Solid ground curing

Figure 6.27. A schematic diagram of solid ground curing.

Fused deposition Solid ground curing Stereolithography... 

Dicyandiamide (sometimes referred to as dicy ) or its derivatives are used in most commercial one-component epoxy adhesives. This curative is a white crystalline solid and is easy to incorporate into an epoxy formulation as a finely ground powder. When cured with epoxy resin, dicyandiamide provides an excellent set of performance properties. 

A solid plastic may be ground to a solid powder and then used to apply a plastic coating to a metal product, either for decorative reasons (color) or for functional performance such as insulation or corrosion resistance. Plastics most often used in this way include nylon, vinyl, acrylic, polyethylene, polypropylene, and epoxy. Coating without solvents is beneficial both economically and environmentally, and 100 percent utilization of material eliminates waste. After the powder is bonded to the metal surface, it is often reheated to flow into a more uniform coating and, in the case of thermosetting resins, to complete the cure reaction. 

Extraction of Cured, Modified Phenol-Formaldehyde Resins. A sample of the modified resin was spread as a thin coating on a sheet of aluminum foil and cured in an oven at 170 °C for 5 minutes. The cured resin was removed from the aluminum foil, weighed, and broken into small pieces that were placed in water (10 to 15 mL) for extraction at room temperature. After 1 to 2 hours, the water was decanted from the solid resin. The resin was extracted in this manner an additional three to four times. The residue from the water extraction at room temperature was dried and ground using a mortar and pestle. The ground resin was extracted with hot water in a Soxhlet apparatus for 24 hours. The room temperature extract and hot water extract were combined, concentrated, and diluted to a known volume for analysis. The quantity of modifier in the extract was determined by HPLC (77). 

Table III shows the properties of particleboards prepared with Phase I whey permeate-based resin. Table IV shows the properties of rice-hull-reinforced building boards using Phase II resin. Low-quality boards are prepared with rice hulls, but their qualities may be improved by using ground hulls or adding sawdust to the formulation. Although whey-based resins have been found to be excellent adhesives for binding solid lignocellulosic materials, these resins tend to require higher cure temperatures and longer cure times as compared to formaldehyde-based resins.

Lewis and co-workers (42) developed improved powder coatings with nitrile rubber-modification of an appropriate epoxy base (solid resin admixture) cured with an imidazoline-accelerated modified phenolic type hardener. Model coatings ground to 55 pm particle size, electrostatically applied to metals, cured 10 170°C, gave excellent therraocycling results as well as retained resistance to solvent attack. Elastomer-modified epoxy powder coatings have been covered extensively by Gelbel, Romanchick and Sohn in Chapter 5 of this volume. 

---