Structure and Morphology of Polyoxymethylene

Abstract

Polyoxymethylene (POM), its blends and composites, show high mechanical strength, excellent abrasion and fatigue resistances, lubricating properties and moldability, and therefore have a variety of applications. Properties of substances depend on the composition, crystalline structure and, particularly for polymer materials, on morphology generated by preparation or crystallization conditions. Th ese factors are thoroughly discussed in this chapter as they are very important to control the fi nal properties of materials. Th e knowledge of a variety of atomic, molecular and supermolecular assemblies of materials, together with the mechanical performances and other chemico-physical properties herein described, allows the identifi cation and use of the most appropriate POM sample for a specifi c application. Th e eff ect of additives on the POM morphology and properties has also been analyzed, beyond orientation, perfection and size of crystals in neat POM.

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

“…ese peaks were assigned to (100), (105), (110), (115), and (205) re ections of POM hexagonal crystals, respectively. e crystal structure of all samples was con rmed with XRD and it was consistent with XRD patterns for POM that are available in the literature [9,44,45]. For composites containing 5% of HA-g-PEG, peaks derived from HA start to show up at 25.9° (002), 29.2° (210), 31.7° (211), 32.1° (112), 32.8° (300), 46.5° (222), and 49.5° (213) which is in accordance with XRD patterns for HA-g-PEG (Figure 2(b)).…”

Overview and critical survey of polyamide6 structural habits: Misconceptions and controversies

“…[2][3][4] This molecular regularity of aliphatic polyamides makes them semicrystalline polymers, and should in principle promote a high degree of crystallinity as it is the case for linear flexible-chain homopolymers such polyethylene [20] or polyoxymethylene. [21] Moreover polyamides generally have rather low molar mass that is another favorable factor for crystallization. However, against logical expectations the crystallinity index, X c , of aliphatic polyamides is rather low: in the case of bulk PA6 of weight-average molecular weight M w = 15-40 kDa upon quiescent crystallization from the melt or after annealing of cast or quenched samples X c ≤ 35%.…”

Bulk copolymerization of 1,3,5-trioxane and 1,3-dioxolane in presence of phosphotungstic acid catalyst and tetrahydrofuran as retarder: crystallinity and thermal properties

“…The WAXD curve for hexagonal structure has four peaks at the 2θ of 22.9°, 34.6°, 48.4°, and 54.1°. These peaks correspond to the lattice planes with Miller indexes (1 0 0), (1 0 5), (1 1 5), and (2 0 5) [19][20][21][22], whereas the orthorhombic structure T p (temperature at the maximum decomposition rate) and also T end (temperature at the end of decomposition) for the second step of degradation, as a measure of the thermal stability of the copolymer samples, were studied. T end and T p for the second stage of degradation and Char residue at 450 °C are shown in Table 4.…”

“…I Ha 6 × 100 shows two peaks at 2θ's with 22° and 33.6° corresponding to planes (1 1 0) and 1 1 1and unit cell dimensions a = 4.77 Å, b = 7.65 Å, and c = 17.80 Å. [22] To determine the crystalline structure of the synthesized samples, they were subjected to wide-angle XRD where the presence of peaks at 2θ with approximately 22.8°, 34.5°, 48.3°, and 54.0° was indicative of a hexagonal structure of the synthesized samples ( Figure 6). Moreover, it can be seen that employing of retarder has made no changes to the hexagonal POM structure.…”