Mohsen Miraftab

The influence of carbon black on properties of orientated polypropylene 2. Thermal and photodegradation

Abstract This paper extends previously reported work and describes the effect of carbon black on thermal and photo-oxidative degradation of oriented polypropylene (PP) geotextile tapes. PP tapes containing carbon black with different particle size, structure (or aggregate shape), specific surface volatile content and concentrations have been exposed separately to circulatory air ovens at 130°C and UVB lamps at 60°C respectively. The exposed tapes were studied using tensile tensiometric, IR spectrophotometric and thermal analytical (DSC) techniques. Thermal stabilities of PP tapes filled with carbon blacks having low volatile contents are comparable to those of unfilled PP tapes. At given oven-exposure times, carbon blacks with varying particle sizes and structures, except for volatile content, show only slight influence on thermal stability of the PP tapes. The thermal stability was not significantly affected in tapes containing increased carbon black concentrations from 2.5 to 5% w/w The carbon black with the highest volatile content adversely affected thermal stability possibly because the surface oxygenated groups present act as sensitisers. Dynamic thermal analysis (DSC) shows that the magnitude of shifts to lower temperatures of the post-fusion oxidative exotherm ( T on ) reflect respective losses in tensile properties and supports previous evidence that T on is a sensitive indicator of the degree of polymer oxidation. However, the presence of carbon black significantly increases UV durability of these filled tapes. The UV resistance in terms of tensile properties is inversely proportional to carbon black particle diameter. The carbon black sample with a high concentration of reactive oxygenated groups, measured as volatile content, shows relative inferior UV resistance to tapes containing low volatile content blacks with similar particle size. No effect of carbon black structure on UV stability was observed, which agreed with the previous results for carbon black-containing polyethylene films under UVA and UVB exposures. The overall evidence suggests that carbon blacks having smallest particle size, possibly high structure and low volatile contents will yield PP tapes having optimum thermal and UV stabilization behaviours. ©

A critical review of modern and emerging absorbent dressings used to treat exuding wounds

Wound management has progressed significantly over the last five decades. This emanates from a greater understanding of wound healing, technological progression and improved clinical and scientific research. There are currently a plethora of absorbent dressings on the wound care market which claim to have the ability to manage exudates whilst encouraging healing. However, it is becoming clear, from analysing randomised controlled trials, that some of these absorbent dressings are not meeting their expectations when applied in a clinical setting. Many clinicians now feel that there should be more focus, not only on a dressings ability to manage exudate efficiently, but on a dressings ability to proactively encourage healing and thus exudate reduction will ensue. This paper proposes to critically review modern and emerging absorbent wound care dressings used to manage exuding wounds and discuses some advances in this area.

Unconfined Compression Strength of Reinforced Clays with Carpet Waste Fibers

This paper presents results of a comprehensive investigation on the utilization of carpet waste fibers in reinforcement of clay soils. Effects of adding proportionate quantities of two different types of shredded carpet waste fibers to clay soils (i.e., 1, 3, and 5% by dry weight of the soil) were investigated and evaluated. The investigation was conducted on specimens prepared at their maximum dry unit weight and optimum moisture content, as well on specimens prepared at variable conditions of dry unit weight and moisture content. A comparison was also made on specimens prepared at the same fiber content by changing dry unit weight while moisture content was kept unchanged or by changing both dry unit weight and moisture content. The investigation revealed that inclusion of carpet waste fibers into clay soils prepared at the same dry unit weight can significantly enhance the unconfined compression strength (UCS), reduce postpeak strength loss, and change the failure behavior from brittle to ductile. The results also showed that the relative benefit of fibers to increase the UCS of the clay soils is highly dependent on initial dry unit weight and moisture content of the soil. Failure patterns were gradually transformed from the apparent classical failure for unreinforced soil specimens to barrel-shaped failures for reinforced specimens at 5% fiber content.

Fibres for wound dressings based on mixed carbohydrate polymer fibres

Polysaccharide-based dressings have increasingly become viable alternatives to somewhat incompatible and often problematic cotton or viscose gauzes traditionally used for wound dressings. Abundant availability of alginates and their relative ease of reversible solubility in particular have been instrumental in their development into fibres and lately their application as vehicles for delivering drugs. This paper reports on the spinning efficiency of various alginate types (i.e. differing mannuronic/guluronic acid ratios) in a laboratory-based extrusion system and explores the effect of proportional inclusion of a second polysaccharide compound, an arabinoxylan named branan ferulate, on tensile properties of the resulting fibres. It was shown that in the chemical assessment of the fibres, that arabinose content, one of the branan ferulate component monosaccharides, could be used as a means of estimating the branan ferulate content of the fibre. Utilising such an analytical approach has enabled the branan ferulate contents of the fibres to be assessed. Accordingly there need be little anxiety over branan ferulate losses during the production of branan ferulate/alginate fibres by the wet spinning production method.

Effect of carbon black on the oxidation of polyolefins: An overview

Abstract The use of carbon black in polyolefins is widespread. Two to three per cent of finely divided carbon black provides an effective light screen protecting the polymer against exposure to light. In geotextile applications, use of carbon black is widespread due to demands for higher durability. Types of carbon black, their usage and interaction with thermal antioxidants are reviewed. Current understanding of the effects of carbon black on the oxidation reaction shows conflicting evidence. Some workers have reported that carbon black accelerates oxidation due to surface catalysis of peroxide decomposition to form free radicals, adsorption of antioxidants from the polymer and increased accessibility of oxygen. Others have produced evidence of the inhibition of oxidation by carbon black because of its activity as a radical scavenger and its ability to decompose peroxides to form stable products. The role of reactive chemical groups on the carbon black surface, particle size and concentration are reviewed. It is evident that a full understanding of the behaviour of carbon black in polyolefins is currently not available and that it may depend on the balance of competing mechanisms of sensitisation and stabilisation in any specific formulation.

Absorbent alginate fibres modified with hydrolysed chitosan for wound care dressings--II. Pilot scale development.

Fibres have been used extensively in wound dressing applications as they provide a high surface area for absorption, ease of fabrication and softness. It is common practice for commercial wound dressings to be produced from natural materials, such a marine polysaccharides, as they are predominantly biocompatible, non-toxic, and often display bioactive properties, such as inherent antimicrobial activity. In this study hydrolysed chitosans were utilised as a sole coagulant for the production of alginate-chitosan fibres via a one-step, direct wet-spinning extrusion process. The levels of chitosan incorporated into the fibres were analysed quantitatively via elemental analysis and qualitatively by staining using Amido Black 10B. It was estimated that the fibres contained between 4.50 and 5.10% (wt.%) chitosan. The presence of chitosan improved tensile properties such as elongation and tenacity of the base alginate fibres. The increased incorporation of chitosan into the fibres also improved the absorption of the fibres in both saline and distilled water; reaching maximum of >30 g/g and >50 g/g, respectively. This work suggests that the observed hydrolysed chitosan content within the fibre may be optimal for the preparation of a novel fibre for wound care application.

Feasibility study of polyurethane shape-memory polymer actuators for pressure bandage application

Abstract The feasibility of laboratory-synthesized polyurethane-based shape-memory polymer (SMPU) actuators has been investigated for possible application in medical pressure bandages where gradient pressure is required between the ankle and the knee for treatment of leg ulcers. In this study, using heat as the stimulant, SMPU strip actuators have been subjected to gradual and cyclic stresses; their recovery force, reproducibility and reusability have been monitored with respect to changes in temperature and circumference of a model leg, and the stress relaxation at various temperatures has been investigated. The findings suggest that SMPU actuators can be used for the development of the next generation of pressure bandages.

A new carbohydrate-based wound dressing fibre with superior absorption and antimicrobial potency.

Heavily exudating wounds can lead to infection and unnecessary trauma if they are not adequately managed. Manufacturers involved in production and marketing of high absorption silver dressings, besides emphasising high absorptions of their dressings are keen to highlight potent antimicrobial abilities of their products against all kinds of pathogens including MRSA. However, there are little or no credible reports on minimal but potent quantities of silver needed in a dressing to eliminate bacteria spread and growth or how effectively the silver within a dressing is released over time. This paper introduces a new hybrid biomaterial fibre made from polysaccharide-based polymers with inbuilt ability to gel and absorb large quantities of pseudo exudates. Furthermore, it will be reported that the new fibre carries up to six times less silver than it is conventionally used in silver dressings and displays a very slow rate of release whilst maintaining full potency over time against known Gram positive, Gram negative micro-organisms including MRSA. The paper concludes that the developed hybrid fibre has long lasting antimicrobial and gelling properties comparable, if not better, than Acticoat AA and Aquacel Ag, two commercially available silver dressings.

The influence of poly(ethylene glycol) ether tetrasuccinimidyl glutarate on the structural, physical, and biological properties of collagen fibers

Various chemical, natural, or synthetic in origin, crosslinking methods have been proposed over the years to stabilise collagen fibers. However, an optimal method has yet to be identified. Herein, we ventured to assess the potential of 4-star poly(ethylene glycol) ether tetrasuccinimidyl glutarate, as opposed to glutaraldehyde (GTA), genipin and carbodiimide, on the structural, physical and biological properties of collagen fibers. The 4-star poly(ethylene glycol) ether tetrasuccinimidyl glutarate induced an intermedium surface smoothness, denaturation temperature and swelling. The 4-star poly(ethylene glycol) ether tetrasuccinimidyl glutarate fibers had significantly higher stress at break values than the carbodiimide fibers, but significantly lower than the GTA and genipin fibers. With respect to strain at break, no significant difference was observed among the crosslinking treatments. The 4-star poly(ethylene glycol) ether tetrasuccinimidyl glutarate fibers exhibited significantly higher cell metabolic activity and DNA concentration that all other crosslinking treatments, promoted consistently cellular elongation along the longitudinal fiber axis and by day 7 they were completely covered by cells. Collectively, this work clearly demonstrates the potential of 4-star poly(ethylene glycol) ether tetrasuccinimidyl glutarate as collagen crosslinker.

Antimicrobial Properties of Alginate-Chitosan (Alchite) Fibers Developed for Wound Care Applications

Alginate fibers are well established as primary wound dressings, given their well-known sodium/calcium ion exchange ability at the wound surface coupled with their good liquid absorption characteristics. Chitosan, the deacetylated form of chitin is also well known for its hemostatic, antimicrobial, and wound-healing properties. Unique combination of these polysaccharides to form a new generic fiber, known as alchite fibers, has been developed in an earlier work. This article reports on the antimicrobial properties of a range of alchite fibers produced from four different types of hydrolyzed chitosans and two brands of sodium alginate. The article discusses different methods of antimicrobial detection including: submerged fiber technique, zone of inhibition, dilution plating, and spectrophotometric analysis at 600 nm when tested against common skin microflora, i.e., Staphylococcus aureus, Staphylococcus epidermidis, and Micrococcus luteus. This study concludes that while most of the alchite fiber samples have certain degree of antimicrobial properties, some have higher antimicrobial properties than others. The study has also shown that quantitative presence of chitosan within an alchite fiber may not necessarily be the reason for good antimicrobial properties. Factors such as chitosan source, degree of deacetylation, molecular weight, and action of hydrolysis may also affect antimicrobial properties. These findings are most important in endorsing the development of the alchite fibers for wound dressings.