Polymers2015, 7(9), 1587-1598; doi:10.3390/polym7091472 - published 26 August 2015 Show/Hide Abstract
Abstract: Ensuring an appropriate casting time window is of great importance for achieving desired quality and performance of aging materials. In this paper, the effects of promoter and cross-linking agent on the working life—the period a mixture stays in a workable condition—of low-temperature-cured acrylic polymer concrete (PC) are investigated in order to develop mixture proportions that can be effectively applied in cold weather conditions. The experimental variables included in this study are: (1) curing temperatures (−20, −10 and 0 °C); (2) N,N-dimethyl-p-toluidine (DMT) contents (0.5, 1.0, 1.5 and 2.0 phr (parts per hundred parts of resin)); and (3) trimethylolpropane trimethacrylate (TMPTMA) contents (0, 2.5 and 5 phr). Results indicated a strong relevance between binder’s setting time and PC’s working life. Additionally, it was observed that the working life of acrylic PC was substantially shortened as the curing temperature and contents of DMT and TMPTMA increased. Results of a two-way analysis of variance (ANOVA) revealed that TMPTMA had a greater impact on the working life than DMT. Finally, this study developed an equation that can be used to estimate PC working life, based on the binder’s setting time. The findings of this study will be used as valuable information for cold weather applications of acrylic PC.
Polymers2015, 7(8), 1577-1586; doi:10.3390/polym7081471 - published 24 August 2015 Show/Hide Abstract
Abstract: Micro/nanofibers prepared by direct-writing using an electrospinning (ES) technique have drawn more attention recently owing to their intriguing physical properties and great potential as building blocks for micro/nanoscale devices. In this work, a wavy direct-writing (WDW) process was developed to directly write serpentine micro/nano structures suitable for the fabrication of micro devices. This fabrication ability will realize the application of electrospun-nanofiber-based wiring of structural and functional components in microelectronics, MEMS, sensor, and micro optoelectronics devices, and, especially, paves the way for the application of electrospinning in printing serpentine interconnector of large-area organic stretchable electronics.
Polymers2015, 7(8), 1564-1576; doi:10.3390/polym7081470 - published 20 August 2015 Show/Hide Abstract
Abstract: As the main force-bearing component of a cable-stayed bridge, a durable stay cable is paramount to the safety and durability of the entire bridge. High-density polyethylene (HDPE) sheathing is the main protective component of a stay cable and is the key to insuring cable durability. To address the issue of HDPE sheathing fracture on service, strain level data for in-service, HDPE bridge cable sheathing was used in this study as the basis for HDPE material aging and fatigue testing. A fatigue yield phenomenon with a yield platform on the hysteresis curve of the fatigue cycles is observed by the fatigue test. The parameters to describe this phenomenon are proposed and defined in this paper. A preliminary examination of the relationship between these parameters and the factors, such as the number of cycles, the strain amplitude, and strain rate, are presented. Based on the results obtained, it is suggested that the condition of fatigue yield of HDPE sheathing be defined as the fatigue durability limit state for the purposes of durability design, assessment, and protection of cable-stayed bridges.
Polymers2015, 7(8), 1541-1563; doi:10.3390/polym7081469 - published 17 August 2015 Show/Hide Abstract
Abstract: Through a straightforward approach, a new meltable, halogen-free, nitrogen-phosphorus-based flame retardant (FR), 6-(2-(4,6-diamino-1,3,5-triazin-2-yl)ethyl) dibenzo[c,e][1,2]oxaphosphinine 6-oxide (DTE-DOPO) was synthesized and incorporated in polyamide 6 (PA6). It was proved that a very low phosphorus content of 1.46 wt% for DTE-DOPO additive improved the flame retardancy of PA6, leading to a non-flammable material. The performance of the new additive was compared to that of the commercially-available Exolit® OP 1230. The PA6 formulations were evaluated by measuring the rheological, mechanical, and flammability behavior. Using compounding by melt extrusion, 17 wt% additives was introduced into PA6 matrix and the corresponding formulations were characterized. The results evidenced a higher homogeneity of DTE-DOPO with PA6, a high thermal stability with a catalyzing decomposition effect on PA6 caused by the presence of the new developed FR, enhanced elasticity for the PA6/DTE-DOPO formulation and a V0 rating for both formulations. Thermal and fire analysis indicated a primary gas-phase activity, combined with a complete suppression of the self-sustained burning for the PA6/DTE-DOPO formulation.
Polymers2015, 7(8), 1522-1540; doi:10.3390/polym7081468 - published 17 August 2015 Show/Hide Abstract
Abstract: Marine and inland pollution by non-degradable plastic bags and other plastic articles is a topic of great concern. Natural degradation processes based on oxidation of plastic pollutants could possibly contribute to limit the extent of pollution. Thermal degradation of polyolefins in the absence of light by non-polluting pro-oxidants has not been presented before. In this study, we show that two amines, stearyl amine and [(3-(11-aminoundecanoyl) amino) propane-1-] silsesquioxane (amino-POSS) in combination with ferric stearate (FeSt3) tremendously accelerate the thermal oxidation of polyolefins compared with reference samples. Both amines and FeSt3 are to a large extent based on renewable resources. Polyethylene and polypropylene samples containing less than 100 ppm of iron and 1% of amine were extremely brittle after 10 days in a circulation oven in the absence of light. No significant degradation could be seen with samples containing iron but no amine. In a different application, the initial oxidation of polyethylene can be used in order to increase its adhesion to cardboard. Excellent adhesion between polyethylene and cardboard is important for liquid packaging based on renewable resources. Amino-POSS has been chosen for food packaging applications due to its expected lower leakage from polyethylene (PE) compared with stearyl amine. Film samples of PE/amino-POSS/FeSt3 blends were partly oxidized in a circulation oven. The oxidation was documented by increased carbonyl index (CI) and melt flow index (MFI). The limited extent of oxidation has been proved by unchanged tensile strength and only moderate changes in elongation at break when compared to reference polyethylene films containing no FeSt3 or amino-POSS. The PE/amino-POSS/FeSt3 blends were compression moulded to paperboard. The adhesion of non-aged blends to paperboard decreased with increasing amino-POSS content which is in good compliance with an earlier reported lubricant effect of high amounts of POSS in PE. Thermal ageing of PE/amino-POSS/FeSt3 films prior to coating however led to a significant increase in adhesion. Improved physical interlocking due to increased MFI and interaction between C=O of the blends and OH of paperboard can explain the adhesion improvement. The films were not brittle after thermal ageing, which makes their use in industrial packaging feasible. A mechanism explaining the role of amines during thermal oxidation of polyolefins in the presence of iron is proposed.
Polymers2015, 7(8), 1510-1521; doi:10.3390/polym7081467 - published 14 August 2015 Show/Hide Abstract
Abstract: The purpose of this study was to investigate the effects of size and type of incorporated model molecules on the polymer degradation and release profile from thermosensitive triblock copolymer based controlled delivery systems. In vitro release of the incorporated molecules demonstrated slow release for risperidone (molecular weight (Mw) = 410.48 Da; partition coefficient (Ko/w) = 3.49), while bovine serum albumin (BSA) (Mw = ~66,400 Da; Ko/w = 0.007) and insulin (Mw = 5808 Da; Ko/w = 0.02) showed initial burst release followed by controlled release. The proton NMR, Gel Permeation Chromatography, and Cryo-SEM studies suggest that the size and partition coefficient of incorporated molecules influence the pore size, polymer degradation, and their release. In spite of using a similar polymer delivery system the polymer degradation rate and drug release notably differ for these model molecules. Therefore, size and oil-water partition coefficient are important factors for designing the controlled release formulation of therapeutics from triblock copolymer based delivery systems.