Vinylester resins have a similar molecular structure to polyester resins but they differ in that the location of their reactive sites are only at the ends of the molecular chain as seen in Figure 10. This enables the whole length of the molecular chain to absorb shock forces which makes a vinylester resin more resilient and tougher than a polyester resin. The fact that vinylester resins have few ester groups enables it to be more water resistant than polyester resins and it also provides a higher resistance to chemical degradation.
The molecular chains of a typical vinylester are represented in Figure 11 and it can be seen that the position of the reactive sites is at the end of the chain and this is different when compared to polyesters as seen in Figure 8. As a result of the fewer esters present in vinylester resin it follows that this makes vinylesters more suitable for marine applications or parts that are immersed in water but in order to achieve these properties as well as the toughness that vinylesters exhibit the resin usually needs to have an elevated temperature post cure.
2.3.4. Comparison of Resin Properties
When selecting the type of resin to be used in composite structures there are three main considerations that need to be taken into account and these are:
• Mechanical properties
• Adhesive properties
• Degradation from water ingress
Since degradation from water ingress is not applicable to this investigation it will be excluded.
The main mechanical properties of a resin that must be considered are the stiffness or tensile modulus and the tensile strength as these pertain directly to the overall performance of the composite. Figure 13 shows the three main types of resins and how their mechanical ...
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...ing process the end result is called a direct roving while if several strands are combined together after manufacture of the glass it is called an assembled roving.
2.4.3. Aramid Fibre
Aramid fibre is a man-made organic polymer that is produced by spinning a solid fibre from a liquid chemical blend. The main properties of aramid fibre are high strength and low density which result in a very high specific strength. All types of aramid fibre have good resistance to impact but compressive strength is not high and is comparable to that of E-glass. Aramid fibres exhibit a nonlinear, ductile behaviour when under compression [6]. Aramid fibres are also resistant to abrasion as well as chemical and thermal degradation but they can degrade slowly when exposed to ultraviolet light. Aramid fibres are usually available in the form of rovings, with tex’s ranging from 20 to 800.
rapid development of polymer chemistry after World War II a host of new synthetic fibers
Strength In terms of strength the effect the plasticizers have on the polymers is that the additive makes the polymer have a weak intermolecular force. As a result of this the polymers will be unstable an easier to handle. Due to this the polymer then can be remoulded and tougher and this will increase the polymers
The Crystallinity of Kevlar Polymer strands, contributes to the unique strength and stiffness of the material. Kevlar is very similar to other common synthetic polymers, including Nylon, Teflon and Lycra. In all Polated to strength. Aromatic refers to the Carbon atoms attached in a ring, and Amides refers to a group of Carbon, Nitrogen and Hydrogen atoms. Kevlar fiber is therefore a “Polyaromatic amide”, as it has a high breaking strength.
Dental composites, also known as "white fillings", are a group of restorative materials composed of a mixture of powdered glass and plastic resin regularly used in modern dentistry to resemble the appearance of the natural tooth. Acrylic resin was first introduced to the dental profession in the mid 1950s. Since their introduction, acrylic based materials have continued to play a pivotal role in restorative and prosthetic dentistry. After the introduction of the bisphenol A glycidyl methacrylate, or BIS-GMA, by Bowen in the early 1960s the potential application of resins has emerged. This composition and formulation possessed a higher molecular weight and therefore better mechanical properties and reduced polymerization shrinkage, the newer polymer offered potential for much greater applications that included anterior and posterior composite resin restorations, indirect inlays/onlays, pit and fissure sealants and more wear resistant denture teeth.
Dental amalgam is a material which is commonly used to fill cavities. This type of filling is also known as silver fillings. There have been many questions raised due to the use of this form of filling. This is due to the fact that dental amalgam is made up of a mixture of metals. These metals consist of liquid mercury and a powdered alloy that is made up of elements such as silver, tin, and copper. The reason why the use of this filling is so controversial is due to the fact that about 50% of dental amalgam is mercury. High amounts of mercury exposure are known to be toxic in humans. One would naturally wonder why this would be a controversial topic. One would think if it is toxic to humans why use it? Well there are reasons for this, and this is because unlike other types of mercury metallic mercury is considered non-toxic. Swallowing metallic mercury causes no type of poisoning or any harm to the human body. However, it is a proven fact that breathing in large quantities of metallic mercury vapor can cause a serious amount of poisoning. Metallic mercury vapors can be absorbed into the bloodstream almost instantly. In dental amalgam large quantities of mercury vapor are not being poured into the lungs, it is actually a
The key difference between the two materials is essentially their optical clarity. Brackets made of monocrystalline alumina or monocrystalline sapphire have a clearer appearance while the polycrystallines are more tooth-colored. These are used as they have better aesthetics, physical strength and favorable optical properties. Being non-porous, they also are more resistant to odors and staining.
These include nylon resin material, acrylic resin and metal. They use metal covered in plastic with plastic teeth for making partial dentures.
Denture teeth can be made of acrylic poly(methyl methacrylate) (PMMA) or composite resins. PMMA is a polymer - a material made the from joining of methyl methacrylate monomers. Properties of PMMA include resistance to abrasion, chemical stability and a high boiling point. (Jun Shen et al. 2011). However, weak flexure and impact strength of PMMA are of concern as they account for denture failure. (Bolayir G, Boztug A and Soygun K. 2013). Composite denture teeth are made of a three distinct phases - filler, matrix and coupling agents. Out of the types of composite teeth available, nano-filled composite teeth are preferred. Composite teeth have a PMMA coating around the tooth and a high content of filler particles. This gives them strength, higher resistance to forces than acrylic teeth and provides compete polymerization due to the PMMA coating. (Anusavice, K. J., Phillips, R. W., Shen, C., & Rawls, H. R, 2012). If the interface between the PMMA denture base and PMMA or composite teeth was weak, the denture will not be able to sustain occlusal forces, making the base-teeth interface, an entity of significance.
This maximises the intermolecular forces between the chains as they are able to pack closely together. However, this reduces the flexibility and is therefore quite rigid and strong. This isotactic polyvinyl chloride structure occurs very little. Another structure that is produced very little is the syndiotactic PVC. The syndiotactic PVC has a regular arrangement and has similar properties of flexibility, rigidity and strength to the isotactic PVC as shown in Figure #.
Different chemistries and production methods of these fibers give them certain advantages. as viscose’s ability to combine with other fibers to create new fabrics easily) and disadvantages. such as nylon’s quickly weakening fibers or natural silk’s difficulty of production. other that make them more or less suitable for certain purposes. For this reason, when? considering silk and artificial silk, it is illogical to pick one fiber that is superior to the others.
The purpose of this experiment was to create a polymer by reacting a mixture of decanedioyl dichloride and dichloromethane with a mixture of water, 1,6-hexadiamine and sodium carbonate. Specifically, we created the polymer Nylon-6,10. Nylon-6,10 polymers are used in a vast majority of things we use in everyday life such as zippers, the bristles in brushes, and even car parts. This experiment was different from the industrial method of making nylon because that takes place at a much higher temperature. A polymer is a substance that has a structure made of similar or identical units bonded together. All polymerizations fall into two categories: step-growth and chain-growth (both of which we used to form our polymer). Step growth polymerization
Polymer-Polyethylene is partially crystalline as well as amorphous because it has crystalline and amorphous regions. Also it has linear chains so this is the simplest structure compared to a branched or network chain. This can be of an advantage to it over other types of materials as its good toughness and elongation makes it very significant in the engineering industry as it can be moulded or extruded into shape...
The type of wood that is being used determines what projects the woodworker is able to accomplish and what tools will be used to decorate it. Also, each type of wood has specific characteristics, meaning they have different colors or textures that will give the finished project a proper appearance. Therefore, woods such as mahogany, red oak, and maple are used for furniture and homes. However, woods such as cherry, walnut, and poplar are used for firearms and instruments respectively. Prior to starting a project, a rough draft or sketch of the overall design should be devised.
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.
Although the fundamental property of bulk polymers is the degree of polymerization, the physical structure of the chain is also an important factor that determines the macroscopic properties.