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Abstract
The article reviews the authors' career, beginning in the scientific field and subsequently becoming involved with the textile industry. It documents the various research projects undertaken and provides details of the publications that proceeded his findings. The author has been presented with the Olney Medal and this article pays homage to his achievement.
xxviii, 224 leaves : ill. ; 30 cm. PolyU Library Call No.: [THS] LG51 .H577P ITC 2005 Zhang This project aims to fabricate and characterize the structures and properties of thermo-regulated fibres and fabrics that can intelligently regulate temperature by absorbing and evolving latent heat, to enhance the development of temperature regulating fabrics and improve the thermo-physiological comfort of textile materials. In this study, nano/microencapsulated n-alkanes (Nano/MicroPCMs) were synthesized by in-situ polymerization of urea-melamine-formaldehyde. Parameters affecting the structures, thermal stabilities and properties of Nano/MicroPCMs, such as oil phase composition and content of cyclohexane, shell composition, stirring rates, content of emulsion and heat-treatment on the properties of MicroPCMs were studied. To analyze the effects of increased content of Nano/MicroPCMs, polypropylene (PP) composite fibres containing 4-24wt% MicroPCMs and polyacrylonitrile-vinylidene chloride (PAN/VDC) fibres containing 5-40wt% Nano/MicroPCMs were melt and wet-spun respectively. The composition and properties of thermo-regulated non-woven fabrics made of the fibres, PET and PP fibres and Nano/MicroPCMs coated knitted fabric were also studied. Results indicated that the average diameters of the microcapsules with enthalpies of melting and enthalpies of crystallization of approximately 160 J/g varied from 9.2 um to 0.8 um with the increase of stirring rates. The core material diffused out of the shell in the heating process. The thermal stability was enhanced by adding 5-28wt% expansion space inside the microcapsules and using copolymer shell. The maximum thermal stable temperatures of the microcapsules were 230℃ and 268℃ in air and nitrogen atmosphere, respectively. The multiple peaks in the DSC cooling curves, which were mainly affected by the average diameters of the microcapsules, were associated with the liquid-rotator, rotator-crystal and liquid-crystal transitions. Adding 10.0wt% 1-octadecanol in the core decreased the degree of supercooling of microencapsulated n-octadecane from 26.0℃ to 10℃. The heat absorbing and evolving temperatures of the melt-spun fibres in which the microcapsules were evenly impregnated in core polymer matrix were approximately 32℃ and 15℃ respectively. The enthalpy of melting and enthalpy of crystallization of the fibres containing 24% MicroPCMs was 11 J/g respectively. The heat absorbing and evolving temperatures of the wet-spun fibres were approximately 30℃ and 22℃, respectively. The enthalpy of melting of the PAN/VDC fibre containing 30wt% MicroPCMs was 27 J/g. The spinnability of the fibre was affected by content of MicroPCMs, diameters, ratio of aggregate microcapsules and spinning parameters etc. The wet-spun fibre had a higher efficiency of enthalpy of melting than that of the melt-spun one. The fabrics absorbed and released heat at 25-34℃ and 10-25℃respectively. The maximum inner temperature difference between the wool felt and the non-woven fabric was 8℃ and -6.5℃ in the heating and cooling process, respectively. The inner temperature difference lasted 16-50min, which depended on the contents of PCM, fabric composition and the measuring condition. The knitted fabrics absorbed and released heat at 32℃ and 17℃ respectively with an amount of 8-20 J/g. The integral heat flux of MicroPCMs coated fabric is significantly higher than that of the control. The research results build up knowledge basis for the development of Nano /MicroPCMs, thermo-regulated fibres and fabrics. The thermo-regulated fabric has a significant temperature regulating function, which can be used as professional clothing materials, decorative fabrics and medical textiles. Ph.D., Institute of Textiles and Clothing, The Hong Kong Polytechnic University, 2005
We report the first user test experience with polyethylene glycol (PEG-1000) permanently affixed to fabric as a phase-change material for next-to-skin use. In 50 subjects, NeutraTherm-treated undergarments are evaluated during skiing and skiing-like conditions for comfort and protective function. When compared to untreated cotton thermal undergarments, initial testing indicates that phase-change materials impart superior qualities as protective clothing, particularly in preventing both overheating and chilling. This particular phase-change material was also shown to be superior in preventing moisture and odor at the skin surface and in the outer garments. Independent laboratory testing reported no detectable formaldehyde in NeutraTherm-treated garments. No skin irritancy attributed to the fabric or any other chemical component of the bound polymer was reported in 200 test subjects.
The use of inorganic phase change materials (PCM's) for thermal storage in residences and in spacecraft has been described. Initial studies demonstrated that CaCl//2. 6H//2O caused desired endotherms and exotherms on heating and cooling in rayon fibers, this system was not useful in hydrophobic fibers and also had the disadvantage that it was only partly congruent in its melting. Thus, congruent melting inorganic (LiNO//3. 3H//2O and Zn (NO//3)//2. 6H//2O) and organic (polyethylene glycol 600) PCM's were evaluated for their ability to produce desirable thermal changes in hydrophilic (rayon) and hydrophobic (polypropylene) hollow fibers that showed little decay after an extensive number of heating and cooling cycles. The results of this investigation are described in this paper.
Cotton/polyester fabrics containing crosslinked polyethylene glycols (PEGs) were evaluated for their antimicrobial activity against a diverse group of bacteria and fungi. The PEG-treated fabrics have substantial resistance to most microorganisms relative to untreated fabrics. Because the level of formaldehyde is extremely low, it is hypothesized that the antimicrobial activity of the modified fabrics is due to a unique combination of physical and physicochemical effects. These may include the hydrophilic nature of the crosslinked PEGs that dessicate microbes and deprive them of needed moisture and/or absorption and release of latent heat by the bound PEG. However, the most probable effects that impeded microbial growth may be attributable to the surfactant-like properties of the bound PEG which disrupt cell membranes due to the dual hydrophilic-hydrophobic characteristics of the PEGs.
Structural changes due to tension applied to caustic-swollen yarns were studied. It was found that the cross-linking of yarns which had been mercerized slack, at normal length, or slack and then restretched to normal length produced differences in tenacity and X-ray orientation. It was concluded that this was due to structural rearrangements induced by the application of load to fiber systems. Differences in wet pickup of the cross-linking resin were shown to produce differences in the fiber fragmentation pattern but not in the layer-expansion pattern.
Only a fraction of the added cross-linking resin was considered to have contributed to the properties usually attributed to cross-linked yarns. The regions believed responsible for the effect of cross-linking are the less ordered lattices close to the crystalline structures. The strength retained after cross-linking was dependent on the tension and the method of its application.
Differences in the degree of conversion of cellulose I to cellulose II were noted in the slack-mercerized yarns treated with different alkali metal hydroxides. These differences, with the exception of lithium hydroxide, correlated with swelling effectiveness of the alkalis used.
Several aqueous bases were found which swell cotton yarn greatly, but, after their removal from the cotton, leave the x-ray diffraction pattern unchanged from that of native cellulose I. Such bases include 9.5% lithium hydroxide and 35% benzyltrimethylammonium hydroxide. However, the addition of as little as 1.5% lithium hydroxide or 5% sodium hydroxide, to the benzyltrimethylammonium hydroxide causes substantial conversion of cellulose I to cellulose II.
This synergistic effect is attributed to the decrystallizing action of the organic base which, by breaking down the cellulose I lattice, facilitates the action of lithium, sodium, and potassium hydroxides in forming alkali cellulose lattices leading to cellulose II. Rubidium and cesium hydroxides failed to produce this effect when added to the organic base. Cellulose swelling, decrystallization, and recrystallization appear to be distinct steps in lattice conversion. These steps may present greatly different requirements as to optimum cation size and coordination, such requirements being more readily met by mixtures of cations than by any one species. In the absence of the quaternary base, but at alkali concentrations giving maximum fiber swelling, no lattice conversion was produced by lithium or cesium hydroxides, a high degree of conversion occurred with sodium hydroxide, and the other alkalies were intermediate in effect. The strength, elongation, energy-to-rupture, and tenacity of treated yarns varied greatly with the cations present in the alkali. In contrast to yarn, fiber bundles underwent slow and partial conversion to cellulose II by the quaternary base.
Native cotton yarn reacts rapidly with phosphoryl chloride in N,N-dimethylformamide to produce highly chlorinated cellulose (degree of substitution of 0.5 or greater), phosphorylated cellulose, and cellulose formate. The ratio of chlorination to phosphorylation was readily controlled by varying the concentration of phosphoryl chloride in N,N-dimethylformamide.Reaction variables studied were the reagent concentration, reaction temperature, and reaction time. The effect that each of these variables has on the tensile and flammability properties of the resultant yarns was investigated. Yarns containing large proportions of chlorine have high tensile-strength and are unusually extensible, whereas yarns containing phosphorus have high flame-resistance. A mechanism for the selective chlorination or phosphorylation of the cotton cellulose is advanced.
Incorporation of 50% aqueous solutions of compounds (exhibiting high ΔH values due to solid—solid transitions prior to melting or crystallization) into hollow fibers or treatment of conventional fibers with these solutions, produced after drying and conditioning, modified fibers with 2–4 times the heat content (Q) of the corresponding untreated fibers in a given temperature interval. Of the compounds evaluated, 2,2-dimethyl-1,3-propanediol and 2-hydroxymethyl-2-methyl-1,3-propanediol produced the most reliable and reproducible thermal effects in the modified fibers that lasted through 50 heating and cooling cycles. Of the treated fibers, hollow rayon was the most effective, followed by cotton, then hollow polypropylene relative to the corresponding untreated fibers. As monitored by differential scanning calorimetry, these modified fibers had thermal storage and release values useful at temperatures as high as 72–102°C on heating and as low as 37-7°C on cooling, with generally little variability in their Q values within the same fiber or between different batches of the same fiber. Other compounds of this type were not effective for use with the fibers due to sublimation/high vapor pressure characteristics (2,2-dimethyl-1-propanol and pentaerythritol) or because of their anomalous and inconsistent thermal behavior (2-amino-2-methyl-1,3-propanediol).
N-(2-Aminoethyl)aminodeoxycellulose cotton (AEAC) was prepared in yarn form by reaction of ethylenediamine with chlorodeoxycellulose. The adsorption of mercuric ion by AEAC (degree of substitution 0.4) was studied over a wide range of concentrations. In the concentration range 0.5-43 g/1., the adsorption of mercuric chloride follows the Freundlich relationship, log 10 x = 0.21 log 10 C + 2.7, where x is the mg of mercuric chloride bound per gram of AEAC and C is the residual concentration in g/1. At concentrations in the range of 3.1-0.6 ppm, 100 mg of AEAC removed about 90% of the mercury present in 200 ml of solution, in a single equilibration. The results of this study suggest the possible use of AEAC as an agent for the collection of mercury in industrial processes.
A specially designed laboratory-type permeameter was used to characterize liquid flow behavior through various combinations of soils and geotextile fabrics subject to different flow rates and hydrostatic pressures of water. Spunbonded geotextiles made from two different fiber types ( e.g., polyester and polypropylene) were selected for the study. Volume flow rates were varied up to 21 cm/second by adjusting hydrostatic pressure differences from 2.5 to 76.2 cm.
The results suggest single layer barriers of the geotextiles alone have small effects on flow rates of water, but sand-geotextile combinations exhibited strikingly different behavior. In prewashed soil-geotextile combinations, the permeability decreased non linearly with increasing depth of soil above the fabrics, independent of the supporting fabric. For soils that were not prewashed, however, fine particles in suspension settled at the soil-water interface to produce an almost impervious layer or cake structure. This caking was a function of time and became the controlling factor of flow throughout the composite.
High clogging in even thin fabrics was observed when sand was replaced by fine material such as Kaolite. The behavior was different than that of the fine material in unwashed sand. In addition, geotextile fabrics showed low resiliency to recovery from cyclic compression. The practical interpretation of this is that the porosity of the fabric may decrease significantly with time if incorporated into structures that are subject to compressive forces.
Treatment of polyester, nylon 66, cotton, and wool fabrics with aqueous solutions of polyethylene glycol phase change materials and of plastic crystal compounds by a conventional pad-dry procedure produced modified fabrics with thermal storage and release properties 2-2.5 times greater than those of untreated fabrics at the same temperature intervals. These modified or temperature-adaptable fabrics are chemically impregnated with phase change or plastic crystal substances that impart balanced thermal storage and release properties at various temperature ranges. Application of another plastic crystal compound in aqueous solution to the fabrics under these con ditions was not suitable, since it sublimed during the fabric drying process. Fiber type and heating rate appeared to have little effect on the overall heat content or thermal performance of the treated fabrics. As in earlier studies, thermal storage and release properties of the modified fabrics were reproducible after 5 cycles and remained es sentially constant for at least 50 heating and cooling cycles.
Developments and research in the present decade on the antibacterial finishing and disinfection of textiles are reviewed. Definitions and concepts of terms such as antimicrobial agent, antibacterial agent, disinfectant, and sanitizers are discussed from both a regulatory and scientific perspective. Quantitative tests for determining antibacterial activity of textiles usually involve sterilization of fabric, inoculation with a microorganism, and determination of bacteria remaining by wash-recovery or colony-count under a low-power microscope. Most qualitative tests for antibacterial activity are based on the ability of the agent to diffuse off the fiber into an agar medium. Most antifungal tests consist of inoculation of fabric, then inspection for visual growth of fungi after varying periods of time.
Microbial ecology of the skin-clothing interface differs in everyday environments and situations from environments conducive to growth of microorganisms and cross- infection ; predominant bacteria and fungi and microbial population on different parts of the body are discussed in this context. Microorganism persistence on textiles is influenced to some extent by fiber type. Recent studies show that synthetics retain more odor-causing bacteria, and that dermatophytic fungi are more persistent on synthetics than on natural fibers; persistence time of pathogenic bacteria,on natural and synthetic fibers is dependent on relative humidity and method of fabric contami nation.
Newer and commercialized processes for producing antibacterial fabrics durable to laundering are evaluated, and frequently-used disinfectants and sanitizers for textiles are stressed. Various techniques for affixing such agents to fibers are listed, and requirements for producing effective antibacterial and antifungal fibers for particular end-uses are enumerated. Some novel and recent uses for antibacterial fibers, such as water disinfection and air purification, are also mentioned.
Kiered, cotton yarns undergo extensive decrystallization when wet in the slack state with 2.1 N aqueous henzyltri methylammonium hydroxide. The decrystallization is temporary, inasmuch as washing and drying cause the yarn to recrystallize to Cellulose I. However, much of the decrystallization can be rendered permanent, if the swollen yarns are aftertreated with aqueous sodium or potassium hydroxide prior to washing and air-drying. The alkali aftertreatment also alters a variety of other physical properties in ways differing from either swelling treatment carried out alone.
The effects of concentration and type of alkali metal hydroxides on the decrystallization, lattice conversion, and physical properties of the yarns are reported. The effect of tension applied during various stages of these dual treatments is dis cussed with respect to textile properties of the yarns before and after crosslinking with DMEU, and also with respect to crystallinity, lattice conversion, and orientation imparted.
Remarkably stable, yet reactive diazonium salts of cotton cellulose fabric have been prepared under ambient conditions by the action of dilute acid and nitrite solutions on cellulose ortho-aminobenzoate. These salts, which may be stored for four to six weeks, coupled readily with phenolic and aromatic amino compounds to produce deeply dyed fabrics.
Specific-heat values are presented, in the temperature range from −70 to 100°C, for a modified wool at various water contents. The modification was analogous to a dyeing process and involved the uptake of 14% of an additive by the wool. As for untreated wool, an endothermic peak resulting from the fusion of absorbed water was found in the range from −30 to 0°C. The absorbed water exhibits a sub-division into freezable and non-freezable fractions. Heats of fusion of freezable absorbed water are given and compared with corresponding results for untreated wool. The integral heat of fusion at saturation water content is much less for treated than for untreated wool, as is the amount of freezable water. It appears that the treatment causes the exclusion of a considerable quantity of loosely held water. This is in accord with the concept, derived from Flory–Huggins solution theory, that one effect of the additive is to swell the wool fibres and thereby cause a greater resistance to further swelling at a given water content.
Torsional fatigue studies in polyester fibers have revealed that the fracture morphology of ruptured fiber surfaces is influenced by the level of torsional strain amplitude. At relatively high strain ampli tude the mechanism of fracture seems to be governed by the propagation of a single large crack. However, at low strain amplitudes, the fibers exhibit a slow and gradual breakdown of structure, starting with the surface layers. The surface morphology and the fracture phenomenon observed in the later case essentially resemble what happens in the formation of pills from polyester fibers in garments.
Polyethylene glycols (PEG's with average molecular weights of 400, 600, 1,000 and 3,350) incorporated as 57% aq. solutions into hollow rayon and polypropylene fibers, after drying and conditioning, produced heat contents (Q) 1.2-2.5 times greater than untreated hollow polypropylene and 2.2-4.4 times greater than untreated hollow rayon fibers. The resultant Q values in a given temperature interval were reproducible for at least 50 heating and cooling cycles with no adverse change in their thermal performance compared to their first heating and cooling cycle. As monitored by differential scanning calorimetry, these modified fibers had thermal storage and release values useful at tempratures as low at -8 to -48°C on cooling and as high as +42 to +77°C on heating, with little variability in Q values within the same fiber or between different batches of the same fiber containing a particular polyethylene glycol.
Water-dispersable products have been prepared from the reaction of magnesium acetate tetrahydrate with hydrogen peroxide at mole ratios of 1 : 2 to 1 : 40 to produce compositions with active oxygen or peroxide contents of 1–30%. The products are believed to be stoichiometric mixtures of HOOMgOAc and HOOMgOOH that vary in composition with the molar ratios used. These new compounds are hydrolytically stable at ambient temperatures for extended periods (at least 60 days) and thermally stable below 300°C.Pad-cure processes are described for applying the above reaction products as a dispersion in water or aqueous hydrogen peroxide or as a foam in aqueous hydrogen peroxide to impart antibacterial activity to celulosics, synthetic fibers and fiber blends. The textiles are treated with dispersions or foam containing 10–17% of the reaction products derived from mole ratios of 1 : 2 to 1 : 40 magnesium acetate tetrahydrate: hydrogen peroxide. On subsequent heating for 2–4 min at 120–150°C, washing and drying, the modified textiles contain durably bound active oxygen or peroxide (0.1–1.7%) that has activity against representative gram-positive and gramnegative bacteria for up to 50 launderings.
Binding of polyethylene glycols to any fibrous substrate (such as a natural cellulosic or wool, or synthetic fibers polyester, polyamide or polyolefin) is achieved by in situ network polymerization with polyfunctional resins and acid catalysts. The modified substrates contain crosslinked polyethylene glycols that impart several improved functional properties. Two of these properties (thermal adaptability and reversible shrinkage in the wet and dry states) make it appropriate to categorize the modified fibrous substrates as “intelligent materials”.The thermal and dimensional/shape memories of the substrates are influenced and, hence, controlled by the molecular weight of the polyol, crosslink density, curing conditions to affix the polyol and construction of the fibrous substrate. Verification of these effects has been noted by thermal analysis and infrared thermography (for thermal memories) and by measurement of power generated and work performed during wet shrinkage of appropriate substrates (for shape memories). Numerous potential commercial applications are described and some are being actively pursued. © 1997 John Wiley & Sons, Ltd.