Rigid foams physico-mechanical properties

By solubilisation of propoxylated bisphenol A with the structure 15.28, in a sucrose-based polyether polyol for rigid foams, an homogeneous mixture is obtained [29]. The viscosities of these mixtures increase with the content of propoxylated bisphenol A. From these mixtures rigid PU foams were obtained. Due to the aromaticity introduced by the propoxylated bisphenol A, the physico-mechanical properties of the resulting rigid PU foams were superior to the rigid PU foams made with the sucrose-based poly ether polyol alone [29]. 

By using the synthesised hydroxyalkyl carbamates of melamine as polyols, rigid PU foams were obtained with good physico-mechanical properties, low friability and inherent self extinguishing properties. A highly aromatic polyol, based on the reaction of benzoguanamine with ethylene carbonate was successfully synthesised [4]. 

Due to the low cost, the excellent physico-mechanical properties of the resulting urethane - isocyanuric foams, thermal and fire resistance and low level of smoke generation, the most important applications of aromatic polyester polyols are for rigid PU/PIR foams in the boardstock market (continuous rigid foam lamination) and for building insulation. 

The rigid PU foams obtained with the synthesised lignin-based polyols have acceptable physico-mechanical properties, but the reactivity in the foaming process is very high, probably due to the content of sodium in the initial lignin. 

By mixing castor oil with polyols such as glycerol (for example 75 % castor oil and 25 % glycerol) a higher hydroxyl number polyol mixture is obtained, which leads to rigid PU foams with good physico-mechanical properties [47]. 

By the transesterification of castor oil with polyols with high functionality and high hydroxyl number [29], or by transamidation with poly amines or alkanolamines [29] new polyols are obtained which are of real use in the fabrication of rigid PU foams with good physico-mechanical properties. These polyols are made without PO. 

Unfortunately, the phosphorus content of phosphonate polyol in reaction 18.13 is lower (around 7-7.5%), but being a tetrafunctional polyol gives rigid PU foams with excellent physico-mechanical properties. 

This relative order explains that numerous physico-mechanical properties of the polyurethanes based on polyester polyols are superior to the polyurethanes derived from polyether polyols or from polyhydrocarbon polyols (this relative order is valuable for PU elastomers, flexible and rigid PU foams). 

The Mannich polyols described are aromatic aminic polyols, the aromatic rings have a real contribution in improving the physico-mechanical, thermal and fire proofing properties of the resulting rigid polyurethane (PU) foams. The Mannich bases, for example the Mannich base resulting from one mol of nonyl-phenol, 2 mols of formaldehyde and 2 mols of... 

Mannich polyols are aromatic polyols, which confer excellent physico-mechanical, thermal and fire proofing properties to rigid PU foams. Mannich polyols, especially those based on p-nonyl phenol, have a very good compatibility with pentanes used as blowing agents (for example sucrose polyether polyols have a poor compatibility with pentanes, giving emulsions at normal concentrations for foaming, but not real solutions). 

The resulting novolak polyols, in spite of their low functionalities and low hydroxyl numbers, give rigid PU foams with a very uniform cellular structure, with excellent physico-mechanical, thermal and fire proofing properties and good dimensional stability, characteristics which are associated with the high aromatic structure of novolak polyols. 

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