Liquid polyurethane systems

The high elasticity, low water permeability and excellent bonding make liquid polyurethane systems suitable for a wide range of waterproofing applications such as for foundations, basements, tunnels, multilevel... 

Linear polyurethanes, 26 Linear step-growth polymerizations, 13 Lipase-catalyzed polyesterifications, 83 Lipases, 82, 84 catalytic site of, 84 Liquefied MDIs, 211, 226-227 Liquid carbon dioxide, 206 Liquid-castable systems, 201 Liquid crystal devices (LCDs), alignment coating for, 269-270 Liquid crystalline aromatic polyesters, 35 Liquid crystalline polyesters, 25, 26, 48-53... 

Coal tar-modified polyurethane is a cold-applied liquid waterproofing system. The system by Sonneborn is an example of this approach to waterproofing. It is applied as a liquid at the rate of 10-15 mils/coat. The coating dries hard, but has some elasticity. This material may be attacked by acids in groundwater but can be defended by a protection board. The performance of any liquid-applied waterproofing systems is limited by the capabilities of the applicator (it is difficult to achieve even coats on vertical surfaces). 

Polymer-modified asphalt is a cold-applied liquid waterproofing system. As with the Sonneborn system mentioned above, the quality of the installation depends on the applicator (it is difficult to achieve an even coating on a vertical surface). High-grade polymer-modified asphalt is superior to coal tar-modified polyurethane in elasticity, crack-spanning ability, and resealability, but inferior in its resistance to chemicals. 

A method of manufacturing rubber articles by pouring a compounded latex into an absorbent hollow mould the skin of rubber thus formed is removed, dried and vulcanised. The term is also apphed to the pouring into moulds of liquid polymer systems based on silicone or polyurethane elastomers. 

Although the use of lignin as an additive to polyurethanes is not new (15-20), even the most judicious selection of lignin isolation or modification schemes has not allowed researchers to overcome the incorporation limit of 25 to 40 weight percent of lignin as an active component in polyurethanes. Solvent fractionation allows for the isolation of lignin fractions with well defined solubilities and functionalities (21,22). Both of these features are critical for the practical inclusion of lignin into liquid polyol systems. 

Catalysts are commonly used to control the pouring and gel times of polyurethane systems. As catalysts are used in small quantities, the addition must be carried out very carefully otherwise, very erratic results may be obtained. Catalysts may be made into a concentrated solution with an inert carrier such as a plasticizer. This reduces a potential dispensing error. They also may be added to a liquid chain extender. 

The addition of phosphorous-based plasticizers will provide a degree of fire retardancy to the polyurethane. Fryol PCF and CEF have been used in polyurethane systems. Most phosphorus-based fire retardants are thin liquids that are compatible with polyurethanes. Because of the very varied nature of fire-resistant tests, the material made must be tested to the appropriate standard. 

Liquid polyurethane waterproofing systems are coal-tar modified products. Two-component materials are catalysed curing systems, and one-component materials are cured by exposure to moisture. Both the materials exhibit comparable properties on complete curing. Two-component materials require on-site mixing of the components. One-component materials can be applied directly, but the problem with this type is polymerisation of the product inside the container if it is improperly sealed. Such products are purged with an inert gas when the pack is sealed. 

The first liquid photopolymer system was the letterflex plate. The process relies on the cross-linking reaction of a polyurethane possessing allylic unsaturation and a polythiol, i.e.. 

Air-release agents are added to liquid epoxy, polyester, and polyurethane systems to remove air bubbles before cure. These function by their surface activity. They are mostly proprietary compositions. 

RRIM is a development of the RIM process (reaction injection moulding). The essential feature of an RIM system is a 2-component liquid resin system which reacts rapidly when the two components mix, to form a fully developed polymer inside the mould. Usually these systems are polyurethanes, although others, especially nylon-based systems, are under development. 

Applications. Rigid polyurethane foam laminates for residential sheating (1.2-2.5-cm-thick with aluminum skins) and roofing board (2.5-10.0 cm thick with roofing paper skins) are the leading products, with about 45 t of liquid spray systems also in use. Metal doors insulated by a pour-in-place process constitute another substantial use. 

---