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Understanding the thermal aging kinetics of animal oils is of vital importance in the storage and applications of animal oils. In this work, we use four different techniques, including UV-Vis spectrometry, viscometry, impedance spectroscopy, and acid–base titration, to study the thermal aging kinetics of tallow, chicken oil, lard, and sheep oil in the temperature range from 120 °C to 180 °C. The evolutions of the UV-Vis absorbance, dynamic viscosity, electric impedance, and acid titration are discussed with the defect kinetics. The evolutions of the color centers, defects for dynamic viscosity, and electric dipoles follow second-order, first-order, and zero-order kinetics, respectively. The temperature dependence of rate constants for the evolutions of the UV-Vis absorbance, dynamic viscosity, electric impedance, and acid titration satisfies the Arrhenius equation with the same activation energy for individual animal oils. The activation energies are ~43.1, ~23.8, ~39.1, and ~37.5 kJ/mol for tallow, chicken oil, lard, and sheep oil, respectively. The thermal aging kinetics of the animal oils are attributed to the oxidation of triglycerides. [ABSTRACT FROM AUTHOR]

There is a great need to develop biodegradable thermoplastics for a variety of applications in a wide range of temperatures. In this work, we prepare polymer blends from polylactic acid (PLA) and thermoplastic polyurethane (TPU) via a melting blend method at 200 °C and study the creep deformation of the PLA/TPU blends in a temperature range of 10 to 40 °C with the focus on transient and steady-state creep. The stress exponent for the power law description of the steady state creep of PLA/TPU blends decreases linearly with the increase of the mass fraction of TPU from 1.73 for the PLA to 1.17 for the TPU. The activation energies of the rate processes for the steady-state creep and transient creep decrease linearly with the increase of the mass fraction of TPU from 97.7 ± 3.9 kJ/mol and 59.4 ± 2.9 kJ/mol for the PLA to 26.3 ± 1.3 kJ/mol and 25.4 ± 1.7 kJ/mol for the TPU, respectively. These linearly decreasing trends can be attributed to the weak interaction between the PLA and the TPU. The creep deformation of the PLA/TPU blends consists of the contributions of individual PLA and TPU. [ABSTRACT FROM AUTHOR]

The graphene/poly (methyl methacrylate) (PMMA) composites are a promising candidate for electronic, optoelectrical, and environmental applications. Understanding the mechanical degradation of PMMA-based materials is of practical importance in improving the reliability and lifespan of the associated structures and systems. In this study, we investigate the effects of functionalized graphene (FG) and UV irradiation on the stress–relaxation of PMMA. Uniaxial tensile and stress –relaxation tests are performed to evaluate the mechanical properties of the composites. The mechanical strength and elongation at the break increase with the graphene concentration but decrease with the increase of the irradiation dose. Raman spectroscopy and intrinsic viscosity measurement are applied to examine the root cause of the degradation in the composites. UV irradiation leads to polymer chain scission and loss of molecular weight. The Kelvin representation of the standard linear solid model (SLSM) is used to describe the stress–relaxation curves of the composites. The value of the elastic modulus in the Kelvin element decreases with the increase in temperature. The viscosity follows the Arrhenius equation. The activation energy of viscosity increases with the increasing FGs concentration because the FGs hinder the chain motion of PMMA. However, UV irradiation makes chain scission of PMMA/FGs composite so that the polymer chain moves more easily and the activation energy of stress relaxation lowers. The steady-state stress follows the van 't Hoff equation that stress relaxation is an exothermal deformation process. Although Maxwell's representation of SLSM is mathematically identical to the Kelvin representation of SLSM, the former cannot interpret the stress–relaxation behavior of PMMA/FGs composite, which is against the concept of Young's modulus as a decreasing temperature function. [ABSTRACT FROM AUTHOR]

Understanding the structural degradation of polymers and polymer-based materials is of practical importance in improving the reliability and lifespan of the associated structures and systems. In this work, we use differential scanning calorimetry to analyze the effect of ultraviolet (UV) irradiation on the physical aging of the blends of poly (lactic acid) (PLA) and poly (methyl methacrylate) (PMMA). Using the Cowie-Ferguson model and the Kohlrausch–Williams–Watts (KWW) stretch function, we determine the thermodynamic and kinetic contributions to the aging of the PLA/PMMA blends with and without UV irradiation. The analyses reveal the linear decrease of the maximum enthalpy loss of the aged specimen at the equilibrium state with the increase of the aging temperature, and the decreasing rate increases slightly with increasing the UV irradiation dose for the same PLA/PMMA blends. The activation energy associated with the kinetic contribution decreases with the UV irradiation dose for the PLA/PMMA blends of the same compositions. [Display omitted] • UV irradiation has no effect on the relation between T g and composition of PLA/PMMA blends. • Increasing UV irradiation reduces the decreasing rate of the maximum enthalpy loss of aged PLA/PMMA blends. • Kinetic analysis of the kinetic contribution to physical aging of PLA/PMMA blends. [ABSTRACT FROM AUTHOR]

Understanding the structural integrity of polymer composites in service conditions is of practical importance for the applications of polymer composites. In this work, we investigate the solvent-induced crack growth in poly(methyl methacrylate)/multiwalled carbon nanotube (PMMA/MWCNT) composites in respective organic solvents of 2-ethylhexyl alcohol (2 EA), cyclohexanol, and 1-butanol at different temperatures after being immersed in methanol at 50 °C for 25 min. The areal density of crack lengths and growth rate of a single crack in the PMMA/MWCNT composites increase with the immersion time and temperature for the solvents of 2 EA and cyclohexanol. The areal density of crack lengths in the PMMA/MWCNT composites immersed in 1-butanol is largest at 30 and 40 °C and smallest at 50 °C. The 1-butanol solvent causes the fastest, steady-state crack growth at 30 and 40 °C and the slowest crack growth at 50 °C. Increasing the fraction of MWCNTs reduces the areal density of crack lengths and the growth rate of a single crack in the healed and non-cracked areas. The crack growth is controlled by a thermally activated process. The crack growth rate is faster in the healed area than in the non-cracked area for the same composite and solvent. The activation energy for the motion of polymer chains associated with the single-crack growth in the non-cracked area is smaller than that for solvent-induced cracking because the interaction between cracks hinders crack growth. [Display omitted] • Methanol desorption controls the cracking in composites for 2 EA and cyclohexanol. • 1-butanol absorption controls the cracking in composites for 1-butanol at high temp. • Methanol desorption controls the cracking in composites for 1-butanol at low temp. • Increasing the MWCNT fraction hinders the growth of the cracks in composites. • The crack growth in PMMA/MWCNT composites is a thermally activated process. [ABSTRACT FROM AUTHOR]