilibrium water sorption isotherms have been deduced from weight variations of the fibres under water vapor pressure increments. Several specific physico-chemical models have been tested to describe the water sorption isotherms. The Park’s model was found to describe the experimental results accurately and over a wide activity range. The sorption kinetics was also exploited in order to evaluate the diffusivity of water in the fibres. The variation of the water diffusion coefficient with water concentration is in agreement with the triple sorption mode described by the Park’s model. These results show a global increase of moisture resistance of the fibres after chemical treatment. This effect is interpreted in terms of chemical and structural modifications of the cell-wall structure.     

Tensile and shear properties of fingernails as a function of a changing humidity environment

The mechanical properties of fingernails are important because of their impact in preventing damage and in maintaining their appearance. In particular, knowing the effect of local environmental conditions can tell us how they might best be protected. In order to better understand this, tensile tests were carried out to characterise the properties of fingernails at different relative humidities. Cyclic tests were also conducted to investigate the ability of the structure to recover deformation at different moisture contents. Torsional tests were performed to determine the shear modulus of the keratinous matrix material which binds together the fibrous components of the fingernails. This enabled an analysis of how the material may resist bending, torsion and permanent deformation in a natural environment. In particular, it is shown that at low relative humidity the nails are more brittle, and at high moisture contents they are more flexible. Increasing relative humidity lowers torsional stiffness much more than tensile stiffness, suggesting that moisture plasticises the matrix rather than affecting the fibres. The twist to bend ratio is minimised at 55% RH, close to the natural condition of nails which should minimise susceptibility to torsional damage due to plasticisation and a disruption of the matrix material binding the keratin fibres.     

A molecular dynamics investigation on the compression of cross-linked epoxy resins

Molecular dynamics method is employed to simulate the compression deformation of the polymer materials for electronic packaging. The effects of moisture content, conversion degree, strain rate and temperature on the mechanical properties of epoxy resin are investigated. The stress–strain curves, Young's modulus and Poisson ratio are compared with existing experimental data. The results show that mechanical properties of epoxy resin decrease obviously with increasing moisture content and temperature. However, the high cross-linking conversion and strain rate enhance the mechanical properties of resin.     

Pectinase treatments on technical fibres of flax: Effects on water sorption and mechanical properties

This study is focused on enzymatically upgrading the functional properties of flax fibres. Green flax fibres were treated with a polygalacturonase and a pectate lyase (PaL) and their properties were compared with dew-retted fibres. Morphological observations, vapour-sorption analyses and mechanical measurements showed that PaL-treatment was able not only to mime retting in terms of bundle division, but also to improve the mechanical properties of technical fibres. Conversely, these properties were shifted down after the polygalacturonase treatment, mainly due to the presence of contaminating glycanases. At the level of the elementary fibres, nanoindentation data indicated the highest stiffness of the secondary wall for PaL-treated fibres. The tensile properties exhibited equal, but moderate values of the Young's modulus (∼37 ± 14 GPa) and breaking strength (∼650 ± 300 MPa) for retted and PaL-treated fibres; we hypothesize an impact of the growth conditions on the fibre chemical structure with an excess of matrix pectins compared to the amount of glucomannan coating the cellulose microfibrils.     

Impact Response of Bamboo-Plastic Composites with the Properties of Bamboo and Polyvinylchloride (PVC)

This paper investigates the impacts of moisture content, granular size of bamboo particles and the proportion between bamboo and Polyvinyl Chloride (PVC) on the stability and mechanical properties of bamboo-plastic composites, which were made using virgin PVC with bamboo granule as filler. Composite panels which were made with higher moisture content of bamboo through hot-press moulding exhibited excellent dimensional stability. The tensile and flexural properties of the composites were optimal at 40 mesh granule size of bamboo. Dimensional stability and strength properties of the composites can be improved by increasing the polymer content.     

Lignin deficiency in transgenic flax resulted in plants with improved mechanical properties

Flax (Linum usitatissimum L.) is a very important source of natural fibres used by the textile industry. Flax fibres are called lignocellulosic, because they contain mainly cellulose (about 70%), with hemicellulose, pectin and lignin. Lignin is a three-dimensional polymer with a high molecular weight, and it gives rigidity and mechanical resistance to the fibre and plant. Its presence means the fibres have worse elastic properties than non-lignocellulosic fibres, e.g. cotton fibres, which contain no lignin. The main aim of this study was to produce low-lignin flax plants with fibres with modified elastic properties. An improvement in the mechanical properties was expected. The used strategy for CAD down-regulation was based on gene silencing RNAi technology. Manipulation of the CAD gene caused changes in enzyme activity, lignin content and in the composition of the cell wall in the transgenic plants. The detected reduction in the lignin level in the CAD-deficient plants resulted in improved mechanical properties. Young's modulus was up to 75% higher in the generated transgenic plants (CAD33) relative to the control plants. A significant increase in the lignin precursor contents and a reduction in the pectin and hemicellulose constituents was also detected. A decrease in pectin and hemicellulose, as well as a lower lignin content, might lead to improved extractability of the fibres. However, the resistance of the transgenic lines to Fusarium oxysporum was over two-fold lower than for the non-transformed plants. Since Fusarium species are used as retting organisms and had been isolated from retted flax, the increased sensitivity of the CAD-deficient plant to F. oxysporum infection might lead to improved flax retting.     

Mechanical properties of rat tail tendon in relation to proximal-distal sampling position and age

The mechanical properties of 3, 15 and 25 month-old rat tail tendons were investigated in relation to proximal-distal sampling location along the fibre length. For the 15 and 25 month-old tendons maximum load as well as collagen content per mm fibre length (unit collagen) increased markedly from the proximal to the distal location. A linear regression analysis of the collagen content and mechanical parameters (maximum load, maximum slope of the load-strain curve and energy absorption) showed that these parameters were linearly correlated to the collagen content. However, normalization of the mechanical parameters with regard to the collagen content did not cancel the dependency of the parameters on proximal-distal sampling location. Normalized load and energy values for the 3 month-old tendons and normalized slope values for the 15 and 25 month-old tendons were found to decrease from proximal to distal location. These findings showed that tail tendons are heterogeneous along their length in respect to mechanical strength. The regression analysis also indicated the existence of an inverse relationship between unit collagen and mechanical quality of the collagen. Alternatively, the mechanical properties of tendon fibres might be influenced by other components than collagen.     

Crushing rolls to accelerate napiergrass drying

Napiergrass stalks with an initial moisture content of 73% were crushed by one of five mechanical treatments in the laboratory to simulate possible field methods for crushing. Treatments were evaluated for effectiveness by comparing drying constants determined from oven drying tests. Crushing roll rotational frequency and stalk diameter did not significantly influence the drying constants. Space between the crushing rolls was an important factor for all roll types studied. Stalks crushed on-the-nodes dried four times than stalks that were not crushed.     

Starch-vegetable fibre composites to protect food products

The influence of wheat bran content in biodegradable composites based on cassava starch and containing glycerol and potassium sorbate were studied. Films were produced by casting and three different fractions of wheat bran fibre were used: 1.5 mg, 13.5 mg and 27.1 mg/g of matrix.It was observed that the addition of wheat bran, which contains 40 g of water insoluble fibre per 100 g of bran, shifted the glycerol-rich phase glass transition temperature toward higher temperatures, broadening and diminishing in intensity the peak associated with this relaxation. This effect suggests that the presence of fibre led to an enhancement in the glycerol dispersion.At room temperature, an increase in fibre content did not affect density of the matrix but caused the increase of the storage modulus and the decrease of loss tangent, moisture content and water vapor permeability. Besides, the addition of fibres led to the increase of the yellow index.The improvement in water vapor barrier properties jointly with the enhancement of mechanical properties when fibre was present, lead to the idea that the composite developed can be used to protect food and extend its shelf life.     

Effect of chemical treatments on water sorption and mechanical properties of flax fibres

In this work, in order to improve the adhesion between a polyester matrix (unsaturated polyester resin) and flax fibres (Linum usitatissimum L.) and to increase their moisture resistance, chemical surface treatments have been used. These different treatments were performed with maleic anhydride (MA), acetic anhydride (Ac), silane (Si) and styrene (S). The modified flax fibres were characterized by means of infrared spectroscopy and surface energy analysis. The effect of these treatments on water sorption was investigated by using a gravimetric static equilibrium method. Water sorption isotherms were derived from kinetic data. The Park model based on the three sorption modes: Langmuir, Henry’s law and clustering, was successfully used to simulate the experimental sorption data. It was found that the (Ac) and particularly (S) treatments reduced overall water uptake of flax fibres. We show that tensile modulus, breaking strength and breaking strain depend on the chemical treatment used.     

蜘蛛丝的分子结构与力学性能研究

蜘蛛丝尤其是蜘蛛大囊状腺产生的拖丝,具有独特的机械性能,是自然界颇具应用潜力的生物材料。现代分子生物学技术使蜘蛛丝蛋白基因得以克隆,通过高分子物理化学手段方法的利用,有利于揭示蜘蛛丝蛋白质序列、分子结构、以及分子结构和力学性能之间的关系。对不同种类蜘蛛丝蛋白的深入研究,将为基因工程方法人工合成并改造蜘蛛丝成为可能。     

Technologically indicative properties of straw fractions of flax, linseed (Linum usitatissimum L.) and fibre hemp (Cannabis sativa L.)

In this study of the behaviour of the fractions of unretted and frost-retted fibre straws in damp air, a production scale method to separate fibre and shive from fibre plants was introduced and tested on bast fibre plants (Linum usitatissimum L. and Cannabis sativa L.). The method consists of optional drying of stalks, unloading bales, milling the straws with a hammer mill, separating the fractions from air stream with a cyclone and finally separating fibres from shives with a screening drum. Fractions were characterized focusing on technologically indicative properties such as equilibrium moisture content, ash and microbiological quality. Unretted fractions of the bast fibre plant stem reached higher equilibrium moisture contents than the retted fractions, and hemp fibres absorbed more moisture from air than did the Linum fibres. In very humid air, all fractions began to lose weight due to moulding. The weight decrease during the first week was lower in frost-retted than in unretted fractions. The frost-retted fractions appeared to be more resistant to humidity in the short term. The total number of microbes and especially the numbers of yeasts and moulds can be used as a criterion of hygienic level. For green fractions, the mould level was similar in fibres and in shives, but frost-retted shives contained more moulds than the unretted shives. The mould content of a fraction had no direct correlation with the moulding tendency of the fraction. The ash contents of fibres were somewhat higher than those of shives, due to a probable soil contamination. Ash content did not have significant correlation with microbiological quality, although ash is a possible risk factor for hygienic quality. According to the results of this study it is highly important to study the quality of the production chain of bast fibre plants to ensure the quality of industrial products. From the producer's point of view, raw material with defined quality can be directed to the most suitable application. The behaviour of fractions in various ambient atmospheres, and other quality aspects such as hygienic level can be used as criteria for defining the most appropriate product applications.     

The properties of the extraocular muscles of the frog. III. Morphological, mechanical and pharmacological properties of the isolated retractor bulbi muscle.

Some morphological, physiological, and pharmacological properties of the retractor bulbi muscle of the frog were tested. The enzyme-histochemical investigation shows that the retractor bulbi muscle contains twitch muscle fibres only. Two types of twitch muscle fibres, which are especially different in their diameter and in the content of mitochondria, build the muscle in an irregular arrangement; tonic muscle fibres were not observed. On the average, the isolated retractor bulbi muscle has at room temperature a contraction time of 26 ms, a half-relaxation time of 28 ms, a fusion frequency of 75 stimuli/s, and a twitch-tetanus ratio of 0.28. The fatigability of this muscle is higher than in oculorotatory eye muscles but lower than in skeletal muscles of the frog. An increase of the extracellular K+-concentration elicits in retractor bulbi muscles a quickly transient contracture; the mechanical threshold of the muscle fibres is found in a range between 20 and 25 mM K+ in Ringer solution. Similar short-lasting contractures, which are probably caused by twitch fibres, rich in mitochondria, are also evoked by application of depolarizing drugs like acetylcholine. The properties of the retractor bulbi muscle are compared with those of the sartorius muscle of the frog, which likewise contains twitch muscle fibres only.     

Effect of Root Moisture Content and Diameter on Root Tensile Properties

The stabilization of slopes by vegetation has been a topical issue for many years. Root mechanical characteristics significantly influence soil reinforcement; therefore it is necessary to research into the indicators of root tensile properties. In this study, we explored the influence of root moisture content on tensile resistance and strength with different root diameters and for different tree species. Betula platyphylla, Quercus mongolica, Pinus tabulaeformis, and Larix gmelinii, the most popular tree species used for slope stabilization in the rocky mountainous areas of northern China, were used in this study. A tensile test was conducted after root samples were grouped by diameter and moisture content. The results showedthat:1) root moisture content had a significant influence on tensile properties; 2) slightly loss of root moisture content could enhance tensile strength, but too much loss of water resulted in weaker capacity for root elongation, and consequently reduced tensile strength; 3) root diameter had a strong positive correlation with tensile resistance; and4) the roots of Betula platyphylla had the best tensile properties when both diameter and moisture content being controlled. These findings improve our understanding of root tensile properties with root size and moisture, and could be useful for slope stabilization using vegetation.     

Using the Internal Stress Concept to Assess the Importance of Moisture Sorption-induced Swelling on the Moisture Transport through the Glassy HPMC Films

The purpose of this research was to elucidate the significance of the changes in the mechanical and the volumetric properties on the moisture diffusivity through the polymer films. The internal stress concept was adapted and applied to estimate the relative impact of these property changes on the total stress experienced by a polymer film during storage. Hydroxypropyl Methylcellulose free films were used as a model material prepared at various conditions and stored at different relative humidities. The changes in the internal stress of these films due to the moisture sorption were studied. It was demonstrated that the stress-relaxation of the films increases at increasing moisture content. At the point when there is a definite loss of stress in the film, which is at moisture content higher than 6%, was shown to correlate with the significant increase of the moisture diffusivity. Further investigations revealed that the loss of stress is especially due to the swelling of the polymer rather than the changes in the inherent strain (the quotient between the tensile strength and the modulus of elasticity) of the HPMC films. This implies that the impact of the moisture sorption on the diffusivity is predominantly via volume addition rather than via altering the mechanical properties. Additionally, the approach presented here also brings up a new application of the internal stress concept, which in essence suggests the possibility to estimate the diffusion coefficient from the sorption isotherm and the mechanical analysis data.     

Properties of a plasticised starch blend. Part 1: Influence of moisture content on fracture properties

The effect of moisture content on tensile and fracture properties of a plasticised starch/high molecular weight polyol blend was investigated. A wide range of mechanical behaviour was achieved by varying slightly the water uptake of this material. At low moisture content, the Young’s modulus was 3800 MPa and the yield stress, 54 MPa. When the moisture content reached 15 wt%, their values dropped, respectively, to around 1500 MPa and 21 MPa. As the material behaviour varies greatly over the moisture content range, two fracture mechanics techniques were employed: the linear elastic fracture mechanics approach to characterise brittle behaviour and the essential work of fracture method to investigate a more ductile material. At low moisture content, the measured strain energy release rate at fracture, J_Q was very low and showed little dependency on the moisture content. As the moisture content increases, the material becomes increasingly ductile and displayed a brittle-to-ductile transition at 12% of moisture content, which corresponded to the glass transition temperature of the added polyol.     

Mechanical and water soaking properties of medium density fiberboard with wood fiber and soybean protein adhesive

Soybean protein is a renewable and abundant material that offers an alternative to formaldehyde-based resins. In this study, soybean protein was modified with sodium dodecyl sulfate (SDS) as an adhesive for wood fiber medium density fiberboard (MDF) preparation. Second-order response surface regression models were used to study the effects and interactions of initial moisture content (IMC) of coated wood fiber, press time (PT) and temperature on mechanical and water soaking properties of MDF. Results showed that IMC of coated fiber was the dominant influencing factor. Mechanical and soaking properties improved as IMC increased and reached their highest point at an IMC of 35%. Press time and temperature also had a significant effect on mechanical and water soaking properties of MDF. Second-order regression results showed that there were strong relationships between mechanical and soaking properties of MDF and processing parameters. Properties of MDF made using soybean protein adhesive are similar to those of commercial board.     

Influence of soil moisture on supercooling capacity and associated physiological parameters of overwintering larvae of rice stem borer

Influence of soil moisture on the supercooling capacity and associated physiological parameters of overwintering larvae of the rice stem borer Chilo suppressalis was examined by exposing larvae to soil moistures of 25, 50, 75 and 100% of saturated soil water content (SSWC) at ambient temperature for 30 d from December 2007 to January 2008 in Beijing, China. At the end of the exposure, supercooling points (SCPs) varied significantly among the treatments, the lowest being in the larvae exposed to soil moisture of 25% SSWC. Fresh weight was significantly higher in the larvae exposed to soil moisture of 100% SSWC than in those kept at 25 and 50% SSWC. Dry weight and body water content (% fresh weight) were not different among the treatments. Glucose and trehalose contents were markedly lower, and glycerol content was significantly higher in the larvae confined to soil moisture of 25% SSWC than in those exposed to the other soil moisture treatments. It is suggested that variation in body water content (% fresh weight) contributes to the differences in SCPs of the overwintering C. suppressalis larvae in all treatments, but the influence of soil moisture treatments on supercooling capacity are caused through changes in glycerol content.     

A mechanical investigation of the retting process in dew-retted hemp (Cannabis sativa)

Hemp (Cannabis sativa) produces phloem fibres, which are formed in bundles towards the periphery of the stem. This study investigated one aspect of the retting process, the dissociation of these fibres from the core of the stem, which is influenced by the action of micro-organisms. Peel tests were used to investigate the work required to remove a tissue peel, rich in fibres, from the core of the stem. Two separate experiments studied (1) the effects of tissue dehydration as stems were dried out in the oven; and (2) the progress of retting in stems that were dew-retted in the field. A comparison between two different types of peel tests, where the stems were clamped either vertically or horizontally in the jaws of a tensile testing machine and the load applied vertically, showed that the work required to peel stems in the vertical position was over 20% greater than that for the horizontal position. Freshly harvested stems were dehydrated in an oven at 40°C over a period of 42 h and as the moisture content decreased there was a significant increase in the work to peel. In contrast, stems that had been dew-retted in the field showed a significant decrease in work to peel. When the moisture content of stems dried in the oven decreased below 12%, the work to peel rapidly decreased. As the plant tissues dehydrated their fracture characteristics changed and this was reflected in the increase in the work to peel seen in the oven-dried samples. This, however, was not evident in the field-retted samples, in which there was a decrease in work to peel. The field-retted samples were exposed to the activity of micro-organisms for a prolonged period of time compared with the oven-dried samples; this increased the potential degradation caused by microbial enzymes. Thus, the reduced work to peel in dew-retted stems is thought to be due to the colonisation of the stem by micro-organisms and the subsequent retting process. The dramatic decrease in work to peel at low moisture content in the oven-dried stems is thought to result from mechanical changes leading to brittle fracture characteristics. This study indicates that peel tests can be used to objectively monitor the reduction in work to peel for dew-retted stems and relate this reduction to the progress of retting. Thus, peel tests may be used to monitor the effects of different factors on the process of retting in hemp.