By Roger Corneliussen
By Roger Corneliussen
By Roger Corneliussen
CO2-Based Polycarbonate
U.S. Patent 8,981,043 (March 17, 2015), “Catalytic System for CO2/Epoxide Copolymerization,” Jisu Jeong, Sujith Sudevan, Myungahn Ok, Jieun Yoo, BunYeoul Lee, and SungJae Na (SK Innovation Co., Ltd., Seoul, South Korea).
Using CO2 as a raw material for polymersremoves a warming gas from the atmosphere. Meanwhile, biodegradable polymers are badly needed in an environmentally sensitive world weary of growing landfills and atmospheric pollution. Traditional polycarbonates are very useful but are not biodegradable or renewable.
Jeong et al. produced a biodegradable polycarbonate by copolymerizing an epoxy with CO2 using cobalt(III) or chromium(III) catalysts. These catalysts are unique, with high activities. The polymerization process can be batch, semibatch, or continuous. The resulting polymer number-average molecular weight (Mn) is 5,000 to 1,000,000, with molecular weight distributions (Mw/Mn) of 1.05 to 4.0. The aliphatic polycarbonate contains 80% or more carbonate linkages and is said to be easily degradable. The materials are useful for packaging, insulation, and coatings.
The Heat Problem
U.S. Patent 8,980,984 (March 17, 2015), “Thermally Conductive Polymer Compositions and Articles Made Therefrom,” Yuji Saga (Ticona LLC, Florence, Kentucky, USA).
Because of their excellent mechanical and electrical insulation properties, polymeric materials are used in a broad range of applications including automotive, electrical, and machinery. However, as applications expand and product dimensions decrease, overheating becomes a problem. Polymeric materials typically have poor heat conduction and are heat sensitive, so increasing thermal conductivity is a new challenge for developers.
Saga developed thermally conductive polymeric materials using moisture-resistant magnesium oxide. These materials consist of 15 to 75 wt% of resin ranging from polyolefins to polyetheretherketones. Critically important is the 20 to 60 wt% of 200-micron or smaller magnesium oxide particles with aspect ratios less than five, reinforced with 5 to 50 wt% fibers. These materials may be processed by injection molding, blow molding, extrusion, or press molding, and may replace aluminum or other metals in many applications.
Reduced Thermal Expansion
U.S. Patent 8,974,729 (March 10, 2015), “Anti-Thermally-Expansive Resin and Anti-Thermally-Expansive Metal,” Makoto Kubota, Kaoru Miura, Hisato Yabuta, Yoshihiko Matsumura, Yuichi Shimakawa, and Masaki Azuma (Canon Kabushiki Kaisha, Tokyo, and Kyoto University, Kyoto, Japan).
In long-term use under varying temperatures, large or mismatched thermal expansions between parts are a problem, especially for plastics with very large expansion. This can be especially critical in precision equipment. One approach is to fill a resin with a large positive thermal expansion with a filler with matching negative thermal expansion, but such fillers are not common.
Kubota et al. developed polymeric composites with small thermal expansion by mixing resins with fillers having negative thermal expansion. The
high-expansion resins range from polybenzimidazole (PBI) to fluorocarbons and polycarbonates, including thermosets and thermoplastics. Typically the negative thermal expansion particles are special metal oxides like (Bi1-xMx)NiO3, where “M” is a rare-earth element (the negative expansion is due to complex phase transitions). In an example composite, the linear expansion coefficient of PBI at the glass transition temperature or lower is +23 x 10 class="s4">-6/K. In contrast, the linear expansion coefficient of the oxide particle is about -20 x 10-6/K. When the solid particle is dispersed in the PBI matrix, the usual interfacial thermal stress is cancelled at the contact interface, and local thermal strains are eliminated.
Transparent “Superhydrophobic” Surfaces
U.S. Patent 8,974,714 (March 10, 2015), “Process for the Preparation of Superhydrophobic Film,” Alessandro Garibbo, Corrado Boragno, and Francesco Gagliardi (Universita Degli Studi Di Genova, Genoa, Italy).
“Superhydrophobicity” or the “Lotus Effect” refers to surfaces on which water runs off the surface in spherical drops without wetting the surface. The basis of this effect is hydrophobic surface nanoprojections or nanofibers. However, this roughness scatters light, eliminating optical transparency.
Garibbo, Boragno, and Gagliardi prepared a superhydrophobic film by first coating the surface with a liquid prepolymer and then covering that coated surface with a porous hydrophobic membrane with 105 to 108 pores/cm2 of less than 3 micron in diameter. The liquid prepolymer fills the holes and is cured by heating. The membrane is then removed, leaving a superhydrophopbic surface. The resulting structure is a jangled network of disorganized protruding fibers, maintaining transparency while retaining its superhydrophobic character.
Quantum Dot Sensors
U.S. Patent 8,969,470 (March 3, 2015), “Quantum Dot-Polymer Nanocomposite for Optical Sensing,” Sichu Li (Mitre Corporation, McLean, Virginia, USA).
Quantum Dots (QDs) are nanocrystals which are miniature semiconductor devices and can be embedded like filler particles into polymeric materials. However, these small particles must be functionalized to avoid agglomeration and fluorescence quenching. Their potential for chemical and biological sensing is largely unexplored.
Attachment to the matrix structure is necessary to prevent agglomeration. Li developed a QD-polymer nanocomposite for optical chemical and biological sensing by inserting functionalized quantum dots into a pH-sensitive hydrogel. First, quantum dots are suspended in an acrylic monomer, an acrylate monomer, a crosslinking agent, and a photo-initiator. This suspension is cured to form the quantum-dot polymer nanocomposite. The nanocomposites can be applied to a wide array of biological and chemical-sensing applications, such as monitoring microorganism growth and pH and in drug delivery.
Polymer-Ceramic Implants
U.S. Patent 8,969,430 (March 3, 2015), “Biocompatible Ceramic-Polymer Hybrids,” Mamoru Aizawa and Masahiro Rikukawa (Showa-Ika Kogyo Co. Ltd., Aichi-ken, Japan).
Bone fractures involve damage to hard tissues, and materials that promote healing should match the mechanical properties of the fractured bones. Hydroxyapatite is a natural material found in teeth and bones within the human body and is an excellent compatible agent for bone repair. Nevertheless the mechanical properties of hydroxyapatite materials are different from living bones, creating problems.
Aizawa and Rikukawa developed a hydroxyapatite ceramic hybrid material consisting of a porous ceramic structure filled with a biodegradable polymer such as a poly L-lactic acid. The porous ceramic is prepared from a slurry of hydroxyapatite fibers and heat-degradable particles. This slurry is filtered to obtain a paste and molded to form a green compact which is fired above 1000°C to form a structure with 30-80% porosity. This porous structure is soaked with a lactic acid/enzyme solution which is then polymerized by heating. The hybrid is dried and polished for implantation. This composite is compatible with the bone structure, enabling tissue growth into the pores.
Heat-Absorbing Windows
U.S. Patent 8,968,610 (March 3, 2015), “Polymer Composition Having Heat-Absorbing Properties and High Stability to Weathering,” Alexander Meyer, Gunther Stollwerck, and Joerg Reichenauer (Bayer MaterialScience AG, Leverkusen, Germany).
Polycarbonate glazing has many advantages over conventional glass glazing, but high heat transmissibility remains a problem. Meyer, Stollwerck, and Reichenauer developed a polymer composition that absorbs infrared radiation using a boride infrared absorber. In one example, nanofillers of carbon black and lanthanum hexaboride are used. Loadings range from 0.00150 to 0.015 wt% borides and 0.0002 to 0.0035 wt% carbon black. The small particles sizes and loadings reportedly do not interfere with transparency.