Investigation Of Phosphorus-containing Flame-retardant Systems For Rigid Polyurethane Foam

In recent years, the increasing high-rise building fire cases which caused great losses of human and properties have attracted much attention. The reason is mainly due to the ignition of organic exterior wall thermal insulation materials. Rigid polyurethane foam (RPUF), due to its unique properties, such as low density, low thermal conductivity, high strength, excellent adhesion and superior mechanical property has been widely used in building insulation appliances. However, the inflammability of RPUF is a fire safety important hidden danger. Consequently, improving the flame retardancy and fire safety of RPUF is particularly necessary. The development trend of the flame retardant now is toward non-halogen and environmentally friendly flame retardants. Among the non-halogen flame retardants, phosphorus-containing compounds, owning to their high flame-retardant efficiency, have received considerable attention. From the previous reports, it can be found that many kinds of phosphorus-containing compounds have been used to improve the flame retardancy of RPUF. However, the wide variety of phosphorus-containing compounds caused by the variability of phosphorus oxidation state possessed different flame retardant mechanisms and efficiency, which is confusing and complicated for choosing effective flame retardant system for RPUF. Therefore, a systematic study of the influence of phosphorus oxidation state and structure-property relationship of phosphorus based compounds on flame retardancy of RPUF is extremely necessary for developing high flame-retardant and fire safety RPUF insulation materials.In this dissertation, different kinds of phosphorus-containing polyols with similar structures and different phosphorus oxidation state were synthesized by the way of molecular design and well characterized, and then introduced into RPUF matrix by ’reactive’methods. The influence of phosphorus oxidation state on thermal stability and flame retardancy of RPUF have been evaluated and discussed. For comparison, different kinds of phosphorus-containing melamine salts with similar structures and different phosphorus valency were synthesized and then adding into RPUF matrix by ’additive’ methods. The influence of phosphorus oxidation state on thermal stability and flame retardancy of RPUF also have been evaluated and discussed. To further improve the flame retardancy of RPUF, expandable graphite (EG), which possess high flame retardant efficiency in condense phase was selected to study its synergistic effect with the phosphorus-containing polyols and melamine salts mentioned above on flame retardancy of RPUF. On the other hand, optimal design of molecular structure of polyurethane foam itself also has been considered for improving flame retardancy of RPUF. To achieve higher flame retardant rating, structural flame-retardant, condense phase flame-retardant and gas phase flame-retardant techniques are combined. Finally, the preliminary investigation of smoke production behaviors of rigid polyurethane foam and smoke suppression properties of several kinds of smoke suppressants have been carried out. The research work of this dissertation is presented as follows:1. Three reactive phosphorus based polyols:bis (4-hydroxybutyl) phenylphosphate (BHPP-1), bis (4-hydroxybutyl) phenylphosphonate (BHPP-2) and2-carboxyethyl phenylphosphinic acid glycol ester (CEPPG) were successfully synthesized and well characterized. RPUF samples with various phosphorus content and phosphorus oxidation state were prepared by in situ polymerization between polyols and isocyanate. The flame retardant and thermal properties of the composites were evaluated by LOI, Cone and TGA. The thermal degradation processes were investigated by RT-FTIR. The results obtained from LOI results indicated that the flame retarded efficiency of these three compounds in RPUF matrix follows the sequence of BHPP-2> BHPP-1> CEPPG at the same phosphorus content. Meanwhile, the PHRR and THR of modified RPUF samples were significantly reduced compared with that of pure RPUF. However, the smoke production of modified foam increased obviously, which is undesirable.2. Three additive phosphorus based melamine salts:melamine phosphate (MP), melamine phosphite (MPi) and melamine hypophosphite (MHP) were successfully synthesized and well characterized. RPUF samples with various phosphorus content and phosphorus oxidation state were prepared by mixing these compounds with the raw materials before the foaming process of RPUF. The flame retardant thermal properties were evaluated by LOI, UL-94, Cone and TGA test, respectively. The thermal oxidative degradation of selected RPUF samples was tested by RT-FTIR. The results obtained from LOI results indicated that the flame retarded efficiency of these three compounds in RPUF matrix follows the sequence of MHP> MPi> MP at the same loadings and the same phosphorus content. Meanwhile, the PHRR and THR of modified RPUF samples were significantly reduced compared with that of pure RPUF. 3. EG in combination with phosphorus based polyols and phosphorus based melamine salts as synergistic flame retardant systems for RPUF have been prepared is varying proportions and well studied. The flame retardant thermal properties of RPUF/EG/phosphorus-containing polyols system and RPUF/EG/phosphorus-containing melamine salts system were evaluated by LOI, Cone and TGA test, respectively. For the former system, significant improved LOI values and reduced PHRR values can be observed when simultaneously adding EG and P-containing polyols into RPUF. The best flame-retardant synergistic effect exist between EG and CEPPG. For the latter system, flame retardant synergistic effect exist between EG and MP or MPi at mass ratio of1:1. However, the synergistic effect between EG and MHP is not obvious. From the experimental analysis, the foamy density was found as an important factor to affect the combustion properties of RPUF. The PHRR, THR values and the combustion time are basically increasing with the increase of foamy density.4. Polyisocyanurate modified polyurethane (PIR-PUR) foam filled with ammonium polyphosphate (APP) and dimethyl methyl phosphonate (DMMP) were prepared with the different APP/DMMP ratios. The flame-retardant effects of APP and DMMP on PIR-PUR foam have been investigated through means of LOI test, UL-94vertical burning test, microscale combustion calorimeter (MCC), cone calorimetry and thermogravimetric analysis (TGA). The LOI results showed that15wt%of APP addition into PIR-PUR can increase the LOI value to29.5%from23%. However, further increased the loading of APP to20wt%in PIR-PUR can’t increase the LOI value. After adding3wt%of DMMP and12wt%of APP into PIR-PUR, a high LOI value as31.5%can be achieved. Cone results indicated that the presence of DMMP can delay the ignition of specimen and delay the time to reach the maximal PHRR.5. Melamine fumarate (MF), as a kind of fumaric acid (Reported as smoke suppressant) derivative was synthesized and well characterized. A series of flame retardant PIR-PUR foams filled with melamine fumarate or several kinds of metal compounds which also used as smoke suppressants from the previous reports have been prepared. The flame retardant and smoke suppression properties were evaluated by LOI test and cone calorimetry. For smoke production behavior, all of the additives showed a certain degree of smoke suppression effect on both PIR-PUR and flame-retardant PIR-PUR systems. For MF, the total smoke release was reduced by20%in the flame-retardant system. Cu2O possessed the highest smoke suppression efficiency in both PIR-PUR and flame-retardant PIR-PUR system. From the cone results, all these additives have no heat retarded effect on the pure PIR-PUR, but showed reduced heat release in the flame-retardant PIR-PUR except for ferrocene.