Anhydrous cerium chloride manufacturers share the application research progress of nano cerium oxide in the pharmaceutical field

As a common polymer material, phenolic resin has the advantages of low cost and convenient synthesis process. It is often used as heat insulation, heat insulation, insulation and other materials in the electrical industry, construction industry and other fields. However, phenolic resin also has the defects of easy combustion and poor flame retardancy, which limits its application in industrial production and daily life. In order to improve the flame retardancy of phenolic resin, flame retardant materials, such as halogen flame retardant, antimony trioxide, phosphorus flame retardant, etc., are usually added to phenolic resin to improve the flame retardancy of phenolic resin. However, these flame-retardant materials are easy to release toxic gases when burning, which will cause harm to the environment. Therefore, it is necessary to seek an environmental friendly flame retardant material to improve the flame retardancy of phenolic resin.

Cerium oxide (CeO2), as a new flame retardant additive, has the advantages of free radical capture and Combustion Catalysis. It can be used as a substitute for phosphorus based flame retardants. Its application in polymer materials can improve the flame retardancy of materials. Wu Wei et al. Added CeO2 to epoxy resin to improve the flame retardancy of epoxy resin. Experiments show that CeO2 can improve the limiting oxygen index (LOI) of epoxy resin combustion, reduce the initial decomposition temperature, and help improve the flame retardancy of epoxy resin. Feng Houjun et al. Added CeO2 to acrylic resin to make LOI value of acrylic resin as high as 30% and improve combustion thermal stability. However, when CeO2 is added to phenolic resin, there are few reports on the flame retardant and heat insulation properties of the composite. In this experiment, CeO2 was added to phenolic resin to prepare phenolic resin / CeO2 composite, and the effect of CeO2 content on the flame retardancy and thermal insulation performance of the composite was studied.

1.experimental part

1.1 main raw materials

Formaldehyde, analytical pure, Jinan Junteng Chemical Co., Ltd; Phenol, analytical pure, Cangzhou Sansu Co., Ltd; Sodium hydroxide, analytical pure, Sinopharm Pharmaceutical Co., Ltd; Cerium oxide (CeO2), analytical purity, silane coupling agent KH-560, purity 99%, Tianjin kemio Chemical Reagent Co., Ltd.

1.2 instruments and equipment

Magnetic stirrer, h550, Shanghai Yuezhong Instrument Equipment Co., Ltd; Vacuum drying oven, vo-6020t, Shanghai Denglian Instrument Manufacturing Co., Ltd; Granulator, xsn-3, Taixing Ruixing rubber and Plastic Machinery Co., Ltd; Ball mill, tjgn-450, Tianjin Dongfang Tianjing Technology Development Co., Ltd; Hot press, PLC, fusion ultrasonic technology (Shanghai) Co., Ltd; Scanning electron microscope (SEM), s4800, Hitachi, Japan; Thermogravimetric analyzer (TGA), q600 SDT, Ta company; Cone calorimeter, bt300-2j, Suzhou Phoenix quality inspection instrument Co., Ltd; Vertical combustion instrument, czf-6, Nanjing Jiangning Analytical Instrument Co., Ltd; Limit oxygen index (LOI), HVI, Shanghai pinkui Electromechanical Technology Co., Ltd; Thermal conductivity meter, dre-2b, Xiangtan Instrument Co., Ltd.

1.3 sample preparation

1.3.1 preparation of phenolic resin

Add 46ml phenol and 138ml formaldehyde to a 500ml three necked flask, add 36ml deionized water to the flask, stir for 60min to ensure that formaldehyde, phenol and water are evenly mixed, add 1g sodium hydroxide to the solution and heat and stir the mixed solution. When the heating temperature reaches 70 ℃, sonicate the reaction solution for 240Min, put it into a vacuum drying oven, heat it to 130 ℃ for vacuum dehydration, The phenolic resin is cut into granules by a granulator.

1.3.2 preparation of modified CeO2

Add CeO2 into a 100ml three necked flask, add 50ml of distilled water and 1.5ml of KH-560, stir and heat to 60 ℃ for reaction, stop stirring after 30min of reaction, obtain modified CeO2 by suction filtration, and heat and dry at room temperature.

1.3.3 preparation of phenolic resin / CeO2 composite

Table 1 shows the formulations of different phenolic resin / CeO2 composites. According to the formula in Table 1, the raw materials and modified CeO2 are mixed, and the two are ground and mixed by a ball mill, and then put into a stainless steel mold for hot pressing. Preheat the hot press for 30min, put the phenolic resin and CeO2 into the mold for thermal curing, heat the hot press to 150 ℃ and keep it for 30min, cool it to room temperature and take it out to obtain the phenolic resin / CeO2 composite.

Table 1 formula of different phenolic resin / CeO2 composites / g

1.4 performance test and characterization

SEM analysis: the samples were frozen and brittle with liquid nitrogen. The samples were sprayed with gold and the voltage was 5kV.

TG analysis: sample mass is 0.5g, N2 atmosphere, temperature range is 30 ~ 400 ℃, and heating rate is 2 ℃ / min.

Cone calorimeter test: test according to iso5660-1:2015, power 50KW / m2, sample size 80mm × 80mm × 20mm。

Vertical combustion test: test as per GB / T 8333-2008, sample size 100mm × 10mm × 3mm, methane is selected as the ignition source, and the ignition time is 10s. The spontaneous combustion time and droplet phenomenon of the flame are recorded.

Loi test: test according to GB / t2406.2-2009, sample size 120mm × 6mm × 3mm。

Thermal conductivity test: according to GB / t3139-2005, the sample size is 30mm × 20mm × 5mm, test temperature 37 ℃.

2.results and discussion

2.1 SEM analysis of phenolic resin / CeO2 composite

Fig. 1 is a SEM photograph of modified CeO2, phenolic resin and phenolic resin / CeO2 composite. As can be seen from Fig. 1a, the particle size of the modified CeO2 was about 1 μ m。 It can be seen from Fig. 1b that the surface of pure phenolic resin is smooth. As can be seen from Fig. 1C to Fig. 1f, with the increase of CeO2 addition, the phenolic resin / CeO2 composite begins to become rough, and excessive CeO2 appears agglomeration in the phenolic resin. SEM results show that appropriate amount of CeO2 can be evenly dispersed in phenolic resin. Due to the presence of coupling agent, phenolic resin can be closely combined with CeO2. However, CeO2 particles agglomerate due to excessive addition of GeO2.

Fig. 1 SEM photos of modified CeO2, phenolic resin and phenolic resin / CeO2 Composites

2.2 thermal stability analysis of phenolic resin / CeO2 composite

Fig. 2 shows the TG curves of pure CeO2, phenolic resin and different phenolic resin / CeO2 composites. It can be seen from Fig. 2 that the weight loss range of pure CeO2 is low in the range of 30 ~ 400 ℃, indicating that CeO2 has high thermal stability. However, the quality of pure phenolic resin decreased obviously at about 225 ℃; With the increase of temperature, the TG curve does not change around 340 ℃. In the range of 225 ~ 340 ℃, the phenolic resin is thermally degraded, which is mainly manifested by the decomposition of hydrocarbons in aramid fiber and the process of carbon formation. When CeO2 was added to phenolic resin, the initial thermal decomposition temperature of phenolic resin / CeO2 composite increased, and when the amount of CeO2 was increased from 0 to 40%, the initial thermal decomposition temperature increased from 225 ℃ to 307 ℃, an increase of about 36.4%. It shows that the introduction of CeO2 can obviously improve the initial thermal stability of the composite. CeO2 catalyzes the carbonization reaction of phenolic resin in the combustion process, forms an oxygen isolation layer and captures the free radicals generated by combustion to suppress combustion. The introduction of coupling agent also increases the bonding property between phenolic resin and reinforcement, which requires more energy for the decomposition of phenolic matrix, thus increasing the thermal stability of the composite.

Figure 2 TG curves of pure CeO2, phenolic resin and different phenolic resin / CeO2 Composites

2.3 analysis of flame retardancy of phenolic resin / CeO2 composite

Fig. 3 shows the LOI values of phenolic resin and different phenolic resin / CeO2 composites. It can be seen from Fig. 3 that with the increase of the amount of CeO2, the upper limit of LOI value of phenolic resin composite can reach 29.2%, which is 7.9% higher than that of pure phenolic resin (21.3%), indicating that the addition of CeO2 can better improve the flame retardancy. CeO2 can promote the catalytic formation of a carbon layer on the phenolic resin matrix during the combustion process. The presence of the carbon layer can effectively isolate the contact area between oxygen and the phenolic resin matrix, thus improving the flame retardancy of the composite. Moreover, CeO2 also has the function of trapping free radicals, which also improves the flame retardancy.

Figure 3 LOI values of phenolic resin and different phenolic resin / CeO2 Composites

Fig. 4 is a graph showing the total combustion heat release (THR), vertical combustion autoignition time (TTI) and heat release rate (HRR) of phenolic resin and different phenolic resin / CeO2 composites.

Fig. 4 | THR, TTI and HRR curves of phenolic resin and different phenolic resin / CeO2 Composites

It can be seen from FIG. 4A that the thr of pure phenolic resin is 107.8mj/m ²， It shows that phenolic resin can release higher heat. When CeO2 was added to phenolic resin, the thr of phenolic resin / CeO2 composite was significantly reduced, and the thr of phenolic resin / 30% CeO2 was lower, 64.0mj/m ²。 Compared with pure phenolic resin, the thr of phenolic resin / 30% CeO2 decreased by 40.6%. During the combustion of phenolic resin / CeO2, CeO2 promotes the formation of carbon layer and captures free radicals, and suppresses the combustion and heat release of the material, which indicates that the presence of CeO2 is conducive to improving the flame retardancy of phenolic resin. It can be seen from Fig. 4B that the flame initiation TTI increased from 49S to 72s by 46.9% when CeO2 flame retardant was added to the system. It can be seen from Fig. 4C that the peak heat release rate (phrr) of phenolic resin / 30% composite is lower than that of phenolic resin / 40% composite. The phenolic resin composite added with CeO2 has a shorter time to reach phrr, which indicates that CeO2 can improve the flame retardancy of phenolic resin. Combined with SEM analysis, it can be seen that due to the excessive addition of CeO2, more CeO2 in the phenolic resin matrix is agglomerated, and more pores appear in the phenolic resin matrix, making it easier for oxygen to enter the phenolic resin matrix to participate in the combustion reaction. Therefore, adding an appropriate amount of CeO2 is conducive to improving the flame retardancy of phenolic resin. When the amount of CeO2 is 30%, the flame retardancy of phenolic resin composite is better.

Table 2 shows the combustion states and grades of phenolic resin and phenolic resin composites. It can be seen from table 2 that the spontaneous combustion time of pure phenolic resin is 33S, and there is obvious melt dripping, which indicates that it is easy to burn, and there is no grade in UL-94 test. When CeO2 is added, the spontaneous combustion time of phenolic resin composite is obviously lower than that of pure phenolic resin. However, due to the combustion reaction, the adhesion between CeO2 and phenolic resin matrix is reduced, and CeO2 falls off. With the increase of CeO2 addition, the more obvious the fall off phenomenon of composite is. The phenolic resin / 30% CeO2 composite has better flame retardancy, and the spontaneous combustion time is reduced to 5S, which is 84.8% lower than that of pure phenolic resin. It has relatively high flame retardancy, and reaches V-0 level in UL-94 test. Therefore, phenolic resin / 30% CeO2 composite has ideal flame retardancy.

Table 2 combustion state and grade of phenolic resin and different phenolic resin / CeO2 Composites

2.4 thermal insulation performance analysis of phenolic resin / CeO2 composite

CeO2, as an inorganic additive, has a high thermal conductivity. Adding CeO2 into phenolic resin can reduce the heat insulation performance of the resin. Table 3 shows the thermal conductivity of phenolic resin and different phenolic resin / CeO2 composites. It can be seen from table 3 that the thermal conductivity of phenolic resin / CeO2 composite increases with the increase of CeO2 addition. When the amount of CeO2 is 30%, the thermal conductivity of phenolic resin composite is 0.3954w / (m · K), which has low thermal conductivity, indicating that the introduction of CeO2 will not have a great impact on the thermal insulation performance of phenolic resin / CeO2 composite.

Table 3 thermal conductivity of phenolic resin and different phenolic resin / CeO2 Composites

3. Conclusion

(1) The phenolic resin / CeO2 composite was prepared by hot pressing by mixing CeO2 with phenolic resin. TG results show that adding 40% CeO2 to phenolic resin can increase the initial thermal decomposition temperature of phenolic resin, and the decomposition temperature increases by about 36.4%. CeO2 increases the thermal stability of phenolic resin.

(2) The flame retardancy of phenolic resin / 30% CeO2 composite is better, and its thr and TTI are reduced by 40.6% and 84.8% respectively compared with pure phenolic resin, which proves that CeO2 as a flame retardant can improve the flame retardancy of phenolic resin.

(3) The addition of CeO2 reduced the thermal conductivity of phenolic resin, but the thermal conductivity of phenolic resin / 30% CeO2 composite was 0.3954w / (m · K), which was low. Therefore, phenolic resin composites can be used as thermal insulation materials for building facilities.

Plastic science and technology, 2022 (4): 46-49

Author: Wang Qidong