جستجوی مقالات مرتبط با کلیدواژه « خواص حرارتی » در نشریات گروه « مهندسی شیمی، نفت و پلیمر »

Due to the drought and lack of water resources, many efforts have been made to store water properly recently. Using of multilayer polyethylene tanks is an efficient measure in order to solve this problem and it has received considerable attention. Proper manufacturing conditions will greatly improve the strength of these tanks and their applications.

In this study, the effect of cooling process on the final properties of polyethylene tanks prepared by rotational molding method is investigated. Three different cooling methods comprised of cooling with water, cooling by air, and quiescent cooling is selected and their mechanical and thermal properties were investigated.

The results of the tensile test show that as the tank is cooled faster, the elongation at break will be higher. It is also demonstrated that the air cooling method results in the lower elongation at break. The results of the thermal properties show that higher cooling rate creates thicker crystals in the fragment which requires higher energy to overcome these thick crystals. According to the results of the thermal properties and using the softening temperature test it is found that by increasing the cooling rate, the softening temperature will be increased as well which will improve the application of the tank in high temperature conditions. Melt flow rate and density tests are also performed to confirm the results of mechanical and thermal properties, respectively. Charpy impact test is performed at ambient temperature to confirm mechanical behavior induced by crystal structure. All in all, cooling by water performs better than other methods in terms of mechanical and thermal properties.

The current study is based on synthesis a low cost carbon aerogel with improved properties and thermal insulator approach. In this work cheap novolac resin are used as a raw material for producing polymer aerogel by ambient drying method; then the coal tar pitch is added to samples by immerging them in pitch solution. In next step novolac-pitch polymer aerogels is converted to carbon nano-structure aerogels by pyrolysis heat treatment at inert atmosphere. The results proved, nano-structured aerogels with predictable density will be achieved by this method; also by studying on microstructure and morphology of aerogels it founded these aerogels have high porosity, low density(about 0.1-0.4 g/cm3) and high specific surface area (about 600 m2/g). The charring pitch was a lot and using of it made improved thermal properties that resulted in at least 100s delay in increasing temperature in time-temperature history test; as a result a high performance thermal insulator achieved.

Polyethylenes are among of the commodity polymers with wide-spread applications. They are being used in transportation، wire and cable، food packaging، and building industries، for instance. Ethylene-octene copolymers contain more branches in respect to that of the high density polyethylene، therefore، their crystallinities and melting points are lower and can also be processed much easier. Nowadays، there are huge interests in using polymer-clay nanocomposites because of their higher desired physical and mechanical properties such as thermal stability، tensile strength and barrier resistance in comparison with that of the unfilled polymers or the polymers which are reinforced with the same amount of micro-sized fillers. Nanoclays are modified using organic modifiers such as alkylammonium ions in order to enhance their compatibility with polymers. They can also act as a nucleating agent and change the crystallinity of polymeric materials. This nano-sized filler could also affect the thermal stability and flame retardancy but the amount of influence depends on the morphology developed. In this article، our aim is to present some information about the above-mentioned nanocomposites by reviewing the recently published papers in this area.

In recent decades due to decreasing environmental pollution many attempts have been carried out for developing biodegradable packaging systems and improving its efficiency. Composites containing fillers that have one dimension in a nano-size are called nanocomposites. During recent years many efforts have been carried out to produce fully biodegradable nanocomposites by using of mixing different polysaccharide nanocrystals (from various sources as filler) with a biodegradable polymer matrix. Using of cellulose micro andnanocrystals has been considerd in the nanocomposites due to have good mechanical strength, high thermal stability and low density as fillers and reinforcement material. Replacement nanoclay with cellulose nanocrystals is leading to production of fully biodegradable nanocomposite. The producing nanocomposite with good mechanical, thermal, permeability properties and completely biodegradable structure, can be suitable progress in producing packaging system.

Proteins are major class of edible biodegradable biopolymers. Whey protein is one of the important protein sources. One of the potential uses of this protein is for production of biodegradable films and coatings. edible, biodegradable films and coatings, by acting as barriers to control the transfer of moisture, oxygen, carbon dioxide, lipids, and flavor compounds, can prevent quality deterioration and increase the shelf life of the food products. In addition, edible films or coatings may provide mechanical integrity and improve the handling characteristics of the food. They can be effective carriers of many functional ingredients, such as antimicrobial agents to improve safety and stability of foods, antioxidants to prevent lipid oxidation, and flavorings and pigments to improve quality of foods. in this manuscript, physico chemical properties of these films (including water vapor and oxygen barrier properties, mechanical, thermal and thermomechanical properties) were investigated.