adhesives

Polyalkyl 2-cyanoacrylates begin to retropolymerize and deteriorate dramatically at temperatures above 80°C. They bond rapidly to the metal surfaces and readily lose strength even at ambient temperatures. These two drawbacks of the cyanoacrylates have made this class of adhesives unpopular as structural adhesives. Several attempts have been made to increase the thermal stability and the stability of the bond between the metal surfaces by adding chemicals like cyclopentadienoates and anhydrides to the cyanoacrylates.

The introduction of high molecular weight poly(methyl methacrylate) or poly(butadiene-co-acrylonitrile) into ethyl 2-cyanoacrylate produced viscous adhesives with a homogeneous or heterogeneous structure after cure. Steel joints bonded with these adhesives are shown to have improved tensile shear strength, deformability and stress relaxation of bonds compared with pure cyanoacrylate adhesive. Poly(methyl methacrylate)-modified adhesive is recommended for static load-bearing joints while poly(butadiene-co-acrylonitrile)-modified adhesive is more suited to cyclic or vibrating loads.

Cyanoacrylate polymer foams can be obtained by blending cyanoacrylate monomer with an appropriate solvent and a polymerization initiator. Foaming takes place in seconds at room temperature. Various monomers, solvents and initiators were tested and best performance compositions and ratios were determined. The resultant foams are lightweight and can occupy volume up to 30 times that of the original cyanoacrylate monomer. The onset time and temperature of foaming can be regulated in wide ranges. Odourless foaming compositions were obtained.

The bonding strength between bone and α-2-cyanoacrylate polymers, with or without the addition of powdered hydroxyapatite, was determined. The tensile strength of a bone-cyanoacrylatebond was measured for each polymer: 4.31± 0.88 M Pa(methyl-), 5.74 ± 0.62 MPa (ethyl-), and 8.33 ± 0.41 MPa (isobutyl-). The tensile strength of the isobutyl-2-cyanoacrylatebond increased to 12.03 ± 0.72 MPa with the addition of 10% (w/v) hydroxyapatite before decreasing to 7.89 ± 0.58 Mpa on addition of 15% (w/v)hydroxyapatite.