In situ Observation of Nucleated Polymer Crystallization in Polyoxymethylene Sandwich Composites

Abstract

We introduce a dynamic sandwich method, which can be used for in situ observation and quantification of polymer crystallization nucleated by micro/nanoparticles. The method was applied on polyoxymethylene (POM) composites with three nucleating agents: talc micropowder (POM/mTalc), chalk nanopowder (POM/nChalk), and titanate nanotubes (POM/TiNT). The nucleating agents were deposited between polymer films, the resulting sandwich samples were consolidated by thermal treatment, and their microtomed cross-sections were observed during isothermal crystallization by polarized light microscopy (PLM). As the intensity of polarized light was shown to be proportional to the relative crystallinity, the PLM results could be fitted to Avrami equation and the nucleating activity of all investigated particles could be quantified by means of Avrami parameters (n, k ). The crystallization half-times increased reproducibly in the following order: POM/nChalk < POM/mTalc < POM/TiNT~POM. For strong nucleating agents (mTalc, nChalk), the crystallization kinetics corresponded to spontaneous crystallization starting from central nucleating layer, which was verified by computer simulations. The results were also confirmed by differential scanning calorimetry. We concluded that the sandwich method is an efficient microscopic technique for detailed evaluation of nucleating activity of arbitrary micro/nanoparticles in polymer systems.

Enhanced ion transport behaviors in composite polymer electrolyte: the case of a looser chain folding structure

“…Thus, when the inorganic nanoparticles were added to PCL, they not only reduced the degree of crystallinity, but also inevitably acted as a nucleating agent to change the crystalline process, which may have increased the number of nucleation sites and decreased the average size of the polymer spherulites. 29 Although nanoparticles are beneficial to promote the formation and growth of crystal nuclei and the crystallization speed, the movement of the PCL molecular chains will be restricted, reducing the crystalline region, which can be attributed to the nucleation agent effect. 30 In addition, the 30 nm-sized Al 2 O 3 nanoparticles inevitably aggregated into clusters with an uneven distribution, which led to an uneven distribution of the polymer crystalline morphology in space.…”

Polyoxymethylene/talc composite: Investigation of warpage, mechanical and thermal properties for thin walled‐injection molding applications

“…1 The warpage of parts during molding depends on the crystallinity of the material. It crystallizes with grains of coarse crystalline nature when cooling with 85% of crystallinity 2,3 and leaves higher shrinkage, ranging from 2.5% to 3.5% during molding.…”

Synergistic effect of thermoplastic phenolic resin and multiwalled carbon nanotubes on the crystallization of polyoxymethylene

“…The POM has two characteristics, namely rapid crystallization, and poor thermal stability. Due to the marked flexibility of the molecular chains, it crystallizes fairly quickly with a crystallinity as high as about 85% in forms of coarse crystalline grains . The high crystallinity contributes to the high tensile strength, high stiffness and hardness, and so forth, which make it an excellent engineering plastics .…”

“…Due to the marked flexibility of the molecular chains, it crystallizes fairly quickly with a crystallinity as high as about 85% in forms of coarse crystalline grains. [7,8] The high crystallinity contributes to the high tensile strength, high stiffness and hardness, and so forth, which make it an excellent engineering plastics. [1][2][3][4] However, the high crystallinity leads to significant shrinkage (around 3-3.5%) of the products during molding because of the apparent density difference between the crystalline (1.49 g/cm 3 ) and amorphous (1.21 g/cm 3 ) phases.…”