The use of urea condensates as novel flame retardant materials

• Main Author: Sharzehee, Maryam
• Format: Dissertation
• Language: English
• Published: University of Leeds 2009

The aim of this work was to produce environmentally safe flame-proofing compositions to give a wash-durable finish on textile and other substrates. Thus this work describes the preparation and application of new urea condensates formed from the reaction of urea with a variety of chemicals including phosphoric acid, phosphorous acid and sulphamic acid; the condensates gave different degrees of flame retardancy (FR) on a variety of substrates. Studies of urea thermal decomposition showed the production of isocyanic acid and ammonia, above "the urea melting point (l3S•C). Using an open reaction vessel, urea, sulphamic acid and phosphorous acid gave an exothermic reaction over the temperature range 120 - 140'C with gas liberation. The condensates thus formed contained aliphatic polyamide chains, containing urea groups and sulphur and phosphorus residues. According to the type and amount of initial materials, various urea condensates, capable of imparting different degrees of flame retardancy, were synthesized. The sulphamic acid/urea (SIU), phosphoric acid /urea (P AIU), sulphamic acid/phosphoric acid/urea (SJPAIU) and also sulphamic acid/phosphorous acid/urea (S/PH/U) condensates were produced. When these urea condensates were cooled down, Water-soluble products were produced, and these materials could be applied to the textile substrate using a pad-bake technique. Cotton fabrics were treated with these condensates: typically a pad-liquor contained 500 g/l of urea condensate, 10 g/I of wetting agent; fabric was padded to 80% wet pick-up, dried (80'C) and cured for two minutes (l65'C). These urea condensates, when cured on cotton at high temperature (16S'C), change to water-insoluble products; as a result of reactions between cellulose hydroxyl group and the urea condensate a complicated polymer structure network can be produced on the surface of a fabric and a flame retardant effect imparted. The SIU condensate only produced partial FR properties, while the rest of the compounds produced completely flame retardant fabrics. FT-IR analysis and NMR analysis was carried out on the urea condensates and also on the flame retardant fabrics. DSC thermal analysis was performed on the initial materials, urea condensates and also the treated fabrics. The characterization of urea condensate treated fabrics were studied further using SEM and energy dispersion X-ray micro analysis. In the case of the urea condensates a small amount of sulphamic acid has a significant influence on the reaction between phosphating agents and urea; in fact the presence of SA reduces the exothennic reaction. However, at high concentrations of urea, the exothermic reaction occurred at a higher temperature and a hard crystalline product was produced, thus application required dissolution in warm water (50•C). A urea condensate of 1 mole sulphamic acid, 1 mole phosphorus acid and up to 18 moles of urea could produce a durable flame retardant finish on cotton fabric. A higher amount of phosphorous acid in the urea ~ondensate products (IS/2PH/IOU) reduced the exotherm temperature and a high quality flame retardant effect was produced on cotton fabric. The evenness of phosphorus and sulphur elemental distribution on the surface and cross section of treated fibre was confirmed using SEM. Desirable flame retardancy effects from the urea condensate treated fabrics were obtained with comparatively low levels of sulphur and phosphorus (in comparison with the current commercially available Proban and Pyrovatex treated fabrics). However, in the washing process of the condensate-treated fabr ics, no significant reduction in P or S concentration/level was found. The excellent flame retardancy of the new system can be explained due to the N/P/S containing polymer formed on the surface of the fabric. DSC results from the treated fabrics confirmed these observations. Fabrics treated with Pro ban and Pyrovatex showed a very sharp exotherm after 300'C, but for fabrics treated with the urea condensates only a small exotherm effect appeared. In FT-IR analysis and NMR analysis, the production of aliphatic polymer chains of different length was verified , however, for the insoluble product formed in situ by heating at 160'C, and also for the condensates formed on the fabric at high temperature, a complicated polymer structure was shown to contain a possible combination of cyanuric acid, cyclic urea, triazine and melamine. All these materials have been identified in the FT-IR spectra of a water- insoluble urea product formed at 160•C. To make a model reaction with other hydroxyl group-containing substrates, starch and polyvinyl alcohol were treated with the ISI2PH/IOU condensate. The flame retardancy effect on both these treated substrates was confirmed by DSC thermal analysis. Advantages of this new wash-durable FR system over the currently available Proban/Pyrovatex systems include: no formaldehyde, low cost, ready availability of materials, simplicity of the treatment (no specific equipment required), and maintenance of all the desirable physical properties of the fabric, such as soft handle, acceptable tensile strength, no effect on dyed grounds and also no yellowing of the fabric.