Abstract
In this paper, the influence of mass-average molar mass (M w) of polyoxymethylene (POM) copolymer on the thermooxidative degradation behavior of its nanocomposites with hydroxyapatite (HAp) is reported. POM copolymers’ thermal stability slightly decreases with a decrease in mass-average molar mass. Thermal stability of POM/HAp nanocomposites is lower in comparison with pure POM, and it gets lower with a decrease in mass-average molar mass of POM copolymer. For POM copolymer with the highest molar mass, thermal stability of POM/HAp nanocomposite was ca. 30 °C lower than for pure POM. To get a more in-depth insight into the decomposition process, kinetic analysis of POM/HAp nanocomposite thermal degradation process was performed using Friedman, Ozawa–Flynn–Wall and multiple nonlinear regression methods. The best fit for pristine T2, T3 and T4 copolymers with different molar mass of 100768, 74727 and 68377 g mol−1, respectively, was obtained for one-stage degradation mechanism with autocatalysis, while for T2/10 % HAp and T3/10 % it was parallel reaction model with autocatalysis (Bna) and phase-boundary reaction models (R3). For T4/10 % HAp, the best approximation was found for R2–Bna–D3 reaction model. From hyphenated TG–MS and TG–FTIR thermoanalytical studies, it was found that the main degradation product for POM/HAp nanocomposites is formaldehyde and the amount of other degradation products is lower in comparison with nonmodified POM copolymers.
Highlights
Polyoxymethylene (POM), known as polyacetal, is a popular and attractive thermoplastic engineering polymer due to its properties of fatigue endurance, high stiffness, resistance to creep and low friction coefficient
Pan et al [6] postulated that the degradation process of POM copolymer could be divided into three stages with a gradually increasing degradation rate: (1) At the beginning, POM chain tends to split off formaldehyde, starting at the chain ends, some of which were not ended by ethylene oxide (EO) units; (2) in the second stage, the thermooxidation of POM takes place in the amorphous phase, and in the last stage, further random chain scission and unzipping occur in the crystalline phase
It has been found that in T4/ HAp nanocomposite a major decrease in the thermal stability in TG experiment of ca. 59 °C occurred, and in T2/ HAp and T3, the thermal stability was lowered by ca. 30 °C
Summary
Polyoxymethylene (POM), known as polyacetal, is a popular and attractive thermoplastic engineering polymer due to its properties of fatigue endurance, high stiffness, resistance to creep and low friction coefficient. POM copolymers are characterized by higher thermal stability, but their crystallinity degree is reduced in comparison with POM homopolymer This is a result of lower carbon–carbon group interactions as these groups are separated in the macrochain. Pan et al [6] postulated that the degradation process of POM copolymer could be divided into three stages with a gradually increasing degradation rate: (1) At the beginning, POM chain tends to split off formaldehyde, starting at the chain ends, some of which were not ended by ethylene oxide (EO) units; (2) in the second stage, the thermooxidation of POM takes place in the amorphous phase, and in the last stage, further random chain scission and unzipping occur in the crystalline phase. In this study, the influence of mass-average molar mass of POM on the thermooxidative degradation behavior of POM and its nanocomposites with hydroxyapatite (HAp) is reported
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