The oldest and most common flammability test for plastic materials thicker than .050 of an inch is ASTM D635. This test measures the burning rate and the average time and extent of burn in a plastics sample measuring 1/2" by 5". The thickness of the material must be uniform.
Ten samples are tested in an "as received" condition. The specimens are marked off every inch. The specimen is clamped at one end on a ring stand The specimen is positioned horizontally and inclined to the side at a 45 degree angle, see Figure 3-26. A 20-mesh Bunsen burner gauze is clamped horizontally 3/8" below the specimen. A Bunsen burner is placed so the flame contacts the end of the specimen. The flame is held in contact with the end of the specimen for 30 seconds. If the specimen does not ignite, the flame is returned for another
30-seconds. The extent of burning is measured along the lower edge of the specimen.
If the specimen does not ignite, it is classed as flame retarding. If the specimen continues to burn, it is timed until it stops or the 4" mark is reached. A specimen which burns to the 4 inch mark is classed as highly flammable. The rate of burn is equal to the inches burned, divided by minutes. If the specimen dose not continue burning to the 4 inch mark, it is classed as flammable. The length of the burned portion is reported as the extend of burning. This test is used for material comparison, quality control, and specification testing. There is a poor relationship between this test and the actual fire hazard that a product is subjected to.
The low melting and decomposition temperatures of plastics products used in the home or office have increased the interest in plastics as a potential fuel source for fires. The flammability of plastics has two distinct properties, ignition and burning. The ignition rate of a plastic is how easily and under what conditions the material ignites. (The burning rate is the speed at which a flame spreads, smoke or heat is released and materials toxicity.) The ignition temperatures of plastics fall into the two categories of flash ignition and self ignition. Flash ignition (flash point) is the lowest temperature sufficient to produce combustible gas. The self ignition of a plastic is the lowest temperature at which ignition occurs without an ignition source. Self-ignition can take the form of an explosion, flame, or sustained glow. The flash and self ignition temperature for common plastics and other materials are listed in Table 3-4.
When a plastic material reaches ignition, the temperature at which it generates a volatile gas, it will burn easily. If the volatile gas is not burned it's a toxic hazard. The toxicity of plastics materials is covered in chapter 5. Since plastics are excellent insulators heat does not initially penetrate below the surface molecules. The flame, either external or supported by the plastic flammable gases, generates additional heating fuel which decomposes more plastic, generating more volatile. As long as the flame is present, the circular process continue until all material is consumed or until the volatile gas is terminated. Most plastics materials have an inherent flammability, which means an external flame is applied to it, the plastic will decompose, generate volatile gas, and finally ignite.
The flammability of all plastics can be divided into three general categories: highly flammable, flammable, and flame retarding. Some plastics light very easily and continue to burn very rapidly; these are considered to be highly flammable plastics. The most important of these are; polystyrene, acrylics, polyethylene, cellulose, polyethylene terphthalate (PETE), and polyurethane. Most of these are commonly used in packaging, home and office appliances. Polyurethane's are used in bedding, carpets, clothing, wall covering, and insulation. Plastics which are flammable are those that do not light or burn very easily. These plastics are the polycarbonate, silicones and polysulfones. The flame retarding plastics burn as long as an external flame is present. However, once the flame is removed, the plastics will self-extinguish. These plastics are the polyvinyl chloride, Teflon, nylons, polyesters, and any chlorinated plastic. The flame retarding properties of these plastics are the result of their ability to develop a crust or oxide layer over the plastic melt which inhibits volatile gas from escaping. Other plastics which are included in this category are the thermoset plastics which do not melt and when exposed to combustion their surface molecules rapidly decompose to produce a dense charring.
The inherent nature of plastics materials to burn easily gives added importance to testing their flammability. Presently there are eleven ASTM, several Underwriter Laboratory, private testing agencies, and government approve tests for assessing the flammability characteristics of plastics. These tests measure various flammability properties such as burn rate, extent of burning, flash and self-ignition temperature, oxygen index, smoke density, flame spread, ignition time, flame travel, and smoke percent and release rate. Insurance underwriter groups, manufacturing associations, plus trade and building code associations have established codes and flammability requirements for plastic products. Every area of manufacturing plastic products establishes specific requirements for smoke generation, toxic fume emission and burning temperatures codes.
In the plastic extrusion process, raw plastic is fed into a heated extruder cavity or cylinder. Typically, the raw plastic is in bead form and may be mixed with colorants before the extrusion process begins. In some plastic extrusion processes, ultraviolet (UV) inhibitors may be added to the raw plastic beads as well. Once inside the plastic extrusion machine, the plastic beads, and any accompanying material, move through an opening in the extruder cavity towards a screw mechanism. The screw rotates, forcing the plastic material to advance through the extruder cavity.
Inside the extruder cavity, the temperature is very high, often reaching about 400°F (200 °C). The cavity needs to be so high in order to match the preferable melt temperature of the plastic material. Many plastic extrusion processes involve the use of three different heaters set to gradually increase heat inside the cavity. This reduces the potential for overheating.
Friction and pressure within the cavity of the extruder serve to produce extra heat that is independent of the heaters. Sometimes, the pressure and friction inside the cavity produces so much heat that the heaters may be shut off. When this happens, the desired temperature is maintained by the friction and pressure. Cooling fans are also employed frequently, helping to keep the plastic extrusion cavity at the desired temperature.
When the molten plastic reaches the front of the barrel, it moves away from the screw and journeys through a special screen designed to filter contaminants from the plastic. The molten plastic then moves into a die. The die is responsible for giving the molten plastic its profile. The plastic must then be cooled, often by a sealed-water bath; care must be taken to prevent the collapse of the newly formed product in its still molten state. Plastic sheeting and certain other products are cooled by special cooling rolls, instead of water baths.
After cooling, the product is spooled, coiled, or cut to length. In addition to plastics, a variety of other materials may be extruded. Aluminum and rubber are examples of materials that can be extruded. Even clay and certain types of foods may be extruded. However, the process used may differ from that employed for the purpose of plastic extrusion.
Source : www.plasticimpex.com
The use of halogenated flame retardants in plastics is steadily declining because they are volatile, pose an environmental risk and are difficult to recycle. Microcapsules, fibers and melamine resin foams represent some of the chief alternatives.
As successfully as the endless variety of plastics have established themselves on the market, these multifaceted materials show another face when it comes to fire. They melt and feed the flames like the petroleum from which they were ultimately produced. As a preventative measure, a variety of flame retardants are added to plastics, yet this introduces a number of problems. Additives often alter the mechanical properties and electrical insulating effect of plastics. Especially brominated and chlorinated additives migrate through the material and can damage metal and electronic components. Moreover, they represent a health risk and interfere with the recycling process. Yet fire safety regulations require the use of flame retardants.
The Fraunhofer Institute for Applied Polymer Research IAP is developing combustion-resistant and self-extinguishing plastics. Last November members of the working group, directed by Dr. Gerald Rafler, received the Friedrichs Prize for new technologies, along with 15,000 Euro in prize money, for their innovations and development of new materials. The prize is awarded by the German Federation of Industrial Cooperative Research Associations "Otto von Guericke" AiF. The new materials are already being tested and prepared for market introduction by the Austrian company Agrolinz Melamin GmbH.
"The microencapsulation of flame retardants is one of three strategies we are currently pursuing," explains Rafler. "The outer shell of the microscopic capsules is made of nonfusable, flame-resistant melamine resin like that used for frying pan handles or power plugs. The flame retardants remain enclosed in the capsules and are only released in the event of fire." Even substances incompatible with the base plastic material can be used if encapsulated. Nitrogen, carbon dioxide and compounds designed to produce extinguishing gases in reaction to heat are some examples. Gas-filled microcapsules are pressure-resistant and withstand plastics processing procedures such as extrusion, granulation and injection molding without rupturing.
The IAP research team has developed two further concepts to replace halogenated flame retardants. They manufacture fiber-reinforced polymers made of melt-spun melamine fibers. Such composite materials are easier to process and recycle than those reinforced with glass fiber. Finally, they manufacture high tenacity melamine foams that begin to slowly decompose at temperatures above 360 °C.
Source : innovations-report.com
In recent studies, it has been found the certain plastic reusable bottles may be a cancer risk. The risk is due to a chemical called BPA (Bisphenol A) that can be released when the bottle is washed, heated, and/or re-used. This impacts adults as well as children. Here are a very ways to limit the risk of BPA in plastic bottles:
Look for "BPA-free" claims on toys, baby bottles and containers. A lot of companies are starting to roll out BPA free baby bottles, bottle liners, and re-usable containers.
Avoid polycarbonate and PVC (polyvinyl chloride) plastics, both of which contain BPA. At the bottom of the plastic, there should be a recylcing code. Anything with code 7 is at risk. Alternatives include polyethylene plastic (also labeled PETE) and containers marked with recycling code 1, 2 (HDPE) and 4 (LDPE). Polypropylene (recycling code 5, or PP) are also safe.
If you use hard polycarbonate plastics (Nalgene bottles, baby bottles, sippy cups), do not heat or use them for warm or hot liquids. This includes running in the dishwasher. Nalgene just recently did a recall around a lot of their bottles.
Do not wash polycarbonate plastic containers in the dishwasher with harsh detergents.
Source : medhelp.org
Polyester is a category of polymers which contain the ester functional group in their main chain. Although there are many polyesters, the term "polyester" as a specific material most commonly refers to polyethylene terephthalate (PET). Polyesters include naturally-occurring chemicals, such as in the cutin of plant cuticles, as well as synthetics through step-growth polymerization such as polycarbonate and polybutyrate. Natural polyesters and a few synthetic ones are biodegradable, but most synthetic polyesters are not.
Depending on the chemical structure polyester can be a thermoplastic or thermoset, however the most common polyesters are thermoplastics.
Fabrics woven from polyester thread or yarn are used extensively in apparel and home furnishings, from shirts and pants to jackets and hats, bed sheets, blankets and upholstered furniture. Industrial polyester fibers, yarns and ropes are used in tyre reinforcements, fabrics for conveyor belts, safety belts, coated fabrics and plastic reinforcements with high-energy absorption. Polyester fiber is used as cushioning and insulating material in pillows, comforters and upholstery padding.
While synthetic clothing in general is perceived by some as having a less-natural feel compared to fabrics woven from natural fibres (such as cotton and wool), polyester fabrics can provide specific advantages over natural fabrics, such as improved wrinkle resistance. As a result, polyester fibres are sometimes spun together with natural fibres to produce a cloth with blended properties. Synthetic fibres also can create materials with superior water, wind and environmental resistance compared to plant-derived fibres.
Polyesters are also used to make "plastic" bottles, films, tarpaulin, canoes, liquid crystal displays, holograms, filters, dielectric film for capacitors, film insulation for wire and insulating tapes.
Liquid crystalline polyesters are among the first industrially-used liquid crystalline polymers. They are used for their mechanical properties and heat-resistance. These traits are also important in their application as an abradable seal in jet engines.
Polyesters are widely used as a finish on high-quality wood products such as guitars, pianos and vehicle / yacht interiors. Burns Guitars, Rolls Royce and Sunseeker are a few companies that use polyesters to finish their products. Thixotropic properties of spray-applicable polyesters make them ideal for use on open-grain timbers, as they can quickly fill wood grain, with a high-build film thickness per coat. Cured polyesters can be sanded and polished to a high-gloss, durable finish.
Source : Wikipedia