“A blowing agent is a substance which is capable of producing a cellular structure via a foaming process in a variety of materials that undergo hardening or phase transition, such as polymers, plastics, and metals. They are typically applied when the blown material is in a liquid stage. The cellular structure in a matrix reduces density, increasing thermal and acoustic insulation, while increasing relative stiffness of the original polymer.
Blowing agents (also known as 'pneumatogens') or related mechanisms to create holes in a matrix producing cellular materials, have been classified as follows: Physical blowing agents e.g. CFCs (however, these are ozone depletents, banned by Montreal Protocol of 1987), HCFCs (replaced CFCs, but are still ozone depletents, therefore being phased out), hydrocarbons (e.g. pentane, isopentane, cyclopentane), liquid CO2. The bubble/foam-making process is reversible and endothermic, i.e. it needs heat (e.g. from a melt process or the chemical exotherm due to cross-linking), to volatile a liquid blowing agent. However, on cooling the blowing agent will condense, i.e. a reversible process.
Chemical blowing agents e.g. isocyanate and water (for PUs), azo-, hydrazine and other nitrogen-based materials (for thermoplastic and elastomeric foams), sodium bicarbonate (aka baking powder, used in thermoplastic foams). Here gaseous products and other by-products are formed by a chemical reaction(s), promoted by process or a reacting polymer's exothermic heat. Since the blowing reaction occurs forming low molecular weight compounds acting as the blowing gas, additional exothermic heat is also released. Powdered titanium hydride is used as a foaming agent in the production of metal foams, as it decomposes to form titanium and hydrogen gas at elevated temperatures. Zirconium(II) hydride is used for the same purpose. Once formed the low molecular weight compounds will never revert to the original blowing agent(s), i.e. the reaction is irreversible.
Mixed physical/chemical blowing agents — e.g. used to produce flexible PU foams with very low densities. Here both the chemical and physical blowing are used in tandem, to balance each other out with respect to thermal energy released/absorbed, so minimizing temperature rise. Otherwise excessive exothermic heat because of high loading of a physical blowing agent can cause thermal degradation of a developing thermoset or polyurethane material. For instance, to avoid this in polyurethane systems isocyanate and water (which react to form carbon dioxide) are used in combination with liquid carbon dioxide (which boils to give gaseous form) in the production of very low density flexible PU foams for mattresses.
Mechanically made foams and froths, involves methods of introducing bubbles into liquid polymerisable matrices (e.g. an unvulcanised elastomer in the form of a liquid latex). Methods include whisking-in air or other gases or low boiling volatile liquids in low viscosity lattices, or the injection of a gas into an extruder barrel or a die, or into injection molding barrels or nozzles and allowing the shear/mix action of the screw to disperse the gas uniformly to form very fine bubbles or a solution of gas in the melt. When the melt is molded or extruded and the part is at atmospheric pressure, the gas comes out of solution expanding the polymer melt immediately before solidification. Frothing (akin to beating egg whites making a meringue), is also used to stabilize foamed liquid reactants, e.g. to prevent slumping occurring on vertical walls before cure – (i.e. avoiding foam collapse and sliding down a vertical face due to gravity).
Soluble fillers, e.g. solid sodium chloride crystals mixed into a liquid urethane system, which is then shaped into a solid polymer part, the sodium chloride is later washed out by immersing the solid molded part in water for some time, to leave small inter-connected holes in relatively high density polymer products, (e.g. Porvair synthetic leather materials for shoe uppers).
Hollow spheres and porous particles (e.g. glass shells/spheres, epoxide shells, PVDC shells, fly ash, vermiculite, other reticulated materials) are mixed and dispersed in the liquid reactants, which are then shaped into a solid polymer part containing a network of voids.”
(Expandable Polymers, Wikipedia, 9/2/2013)
For earlier Patent Titles, go to Sorted Patents /Materials /Expandable Materials.
Expandable thermoplastic nanocomposite polymeric compositions with an improved thermal insulation capacity
Expandable polyamide composition and polyamide foam obtained therefrom
Apparatus and method for continuously forming an element made of expanded plastic material and construction element
Expandable functional TFE copolymer fine powder, expanded products and reacted products therefrom
Polypropylene resin composition, expansion-molded article using the resin composition, and process for production of the expansion-molded article
Expanded TFE copolymers, method of making and porous, expanded articles thereof
Expandable composite resin particles for long-term storage, pre-expanded particles formed therefrom and expanded molded articles
Particulate, expandable polymer, a method for preparing the same as well as the use thereof
Expandable functional TFE copolymer fine powder, the expandable functional products obtained therefrom and reaction of the expanded products
Process for the preparation of granules based on expandable thermoplastic polymers and relative product
Production of pearls based on expanded polymers
Process of expediting activation of heat-expandable adhesives/coatings used in making packaging substrates
Enhanced process for the production of expanded PVC and plastic materials based on expanded PVC obtained therewith
Web, stampable sheet and stampable sheet expanded product as well as method of producing the same
Bookmark this page to follow future developments!.
Roger D. Corneliussen
Maro Polymer Links
Tel: 610 363 9920
Fax: 610 363 9921
Copyright 2013 by Roger D. Corneliussen.
No part of this transmission is to be duplicated in any manner or forwarded by electronic mail without the express written permission of Roger D. Corneliussen
* Date of latest addition; date of first entry is 9/2/2013.