**7. SO based polymers for PU production**

As discussed earlier, SO undergo numerous transformations yielding various derivatives. Some of these derivatives bearing (inter or intra located) hydroxyls serve as excellent starting materials for PU production. A large number of PU are prepared from SO polymers such as polyesters, alkyds, polyesteramides, polyetheramides [Figure 1], which find profound applications in paints and coatings.

#### **8. Summary**

424 Polyurethane

SO polyols may also undergo amidation with diethanolamine to yield fatty amide polyols (FAP) [49]. Similar to FAD and FAT, FAP also house two hydroxyl ethyl amides directly attached to amide nitrogen and multiple hydroxyl groups located on the pendant fatty alkyl chains, which were part of the triglyceride molecule in parent SO bearing double bonds at the site of hydroxyl groups in FAP. The properties of SO polyols obtained by either method mentioned previously, also influence the properties of FAP. Hydroxylated, hydroxymethylated, carboxylated SO followed by their amidation yield polyols with higher number of hydroxyl groups with improved distribution [50‐56]. These are ideal candidates to produce PU foams. The approach has been accomplished on CO, LO, PO, Rapeseed, Safflower, Soybean oils and refined bleached deodorized Palm Kernel Olein. These polyols have been used as non‐ionic surfactants in the household and cosmetic industries and also to produce PU foams on treatment with suitable isocyanates. Such polyols prove to be advantageous over CO as they can be incorporated in higher amounts during PU formulations. Foams obtained show improvement in terms of high

close cell contents, good dimensional stability and compression strength.

Alkanolamide polyols serve as excellent starting materials for PU foams [50‐56]. The variations in fatty acid components of starting SO, number and position of hydroxyl groups and also the presence of dangling chains in the polyol confer differences in performance and cellular structures in PU foams. The hydroxyl content of PU determines the suitability of PU foams ranging from flexible to rigid foams. A. Palaniswamy et al. produced PU foams from FAP derived from PO and Polymeric Diphenylmethane Diisocyanate (PMDI) by hand foaming. It was found that the decreased FAP content led to increase in compressive strength and density of PU foam [50]. In another research work, they have produced PU foams from PMDI and CO, in the presence of stannous octoate as catalyst and Tegostab by hand mixing process with carbon dioxide as the blowing agent generated from reaction between excess PMDI and water. PU foams with varying FAP content, catalyst and molecular weight of poly propylene glycol were studied with respect to their effect on

The epoxidized oil based alkanolamides are also classified as polyols for PU foams [56, 57]. PU show low thermal stability, thus with view to improve the thermal stability and mechanical properties of PU, heterocyclic groups such as isocyanurate, imide, phosphazene and oxazolidone, are incorporated in SO PU. The latter is formed by the chemical reaction between an oxirane ring and isocyanate in presence of a catalyst, the approach improving both thermal stability as well as stress‐strain properties of the modified product with respect to the pristine material. PU foams derived from epoxidised alkanolamides show better compression strength, thermal conductivity, close cell contents

**6.1. PU foams from SO FAP** 

density and compression strength [50, 51].

**6.2. PU foams from SO based FAD epoxies** 

FAD, FAT and FAP serve as good starting materials for PU production. LFADU, PFADU, CFATU have similar structural characteristics; the difference being due to the pendant fatty amide chains attributed to the fatty acid composition of the parent SO. LFADU, PFADU,and CFATU are formed at a particular NCO/OH ratio. An astonishingly abnormal rise in viscosity was observed in LFADU and PFADU above 1.5moles and in CFATU above 1.2moles of addition of TDI, followed by the formation of lumpy aggregates. According to the general chemistry of PU, a particular NCO/OH ratio is required for a particular application. The best properties in PU are achieved when this ratio is kept as or closer to 1 or 1.1, i.e., when one equivalent weight of isocyanate reacts with one equivalent weight of polyol, to achieve the highest molecular weight. In certain applications this ratio is kept well below the stoichiometry (higher hydroxyl content relative to isocyanate) to obtain low molecular weight PU for applications as adhesives and coatings as described in the chapter. NCO/OH ratio is varied by the formulator based on the type of end use application of PU. Properties of PU mentioned here also depend on the chemical route of raw materials (polyol, isocyanate), functionality and type of the raw materials (diol, triol, polyol and isocyanates‐aliphatic, aromatic), the number of urethane groups per unit volume, non‐isocyanate PU, as well as other structural differences such as the presence of modifiers (acrylics, metals, nanosized metal oxides, MMT clay).

The preparation through MW technique offers advantages of reduced times and improved yield. Most of these PU are used for coatings and foams. The incorporation of inorganic constituent led to improved thermal and hydrolytic stability as well as coating performance of PU. Another area that is presently being explored is the preparation of green PU from fatty isocyanates or non‐isocyanate PU. Due to their numerous applications and advantages SO PU have been extensively studied and extensive research is still going on.
