Abstract
Polystyrene foams have become more and more important owing to their lightweight potential and their insulation properties. Progress in this field is expected to be realized by foams featuring a microcellular morphology. However, large-scale processing of low-density foams with a closed-cell structure and volume expansion ratio of larger than 10, exhibiting a homogenous morphology with a mean cell size of approximately 10 µm, remains challenging. Here, we report on a series of 4,4′-diphenylmethane substituted bisamides, which we refer to as kinked bisamides, acting as efficient supramolecular foam cell nucleating agents for polystyrene. Self-assembly experiments from solution showed that these bisamides form supramolecular fibrillary or ribbon-like nanoobjects. These kinked bisamides can be dissolved at elevated temperatures in a large concentration range, forming dispersed nano-objects upon cooling. Batch foaming experiments using 1.0 wt.% of a selected kinked bisamide revealed that the mean cell size can be as low as 3.5 µm. To demonstrate the applicability of kinked bisamides in a high-throughput continuous foam process, we performed foam extrusion. Using 0.5 wt.% of a kinked bisamide yielded polymer foams with a foam density of 71 kg/m3 and a homogeneous microcellular morphology with cell sizes of ≈10 µm, which is two orders of magnitude lower compared to the neat polystyrene reference foam with a comparable foam density.
Highlights
IntroductionUsing BTAs at large concentrations in lar polymers remains challenging due to restrictions in the solubility and the co tion-dependent formation of larger sized objects
We demonstrated that the class of kinked bisamides, based on various 4,40 -diphenylmethane central units and via amide-linked peripheral side groups, is highly suitable to act as efficient supramolecular foam cell nucleating agents for PS
Structural elucidation on a selected kinked bisamide reveals that such an elongated fibrillary or ribbon-like shape is attributed to the formation of two strands of hydrogen bonds, which can be regarded as the main driving force for a preferred one-dimensional crystal growth
Summary
Using BTAs at large concentrations in lar polymers remains challenging due to restrictions in the solubility and the co tion-dependent formation of larger sized objects This probably limits the number dispersed nano-objects in the polymer melt under conventionally employed co and restricts a very large number of nucleation sites necessary for a fin blowing agent, this allows for control over the foam morphology with a homogeneous polymer fine cellularfoam. A novel class of supramolecular polymer additives, which were on cell nu and their nano-object morphology as well as their capability to act based as foam a 4,40 -diaminodiphenylmethane central unit with two side groups linked via two amide agents for polystyrene.
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