Microcellular structure

Polyurethane rubber (PUR). Not only in the thermosets (and the thermoplastics), but also in the field of synthetic elastomers polyurethanes have found a position, namely as a softer type. It is, again, formed from two components and is, with a blowing agent, processed into a foam. Polyether mattresses belong to this category, but also microcellular structural foams, used in bumpers, head- and arm-rests in motorcars, etc. 

A further study of the microcellular structure of oligon ric foams and the development of models taking into account both mararo- and microcells are equally important. 

Nelson (16, 39) reported a method of making polyurethane-foam composites by means of the SRIM process. Two different types of polyurethane materials were used an amine-modified polyurethane suitable for static elastomer uses and a polyurethane material with high crosslink density designed for use as a microcellular structural material. 

The reasons for this Include such things as reduced density to lower cost, Increased ease of mold filling, and Improved part surface apppearance. The microcellular structure which makes these benefits realizable Is achieved by nucleatlon, either with a gas such as air or nitrogen, or by Incorporating a blowing agent In the system formulation. An IMR agent must, therefore, not affect the cell structure or the stability of the nucleated froth It must... 

The use of NMP and/or plasticizers as well as varying foaming conditions was incorporated in a high-throughput experimental methodology during the downselec-tion for the polymer. For the premade VDC-based copolymer from the polymerization track, an RBl-201 VDC-based copolymer product described in Section 4.3.2 resulted in microcellular structures (Fig. 4.5.2). 

Table 2. Comparison of Injection-Molding Process for Various Products with and without Microcellular Structure ...

Mkrolite (1) An expanded volcanic mineral, white spheroidal granules of a metastable amorphous aluminium silicate with a honeycomb, microcellular structure. 

The greatest increases in crystallinity under room temperature conditions were observed at pressures between 2.1 and 2.8 MPa, and this induced crystallinity significantly affected the PLA foamability. In fact, lower saturation pressure (up to 2.8 MPa) led to more uniform microcellular structures with cell diameters on the order of 30-40/ m and... 

Comparison between the two nanocomposites revealed that the number of the stacked individual silicate layers D 001) for PLA/SBE nanocomposites was much lower than for PLA/ODA nanocomposites, suggesting that intercalated silicate layers were more homogeneously and finely dispersed in the case of PLA/SBE than in PLA/ODA (Table 17.3). The nature of the dispersion also plays a vital role in controlling the size of the cell during foaming since PLA/SBE5 nanocomposites had nanocellular structure as opposed to the microcellular structure of the PLA/ODA5 nanocomposites. 

The Accurel system has a microporous polymer sponge (e.g., of PP, LDPE, HDPE, polyamide) used as carrier for incorporating liquid additives into a thermoplastic melt. The earner is produced by a thermal phase separation process. A microcellular structure with cells of microns connected by pores of 0.5 microns and internal surface 90m /g, absorb up to 2.5 times its own weight of liquid. The key to this solution is the miscibility of a polymer with... 

Handa Y. R, Zhang, Z., and Wong, B., Solubility, diffusivity and retrograde vitrification in PMMA-COj, and development of sub-microcellular structures. Cellular Polymers 2001, 20, 1-16. 

Jin, W., Xingguo, C., Mingjun, Y, and Jiasong, H. 2001. An investigation on the microcellular structure of polystyrene/LCP blends prepared by using supercritical carbon dioxide. Polymer 42 8265-8275. 

Tsimpliaraki, A., Tsivintzelis, I., Marras, S. I., Zuburtikudis, I., and Panayiotou, C. 2011. The effect of surface chemistry and nanoclay loading on the microcellular structure of porous poly(D,L lactid acid) nanocomposites. Journal of Supercritical Fluids 57 278-287. 

FIGURE 9.14 SEM micrographs of (a) PES and (b) PEI foams showing the sub-microcellular structures with nanoporous walls produced at 240°C. (Reported from Sorrentino, L M. Aurilia, and S. lannace, 2011, Advances in Polymer Technology 30,3, September 8,234-243, doi 10.1002/adv.20219, http //onlinelibrary.wiley.eom/doi/10.1002/adv.20219/full.)... 

The principal advantages of RIM processing of polyurethanes and polyureas are the ability to mold large parts such as automobile fascias and body panels, motor housings, and bodies of recreational vehicles, and that the molded parts made can be lightweight. The microcellular structure of RIM parts permits densities to be quite low, while the stiffness modulus can be... 

Effect of Nano-Clay on the Microcellular Structure and Properties of High Internal Phase... 

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