Introduction
The history of polymers stretch back millions of years. These “primitive” polymers were created by nature to fulfill the needs of information storage, energy storage and information reproduction. Human made polymers are a more recent invention, of the last two hundred years or so. These polymers are general made of highly flammable hydrocarbons and their derivatives. Fires caused by a combination of human careless and the physical properties of hydrocarbons have caused millions of dollars in property damage and claimed an untold number of human lives. It is this fact that has lead to scientists devoting time and resources to making polymers safer. In the following paragraphs the mechanism behind burning polymers will be discussed, as well as the techniques employed to either slow the rate of fire and/or extinguish it altogether. A section will also be devoted to a review of ongoing, within the last five years, research into enhancing the flame retardancy of polymers.
The combustion of a polymer can be classified as an exothermic oxidation reaction. The reaction starts when the polymer is heated to its initiation temperature or when the chemical bonds begin to cleave. As a result, the polymer begins to give off volatile gases (reducers), which mixes with atmospheric oxygen (oxidizer). When this fuel mixture either reaches their autoignition temperature or are exposed to an external source of energy, they undergo combustion or the oxidation reaction. Of which the products are water, carbon dioxide and heat. Although most of the heat is radiated into the surrounding environment, some of it will be used to initiate further polymeric decomposition. The oxygen that was used is replenished via the convection current gener...
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...ed structure. For this series of experiments, the group changed the synthesis method, changing the small molecule surfactant to a cationic copolymer (PVAc). They did this so they can control the morphology of the resulting polymer complex. As a result of this change, the physical properties of polymers with the inclusion of this copolymer was undertaken. They found for the control groups EVA-0 and EVA-NC0, that both the Young's modulus and tensile strength increase and the toughness decreases when compared to the value for unmodified EVA. The toughness rebounded when clay was added. This is opposite to what is expected, as the copolymer is more amorphous than EVA. If the trend was followed the Young's modulus and tensile strength should decrease while the toughness increases. The authors contribute this opposite trend to the fact that the copolymer has Tg than EVA
Fire and thermal properties of PA 66 resin treated with poly-N- aniline- phenyl phosphamide as a flame retardant
Mixing sodium polyacrylate and water resulted in in a thick, clear gel that resembled ice or snow. It was sticky and wouldn’t form a shape if you held it in your hand and molded it. Adding heated water and sprinkling in poly(vinyl alcohol) to the surface of the water produced another sticky
The most common form of polyethylene is petroleum based or olefins based; as before mentioned polyethylene compounds have a wide commercial applicability and are made from non-renewable resources (Harding, Dennis, von Blottnitz, Harrison, & S.T.L., 2007). Its manufacturing processes are regarded as energy intensive and release significant amount of CO2 and heat into the atmosphere (Broderick, 2008). Next a little more detailed description of polyethylene’s production processes will be presented, with a focus on the way the material inputs are extracted and synthesized.
The most commonly produced PVC structure by addition polymerisation is the atactic PVC. As seen in Figure #, the chlorine atoms are branched randomly and asymmetrically along the carbon backbone. Unlike the other two structures, the random orientation prevents the polymers from packing closely together and is described to be ‘amorphous’.
They are amorphous or solely moderately crystalline once injection shaped, but the degree of crystallinity will be abundant redoubled for fiber and film applications by orientation via mechanical stretching. The two most vital polyamides poly(hexamethylene adipamide) Nylon 6,6 and polycaprolactam Nylon 6. Both have wonderful mechanical properties together with high impact strength, high flexibility, high tensile strength, good resilience and low creep. They are straightforward to dye and exhibit wonderful resistance to wear due to a low constant of friction. Both amides have a high melting temperature (500 - 540 K) and glass transition temperature reports in excellent mechanical properties at elevated temperatures. For example, the heat rebound temperature of PA-6, 6 is usually between 180- 240°C that exceeds those of polycarbonate and polyester. They also have excellent resistance to fungi, oils, bases, etc. The main limitation is that the strong wet sensitivity water acts as a plasticizer and therefore the ensuring changes in mechanical properties. For example, the tensile strength of moist polyamide is 50% below that of dry polyamide. Another important polyamide is Nylon 6,12. It is less hydrophilic than Nylons 6,6 and 6 due to the larger range of chemical group of methylene within the compound backbone. For this reason, it has better dimensional
Thermoset polymers contain no set arrangement of chains and as such they can be classified as amorphous i.e. they contain no distinct crystalline structure [3]. Thermoset materials are formed from a chemical reaction of a resin and a hardener or catalyst and this reaction is irreversible and produces a hard and infusible material [4]. Cured thermosets will not become liquid again if heated but above a certain temperature their mechanical properties can change substantially. The temperature at which this change can occur is called the Glass Transition Temperature (Tg) and it varies depending on the particular resin and hardener/catalyst used as well as its degree of cure and whether it was mixed properly. If the temperature of a thermoset material is raised above the Tg, the molecular structure changes from that of a hard crystalline polymer to a more flexible amorphous polymer. At this elevated temperature the properties of the thermoset such as resin modulus (stiffness) drop significantly and as a result the compressive and shear strength of the composite will do the same. Other properties such as water resistance and colour stability also reduce above the resin’s Tg This change can be reversed by cooling the material back down to below the Tg.
chains instead of hydrogen atoms. Cross-linking is another way in which the polymer can be made stronger. This involves ultraviolet radiation that bombards the polymer with electrons and formulates bonds between the molecular chains of the polymers. This is like linear polyethylene but different in that it is more impact resistant, and it has a much higher density. This allows it to be stored or be used with different chemicals that would normally cause the polymer to desolve.3 This can start to become a problem because as the polymer continues to become chemically enhanced. So the ways of dissolving and recycling the polymer become more difficult.
Flame retardants refer to a class of several chemicals that are used to slow or prevent the ignition or growth of fires. A variation of different chemicals, with diverse properties and structures, are combined in different ways to suit the different types of materials to make them fire-resistant without interfering with their intended use or performance. Since the 1970’s, FRs have been and still are widely added or applied to a big variety of major consumer products.
Recently , biomacromolecules such as proteins and deoxyribonucleic acid have shown unexpected flame retardant features when deposited on cellulosic or synthetic substrates , like cotton , polyester or cotton polyester blends . The use of some of these biomacromolecules as flame retardants , is a significant advantage , since they can be considered as water or by – products from the cheese and milk industry .
Thermal properties of material (Tg, Tm, Td) are those properties that response to temperature. They can be studied by thermal analysis techniques including DSC, TGA, DTA and dielectric thermal analysis. The nanometer-sized of inorganic particles incorporated into the polymer matrix can improve thermal stability by acting as a superior thermal insulator and as a mass transport barrier to the volatile products generated during decomposition [117]. Khanna et al. [57] reported the thermal (TGA) analysis of the PVA/Ag nanocomposite. They observed that the decomposition profile starting at about 330 ◦C and continuing till about 430 ◦C. They also found the PVA/Ag nanocomposites have higher thermal stability than the PVA alone. Mbhele et al. [99] also observed that that the pure PVA starts decomposing at about 280 ◦C and
Unfortunately, the majority of the polymer investigations cited have been performed under the classic conditions of slow heating rates or isothermal conditions in vacuum environments. However, the residence time of a polymer element at the solid surface during the normal ignition and combustion of a propellant is usually in the order of milliseconds. Further more, the pressure level is normally several hundred pounds per square inch in most actual combustion environments. Then the direct application of the low-pressure isothermal decomposition data to the propellant combustion may be questionable [34, 35].
Polymers are made from relatively small molecular fragments known as monomers that are joined together. Synthetic polymers which include the large group known as plastics are divided into three groups: commodity thermoplastic, engineering thermoplastics (ETP), and advanced engineering thermoplastics (AETP). The engineering thermoplastics (ETP) have heat resistance, strong mechanical properties, lightness, self-lubrication, and easy manufacturing. This plastic category has been lately used to replace wood and metal applications.
Figure. 2 gives a brief summary of the applications of biomass-derived degradable polymers. Nowadays, there are tremendous interest in research and using of biopolymers in packaging, civil engineering, biomedical and automotive mystery
The same procedure was used to calculate the enthalpy change of combustion for the other alcohols used in this experiment and their
A polymer is a large molecule that is known as an organic compound. Polymers are used in many different ways to form different structures but mostly polymers are used to create various kinds of plastics. A polymer is made from the covalent bonding of smaller repetitive molecules. As seen in figure 1. These repeating molecules are built into chains, and different polymers have varied chain lengths. These smaller molecules which make up the polymer are known as monomers. Through the reaction of polymerization which generally requires a catalyst polymers are formed. Various Polymers are built of different types of monomers, some contain only one type of monomer whereas others can contain up to two or more monomers. These polymers are known as natural polymers, they occur in nature and then are extracted for use. Natural polymers are often water based, examples are silk,