Thermal Stabilization of Polyoxymethylene by PEG-Functionalized Hydroxyapatite: Examining the Effects of Reduced Formaldehyde Release and Enhanced Bioactivity

Abstract

Nanostructured hydroxyapatite (HA) functionalized with poly(ethylene glycol) (HA-g-PEG) of different molar mass was used as a thermal stabilizer to prepare polyoxymethylene (POM) composites by a melt processing method. The chemical and crystalline structure of (HA-g-PEG) and POM/HA-g-PEG composites was investigated by means of FTIR and XRD. The thermal properties, degree of crystallinity, and melting behaviour of POM-based composites were analysed with TG, DSC, and TOPEM DSC methods. The tensile strength, Young’s modulus, toughness, and wettability of POM were investigated as well. A preliminary assessment of bioactivity, in vitro chemical stability, and formaldehyde release from POM/HA-g-PEG composites by Schiff’s test was also performed. An SEM/EDX method was used to observe the morphology of POM/HA-g-PEG composites. The results indicate that the addition of 1% HA-g-PEG slightly increases the melting temperature and degree of crystallinity. In small amounts, HA-g-PEG particles probably act as nucleating agents for the POM crystallization process. Incorporation of 5% HA-g-PEG to POM caused a decrease in the crystallinity of the polymer matrix, as a result, some mechanical properties of POM/HA-g-PEG composites also decreased. The thermal stability of POM/HA-g-PEG composites improved significantly from 309°C for unmodified POM to 342°C for POM/10.0% HA-g-PEG 600. The most effective thermal stabilizer was synthesized with the lowest mass-average molar mass PEG. The in vitro bioactivity test confirmed that, as the average molar mass of PEG in HA-g-PEG hybrids increased, POM-based composites indicated higher bioactivity. The in vitro chemical stability analysis results showed that both the POM matrix and the HA-g-PEG additive remain stable during the whole incubation time. Importantly, after seven days of dynamic incubation, no formaldehyde was detected in all filtrates, which is crucial in biomedical applications, among others.

Quaternary‐Ammonium‐Based Gels with Varied Alkyl Chains for the Efficient Removal of Toxic Acid Orange 7

“…To analyse the thermal stability, thermo gravimetric analysis (TGA) of the three gels were performed at ramping rate of 10 °C/min (Figure a and b). Pielichowska et al have reported that the thermal stability of the material primarily depends on the chemical structure and the molecular weight . Thus, the influence of the length of the alkyl chain in the quaternary and ammonium moiety on the thermal degradation was monitored and the results are depicted in the Table 1.…”

“…The melting and crystallisation behaviour of the as synthesised gels were monitored by Differential scanning calorimetry study (Figure S18). Generally, the thermal property of a material is influenced by the extent of crosslinking . The melting temperature of the crosslinker was observed at 49°C which was associated to the melting of the PEG chains.…”

“…Pielichowska et al have reported that the thermal stability of the material primarily depends on the chemical structure and the molecular weight. [43] Thus, the influence of the length of the alkyl chain in the quaternary and ammonium moiety on the thermal degradation was monitored and the results are depicted in the Table 1. The results indicate that all the gels display initial degradation near 100°C which refers to the loss of absorbed water.…”

“…Generally, the thermal property of a material is influenced by the extent of crosslinking. [43][44] The melting temperature of the crosslinker was observed at 49°C which was associated to the melting of the PEG chains. Interestingly, after photo crosslinking the melting temperature reduced and was observed in the range 45°C to 41°C for CG1 to CG3.…”

Polyoxymethylene/graphene nanocomposites: thermal, crystallization, melting and rheological behavior

“…Another strategy widely employed to minimize thermal decomposition mechanisms, which do not necessarily sacrifices mechanical properties, is the addition of inorganic nanoparticles such as hydroxyapatite, 3,9,10 clays, [11][12][13] silica, 14 titanium dioxide, 15 zinc oxide, [16][17][18][19][20] zirconium oxide 21 and aluminum oxide. 22,23 Carbonaceous nanoparticles such as graphene oxide (GO) 24 and carbon nanotubes (CNT) 25,26 have also been studied as nanofillers to POM-based systems.…”