Polymethyl methacrylate was prepared by free radical polymerization of methyl methacrylate. The polymerization process includes solution, suspension polymerization, bulk polymerization, etc., and the polymerization equipment includes kettle, tube and tube in series. The polymerization process includes low temperature polymerization and high temperature polymerization. Among them, the high temperature continuous bulk polymerization method is more advanced, which solves the influence of "automatic acceleration" on the production of polymethyl methacrylate in the process of polymerization.
In this paper, polymethyl methacrylate, commonly known as PMMA., was produced on the basis of high temperature continuous bulk polymerization. In the process of preparing polymethyl methacrylate by high temperature continuous bulk polymerization, the polymer passes through the screw extruder, which leads to the degradation and depolymerization of PMMA due to high temperature and high shear. In addition, polymers are degraded and aged by oxygen, ozone and water in the air.
In this paper, these two problems are solved: in the process of high temperature continuous bulk polymerization, light stabilizer is added in the polymerization process, thermal oxygen stabilizer is added in the extrusion process, or PMMA resin particles are mixed with heating oxygen stabilizer by screw extruder. The thermal oxygen stability of PMMA resin particles was improved by about 70 ℃, and the UV absorption effect of PMMA resin particles between 300~400nm was better with the addition of light stabilizer.
The experimental results showed that:
- Thermal oxygen stabilizer was 1010，1076，168，GS，0.1 to 1.0 wt%，main antioxidant and auxiliary antioxidant were combined, with a ratio of 3:1.
- The optical stabilizer is UV-234，5411，7401，7402, with a range of 0.1~1.0wt%, which can be used in combination.
- The addition method of hot oxygen stabilizer is as follows:solvent solution and extruder blending.
- The addition of light stabilizer was added by polymerization process, and it was found that the thermal stability of PMMA resin pellet decreased.
- The combination of thermal oxygen stabilizer and light stabilizer can effectively improve the thermal oxygen stability and light resistance of PMMA resin.
Polymethyl methacrylate, polymer amorphous crystalline material, density 1.18 ~ 1.19g/cm3, lighter than ordinary inorganic glass, refractive index 1.49, good optical properties, light transmittance can reach 93%, good light transmittance for different wavelengths of light in visible light, is an excellent polymer light guide and light transmitting material .
In 2016, the world MMA production expansion, PMMA resin production (molded plastics and sheets) reached about 276.2 million tons/a, mainly concentrated in Asia, North America and Europe, of which about 70% in Asia, 16% in North America and 14% in Europe. However, the molecular structure of PMMA resin is defective, resulting in high water absorption, poor abrasion resistance, poor organic solvent resistance and poor heat and oxygen stability, which limits its use. It is also found that PMMA resin pellets will become yellow, sticky, crystalline and discolored when stored for a long time, and PMMA resin polymers are susceptible to degradation during extrusion and drawing processes at temperatures above 200°C, resulting in a decrease in light transmission and mechanical properties of the resin pellets.
The degradation and depolymerization of PMMA resin polymers in the polymerization and extrusion process have also become a research topic. The addition of various synthetic additives during the polymerization of PMMA resin, or the addition of various synthetic additives in the polymerization, pre-extruder, tail line feed solvent or post-processing melt blending, will enable the most effective and simple way to improve the PMMA resin properties without changing the original polymerization method, thus achieving PMMA resin performance optimization.
The expansion of MMA production in China has reduced the production cost of PMMA resin and enhanced the competitiveness of PMMA resin with similar products. Meanwhile, the diversification, serialization and functionalization of PMMA resin varieties promote the development of PMMA resin industry. High value-added, high-tech PMMA resin products, as a substitute for other transparent materials, meet the requirements of product serialization, diversification and specialization, and product quality is greatly improved.
1. PMMA resin synthesis additive design
The configuration methods of synthetic additives include: mechanical compounding method, co-solvent method, emulsion compounding method, copolymer-hybrid method, and various interpenetrating network polymers method. According to the polymer process technology requirements and synthetic additives process requirements, the design of synthetic additives to add programs.
In this paper, the high temperature continuous ontology polymerization method is used as the technical basis for the production of PMMA resin polymers, and the synthetic additives are added according to the polymerization process to design the addition scheme. The selection of the appropriate additive program.
PMMA resin synthesis additives additive methods include the following.
(1) mechanical blending method
PMMA resin masterbatch and synthetic additives are mixed using this method. PMMA resin masterbatch and synthetic additives are mixed by high-speed mixing machine, and then melt blended by twin-screw extruder, twin-screw extruder temperature control in the polymer PMMA resin masterbatch and antioxidants, plasticizers, impact modifiers, etc. can be modified by this method.
Screw extrusion equipment as melt blending equipment is also used in the PMMA resin polymerization process, in the screw extruder to complete the polymerization of PMMA resin polymers, stretching, alignment, de volatile.
(2) Co-solvent method
Synthetic additives dissolved in a suitable solvent, through the solvent and polymer co-solvent, at the appropriate temperature mixing uniform, and then in the appropriate conditions to remove the solvent method is called co-solvent method.
Co-solvent method is commonly used equipment for extrusion equipment, de volatile equipment, etc.. For example: PMMA resin synthesis additive addition method can be used in the laboratory to qualitatively analyze the PMMA resin synthesis additive addition; PMMA resin polymerization process can be achieved through this method synthesis additive tail line solvent feed; desolvation screw extrusion equipment to remove volatile parts. The scheme design of the co-solvent method of PMMA resin synthesis additives is completed.
(3) copolymerization - co-blending method
It refers to the synthesis of additives and polymers through chemical methods to add, copolymerization - co-blending method and mechanical mixing of physical methods are different. For example: the addition of PMMA resin pellets light stabilizer is used in this method, light stabilizer and MMA copolymerization - blending, after high temperature polymerization and MMA polymer together, the filtering effect of UV light is better.
(4) various interpenetrating network polymer (IPN) technology. the IPN method opens up a new method for the formulation of additives.
IPN method to form interpenetrating network polymer blends, is a chemical method to prepare physical blends.
The IPN method is based on the polymerization conditions of polymers, on the basis of which the IPN method is optimized by selecting the appropriate IPN additive, taking into account the amount of IPN additive, the type of IPN additive and the method of compounding.
2. PMMA Resin Synthesis Additive Optimization
PMMA resin synthesis additives are added as follows.
PMMA resin synthesis additives from thermal oxygen stabilizer and light stabilizer, thermal oxygen stabilizer to the main antioxidant and auxiliary antioxidant compounding, the main antioxidant selection 1010, 1076 and GS, auxiliary antioxidant selection 168. light stabilizer to UV absorbers, preferably benzotriazole class and organic esters, namely 5411, 234, 7401 and 7402. fluorescent whitening agent using OB-1, Synthetic additives additive program formulation methods can be used.
(1) Co-solvent method
The laboratory used polymer and synthetic additives solvent dissolution, vacuum defoaming volatilization, qualitative characterization of synthetic additives properties. Pure PMMA resin pellets are weighed and poured into conical flasks, synthetic additives are added to the conical flasks according to different ratios, acetone solvent is added, and the conical flasks are placed on a magnetic heating stirrer, heated and mixed thoroughly. The prepared PMMA resin synthesis additives acetone solution is poured into the surface dish, and the sample is put into the vacuum oven to take off the solvent.
(2) Copolymerization-hybridization method
Through the PMMA resin high-pressure polymerization reactor, the copolymerization and copolymerization test is carried out, and the PMMA resin polymerization method adopts the high temperature continuous ontology polymerization method. Light stabilizer, polymerization monomer MMA, MA dissolved in toluene, polymerization reactor high temperature and high pressure polymerization, extrusion granulation. On the other hand, the thermal oxygen stabilizer and light stabilizer can be dissolved in solvent tank and extruded to granulate.
(3)Mechanical blending method
Synthetic additives and PMMA resin masterbatch are blended by grinding machine and added into screw extruder, screw extruder temperature 220℃, glass transition temperature on the melt blending, TG, DSC, IR spectra, nuclear magnetic spectra to characterize the performance of synthetic additives of PMMA resin pellets.
Polymethyl methacrylate (PMMA) is prepared by high temperature continuous ontogenetic polymerization. In the extrusion and drawing process, PMMA resin polymers are susceptible to degradation and depolymerization due to the high temperature and high speed shear of the extruder. The addition of thermal oxygen stabilizers effectively improves the thermal oxygen stability of PMMA resin polymers. The addition of light stabilizer in the polymerization process improves the light stability of PMMA resin polymer and solves the problems of heat resistance and UV filtering and oxygen stability during the preparation process of PMMA resin polymer. The physical properties of the PMMA resin were tested, and the test results showed that the performance of the PMMA resin met the performance requirements of the benchmark product.