Introduction At present, rigid polyvinyl chloride (PVC) pipes and fittings are one of the application fields of polyvinyl chloride products. After years of vigorous development, domestic special pipe resins such as spherical resins and green building materials resins have been developed to meet the needs of users. However, compared with developed countries, there are fewer special materials for PVC pipe fittings currently developed in China, and the market has yet to be developed. At present, plastic processing manufacturers generally use PVC resin with a polymerization degree of 1000 to process pipes, and the matching pipe fittings and valves generally use low polymerization degree SG-7 or SG-8 resin to manufacture PVC pipe fittings. The WS-800 grade resin produced by our company’s imported equipment is not only used in sheet and packaging material processing, but also used in pipe fittings processing. According to users’ feedback, the molecular weight of the 800PVC resin with a degree of polymerization is relatively high, and the dry fluidity and processing rheology of the resin used for processing pipe fittings are relatively poor, which is likely to cause poor surface finish of the product and uneven mold opening during injection molding. Therefore, users strongly hope that Chlor-Alkali Company can provide pipe fittings with a degree of polymerization of 700 to overcome the shortcomings of PSOOPVC resin processing pipe fittings. In view of the above shortcomings, the easy-to-process PVC resin for pipe fittings developed by our company’s technical center is undoubtedly another gratifying step in the development of the company’s special PVC resin. Together with the special resin for pipes, it becomes a series of products. Based on the successful development of the 10L kettle for PVC resin for pipe fittings, this project further optimized the process formula through the expansion test of the 300L kettle. The characteristics of the special PVC resin particles for pipe fittings with a degree of polymerization of 700 produced by the 300L reactor expansion test are close to the measured quality level of Shin-Etsu TK700 PVC resin.
1 Test part
1.1 Main equipment and instruments CONF-10-4 10L polymerizer, w mini plunger metering pump, Mastersizer Ms 20 laser particle size analyzer.
1.2 The main raw materials VCM (meet Mitsui East Pressure Standard), mercaptoethanol (NG) Sichuan Natural Gas Chemical Research Institute), initiators, dispersants, desalinated water and other additives used in the production of polyvinyl chloride.
1.3 Basic formula for polymerization test (Table 1) Table 1 Basic formula for polymerization test in 10L kettle Polymerization resin temperature grade VC DW EHP Tx36 IB IC ID BD NG1 NG2 UG62.3℃ 7oo l00 240 some some some some some some some 0.04 O． oo83 0.0142 O. 0D91.4 Polymerization test process operation (1) Add demineralized water, dispersant, initiator and other auxiliary agents into the IOL polymerizer in sequence;
(2) Blow the kettle with nitrogen to test the pressure;
(3) Deoxidize by vacuum, the vacuum degree is 640mmHg;
(4) Add VCM, cool and stir for 20 minutes, stirring speed 500r. P. m;
(5) Raise the temperature for 10-20 minutes to the predetermined polymerization temperature;
(6) 1.5 hours after the start of the polymerization reaction, the second batch of chain transfer agent was added within 15 hours according to the requirements of the formula;
(7) When the polymerization pressure drops to 0.7MPa, the material is discharged under pressure, and the slurry is dehydrated by centrifugation and dried with steam.
2 Test results and discussion
2.1 Basic research on small test
2.1.1 The influence of the initiator system on the polymerization reaction and the degree of polymerization. The degree of polymerization 700 low molecular weight resin is manufactured at a higher polymerization temperature in the presence of a chain transfer agent. Therefore, the selected initiator activity must match the higher polymerization temperature. , It is necessary to consider the small effect with the chain transfer agent and low polymerization inhibition effect. At present, the initiators suitable for the manufacture of low molecular weight PVC can be provided by initiator manufacturers at home and abroad mainly include the following types, as shown in Table 2. Table 2 Medium and low activity initiator technical performance half-life’temperature/’E storage temperature water-soluble chemical structure initiator name AKZO trade name molecular weight activity l, Oh lOh / ℃ / ppm classification of peroxide dicarbonate di-(2-ethyl) Hexyl ester) TrigonoxEHP C75 346.5 64 47-15<l tert-butyl peroxyneodecanoate Tdgonox23 C75 244.4 live 64 46-10 8 glutinous peroxide Tfigonox257 C70 202, 3 Sex 68 50-lO 29o Glutoazobisisobisiso ABVN 248.2 69 5l 10 <l Tfigonox125 C75 188.3 72 55 -lO 8l5 Glucoperoxide tert-butyl peroxide Trigonox25 C75 174.3 Low 75 57 — 5 2330 Diaphragm peroxide (3,5,5-trimethylhexanoyl) Tfigonox36 CD75 3l4.5 77 59 O l-2 Acyl peroxide- ,q Cinnamoyl LaLU’OX 38.6 79 61 30
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