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Thermal degradation of polyethylene terephthalate (PET)/carbon nano tube (CNT) nanocomposites is a serious issue in the manufacturing process of this nanocomposite that can limit the applications of the nanocomposite. In this study, the effects of two kinds of chain extenders, pyromellitic dianhydride (PMDA) and pentaerythritol (PENTA), on the rheological behavior, thermal characteristics, and crystallinity of the PET were investigated. The results of shear rheology revealed improvement of the storage modulus and complex viscosity, which indicated the recoupling of broken chains, increasing the chain length, and the generation of long branches was the reason for chain extension. Also, differential scanning calorimetry (DSC) results clarified an increase in PET crystallization rate in the presence of CNT and chain extenders. Furthermore, SEM was performed to detect CNT dispersion in the nanocomposite, and four-probe technique test was utilized to determine the influence of CNT on the electrical properties of PET. KEYWORDS carbon nanotube, chain extenders, electrical percolation, polyethylene terephthalate, rheology, 1 | INTRODUCTION Polyethylene terephthalate (PET) as a semicrystalline thermoplastic aromatic polyester [1-5] that is frequently utilized owes excellent mechanical properties, sufficient chemical and thermal resistance, and simplicity of manufacturing [...]

This study aimed to enhance the melt strength, foamability, and microstructural properties of poly(ethylene terephthalate) (PET) foam by addition of styrene maleic anhydride (SMA) as a chain extender. The addition of SMA to the polymer increased the complex viscosity by 375%. The calculated dissipation factor for chain‐extended‐PET (CE‐PET) samples demonstrated a rise in polymer viscous behavior with increasing SMA content. The CE‐PET was more elastic than pure PET. Smaller oval‐shaped cells were produced with lower amounts of foaming agent/SMA, whereas higher ratios resulted in larger spree‐shaped cells. The reaction of SMA anhydrides with the end functional groups of the PET chains increased the chain length significantly followed by more entanglement. This behavior prevented cell growth during the foaming process. The confrontation between the physical and chemical forces among the PET chains and the gas pressure created by the foaming agent was the main mechanism of cell growth in the polymer matrix. This variation caused a 30% reduction in foam density. Statistical analysis revealed that CE‐PET foams with the largest cell size and lowest density were achieved with foaming agent amounts between 0.9 and 1.4 wt.% and SMA amounts between 4.7 and 7.3 wt.%. [ABSTRACT FROM AUTHOR]

This study presents a new solution algorithm to calculate the bearing capacity coefficient Nγ for a fully rough strip footing located on an infinite slope considering different soil friction angles φ and ground slopes β° using the stress characteristics method. The results showed that Nγ coefficients decreased with an increase in slope inclination, and roughness contribution prevented further reduction, particularly for higher φ values. The higher contribution of the upside-sloping ground for footing laid on the infinite slope led to a lower reduction of the Nγ coefficients compared with the footing placed at the slope vicinity in terms of a larger area affected by the stress field, and a larger plastic region of the downface slope. The reduction value was more eminent for steeper slopes β ≥ 20° due to the tendency for nonsymmetrical failure pattern, especially for higher φ values. The findings of the current research and those described in the literature were in good agreement, so much so that the lower-bound limit analysis and the current solution technique virtually reflect the same trend. The load inclination values for footings located adjacent to the slope with β ≤ 30° were not meaningful, whereas for footing resting on an infinite slope with β ≥ 25° it exceeds 15°, which reflects the fact that its effect should not be neglected, especially for ground slopes greater than 20°. By increasing β°, the maximum values of plastic length and plastic depth on the left and right sides of the footing decrease and increase, respectively. The maximum depth of the plastic region for β ≥ 20° from around the right side of the footing shifts toward the downward-sloping face. The maximum width of the elastic wedge gradually reduces, and the intersection point of the left and right plastic regions slowly shifts to the left and upside of the footing. [ABSTRACT FROM AUTHOR]

As a packaging materials candidate, based on a polylactic acid/ polybutylene adipate terephthalate (PLA/PBAT) blends (90/10 and 75/25 wt/wt) containing 1, 3, and 5 phr hydrophilic (HPL) and hydrophobic (HPB) nanosilica (NS) particles in the presence of a multifunctional epoxide compatibilizer were prepared by melt mixing, in a twin-screw extruder. Scanning electron microscopic studies confirmed a matrixdroplet morphology with finer dispersed domains at higher NS content. Energy dispersive spectroscopy mapping also indicated uniform dispersion of NS in blends, with some agglomerates at higher content of nanoparticles. Moreover, transmission electron microscope was applied to study the impact of nanofillers' localization on the systems' morphology. It was observed that NS particles localized at the PLA-PBAT interface. In addition, thermogravimetric analysis (TGA) was used to investigate thermal stability and thermal degradation kinetics. Data indicates that hydrophobic NS improved thermal stability. The activation energy of degradation was calculated using several techniques of data modeling, including Friedman, Flynn-Ozawa-Wall, and Kissinger-Akahira-Sunose models. Among blend nanocomposites, 75/25 blend containing 5 phr HPB NS had the maximum degradation activation energy, suggesting that this sample had the most resistance to heat degradation. The intensity of the TGA/FTIR peaks of the evolved products was found to be correlated with the activation energy. The Criado's technique was also used to investigate the changes in the thermal degradation mechanism. [ABSTRACT FROM AUTHOR]

Heat seal and mechanical properties of 1‐octene grafted low density polyethylene films containing various concentrations of Dicumyl peroxide as the initiator and 1‐octene grafting agent is investigated through using experimental measurements. The results of differential scanning calorimeter (DSC) measurements revealed that the melting temperature shifts to higher values and the peak of the DSC curve becomes wider with the increase of 1‐octene concentrations. Thermogravimetric analysis (TGA) revealed a higher thermal stability up to 20 °C for 1‐octene grafted PE compared with neat LDPE alloy. The results of stress–strain measurements revealed that the 1‐octene grafted PE alloys has higher tensile strength in comparison with neat PE alloy and samples containing only DCP initiator. The results of heat seal analysis indicated that both DCP initiator and 1‐octene tended to offer a moderate increase peel strength of PE alloy. DMTA measurements for various grafted PE alloys show a higher damping factor in comparison with neat LDPE alloy. Rheological measurements indicated a higher storage modulus up to 25% and higher complex viscosity for grafted PE samples containing 1‐octene comonomer. [ABSTRACT FROM AUTHOR]

This review aims to provide a concise insight into the rapidly growing anionic ring-opening copolymerization of nylon 6/12 and its related structures. This study analyzes the relationship between the structures of polymerization components and the relevant properties to achieve optimum copolymerization formulation. Specific emphasis is placed on how the catalyst type and temperature influence the final copolymer structure. The present work reviews available literature about nylon 6/12 synthesis published between 1960 and 2017 and investigates structures linked to polymerization mechanisms behind them. Moreover, experimental results derived from direct/indirect identification methods of structures are presented. The crystalline morphology of different structures was also evaluated. The thermal behaviors of synthesized copolymers are explored comprehensively. Finally, mechanical properties alteration and enhanced water absorption results are reported., INTRODUCTION Both ring-opening polymerization and copolymerization of cyclic amides (lactams) are of commercial interest for their use in a wide variety of applications [1-5]. Lactam polymerization can be initiated not [...]

Two-dimensional molybdenum disulfide (MoS2) is used as a promising flame retardant and smoke suppressant nano additive in polymer composites due to its high thermal stability and layered structure. In this study, thermoplastic polyurethane (TPU) was melt-blended with MoS2 (1 wt. %) and a halogen-free intumescent flame retardant (IFR) system. The IFR system consisted of ammonium polyphosphate (APP), Melamine polyphosphate (MPP), and pentaerythritol (PER), with a total amount of 25 wt.%. The TPU/IFR/MoS2 composite exhibited outstanding flame-retardant properties, achieving a UL-94 V-0 rating and a limiting oxygen index (LOI) value of 34%. Reaction-to-fire performance of the TPU/IFR/MoS2 composite was evaluated by cone calorimeter test (CCT). The CCT results indicated high flame-retardant efficiency and considerable smoke suppression performance, along with a significant decrease in the peak heat release rate (PHRR: 65.9%), peak smoke production rate (PSPR: 65.6%), and peak CO production (PCOP: 60.7%) compared to the neat TPU. The significant improvement in fire performance of TPU composite was mainly attributed to the effects of the physical barrier of MoS2 and catalytic carbonization of the IFR system. These formed an intumescent compact carbonized layer during the combustion, effectively restricting dripping. FESEM revealed the continuous structure of the residual char. Thermogravimetric analysis (TGA) indicated improved thermal behavior of the TPU composite in high temperatures. This work provides an effective method to improve the reaction to fire of TPU composites by incorporating traditional IFRs and MoS2, resulting in enhanced fire safety. [ABSTRACT FROM AUTHOR]