Thermal and mechanical properties of LDPE by the effects of organic peroxides

WOS: 000403007800012In this study, the effect of different organic peroxides on different types of low-density polyethylene (LDPE) was investigated. LDPE products like F2-21T, F5-21T, and I22-19T were mixed in different proportions with dialkyl peroxide, dibenzoyl peroxide, and dilauroyl peroxide. Melt flow rates, mechanical properties (tensile strength at yield, tensile strength at break, elongation at break, and stress-strain effect), thermal analysis (differential scanning calorimetric and thermogravimetric analysis), and scanning electron microscopy images of the prepared mixtures were examined. Cross-linking occurred in the structure of LDPE types having different molecular weight distribution by the addition of even small amounts of peroxide (e.g. 0-0.12wt%). Copyright (c) 2017 John Wiley & Sons, Ltd

Parametric Investigation of Optimum Thermal Insulation Thickness for External Walls

Numerous studies have estimated the optimum thickness of thermal insulation materials used in building walls for different climate conditions. The economic parameters (inflation rate, discount rate, lifetime and energy costs), the heating/cooling loads of the building, the wall structure and the properties of the insulation material all affect the optimum insulation thickness. This study focused on the investigation of these parameters that affect the optimum thermal insulation thickness for building walls. To determine the optimum thickness and payback period, an economic model based on life-cycle cost analysis was used. As a result, the optimum thermal insulation thickness increased with increasing the heating and cooling energy requirements, the lifetime of the building, the inflation rate, energy costs and thermal conductivity of insulation. However, the thickness decreased with increasing the discount rate, the insulation material cost, the total wall resistance, the coefficient of performance (COP) of the cooling system and the solar radiation incident on a wall. In addition, the effects of these parameters on the total life-cycle cost, payback periods and energy savings were also investigated

Introducing freshmen students to the practice of solid-phase synthesis

A one-semester laboratory project on solid-phase peptide chemistry was designed pedagogically to cater to freshman science students. The approach not only permitted multistep syntheses that would be considered impractical in solution, but also gave students insight into fundamental aspects of research at an early stage of development. Young scientists prepared Bz-Asn-Asn-Phe and Bz-Asn-Gln-Phe--peptides envisaged as potential competitive inhibitors of chymotrypsin. The synthesis, defined by an attachment-deprotection cycle, two elongation-deprotection cycles, and a benzoyl-capping protocol, was completed manually on Wang resin using Fmoc chemistry. Students quantified the yield of each condensation and deprotection reaction by measuring levels of dibenzylfulvene chromophore, a stoichiometrically afforded by-product. Benzoylation of the N-terminus was confirmed by employing a cadmium-ninhydrin reagent. The group also ascertained, through use of a chromogenic substrate, that chymotrypsin-catalyzed hydrolysis was impeded slightly when carried out in the presence of target peptides. Supplementary analyses supporting peptide purity and composition were given to students. Grading was based on laboratory participation, project proposals, reports, and a concluding slide-show presentation made to peers and colleagues. While the project was time-consuming overall, students acquired an impression of research work and an appreciation of the utility of solid-phase methods