Expandable graphite flame retardant semi-rigid polyurethane material application
Polyurethane semi-rigid foam (SPUF) has excellent performance and is widely used, but it is a flammable material and is highly toxic when burned, which may adversely affect the environment. The refractory graphite (EG) and silane coupling agent KH791 were used to modify EG to flame retard all-water foamed polyurethane semi-rigid foam. The thermal degradation behavior of polyurethane foam was studied by thermogravimetric analysis and carbon residue morphology. The effects of EG modification on the flame retardancy, thermal stability, mechanical properties and cell morphology of the full-water foamed polyurethane semi-rigid foam were investigated. The results show that when the mass fraction of EG is 20%, the oxygen index of the expandable graphite flame retardant polyurethane foam can reach 29.4%, which meets the requirements of HF-1 level test in UL94HB fire test; after KH791 modified EG, The flame retardant effect is slightly reduced, but the modified EG has less influence on the cell morphology of the foam, and can increase the density and compressive strength of the full-water foamed polyurethane semi-rigid foam.
Key words: expandable graphite; flame retardant material; surface modification; flame retardant property; thermal stability
Polyurethane foam is a polymer material synthesized by the reaction of polyether polyol, isocyanate and auxiliary agent. It has excellent physical and mechanical properties, acoustic properties, electrical properties and chemical resistance. Polyurethane foam is divided into soft foam, semi-rigid foam and hard foam according to different raw materials and formulas. Polyurethane semi-rigid foam exhibits good shock absorption performance, damping performance and sound absorption performance due to the equivalent opening and closed cell structure. . Excellent performance makes polyurethane semi-rigid foams commonly used as automotive interior materials (such as automotive bumper fillers), industrial cushioning materials and packaging materials. However, the polyurethane semi-rigid foam has a high opening ratio, and oxygen and heat easily permeate into the interior of the material during combustion, and it is not easy to self-extinguish, which brings difficulties to fire extinguishing. Therefore, for the open porosity of polyurethane, the selection of suitable flame retardant and flame retardant method is the current research hotspot.
Expandable graphite (EG) is a halogen-free environmentally friendly flame retardant. It has a high instantaneous expansion rate and exhibits a "worm"-like porous carbon layer after expansion. It can inhibit or terminate combustion. The porous carbon layer formed can adsorb flammable gas and melt. Things and poison gas. At present, there are many studies on the flame retardancy of rigid polyurethane foam (RPUF) for the EG content, EG particle size and the combination of EG and other flame retardants. The study found that when the mass fraction of EG is 20%~25%, RPUF has the best flame retardant performance, but the mechanical properties are reduced. The particle size of EG has a great influence on the flame retardancy of polyurethane materials. The larger the EG particle size, the better the flame retardant effect and the smoke suppression effect. Shi Lei et al studied the flame retardant RPUF of EG particles with an average diameter of 39.8μm and 196.6μm. It was found that RPUF had better flame retardant and smoke suppression effects when the average diameter of EG was 196.6μm. Modesti and other flame retardants obtained by compounding EG with triethyl phosphate (TEP) or red phosphorus (RP) can significantly improve the flame retardancy of the material, but the mechanical properties will be degraded; Hu Xingsheng et al found EG and flame retardant The synergistic effect of ammonium polyphosphate (APP) and TEP is the best; Zhang Zhonghou et al. proved that the synergistic flame retardant is better than the flame retardant effect of adding any one of the flame retardants alone. However, when the amount of the composite flame retardant exceeds 16 phr, the cells of the foam may be severely defective, resulting in failure of foaming, and the smoke density level is greatly increased. Therefore, the amount of the composite flame retardant is limited.
At present, EG has also been studied for use in flexible polyurethane foam (FPUF) and semi-rigid polyurethane foam (SPUF) to improve the flame retardancy of open-cell PU. Xie Fei et al. explored the synergistic flame retardant FPUF between TPP and EG. When the amount of compound flame retardant is 30 phr, the TPP/EG ratio is 1/3, and the LOI value of flame retardant FPUF reaches 25%. The smog resistance? Li et al. studied the flame retardant effect of EG in SPUF and found that EG with larger particle size can effectively improve the flame retardant properties of the material.
However, EG is an inorganic millimeter-sized large particle, which is not easy to be uniformly dispersed in the polyurethane matrix, and the interface compatibility between the two is poor, and it is difficult to form a good bond and bond, and the bubble of the foam matrix is enhanced while enhancing the flame retardant property. Hole morphology and mechanical properties cause adverse effects. In order to improve the compatibility of the interface between EG and the polyurethane matrix, the EG surface is usually treated. Xu Dongmei et al. prepared a modified EG (MEG) by supporting boric acid on the surface of EG, which improved the flame retardancy and thermal stability of the material, and made the expanded carbon layer of MEG and RPUF/MEG system more dense. Xu Yang et al. treated the EG with a titanate coupling agent for the modification of polypropylene (PP)/thermoplastic polyurethane (TPU) composites, and improved the mechanical properties of PP/TPU/EG composites.
In this paper, EG was modified by aminosilane coupling agent KH791. The alcohol in the structure was hydrolyzed to form silanol, which reacted with the hydroxyl group on the surface of EG. The amino group in the structure reacted with isocyanate, so KH791 It can play a "connection" between EG and polyurethane matrix to improve the interfacial compatibility between the two. The EG and KH791 modified EG content is studied for the flame retardancy and heat of the whole water foamed polyurethane semi-rigid foam. Stability, mechanical properties and cell morphology.
1 Experimental part
1.1 Raw materials and reagents
Polyether polyol 3630: hydroxyl value 25~29 mg KOH/g, functionality f ≈3, 25 °C viscosity 1200~1800 mPa·s, Yiju Polymer Material Co., Ltd.; polyether polyol 330N: hydroxyl value 33~ 37 mg KOH/g, functionality f ≈3, 25°C viscosity 750~950 mPa·s, Yiju Polymer Material Co., Ltd.; expandable graphite (EG): model E300, sulfuric acid intercalation, particle size 80mesh, expansion ratio >270mL/g, purity 95%~99%, Qingdao Yanhai Carbon Materials Co., Ltd.; triethanolamine: analytical grade, Beijing Chemical Plant; isocyanate MDI: percent isocyanate NCO% 26%~27%, 25°C viscosity 110 ~150mPa·s, Yiju Polymer Material Co., Ltd.; Silicone oil: Model 8681, Yiju Polymer Material Co., Ltd.; Amine catalyst (triethylenediamine): chemically pure, Yiju Polymer Material Co., Ltd.; water (deionized) Water): laboratory-made; silane coupling agent: model KH791, Nanjing Qianjin Chemical Co., Ltd.; organotin catalyst (stannous octoate): chemically pure, Yiju Polymer Materials Co., Ltd.
1.2 Preparation of foam
This experiment uses a one-step method to synthesize polyurethane foam. Add all raw materials except MDI, ie component A, to the plastic cup, specifically including 9.375 g of polyether polyol 3630, 9.375 g of polyether polyol 330N, 0.34 g of triethanolamine, 0.75 g of water, 0.3 g of silicone oil, 0.26 g The catalyst and the flame retardant were stirred uniformly with a mixer for a control time of 60 s. Further, 16.88 g of MDI, component B, was added. After rapid stirring, the mixture was transferred to a self-made foaming box (15 cm × 15 cm × 6 cm). After 15 minutes, the foam was placed in a 50 ° C oven when the foaming volume was constant. After aging for 24 hours, the sample was taken out and subjected to characterization test.
Preparation of silane coupling agent KH791 modified EG: The silane coupling agent 791 is formulated into a 5% aqueous solution, stirred to hydrolysis, mixed with EG powder at a mass ratio of 1:2, and thoroughly dispersed by a stirrer at a low speed for 30 minutes, and then recycled. The water vacuum pump was suction filtered, placed in an oven at 80 ° C for 5 h, and then heated to 120 ° C for 30 min and then taken out to obtain a silane coupling agent KH791 modified EG.
The addition amount of the flame retardant EG and KH791 modified EG is increased by 5%, 10%, 15%, 20%, and 25% of the total mass of the foaming system. When the addition amount exceeds 25%, the viscosity of the raw material system is too high, the foam will shrink, and the foaming phenomenon is too slow, which is not conducive to the synthesis of the semi-rigid polyurethane foam.
1.3 Performance testing and characterization
1.3.1 Density test: Take 6 samples and take the average value. The sample size is 50mm×50mm×50mm. The apparent density of the foam sample is determined by the method of GB/T6343-1995.
1.3.2 Shore hardness analysis: The foam hardness test refers to the hardness test standard of polyurethane foam in the soft car dashboard, and the hardness of the polyvinyl chloride (PVC) skin foam is measured by a Shore A hardness tester, and 10 samples per sample are taken. The points are measured and averaged.
1.3.3 Polarized light microscope observation: The foam cross-section sample was observed using a 59XC optical microscope from Xiamen McDean Manufacturing Co., Ltd.
1.3.4 Compressive performance test: The compressive strength and compressive modulus of the foam sample are determined by the WSM-5KN electronic universal testing machine of Changchun Intelligent Instrument Equipment Co., Ltd. according to the GB8813-88 standard. The sample size was 50 mm × 50 mm × 50 mm, the compression ratio was 25%, and the compression rate was 10 mm/min.
1.3.5 Scanning electron microscope observation: The foam cross-section sample and the morphology of the burned carbon layer were observed at a voltage of 20 kV using a Zeiss EVO18 scanning electron microscope from Carl Zeiss, Germany.
1.3.6 Differential Scanning Calorimeter (DSC) Test: The liberation heat of the sample was measured by the CDR-4P differential thermal analyzer of Shanghai Precision Scientific Instrument Co., Ltd. The test temperature range is 50 to 500 ° C and the heating rate is 20 ° C / min.
1.3.7 Thermogravimetric Analysis (TG): The quality change of the foam sample during thermal decomposition was tested by the German NETZSCHSTA449F3 type thermogravimetric analyzer. The test temperature range is 25 to 800 ° C, the heating rate is 10 ° C / min, and the nitrogen flow rate is 40 mL / min.
1.3.8 Horizontal Burning Test: The horizontal burning performance test of foam samples refers to the flame retardant standard FMVSS302 of American automotive interior materials. The test was carried out using the automotive interior material combustion characteristic tester of Changchun City and Shili Applied Technology Research Institute. The sample size was 130mm×70mm×10mm.
1.3.9 Limiting Oxygen Index (LOI) test: The limiting oxygen index of the foam sample is tested according to ASTM D1863-97. The instrument used is the JF-3 oxygen index measuring instrument of Nanjing Huining District Analytical Instrument Factory. The sample size is 130mm×10mm. ×10mm.