Acetal-polyurethane alloys

Blends or alloys of polyacetals with polyurethane elastomers were first introduced by Hoechst in 1982, who were then followed by other manufacturers. The key features of these materials are their improved toughness with little change in other important properties. There are two aspects with respect to the impact toughness  

Where the polyurethane comprises 30% of the blend, the polyurethane remains in discrete droplets within the polyacetal matrix. In this range the particle size and particle size distribution of the elastomer particles are of importance. Where the elastomer component is in excess of 30%, interpenetrating polymer networks exist in the sense that there are two interpenetrating continuous phases (as opposed to two cross-linked interpenetrating polymer systems). 

Charpy notched impact strengths in excess of 55 kJ/m have been reported for alloys with homopolymers and in excess of 20kJ/m for copolymers. 

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POLYURETHANES POLY ACETALS ACRYLIC/PVC ALLOY ABS/POLYURETHANE ALLOY POLYSULFONES PPO BASED... 

Thermoplastics in the form of a lacquer have poorer mechanical strength than the thermosetting resins but are more easily removed, should this prove necessary. Polyvinyl acetate and polyurethane are good examples of this class of consolidants, particularly on wrought iron artefacts. Many of the copper and copper-based alloys, such as bronzes and brasses recovered from the Mary Rose, were consolidated with a solution of acrylic resin dissolved in toluene (Incralac). 

Polyurethane (Cont d) Elastomeric Alloys PVC and PVC-acetate, MC, Sheets, Rods, and Tubes... 

Adhesives recommended include epoxies, vinyl alcohol—vinyl acetate copolymer, polyvinyl alkyl ether, polyacrylate (carboxylic), polyurethane (two-part), epoxy-phenolics, silicones, and cyanoacrylates. The high-strength thermoset and alloy adhesives are rarely justified for bonding lead. Even when other properties recommend these adhesives, the designer should check to see whether some low-cost or easier-to-use adhesive is also suitable. An exception is teme (lead-coated steel). This is a much stronger metal than lead, and lap-shear strengths exceeding 2.1 MPa are reported for adhesive joints with teme.° ... 

Different types of polymers can be used to plasticize PVC compositions. For example, nitrile mbber (NBR), thermoplastic polyurethane, and ethylene vinyl acetate(EVA) co- and terpolymers can be used to alloy with PVC. These types of compositions are discussed in Chapter 15. This section will focus on the class of polyesto polymeric plasticizers. These have average molecular weights ranging from less than 1000 to about 25,000, and are viscous liquids to semisolids at room temperature. 

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