Synthetic Fiber

Synthetic fibers are made of polymers that originate from small organic molecules that combine with water and air.

From: Fundamentals of Forensic Science (Third Edition), 2015

Drugs Acting on the Gastrointestinal Tract

David H. Shaw, in Pharmacology and Therapeutics for Dentistry (Seventh Edition), 2017

Bulk-Forming Agents

Bulk-forming agents include synthetic fibers (polycarbophil) and natural plant products (psyllium and methylcellulose). They possess the property of absorbing water and expanding, increasing the bulk of the intestinal contents. The elevated luminal pressure stimulates reflex peristalsis, and the increased water content softens the stool. These agents are not absorbed and do not interfere with the absorption of nutrients from the gastrointestinal tract. Several days of medication may be required to achieve the full therapeutic benefit, although the usual onset of action is 12 to 24 hours. Some patients prefer to add foods such as bran or dried fruit (e.g., prunes and figs) to their diet that exert the same effect rather than use a bulk-forming laxative. These laxatives have the advantage of having few systemic effects and are unlikely to produce laxative abuse. Cellulose agents may physically bind with other drugs if administered concurrently (e.g., salicylates, warfarin, digitalis glycosides) and hinder their absorption. Patients should not take a calcium polycarbophil laxative within 2 hours of taking tetracycline for the same reason.

Laxatives with psyllium come in a powdered mixture containing approximately 50% powdered psyllium seeds and 50% dextrose or sucrose. Sugar-free products are also available. Psyllium seeds are rich in a hemicellulose that forms a gelatinous mass with water. The refined hydrophilic colloid from the seeds is the most widely used form of this agent. Methylcellulose is indigestible and not absorbed systemically. Bloating and flatus have been reported after the use of psyllium products because of bacterial digestion of the plant fibers within the colon.

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Fibers with High Modulus

A.R. Bunsell, in Encyclopedia of Materials: Science and Technology, 2001

1 Fiber Development

The development of high-modulus synthetic fibers began in the 1930s with the commercial production of glass fibers in the USA. Glass and glass fibers have approximately the same Young’s modulus and density as aluminum. The first synthetic polymeric fibers were produced in 1938. These were polyamide 6.6 developed in the USA, and polyamide 6 fibers produced in Germany. These polyamide or “nylon” fibers, together with polyester fibers developed in Great Britain in the 1940s, are the most important synthetic textile fibers produced. Although of low stiffness, they were the first of a family of organic fibers which has been developed with elastic moduli rivaling and even exceeding that of steel, but with only a fifth or less of the weight.

Boron and silicon carbide fibers made by chemical vapor deposition on to a filament of tungsten or carbon were first produced in the early 1960s, first in the USA and then in France and Russia. They have the density of glass but twice the Young’s modulus of steel. Carbon fibers, with a density of a quarter that of steel, were first produced in the UK in the mid-1960s. They are made by the pyrolysis of polyacrylonitrile precursor fibers and commonly have moduli up to one and half times the modulus of steel but can be up to three times stiffer. An alternative process developed in the 1970s in the USA uses the pitch residue from oil refining or the coking of coal to give fibers with moduli approaching that of diamond. Fine ceramic fibers started to appear at the end of the 1970s and in the 1980s. One group of these fibers, developed in the UK and in the USA, is based on alumina, whereas others developed in Japan are based on silicon carbide. These fibers have Young’s moduli ranging from one to two times that of steel with densities less than half that of steel.

Most fibers have diameters of the order of 10 μm, which can be compared with the diameter of a human hair which averages 70 μm. Exceptions, however, are the boron and SiC fibers made by chemical vapor deposition (CVD) which are twice as thick as hair. The fineness of fibers allows even the stiffest of materials to be made in a flexible form as bending stiffness is related to the cube of the diameter. However, many high-modulus fibers are completely elastic, at least at room temperature, and are therefore brittle in tension and in bending. They are most suited to be used as reinforcements in composite materials. The oriented polymer fibers are also used as reinforcements but they are not brittle as they deform plastically in compression. They show great toughness which can be exploited in structures such as cables and structures that must resist impacts.

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Types of FRCs used in dentistry

Pekka Vallittu, Jukka Matinlinna, in A Clinical Guide to Fibre Reinforced Composites (FRCs) in Dentistry, 2017

2.4 Glasses Used in Reinforcing Fibers

Most of the today’s reinforcing synthetic fibers in dentistry are glass fibers due their transparency and beneficial surface chemistry, which allows their adhesion to resin matrix via silane coupling agents (silanes) (Matinlinna et al., 2004; Lung and Matinlinna, 2012). Use of other reinforcing fibers like G/F or aramid causes severe cosmetic problems for the restoration. Other benefits of glass fibers in reinforcing acrylic polymers of a brittle nature include low elongation at break and high tensile strength. Glass types of E-glass and S-glass and their behavior as component of dental FRC are recently reviewed in more detail in another source (Vallittu, 2014a). S-glass is divided to subclasses (S2, S3 etc.) based on the surface sizing of the fibers.

It is known that the chemical composition of glass plays an important role in the manufacturing of fibers and in the chemical stability of fibers against effects of water and acids. It has been shown that the chemical resistance of glasses toward glass deterioration relates to the composition, the state of the glass surface, the amount and type of attacking solvent media, temperature, and time. In the presence of water, the strength of the fiber may be reduced, especially with glass fibers of high alkali metal oxide content (Vallittu, 1998a). There are so-called A-, C-, D-, E-, E-CR-, R-, and S-glasses, and the most suitable for use in dental and medical applications are alkali-free glasses E-, R-, and S-glasses (Table 2.3).

Table 2.3. Nominal composition (%) of certain glass fibers (Cheremisinoff, 1990; Vallittu, 2014)

Component Type of glass
Empty Cell E A R S
SiO2 53–55 70–72 60 62–65
Al2O3 14–16 0–2.5 25 20–25
CaO 20–24 5–9 6–9
MgO 20–24 1–4 6–9 10–15
B2O3 6–9 0.5 0–1.2
K2O <1 1.0 0.1
Na2O <1 12–15 0.4 0–1.1
Fe2O3 <1 0–1.5 0.3 0.2

Certain glass forming agents, including boron oxide (B2O3), are leached from the surface of glass fibers, and thereby the supporting glass network can be splat at different places. The process of production of glass fibers may contain elimination of easy leaching oxides from the surface of fibers by acid washing process, which can increase the stability of fibers later on. The chemical composition of glass fibers is different on the fiber surface than in the inner part of the fiber. The surface of E-glass may be enriched with boron and calcium. The glass composition has a considerable effect of resistance of the fibers against the influence of acids and, e.g., E-glass has good resistance in a wide pH range (Nordström et al., 2001) (Fig. 2.13).

Figure 2.13. Resistance of E-glass against dissolution at various pH (Nordström et al., 2001).

Continuous and discontinuous glass fibers in dental FRC products are usually made of alkali-free glass (less than 1% Na2O+K2O), known as E-glass (Cheremisinoff, 1990). Because of the high calcium oxide content, glass similar to this composition shows poor resistance to acidic solutions. For this reason, the composition of E-glass is modified by introducing boron oxide (B2O3) and by decreasing the CaO content. The other type of glass used in dental FRCs is S-glass, which provides slightly higher tensile strength than E-glass. Radiopacity (X-ray opacity) of glass fibers is related to their elemental composition and therefore dental applications may utilize glasses which have been tailored for dental use. Another possibility to enhance radiopacity of FRC is to include radiopaque fillers (i.e., fillers containing some heavy metal ions) to the polymer matrix. However, fillers require space, and therefore volume loading of fibers is reduced, which lowers the strength of the FRC. Table 2.4 lists some physical properties of glass fibers.

Table 2.4. Some physical properties of glass fibers (Cheremisinoff, 1990; Vallittu, 2014)

Property Type of glass
Empty Cell E A R S
Density (g/cm3) 2.54–2.59 2.48 2.50 2.49
Tensile strength (10−2 N/mm2) 25–34 24–31 44–48 49
Young’s modulus (10−3 N/mm2) 73–77 70–7 86 86
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Iron

S.C. Gad, in Encyclopedia of Toxicology (Third Edition), 2014

Human

Iron has been identified as a component of asbestos and other mineral and synthetic fibers. Inhalation of iron and iron oxide fumes or dust may result in deposition of iron particles in lungs, producing an X-ray appearance resembling silicosis. The carcinogenicity of iron is still under debate, for example, for colorectal and liver cancer. An increase in the incidence of lung cancer, as well as in that of tuberculosis and interstitial fibrosis, has been noted in hematite miners. Due to inadequate controls, it is possible that the increased incidence of lung diseases noted in the study is due to smoking or exposure to other carcinogens present in the occupational setting. The American Conference of Governmental Industrial Hygienists (ACGIH) assigns an A4 (not classifiable as a human carcinogen) ranking to iron. Excess free circulating iron damages blood vessels, and hypotension can occur.

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Occupational clothing for nurses: combining improved comfort with economic efficiency

M. Walz, in Handbook of Medical Textiles, 2011

21.8.4 Sustainability

From an ecological perspective, different fibres can have different effects. Comparing synthetic fibres with natural fibres, the floor space required for the production of 1 ton of fibres is, for example, 67 hectare for wool, 1.3 hectare for cotton and 0 for synthetic fibres. The water consumption for 1 ton of fibres is 25 000 m3 for cotton and 4 m3 for polyester. Synthetic fibres are based on crude oil, utilising 0.8% of the general worldwide consumption. However, partially or completely recycled polyester yarns are available on the market.4

There are various eco-labels on the market at present for textiles production. One example is bluesign® which is based on the best available technology. Certified companies can only use tested and approved raw materials. The complete production site must follow an ecological route.

Cambridge University calculated in its study ‘Well dressed?’ that 60% of the carbon dioxide output of a cotton T-shirt is created after 25 washes. This is due to the high energy output whilst drying and ironing.17

E.T.S.A. commissioned a Life Cycle Assessment of surgical gowns. The study assessed the impact of both reusable and disposable gowns. The assessment shows that when all factors are taken into consideration, including costly disposal of hospital waste, the reusable solution is significantly better for the environment. The reason is the lower consumption of energy, water and chemicals. However, there is more to be considered; because reusable surgical textiles cause less waste and emissions, they have considerably less impact on global warming and over-acidification.18

Reusable textiles and rental laundries have a positive influence on the regional economy and offer an important contribution to domestic industry.19,20 In addition to the cost and quality of medical textiles, their impact on the environment should become a serious factor in the decision-making process.

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Paper Products: Classification

J.F. Waterhouse, in Encyclopedia of Materials: Science and Technology, 2001

2.13 Ceramic Papers

The papermaking process can be used to produce papers with high levels of inorganic fiber, metals, and synthetic fibers. Ceramic papers made in this way are precursors to subsequent converting processes to form and mold the material as well as adding high-temperature bonding agents, if not already incorporated. In comparison with wood fibers, ceramic fibers are stiff, noncomformable, and devoid of any natural bonding agent. One approach to forming ceramic papers in papermaking is to incorporate a small fraction of wood fiber with low-level refining and possibly polymeric bonding agents.

The ceramic green sheet, to which it is sometimes referred, has been proposed for use in catalytic converter applications and other high-temperature gas treatment processes. In the catalytic converter, the ceramic green sheet after corrugating can be rolled into a porous tube and fired to produce a true ceramic. Cellulose and other organic additives are pyrolyzed during this process. Following this operation a platinum film can be applied and fired.

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Occupational and Environmental Hepatotoxicity

Matt Cave, ... Craig McClain, in Zakim and Boyer's Hepatology (Sixth Edition), 2012

Dimethylacetamide

Dimethylacetamide (DMAC) is a colorless, polar solvent similar to DMF. Multiple case reports have documented DMAC-associated hepatotoxicity, mainly in synthetic fiber workers. Acute DMAC poisoning is primarily manifested as neuropsychiatric illness, including psychosis, delirium, and seizures, and as systemic disease, including acute hepatitis. The primary route of exposure appears to be dermal absorption of DMAC vapor. Subclinical ALT elevations appear to occur not infrequently in new synthetic fiber workers (within the first 7 months of employment) in a dose-dependent fashion.89,90 The elevation in ALT improved by 50% within 30 days in 90% of persons after DMAC exposure was halted.89 Interestingly, transaminitis appears to occur much less frequently, if at all, in workers exposed longer than 7 months, thus suggesting adaptation to chronic exposure.89-91 However, animal models have documented liver injury following both acute and chronic DMF exposure.92

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Tribology of advanced composites/biocomposites materials

M. Sharma, ... S. Shannigrahi, in Biomedical Composites (Second Edition), 2017

17.2.1 Reinforcement compatibility with polymers

Natural reinforcements, such as sisal, jute, and kenaf have less structural integrity and deteriorated strength in comparison to other high performance and costly synthetic fibres (carbon fibre, glass fibre, and aramid fibre) due to large number of flaws prone to huge stress concentration during loading and wearing process. The reinforcement for natural and/or biocompatible fibres need surface alteration before combining them to the polymeric matrix materials. Fibre sizing is one of the solutions to apply layer of polymers and/or other solvent based materials for increasing their compatibility with the matrix as well as to protect from damage during service conditions. During loading and wearing process the surface distortions flaws or pits act as a stress concentrator for crack propagation and increases the rapidity the fracture process. Polymer sizing's shield the reinforcing fibres from breaking and provide strand integrity. Compatible sizing's also improve adhesion of reinforcement with matrix materials and improve composite processing. The sizing improves the fibre wettability with the polymers and further interfacial adhesion. For advanced composites applications commercially supplied sizings are refinished or modified to improve fibre thermo oxidative stability and mechanical performance (Fuqua et al., 2012).

The bioreinforcement has high moisture absorption and has poor compatibility with polymers. Hence, it is essential to alter their surface properties. There are number of reports on the surface modifications of natural reinforcement and the influence on tribological and mechanical properties of their composites with polymeric materials. There are categories of modification chemicals (acidic etching, acrylation, silanisation, chemical grafting), physical (high energy irradiation, plasma modification) which creates perforation, deeper ridges, or oxygenated functionalities on the fibre surface (in case of former). Most of the abovementioned methods contribute towards mechanical performance of composites but contrary influence the fibre strength properties. There are newly developed modification methods that attach nano particle on the fibre surface which improves interfacial adhesion without affecting much on fibre strength properties (Sharma et al., 2014; Fig. 17.2).

Fig. 17.2. Promoting of fibre–matrix interfacial adhesion by employing surface functionalities on the reinforcement surface (Sharma et al., 2014).

The usage of enzyme for modification is increasingly accepted for modification and processing of natural fibres (Faruk et al., 2014). The key potential for the usage of enzymes technology for natural fibre surface modification is their environmental compatibility and biodegradability. The enzymes' responses are very specific and they are capable of performing the localised action to improve composites properties. Also, in comparison to other chemical methods, these methods are easy to employ and also cost effective. When natural reinforcement combines with polymer to develop the biocomposites they have advantages like low density, thermal and dimensional stability, as well as good tribological properties (reduced frictional coefficient and wear; Basu et al., 2011).

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Pathology

John V. Forrester MB ChB MD FRCS(Ed) FRCP(Glasg) (Hon) FRCOphth(Hon) FMedSci FRSE FARVO, ... Eric Pearlman BSc PhD, in The Eye (Fourth Edition), 2016

Reactions to exogenous non-biological materials

Implantation in tissue of vegetable or organic matter such as wood excites a similar cellular response to that of sutures derived from cotton or synthetic materials. Synthetic fibres or fragments of plant are seen in polarized light as birefringent particles surrounded by macrophages and lymphocytes. Metallic fragments are slowly dissolved in tissue fluids, but elements such as iron are toxic to the retina, which undergoes neuronal loss, so that metallic foreign bodies in the vitreous or retina are especially dangerous. Brass contains copper and tin, and the reaction to copper ions is pyogenic for reasons that are as yet unknown. On occasion, similar reactions may be seen to materials used in ophthalmic surgery (Box 9-9).

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Textile materials and structures for wound care products

B.S. Gupta, J.V. Edwards, in Advanced Textiles for Wound Care, 2009

3.9.3 Polyester

Polyester is one of the most versatile of the manufactured fibers that finds applications in many categories of textile products and is one of the widely used synthetic fibers in medical products. It is also the fiber frequently selected for combining with cotton and rayon in developing needled and spunlaced non-wovens for dressings. The chemical constitution of the commonly used material, poly(ethylene terephthalate) or PET, is shown in Fig. 3.8. The fiber has an aromatic component and an aliphatic sequence. Although the polymer lacks strong functional groups, the molecules, when drawn, pack closely and lead to a semi-crystalline mechanically strong and thermally stable fiber. Because of the lack of polar groups, the fiber has a low attraction for water (moisture regain ~ 0.4% under normal conditions); this makes the material largely hydrophobic. A number of variations of the basic repeat are available but they vary primarily in terms of the proportion of the aromatic and the aliphatic components and, as a result, lead to fibers with different physical and mechanical properties. Some low molecular weight aliphatic polyesters are used as low melt adhesives for binder applications. Aliphatic polyesters capable of hydrolytic degradation are also used in the manufacture of bioabsorbable products, in particular surgical sutures. The polymer can be melt-extruded both as a film and a fiber, the latter in different cross-sectional shapes and sizes to provide materials with various surface, physical, and mechanical properties.

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