A novel graded-modulus-interphase material for polymeric composites

Introduction Filler- (e.g., particulate or fiber) reinforced structural polymers or polymeric composites have changed the way things are made. Today, they are found, for example, in air/ground transportation vehicles, sporting goods, ballistic barrier applications and weapons, electronic packaging, musical instruments, fashion items, and more. As the demand increases, so does the desire to have not only well balanced mechanical properties, but also light weight and low cost. This leads to a constant search for novel constituents and additives, new fabrication methods and analytical techniques. To achieve new or improved composite materials requires more than the identification of the right reinforcements to be used with the right polymer matrix at the right loading. Also, an optimized adhesion between the two phases and a toughened matrix system are needed. Furthermore, structural optimization, associated with fabrication (e.g., avoidance of fiber-fiber touching or particle aggregation), and sometimes special properties, such as electrical conductivity or magnetic susceptibility are necessary. To date, no composite materials with desired mechanical/thermal/electrical properties are made possible without expensive fabrications and complications. This is because these properties are often trade-off properties. For example, the interface between the matrix and the reinforcements is the most highly stressed region in the composite material and is vulnerable to crack initiation when loads are applied. Attempts have been made to reduce stress concentrations by placing a material, called a graded-modulus-interphase, between the reinforcements and the matrix; however, most materials increase adhesion but at the expense of fracture toughness due to an increase in interfacial matrix embrittlement. This calls for an optimized level of adhesion, which is often difficult to achieve. Technology description Researchers at the University of Washington have found a unique class of dendrimer that, when grafted to polystyrene
(PS) particles, leads to an increase in both fracture toughness and tensile/flexural moduli. Dramatic interface stretching and the capability of the dendrimer to ‘harden’ PS particles by diverting cracks through them are responsible for the enhancements. This is made possible due to the interpenetration and chemical interactions among dendrimer, epoxy and PS networks, effectively promoting both interfacial stress relief and stress transfer. The inventors propose to use this material and its derivatives as a novel graded-modulus-interphase material in polymeric composites. Specifically, the dendrimer has the possibility of acting both as an adhesion promoter without inducing interfacial matrix embrittlement, filler spacer and electron carrier, when applied to the filler surface, and as a matrix enhancer, when combined with other materials, with the unique ability to improve mechanical/thermal/electrical properties. These developments should help in the creation of the next generation of polymeric composites. Business Opportunity In 2003, the U.S. market for the polymer composite segment of nanomaterials was estimated at roughly $15M. By 2008, this segment is forecast to grow to $211M. A March 2006 study by the Freedonia Group estimates the U.S. demand alone will be over $2B by 2015. Furthermore, by optimizing the mechanical properties of the interphase, the overall quality of polymeric composites will be tremendously improved, and their applications further developed. Intellectual Property Position UW is currently evaluating this technology for patent protection.

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