Polymerization Time Figures 3a-d show the effect of polymerization time on %GY (Fig. 3a) ; %GE (Fig. 3b); %TC (Fig. 3c) and %HP (Fig. 3d) at four different temperatures ( 50 0 ; 60 0 ; 70 0 and to 80 0C ). It is evident that , as the reaction time became longer , all polymer yield , except %GE , increased. The polymerization time corresponds to 180 min. brought about the maximum percentages for the positively dependence of polymer criteria. Enhancing effect of prolonging the duration of polymerization on grafting (%GY) and homopolymer (%HP) is reflected on the extent of total conversion (%TC) (Fig. 3). The latter increased as the time of polymerization increased particularly during the initial stages of the polymerization reaction. …show more content…
The latter embraced the salts of ferrous ammonium sulphate , manganous sulphate ans cobaltous sulphate. This pre-treatment process was carried out by impregnating the cellulose thiocarbonate fabric in a single metal salt solution at 30 0C for 30 min. , as described in the metathesis procedure. The pre-metallized cellulose thiocarbonate fabric was then grafted using moderate conditions included 4% MAA , 30 mmolL SPB , at 60 0C for 60 min. The results obtained are illustrated in Figure 5a-d. The data of this figure disclose (i) that the percentages graft yield (Fig. 5a) , grafting efficiency (Fig. 5b), and total conversion (Fig. 5c) enlarge by increasing the Fe2+ salt solution concentration and attain maximal at the FAS concentration corresponds to 0.2 mmol/L ; thereafter they decrease. The homopolymer (Fig. 5d) has an adverse deportment , (ii) that all polymer criteria slightly augment by heightening the Mn2+ salt solution concentration up to 0.02 mmolL ,then fall , (iii) that the Co2+ reductant ion fails to further improve the MAA grafting efficiency and graft yield. The %TC decreases by increasing the Co2+ salt solution concentration up to 0.06 mmolL , then increases. The lone prosperity of the Co2+ ion is the enhancement of MAA homopolymer
Laird DF, Mucalo MR, Dias GJ. Vacuum‐assisted infiltration of chitosan or polycaprolactone as a structural reinforcement for sintered cancellous bovine bone graft. Journal of Biomedical Materials Research Part A. 2012;100(10):2581-92.
Because of its ability to break down self-associative tendency of water , it may also reduce the number of water molecules entrapped between the polymeric chains, increasing the degree of postoperative polymerization In addition to post-curing increase in bond strength, the relative decrease in free water would eliminate or decrease the hydrolytic degradation of adhesive in or above the hybrid layer
The following dissertation will discuss on the fabrication of electrospun PCL nanofibre for tissue regeneration. This is to address the limitation faced by current TE scaffold. As there are insufficient focus on the production of PCL nanofibres with surface morphology and even fibre diameters for the use for tissue regeneration. On top of that, biopolymer such as PCL has the ability to degrade over time and still produce the porous structure desired by the nanofibre.[17] Hence, to control the fabrication of PCL nanofibre, the effects of the electrospun parameters is studied in the following dissertation. On top of that, the dissertation will investigate the fabrication of electrospun PCL nanofibre scaffolds for tissue regeneration.
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.
Acrylonitrile-butadiene rubber (NBR) is well-known unsaturated copolymers for concerning five decays [1-2]. It has been used in many industrial required purposes as hoses, o-ring seals, insulation base product and other many packaging materials []. The main components of technically related NBR comprise of 24-30 wt% of acrylonitrile and include some benefits in contrast to other elastomer like polymers. Such as, good processability, resistance to oils as well as hydrocarbons, especially resistance to hydrocarbons and oils, NBR has wide region of service temperature (from -35 oC up to 100 oC) [1-2].
There are many types of polymer degradation mechanisms: thermal, mechanical, photochemical, radiation chemical, biological and chemical degradation (Schnabel, 1981). According to ASTM definition, “degradable plastics are the plastics that are designed to undergo a significant change in its chemical structure under specific environmental conditions, resulting in a loss of some properties that may vary as measured by standard methods appropriate to the plastic and the application in a period of time that determines its classification”. This definition can be applied to many polymer degradation types including photodegradation, thermooxidation, hydrolysis and biodegradation. Autooxidation is the cause of thermooxidative degradation of organic materials without light. In natural photodegradation, sunlight reduces the molecular weight of the polymers by photooxidation and direct bond cleavage (Hand Book of Polymer Degradation, 2000). Another mode of degradation is hygrothermal degradation. Substantial loss of weight and mechanical properties of a material due to the effects of moisture and temperature is called hygrothermal degradation (Balakrishnan, Hassan, Imran, & Wahit, 2011). For instance, aged PLA/jute fiber composites in hygrothermal environment showed 15% decrease in tensile strength after 24 h
Exothermal energy of polymer cure (as in epoxy adhesives), allows determination of the degree and rate of cure.
There are many commercially produced composites used polymer matrix material. There are many different polymers available depending on the raw ingredients. There are some broad categories, and each with numerous variations. The most common used are known as vinyl, polyester, polypropylene, epoxy, polyimide, and others. The reinforcement m...
Scientist discovered, in the 1965 at Du Pont, a new way of making nearly perfect longer polymer chain. This method was found that it makes clear liquefied solution that arises to the repeated of the molecular backbone. The main requirement for t...
Cellulose is an abundant polysaccharide consisting of a β-1, 4 linkage of D-glucose [1,3]. There is an array of applications for cellulose, including, but not limited to: biofuels, reinforcement agents, thickeners, dietary fiber, and even wound care. As of late, cellulose, as a waste product, has been in high demand as a reinforcement agent in synthetic, petroleum-based polymer matrices (petroleum based plastics) [3]. Cellulose I has good flexibility, it is abundant in nature and also biodegradable. Because of its fiber- like structure, it has been compared to carbon nanotubes (CNT’s) [3].
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
Polystyrene is a very common polymer, making up such everyday items as Styrofoam cups, plastic cutlery, packing “peanuts”, CD jewel cases, and insulation. German apothecary Eduard Simon originally distilled the monomer, Styrene, from the resin of the Sweetgum tree. It was later found that when these monomers formed chains, they shared several properties of rubber, and was thus proved to be a versatile polymer. Although it only makes up about one percent of solid waste produced in the United States, th...
Polymer means any of various chemical compounds made of smaller identical molecules called monomers linked together. Some polymers, like cellulose, occur naturally. Polymers have extremely high molecular weights, and made-up of many of the tissues of organisms, and have various uses in industries. The process by which molecules are linked together to form polymers is called polymerization (The American Heritage Science Dictionary, 2005). Polymeric compound is a compound made of many smaller molecules such as cellulose, chitin, soy protein, casein and many more. Polymeric is an organic giant molecule and most of the compound is non-crystalline.
Man-made polymers are generally called ‘resins’ and can be classified under two types; thermoplastic and thermoset, according to the effect of heat on their properties. Thermoplastic materials contain polymer molecules that are held together by weak van der Waals forces or hydrogen bonds [3]. Thermoplastics soften when heated and will eventually melt but they can be hardened again by cooling the material. This process of heating and cooling can be performed many times without having an effect on the material properties and this can be desirable for certain applications. Some types of thermoplastics include ABS, nylon and polypropylene and the main type of dispersed phase used in the creation of composites using thermoplastics is short fibres such as glass [4].
There is several properties analysis of polymer. In this topic, we will discuss further the five polymer properties and behavior.