Rigid, closed-cell, graft-polymer foam; rigid flexible cellular foam; rigid flexible cellular foam mixtures; and method for manufacturing a rigid, closed-cell, graft-polymer foam
Expanded products, more specifically, rigid or semi-flexible foams of low density from 1.5 to 12 lbs/ft 3 or more, with closed cells can be manufactured. The products have a PVC backbone with branches with methacrylate crosslinked with isocyanate through a reaction activated by ultraviolet or microwave radiation. The use of polyfunctional monomers that are sensitive to irradiation yields a higher cross-link density, which improves the physical and mechanical properties such as hardness, resistance to abrasion, ductility, and resistance to friction. The selection of monomers and oligomers allows the manufacturer to determine of the final properties of the foam. The process yields foams with extreme hardness and better shear factors making the foam an ideal product for aerospace and windmill use. These physical properties emerge during the post-curing process, preferably by use of compounds based on methacrylates in dispersion with PVC and isocyanates.
1. A rigid, closed-cell, graft-polymer foam made by a process that comprises:
providing a polyvinylchloride (PVC) polymer backbone;
grafting side chains to said PVC polymer backbone with isocyanate, said side chains including epoxy-acrylate monomers;
initiating free radicals with ultraviolet or microwave radiation; and
crosslinking said side chains to reach a post-cured state by polymerizing said monomers in said side chains with said free radicals.
2. The foam made according to the process of claim 1 , the process further comprising combining the grafted PVC with an isocyanate, an expanding agent, a photoinitiator, and further epoxy-acrylate monomer polymerizable by said photoinitiator, said expanding agent releasing gases when heated, said photoinitiator being activatable a posteriori with ultraviolet radiation to release free radicals.
3. The foam made according to the process of claim 2 , the process further comprising heating after the combining step to release said gases from said expanding agent.
4. The foam made according to the process of claim 2 , process further comprising reducing a reaction pressure during the combining step to a negative pressure to prevent pre-polymerization of said isocyanate due to ambient humidity.
5. The foam made according to the process of claim 2 , the process further comprising exposing said photoinitiator to ultraviolet radiation after the combining step to release said free radicals and to initiate polymerization and cross-linking of said combined monomers.
6. The foam made according to the process of claim 1 , the process further comprising blending said grafted PVC polymer with a solvent having a boiling point at least as low as 75° C.
7. The foam made according to process of claim 6 , the process further comprising selecting said solvent from the group consisting of a fluorocarbon, pentane, hexane, and an acetone.
8. The foam made according to the process of claim 1 , the process further comprising selecting said monomers to set physical and/or mechanical properties of the foam.
9. The foam made according to the process of claim 8 , the process further comprising selecting the physical and/or mechanical properties from the group consisting of flexibility, hardness, resistance to abrasion, and ductility.
10. A rigid closed-cell graft-polymer foam comprising:
a PVC polymer backbone; and
a side chain bonded to said PVC polymer backbone including a copolymerized vinyl monomer and epoxy-acrylate monomer, said copolymerized monomers having reached final expansion and a post-cured state by having a group (CH2=C) polymerized by free radicals initiated by ultraviolet or microwave rays, wherein said said chais are crosslinked with a poly-isocyanate crosslinking agent.