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Polymer Stabilizers
Polymer stabilizers (British English: polymer stabilisers) are chemical additives which may be added to polymeric materials to inhibit or retard their degradation. Mainly they protect plastic and rubber products against heat, oxidation, and UV light. The biggest quantity of stabilizers is used for polyvinyl chloride (PVC), as the production and processing of this type of plastic would not be possible without stabilizing chemicals. Common polymer degradation processes include oxidation, UV-damage, thermal degradation, ozonolysis, combinations thereof such as photo-oxidation, as well as reactions with catalyst residues, dyes, or impurities. All of these degrade the polymer at a chemical level, via chain scission, uncontrolled recombination and cross-linking, which adversely affects many key properties such as strength, malleability, appearance and colour. Stabilizers are used at all stages of the polymer life-cycle. They allow plastic items to be produced faster and with fewer ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
British English
British English is the set of Variety (linguistics), varieties of the English language native to the United Kingdom, especially Great Britain. More narrowly, it can refer specifically to the English language in England, or, more broadly, to the collective dialects of English throughout the United Kingdom taken as a single umbrella variety, for instance additionally incorporating Scottish English, Welsh English, and Northern Irish English. Tom McArthur (linguist), Tom McArthur in the Oxford English Dictionary, Oxford Guide to World English acknowledges that British English shares "all the ambiguities and tensions [with] the word 'British' and as a result can be used and interpreted in two ways, more broadly or more narrowly, within a range of blurring and ambiguity". Variations exist in formal (both written and spoken) English in the United Kingdom. For example, the adjective ''wee'' is almost exclusively used in parts of Scotland, north-east England, Northern Ireland, Ireland ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bioplastic
Bioplastics are plastic materials produced from renewable biomass sources. Timeline of plastic development, Historically, bioplastics made from natural materials like shellac or Celluloid, cellulose had been the first plastics. Since the end of the 19th century they have been increasingly superseded by fossil-fuel plastics derived from petroleum or natural gas (''fossilized'' biomass is not considered to be Renewable resource, renewable in reasonable short time). Today, in the context of bioeconomy and circular economy, bioplastics are gaining interest again. Conventional petro-based polymers are increasingly blended with bioplastics to manufacture "bio-attributed" or "mass-balanced" plastic products - so the difference between bio- and other plastics might be difficult to define. Bioplastics can be produced by: * processing directly from Biopolymer, natural biopolymers including polysaccharides (e.g., corn starch or rice starch, cellulose, chitosan, and alginate) and proteins ( ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Shear Stress
Shear stress (often denoted by , Greek alphabet, Greek: tau) is the component of stress (physics), stress coplanar with a material cross section. It arises from the shear force, the component of force vector parallel to the material cross section. ''Normal stress'', on the other hand, arises from the force vector component perpendicular to the material cross section on which it acts. General shear stress The formula to calculate average shear stress or force per unit area is: \tau = ,where is the force applied and is the cross-sectional area. The area involved corresponds to the material face (geometry), face parallel to the applied force vector, i.e., with surface normal vector perpendicular to the force. Other forms Wall shear stress Wall shear stress expresses the retarding force (per unit area) from a wall in the layers of a fluid flowing next to the wall. It is defined as:\tau_w := \mu\left.\frac\_,where is the dynamic viscosity, is the flow velocity, and is the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hydroxyl Radical
The hydroxyl radical, •HO, is the neutral form of the hydroxide ion (HO–). Hydroxyl radicals are highly reactive and consequently short-lived; however, they form an important part of radical chemistry. Most notably hydroxyl radicals are produced from the decomposition of hydroperoxides (ROOH) or, in atmospheric chemistry, by the reaction of excited atomic oxygen with water. It is also an important radical formed in radiation chemistry, since it leads to the formation of hydrogen peroxide and oxygen, which can accelerate corrosion and stress corrosion cracking in coolant systems subjected to radioactive environments. Hydroxyl radicals are also produced during UV-light dissociation of hydrogen peroxide (H2O2) (suggested in 1879) and likely in Fenton chemistry, where trace amounts of reduced transition metals catalyze peroxide-mediated oxidations of organic compounds. In organic synthesis, hydroxyl radicals are most commonly generated by photolysis of '' 1-Hydroxy-2(1H ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Radical Scavenger
A scavenger in chemistry is a chemical substance added to a mixture in order to remove or de-activate impurities and unwanted reaction products, for example oxygen, to make sure that they will not cause any unfavorable reactions. Their use is wide-ranged: * In atmospheric chemistry, the most common scavenger is the hydroxyl radical, a short-lived radical produced photolytically in the atmosphere. It is the most important oxidant for carbon monoxide, methane and other hydrocarbons, sulfur dioxide, hydrogen sulfide, and most of other contaminants, removing them from the atmosphere. * In molecular laser isotope separation, methane is used as a scavenger gas for fluorine atoms. * Hydrazine and ascorbic acid are used as oxygen scavenger corrosion inhibitors. * Tocopherol and naringenin are bioactive free radical scavengers that act as antioxidants; synthetic catalytic scavengers are their synthetic counterparts * Organotin compounds are used in polymer manufacture as hydrochloric acid ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Polystyrene
Polystyrene (PS) is a synthetic polymer made from monomers of the aromatic hydrocarbon styrene. Polystyrene can be solid or foamed. General-purpose polystyrene is clear, hard, and brittle. It is an inexpensive resin per unit weight. It is a poor barrier to air and water vapor and has a relatively low melting point. Polystyrene is one of the most widely used plastics, with the scale of its production being several million tonnes per year. Polystyrene is naturally transparent to visible light, but can be colored with colorants. Uses include protective packaging (such as packing peanuts and optical disc jewel cases), containers, lids, bottles, trays, tumblers, disposable cutlery, in the making of models, and as an alternative material for phonograph records. As a thermoplastic polymer, polystyrene is in a solid (glassy) state at room temperature but flows if heated above about 100 °C, its glass transition temperature. It becomes rigid again when cooled. This te ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Rubber
Rubber, also called India rubber, latex, Amazonian rubber, ''caucho'', or ''caoutchouc'', as initially produced, consists of polymers of the organic compound isoprene, with minor impurities of other organic compounds. Types of polyisoprene that are used as natural rubbers are classified as elastomers. Currently, rubber is harvested mainly in the form of the latex from the Hevea brasiliensis, Pará rubber tree (''Hevea brasiliensis'') or others. The latex is a sticky, milky and white colloid drawn off by making incisions in the bark and collecting the fluid in vessels in a process called "tapping". Manufacturers refine this latex into the rubber that is ready for commercial processing. Natural rubber is used extensively in many applications and products, either alone or in combination with other materials. In most of its useful forms, it has a large stretch ratio and high resilience and also is buoyant and water-proof. Industrial demand for rubber-like materials began to out ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Polypropylene
Polypropylene (PP), also known as polypropene, is a thermoplastic polymer used in a wide variety of applications. It is produced via chain-growth polymerization from the monomer Propene, propylene. Polypropylene belongs to the group of polyolefins and is Crystallization of polymers#Degree of crystallinity, partially crystalline and Chemical polarity#Nonpolar molecules, non-polar. Its properties are similar to polyethylene, but it is slightly harder and more heat-resistant. It is a white, mechanically rugged material and has a high chemical resistance. Polypropylene is the second-most widely produced Commodity plastics, commodity plastic (after polyethylene). History Phillips Petroleum chemists J. Paul Hogan and Robert Banks (chemist), Robert Banks first demonstrated the polymerization of propylene in 1951. The stereoselective polymerization to the isotactic was discovered by Giulio Natta and Karl Rehn in March 1954. This pioneering discovery led to large-scale commercial producti ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Autocatalysis
In chemistry, a chemical reaction is said to be autocatalytic if one of the reaction products is also a catalyst for the same reaction. Many forms of autocatalysis are recognized.Steinfeld J.I., Francisco J.S. and Hase W.L. ''Chemical Kinetics and Dynamics'' (2nd ed., Prentice-Hall 1999) pp. 151–2 A ''set'' of chemical reactions can be said to be "collectively autocatalytic" if a number of those reactions produce, as reaction products, catalysts for enough of the other reactions that the entire set of chemical reactions is self-sustaining given an input of energy and food molecules (see autocatalytic set). Examples Acid-catalyzed hydrolysis of esters produces carboxylic acids that also catalyze the same reaction. Indeed, the observation of an accelerating hydrolysis of gamma valerolactone to gamma-hydroxyvaleric acid led to the introduction of the concept of autocatalysis in 1890. The oxidation of hydrocarbons by air or oxygen is the basis of autoxidation. Like many radic ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Glass Transition Temperature
The glass–liquid transition, or glass transition, is the gradual and reversible transition in amorphous materials (or in amorphous regions within semicrystalline materials) from a hard and relatively brittle "glassy" state into a viscous or rubbery state as the temperature is increased. ISO 11357-2: Plastics – Differential scanning calorimetry – Part 2: Determination of glass transition temperature (1999). An amorphous solid that exhibits a glass transition is called a glass. The reverse transition, achieved by supercooling a viscous liquid into the glass state, is called vitrification. The glass-transition temperature ''T''g of a material characterizes the range of temperatures over which this glass transition occurs (as an experimental definition, typically marked as 100 s of relaxation time). It is always lower than the melting temperature, ''T''m, of the crystalline state of the material, if one exists, because the glass is a higher energy state (or enthalpy at const ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Injection Molding
Injection moulding (U.S. spelling: injection molding) is a manufacturing process for producing parts by injecting molten material into a mould, or mold. Injection moulding can be performed with a host of materials mainly including metals (for which the process is called die-casting), glasses, elastomers, confections, and most commonly thermoplastic and thermosetting polymers. Material for the part is fed into a heated barrel, mixed (using a helical screw), and injected into a mould cavity, where it cools and hardens to the configuration of the cavity. After a product is designed, usually by an industrial designer or an engineer, moulds are made by a mould-maker (or toolmaker) from metal, usually either steel or aluminium, and precision-machined to form the features of the desired part. Injection moulding is widely used for manufacturing a variety of parts, from the smallest components to entire body panels of cars. Advances in 3D printing technology, using photopolymers t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
