B7: curing agents for epoxies

IA derivatives as curing agents for water-based epoxy resins

   The widely used natural abrasives are silicon carbide and aluminum oxide. Other abrasives which are capable and very efficient for grinding tools are synthetic diamond and CBN (cubic boron nitride), Diamond in the griing tools melts the abrasive and causes excessive wear, while  aluminum oxide is more effective on most steels but less efficient on nonferrous metals and nonmetallic substrates than on SiC. Manufacturers use a variety of trade names for products based on silicon carbide and aluminum oxide.

   Grain sizes of abrasives are traditionally measured by the fraction of bulk grains that can pass through a series of vibrating screens or meshes, having a specified number of openings per square inch. A 60–100 grit size allows the mix to include a small percentage of coarse grains and a somewhat higher percentage of finer grains. Another important property of the abrasives is hardness, which is usually defined as the resistance to penetration by another material. There are a number of hardness scales mostly based on the principle of the depth made in the tested material by a standard indenter under a standard pressure. However, because of the wide range of hardness in materials, no standard covers the entire spectrum of materials hardness. For abrasives, the  most used scales are Rockwell-Cone and Knoop. The abrasive grain shape affects the number and the spatial distribution of cutting edges. The primary function of a adhesive bond is to hold the abrasive grits during the grinding process. The adhesive bond should fulfill several functions:

i) provide adequate grit retention, without premature pull-out from the surface of the abrasive;

ii) allow controlled bond erosion, leading to gradual exposure of new cutting points;

iii) give adequate heat dissipation. The coated abrasive tapes consist of coated abrasive grains bonded onto a backing material in the form of paper, cloth, or fiber strips. Abrasive paper and cloth in the form of belts or endless belts are used for machining metals. Silicon carbide coats are used for soft metals, while aluminum oxide coats are used for steel.

   Surface-active substances and emulsifiers are sometimes added to polishing pastes to intensify the machining and to transmit a higher durability to the abrasive compound, such as thixotropic substances including aluminum soaps, aluminum alcoholates, complex bentonite and fine talc powder. The function of the bonding adhesive is to attach the abrasive grain to the backing. If the product is intended for dry use, the adhesive can be glue. Usually the adhesive may be one of the liquid, such as phenolic resins. The resins can be modified to provide longer or shorter drying times, greater strength, more flexibility, or other properties required. There are three types of backings (i.e. support) is : a) paper  when strength and pliability of the backing is not important; b) cloth backings are utilized, mainly, for resin bonded discs having heavy, hard, strong stiffness.

   The technological transfer concerning on prototypes of polymer matrix composites formed by water-based epoxy resins cured with IA-based derivatives, such as trimethylyol-tri-itaconates, pentaerythritol-tri-itaconates and itaconic acid, will be used for the preparation of coated abrasive tapes. The polymerization reactions will be carried out at relative low temperature ranging from 80 and 120°C. The thermo-induced curing of these water-based resins will be investigated in the same experimental conditions used for phenol-formaldehyde resins at 90 °C for 45 min. The phenol-formaldehyde resins (e.g.resole-type) can be replaced with water- based epoxy resins cured with IA derivatives in a range of temperature between 80° and 120°C. Thermo-mechanical properties of the phenol-formaldehyde resins, obtained by calorimetric and rheological measurements in combination with adhesion test experiments, will be used as reference for the processing control of water-based epoxy resins cured with IA derivatives. The adhesion of these IA-based curing agents will be tested by peeling tests on different supports (e.g paper and PET film).

Beneficiary responsible for implementation: IMPERIAL

advanced polymer materials