Reaction of acetophenone-formaldehyde resin with s-triazone compounds for fire resistance polyurethane

These days; the use of flame retardants is significantly increasing, especially since plastics are an important part of our daily lives. These materials in general; Bromine, chlorine, metal hydroxide, nitrogen-based, phosphorous-containing or mixtures. The annual consumption of flame retardants is more than 1.5 million in the world market. It costs about $ 2.4 billion. It is seen that the market of flame retardants has increased by 5% per year. The flame retardants could be inorganic or organic. These chemicals can sometimes be used alone as an additive, sometimes in the form of a binary formulation. The important problem here is that these flame retardants must be well dispersed in the polymer matrix. Currently, bromine-based flame retardants are used and their using is limited because side effects are observed. The use of chlorine- and bromine-based flame retardant materials has been restricted or prohibited periodically after 2000 due to the generation of harmful gases and harmful gases to the environment. This has prompted the chemical industry to seek a new generation of flame retardant materials whose distribution is good in polymer, and which is unlikely to produce toxic waste after combustion. The discovery of polyurethane dates back to the year 1937 by Otto Bayer and his coworkers at the laboratories of I.G. Farben in Leverkusen, Germany. The initial works focussed on PU products obtained from aliphatic diisocyanate and diamine forming polyurea, till the interesting properties of PU obtained from an aliphatic diisocyanate and glycol, were realized. Polyisocyanates became commercially available in the year 1952, soon after the commercial scale production of PU was witnessed (after World War II) from toluene diisocyanate (TDI) and polyester polyols. In the years that followed (1952-1954), different polyester-polyisocyanate systems were developed by Bayer. Polyester polyols were gradually replaced by polyether polyols owing to their several advantages such as low cost, ease of handling, and improved hydrolytic stability over the former. Poly(tetramethylene ether) glycol (PTMG), was introduced by DuPont in 1956 by polymerizing tetrahydrofuran, as the first commercially available polyether polyol. Later, in 1957, BASF and Dow Chemical produced polyalkylene glycols. Based on PTMG and 4,4'- diphenylmethane diisocyanate (MDI), and ethylene diamine, a Spandex fibre called Lycra was produced by Dupont. With the decades, PU graduated from flexible PU foams (1960) to rigid PU foams (polyisocyanurate foams-1967) as several blowing agents, polyether polyols, and polymeric isocyanate such as poly methylene diphenyl diisocyanate (PMDI) became available. These PMDI based PU foams showed good thermal resistance and flame retardance. Isocyanates are essential components required for PU synthesis. These are di-or polyfunctional isocyanates containg two or more than two –NCO groups per molecule. These can be aliphatic, cycloaliphatic, polycyclic or aromatic in nature such as TDI, MDI, xylene diisocyanate (XDI), meta-tetramethylxylylene diisocyanate (TMXDI), hydrogenated xylene diisocyanate (HXDI), naphthalene 1,5- diisocyanate (NDI), pphenylene diisocyanate (PPDI), 3,3'-dimethyldiphenyl-4, 4'- diisocyanate (DDDI), 1,6 hexamethylene diisocyanate (HDI), 2,2,4- trimethylhexamethylene diisocyanate (TMDI), isophorone diisocyanate (IPDI), 4,4'- dicyclohexylmethane diisocyanate (H12MDI), norbornane diisocyanate (NDI), 4,4'- dibenzyl diisocyanate (DBDI). Figure 1 shows examples of some common isocyanates. Substances bearing plurality of hydroxyl groups are termed as spolyols. They may also contain ester, ether, amide, acrylic, metal, metalloid and other functionalities, along with hydroxyl groups. Polyester polyols (PEP) consist of ester and hydroxylic groups in one backbone. They are generally prepared by the condensation reaction between glycols, i.e., ethylene glycol, 1,4-butane diol, 1,6-hexane diol and a dicarboxylic acid/anhydride (aliphatic or aromatic). The properties of PU also depend upon the degree of cross-linking as well as molecular weight of the starting PEP. While highly branched PEP result in rigid PU with good heat and chemical resistance, less branched PEP give PU with good flexibility (at low temperature) and low chemical resistance. Similarly, low molecular weight polyols produce rigid PU while high molecular weight long chain polyols yield flexible PU. An excellent example of naturally occurring PEP is Castor oil. Other vegetable oils (VO) by chemical transformations also result in PEP. PEP are susceptible to hydrolysis due to the presence of ester groups, and this also leads to the deterioration of their mechanical properties. This problem can be overcome by the addition of little amount of carbodiimides. In general, reactive flame retardants are composed of halogens and phosphorous. Phosphorus-containing flame retardants may be incorporated into the polymer matrix as an inorganic additive or covalently bonded to the polymer main chain to impart flame retardant properties to the material. In the solid phase, the phosphoruscontaining flame retardant reacts with oxygen in the polymer chain or matrix during heating or combustion. Phosphorus compounds which interact with the polymer form phosphoric acid, and the dimerization of these molecules results in the removal of the water molecules and pyrophosphate formation. Phosphorus based additives as well as phosphorus structures covalently bonded to the polymer chain are both academic and industrial interest. The incorporation of additives into the polymer matrix covalently, or the incorporation and use of monomers in flame retardant structures and polymerisation, is at the forefront of new strategies for "nonflammable polymers." There are hundreds of different flame retardants. They are often broken into categories based on chemical structure and properties. In general, flame retardants are grouped based on whether they contain bromine, chlorine, phosphorus, nitrogen, metals, or boron. Brominated flame retardants — Contain bromine and are the most abundantly used flame retardants. Used in many consumer goods, including electronics, furniture, building materials, etc. and have been linked to endocrine disruption among other effects. Polybrominated diphenyl ethers (PBDE's) PBDEs do not chemically bind with the products to which they are added (furniture, electronics, etc.) so they easily release from these products and enter air and dust. PBDEs can lower birth weight/length of children, and impair neurological development. Tetrabromobisphenol A (TBBPA) Widely used to make computer circuit boards and electronics. Also used in some textiles and paper, or as an additive in other flame retardants. Hexabromocyclododecane (HBCD) An additive primarily used in polystyrene foam building materials. The primary risk to humans is from leaching out of products and getting into indoor dust. Low levels of HBCD have also been found in some food products. Organophosphate flame retardants (OPFRs) With the phasing out of PBDEs, some OPFRs have been identified as replacements. NIEHS-supported researchers are also looking at the health effects of newer flame retardant alternatives that are being brought to market. In this study, condensation product of acetophenone formaldehyde resin (AFR) with alendronic acid s-triazone was produced and modified resins were added 20% , 30% of polyol to the solution at room temperature, used as polyol in the production of rigid polyurethane form in order to improve its fire resistance. AFR was synthesized primarily in basic medium. Then, AFR was modified via their hydroxyl groups by reaction with dimethylol s-triazone that was produced by the reaction of urea with the mixture of formaldehyde and alendronic acid. S-triazone reacts with formaldehyde in the presence of basic catalyst to give dimethylol derivatives. Methylol derivatives of s-triazone give condensation products in an acid media with resin. The mol ratio of s-triazone / resin was about 1/5. Insertion of functional striazone cyclic structure to the AF-Resin effected its physical properties considerably. The products were characterized by FTIR, 1H-NMR, 13C-NMR , 31PNMR, TGA and UL94 analysis. In the combustion tests the foam made from the modified resins self-extinguishes after a certain period of time, while the polyurethane foam obtained from the unmodified resin on the left side continues to burn until completely carbonized. Also, the foams obtained from the modified resins have a rigid structure. Cyclohexanone - formaldehyde resins can be produced in acid and basic media successfully. However, acetophenone – formaldehyde resin can only be produced in basic media in presence of potassium hydroxide. Acetophenone – formaldehyde resin formed in acidic media with very low yield and its softening point was about 20- 250C. The results obtained according to the study are as follows; Acetophenone - formaldehyde resin can be obtained efficiently in the presence of potassium hydroxide in basic medium. Resins can be modified with s-triazone compounds. The materials used in the modification of the resins are readily available and inexpensive materials such as urea and formaldehyde. Depending on the composition of the resin, modification of the resin may change some physical properties such as solubility and flammability. It has been observed that the modified resins have a positive effect on the polyurethane nonflammability such as foam. These results may contribute to the use of resin in the area of incombustibility.