Acid–base and dyeing properties of Nigerian Merino,Yankasa, and Merino–Yankasa crossbred wools

The acid–base titration curves of three wools, Merino, Yankasa, and a ?–? Merino–Yankasa crossbred wool, grown in Nigeria, were measured at 25°C in the presence of varying amounts of sodium chloride. Amino acid analysis was carried out on these wools and correlated with the acid–base properties. The isoionic point and titration curves of Merino and the crossbred wool are similar, while those of Yanakasa are somewhat different. The acid–base behavior was interpreted by the Gibbs–Donnan treatment for the acid titrations and the pK₀¹ values for the carboxyl groups obtained, showing the existence of normal and salt-linked carboxyl groups in these wools. Dyeing tests with acidic and basic dyes have shown that the crossbred wool responds almost as well as Merino. Together with the similarity of its mechanical properties, it seems that this crossbred wool is suitable for all the textile applications for which Merino wool is normally preferred.     

Stress relaxation studies on wool fibers

Stress relaxation studies were made on single fibers of Lincoln, Chokla, and Merino wool in water in the temperature range 2–80°C. Differences in the viscoelasticity of the three wool types were related to differences in their fine structure and morphology. Of the three wools, Merino fibers have the lowest crystalline content and the poorest fibril orientation and packing. This results in greater viscoelastic effects in this wool. Stress relaxation studies have been made in the Hookean, yield, and postyield regions, and the molecular mechanisms of stress relaxation have been discussed.     

Creating a high-quality wool-oriented Turkish merino herd and investigation of mechanical and dyeability properties of fabrics produced from Turkish merino in comparison with Australian merino

Today, the need for quality wool suitable for worsted fabric production in the world is mainly met by Australian merino wool. In Turkey, which has a significant sheep population, in addition to domestic breeds, approximately 10% of the total sheep population (around four million head) is composed of merino cross breeds. However, the fleece quality is far from meeting Australian merino wool standards. Therefore, the aim of this study is to ensure a merino herd with high-quality wool in Turkey. For this aim, by carrying out field studies in the Thrace region of Turkey where Turkish Merino sheep are widely bred, sheep with fleece that can meet the demands of the worsted industry were determined. As a result of field studies in which thousands of sheep were examined, it was determined that 43 female and 10 male sheep had fleece that would meet these standards. Then the breeders of the sheep, which had quality fleece, were persuaded and these sheep were purchased, and “Turkey's wool-oriented Turkish (Karacabey) Merino Herd” consisting of 30 sheep and three rams was formed in the farm of Tekirdağ Namık Kemal University. In the second part of this study, a 100% wool fabric produced by using Australian merino was taken as a reference and it was aimed to produce the same fabric from Turkish merino wool. For this aim, the wool-oriented Turkish Merino herd, which was bred at the university farm for 1 year, was shorn in May 2022. Then, Turkish and Australian merino wools were first converted into worsted yarn and then into woven fabric. The results of mechanical (tensile strength, pilling, abrasion resistance, felting shrinkage, Hofmann dimensional change, bending stiffness) and dyeability (dye-uptake, CIE L*a*b* and colour yield (K/S) values; washing, rubbing and light fastness values) properties of fabrics produced from Turkish and Australian merino wool is presented.     

An NMR determination of the physiological water distribution in wood during drying

Proton magnetic resonance has been used to study water in Douglas fir and western red cedar. The free induction decay, when combined with a knowledge of chemical composition of the wood, gives an accurate measure of the absolute moisture content. Spin-lattice relaxation was found to be significantly different for the two species. In sapwood, three distinct spin—spin relaxation times, T₂, were measured and assigned, with the help of anatomical data, to water in and on the cell wall, water in the ray and latewood tracheid lumens, and water in the earlywood tracheid lumens. This T₂ behavior was explained by a model in which free water in a void exchanges with a small fraction of bound water on the lumen surface. The three T₂'s were almost independent of moisture content, suggesting physically separate compartments. The behavior of the three water components during drying was studied. The fiber saturation point could be determined from a single T₂ measurement on a green sapwood sample. Magnetic resonance imaging of logs was investigated.     

Proton spin–lattice and spin–spin relaxation times in isotactic polypropylene. I. Effects of crystallinity and atactic fraction

Spin–lattice relaxation time T₁ and spin–spin relaxation time T₂ were measured at 40°C on the isotactic polypropylene films of varying preparations and thermal history. T₁ increases with increasing crystallinity and two T₁'s appear for the samples annealed at elevated temperatures (>120°C). These variations in T₁ are well interpreted in terms of the spin diffusion and decoupling of the mobile protons with immobile ones. A free induction decay following a 90° pulse is the superposition of three different decay curves, one of which is exponential and other two are nonexponential. There is an increase in T_2a with increasing crystallinity, which is indicative of the enhancement of the chain mobility in the amorphous region. There are differences between the crystallinity calculated from density and the fraction of crystalline region, F_c, obtained by the NMR method, which can be explained by the existence of the microparacrystals and the stress imposed on the amorphous chains on rapid cooling. On the other hand, there is a gradual lowering in T₁ and a considerable increase in T_2a as an atactic fraction is increased. The increase in atactic fraction also results in a decrease in the amount of the isotactic amorphous chains in the amorphous region.     

Effect of morphology on stress relaxation of polypropylene

Samples of isotactic polypropylene having different morphologies and crystallinities were prepared and subjected to stress-relaxation experiments at different levels of strain. The relaxation moduli were determined in the range of temperature between – 20 and 40°C over a period of time from 1 to 1000 seconds. Using the time-temperature superposition principle, the activation energy values of the shift factors a_T were determined and the master curves were obtained for the various structures. Increasing crystallinity and/or crystalline aggregate size increases the relaxation modulus of the material and changes both shape and location of the spectrum of relaxation times so that no simple method can be found to correlate the various master curves.     

LF-NMR online detection of water dynamics in apple cubes during microwave vacuum drying

ABSTRACT

In this study, changes in various states of water in apple cubes were assessed using low-field nuclear magnetic resonance (LF-NMR) during microwave vacuum drying. Apple cubes were dried at different microwave power levels (100, 150, and 200?W). Indicators including moisture content and water activity were measured. The Carr–Purcell–Meiboom–Gill (CPMG) sequence was used to measure transverse relaxation times (T₂). The results showed that three water fractions with different T₂ relaxation times (around 11, 126, and 1335 ms) were detected in fresh apples, which corresponded to different cell compartments. The transverse relaxation time of bulk water (T₂₃) and the signal per mass of the bulk water (A₂₃/g) decreased significantly with increasing drying time at different microwave power levels. The signal per mass of the total water (A_Total/g) had significant correlation with the total moisture content (R²?=?0.9919). Furthermore, good correlation (R²?=?0.9799) between water activity and NMR parameters based on partial least square regression model were observed. This research revealed that LF-NMR spectroscopy, a nondestructive technique, can detect the changes of water in different populations in the matrix.     

Use of low-field-NMR and MRI to characterize water mobility and distribution in pacific oyster (Crassostrea gigas) during drying process

Low-field nuclear magnetic resonance (LF-NMR) and magnetic resonance imaging (MRI) were used to monitor the water mobility and distribution of Pacific oyster during drying process. The results show the mobilities of bulk, immobilized, and free water were reduced, and the immobilized water was removed dramatically. T₂-weighted images displayed the water decrease from the external surface to inner center of oyster during drying. In addition, excellent correlations between the total moisture content and T₂₂ and A₂₂ were observed with coefficients 0.9777 and 0.9832, respectively. Principal component analysis showed the drying degree of oyster could be monitored based on raw relaxation data. Thus, the result revealed that LF-NMR and MRI have great potential in assessing water mobility and distribution in oyster during drying process.     

Differences between constant and intermittent drying in surf clam: Dynamics of water mobility and distribution study

Low-field nuclear magnetic resonance (LF-NMR) has been increasingly popular as analytical tools for evaluating the dynamics of water mobility and distribution. In this study, dynamics of moisture mobility and constitution of surf clam during constant drying process and intermittent drying process were evaluated by LF-NMR, while the differences of physical and chemical indexes were measured. Intermittent drying improved the product quality of clam, such as moisture content, shear force, color indices, sugar content, peroxide value, thiobarbituric acid value, and the bulk water ratio, which were closely related with moisture distribution and microstructure. The moisture constitution of constant drying process and intermittent drying process were distinctly different. Tempering process reduced drying time and resulted in lower moisture content in dried surf clam. In the meanwhile, the boundary between A₂₁ and A₂₂ was acquired by LF-NMR, revealed that bound water and immobilized water transformed from each other. During tempering process, the myofibril stretched out, verifying that moisture approached a relatively homogeneous. In addition, R² value reached 0.9897 and 0.9926 for calibration and validation, respectively, displaying good linear correlations between the T₂₁ parameters and moisture content. This study interpreted the dynamics of water mobility and distribution on the proton level to explain the reason that tempering processes to improve physicochemical indexes of surf clam.     

Effects of gluten and moisture content on water mobility during the drying process for Chinese dried noodles

To investigate the water mobility during a drying process, noodles were prepared with different gluten contents (10.0%, 12.5%, 15.0%, 17.5%, 20.0%, 22.5%, or 25.0%) and moisture contents (30%, 32%, or 34%), and dried on a food moisture analysis technology platform. Three types of water were deduced from relaxation signals measured by low-field nuclear magnetic resonance (LF-NMR) spectroscopy. Peak time T₂₂ increased with gluten and moisture content but decreased with drying time from 4–6 to 1.0–1.7?ms after 1.5?h. Gluten content mainly affected the drying rate (DR) in the middle drying period, whereas initial moisture content had an influence in the middle drying period and final drying period.     

Experimental study on drying characteristics of wheat by low-field nuclear magnetic resonance

The characteristics of transverse relaxation time (T₂) of water in wheat were studied by measuring the relaxation time of low-field nuclear magnetic resonance. Analysis of the exponential distribution of T₂ revealed that wheat contains five water components. The T₂ relaxation time and distribution significantly changed during drying. The dynamic characteristics of five water components during wheat drying were determined using the signal quantity of their characteristic peaks, which showed different features. Weakly chemically bound water (T₂₂) and water ascribed to cell wall (T₂₃) were the main source of water loss. Moreover, most T₂₃ and extracellular water (T₂₄) were removed during drying. Water migration between strongly chemically bound water (T₂₁) and the other water components was bidirectional. This process was not only affected by temperature but also by wheat moisture content and proportion of the five water components. The start time of water migration advanced and growth rate of T₂₁ at the end of drying to that before drying increased at 60, 70, and 80°C. Drying at varied temperatures should be applied according to the characteristics of five water components during the drying process. In addition, high initial temperature was found to be necessary to achieve high drying rate of T₂₃, T₂₄, and free water (T₂₅). The use of drying temperature of 80°C at the early stage and then changing to 70°C reduced the heat consumption by 4.81% and increased the drying time by 9.61%.     

Dielectric properties of poly(α-methyl α-n-propyl-β-propiolactone)/poly(vinyl chloride) blends

The dielectric properties of miscible blends of poly(vinyl chloride) (PVC) and poly(α-methyl-α-n-propy-β-propiolae-tone) (PMPPL) have been investigated at different temperatures above and below T_g. The results were analyzed using the Cole-Cole representation and lead to the conclusion that this mixture does not exhibit micro-scale heterogeneities. Dielectric constant and dielectric loss master curves were constructed using the stress relaxation shift factors determined previously; the same shift factors could be used for the homopolymers and their blends. Similarities between the dielectric master curves and the stress relaxation master curves of PVC, PMPPL, and their blends, are also discussed.     

Pulsed NMR study on the hydration of poly(acrylic acid) salts

Summary Pulsed NMR was applied to measure the spin-lattice (T₁) and spin-spin (T₂) relaxation times of the equilibrium water absorbed in poly(acrylic acid) lithium salt, sodium salt, and potassium salt. T₁ and T₂ relaxation time curves for the samples of lithium and sodium salts studied showed single phase behavior, but the sample of potassium salt exhibited two-phase behavior, indicating the existence of water fraction of higher mobility.     

Study of miscibility of poly(vinyl acetate) and poly(vinyl alcohol) blends by fluorescence spectroscopy

Secondary relaxation of poly(vinyl alcohol) (PVA), poly(vinyl acetate) (PVAc), and their blends in different proportions (9 : 1, 1 : 1, and 1 : 9) were studied by photoluminescence of anthracene, fluorescein, and both probes dissolved in the polymer blends. The temperature of the glass transition in the homopolymers was determined by the radiationless deactivation of anthracene as T_g(PVAc) ? 304 K and the photobleaching of fluorescein as T_g(PVA) ? 350 K. The relaxation processes of the different phases of the polymer blends occur at temperatures close to the homopolymers, which may be explained by the localization of each molecular probe within the matrix. These deactivation curves, however, are not similar to those of the individual homopolymers, suggesting a partial miscibility between these polymers. © 1995 John Wiley & Sons, Inc.     

Conformational motions in immiscible blends of polycarbonate and styrene-acrylonitrile copolymers

Blends of commercial bisphenol-A -polycarbonate and styrene-acrylonitrile copolymers were prepared by precipitation in ethanol from the solution in methylene chloride in order to eliminate the low molecular weight substances contained in the commercial polymers, specially the oligomers contained in commercial SAN copolymers. Two glass transitions appear in the DSC thermograms of the blend at the same temperatures as in the pure components which, in principle, indicates that the blend consists of two phases formed by pure PC and pure SAN. In order to detect small changes in the glass transition process that could be indicative of different mobility of the polymer chains in the blend with respect to the pure polymers, blends of different compositions were subjected to different thermal treatments that included annealing at temperatures below both glass transitions, and then the DSC thermograms were recorded. A broadening in the peaks shown by the c_p(T) curves measured on annealed samples in the zone of the PC transition is detected while no significant differences are shown by the glass transition of the San phase of the blend with respect to pure SAN copolymer. Dielectric relaxation experiments in the frequency domain (from 100 to 3·10⁶Hz) were carried out on the blends. The dielectric relaxation spectrum in the zone of the SAN main relaxation process was fitted with the stretched exponential equation showing no significant difference between the blends and the pure SAN copolymer. The region of the main relaxation process of PC was not analyzed due to the small polar activity of PC and the overlapping with the relaxation of the SAN phase.     

Crosslinking structure of keratin. I. Determination of the number of crosslinks in hair and wool keratins from mechanical properties of the swollen fiber

Hair and wool keratin fibers which had been treated with an 11 M LiBr solution containing N-ethyl maleimide showed typical rubberlike elasticity in a solution composed of equal volume of 8 M LiBr and diethylene glycol mono-n-butyl ether. Stress–strain curves and equilibrium force–temperature relations were measured for swollen hair and wool fibers. The non-Gaussian effects on deformation and the energy component in retractive forces were analyzed. On the basis of rubber elasticity theory, a method for estimation of the number of mechanically effective crosslinks in keratin fibers was proposed. A linear relationship between the crosslink density and the disulfide content was obtained from the data for a variety of keratin fibers (i.e., two different human hairs, horse hair, and 17 different wools). From the results of thermodynamical and non-Gaussian treatments for swollen keratin, it was suggested that the swollen fiber consists of a two-phase structure: a mechanically stable phase of higher crosslinked domains and rubbery phase with lower crosslink density. It was further found that considerable amounts of nondisulfide covalent crosslinks are present in wool and hair keratins.     

Effect of physical aging on tensile stress relaxation and tensile creep of cured EPON 828/epoxy adhesives in the linear viscoelastic region

The effect of physical aging on viscoelastic properties was studied for several cross-linked epoxies in the glassy state. Tensile creep and tensile stress relaxation were measured during isothermal physical aging, following rapid quenching of samples annealed above the glass-transition temperature (T^g). The momentary creep curves measured at 21°C, 45°C, and 61°C below T^g for different epoxies could be fitted to an empirical equation for the creep compliance D(t): Values for β and t_o were obtained, and the dependence of t_o on the aging time was determined. Shift factors were calculated to investigate changes in molecular mobility during physical aging. The momentary stress relaxation was measured on the same epoxy materials as used for the creep studies. The stress relaxation curves were fitted to the following equation for the tensile modulus E(t): Values for α and t_o were obtained. The influence of physical aging on-t_o was again studied by calculating shift factors as a function of the aging time. The results are compared with the results of the creep tests and discussed in the context of current molecular theories of physical aging of glassy polymers.     

Correlating Perceived Crispness Intensity to Physical Changes in an Amorphous Snack Food

Abstract

A crispy amorphous food was equilibrated to different moisture contents. These samples were tested for the glass transition temperature (T_g) using mechanical methods. The brittle-ductile transition temperature (T_b) was determined using force-deformation methods. Finally, the temperature where the onset to the sharp decrease in crispness intensity occurred (T_ci) was determined by a 10-member sensory panel rating the crispness intensity. The relationships of the T_g, the T_b, and the T_ci were determined using three different statistical methods. The results of this research indicated that the T_g, the T_b, and the T_ci were related to one another as a function of moisture content.     

Approach for monitoring the dynamic states of water in shrimp during drying process with LF-NMR and MRI

The dynamic states of water in shrimp during drying process were investigated by low-field nuclear magnetic resonance and magnetic resonance imaging. With the extension of drying time, the transverse relaxation time of immobilized and free water significantly decreased, illustrating their mobility reduced. The signal per mass of immobilized water also decreased significantly, indicating its remarkable loss during drying process. Magnetic resonance imaging results revealed that the water signal intensity decreased from the external surface to inner regions of shrimp. Good correlations between the moisture content, hardness, chewiness, cohesiveness, L*, a* and nuclear magnetic resonance T₂ parameters were observed by linear regression analysis.     

Graft polymerization of methacrylate onto wool using dimethylaniline–benzyl chloride mixture as initiator

Graft polymerization of wool with methyl methacrylate (MMA) initiated by a dimethylaniline–benzyl chloride (DMA/BC) mixture was extensively studied. The grafting and homopolymerization reactions are influenced by the nature of the solvent used; ethanol proved to be the best. Using water as a cosolvent enhances significantly both graft formation and homopolymerization. A mixture of water/ethanol at a ratio of 90:10 constitutes the optimal medium for the grafting reaction. Addition of acetic acid or formic acid in low concentration (0.2 mole/l.) favors grafting. The opposite holds true for sulfuric and hydrochloric acid. Kinetic investigations showed that the rates of total conversion (R_p) and grafting (R_p′) are dependent of the concentrations of DMA, BC, acetic acid (Ac) and amount of wool (W), as well as temperature. They can be expressed by the following equations: The overall activation energies for the total conversion and grafting reactions amount to 8.5 and 9.0 kcal/mole, respectively; whereas the corresponding energies for initiations E_d are E_d′ 7.0 and 8.0 kcal/mole, respectively. The changes in the physical and/or chemical structure of wool via reduction, acetylation, and dinitrophenylation are reflected on the susceptibility of wool toward grafting. While reduced wool showed higher grafting, the graft yields obtained with acetylated and dinitrophenylated wools were quite poor. The alkali solubility of wool graft copolymer was determined and its tendency to felt was examined. Evidences for grafting were provided and a tentative mechanism for grafting initiation was suggested.