Synthetic resins and plastics
Because methylcellulose has excellent dispersibility, it has been used in the suspension polymerization of vinyl chloride since the late 1950s, and small and uniform granular polyvinyl chloride can be obtained. For example, if a water-soluble MC with a viscosity of 500mPa·s is used in the polymerization of vinyl chloride, it can obtain a polyvinyl chloride product with a bulk density of 714kg/m³; if an MC with a viscosity of 100mPa·s is used, it can obtain a product with a density of 600kg/m³; if an anionic surfactant is added and an appropriate peroxide catalyst is selected, the effect will be better. In the suspension polymerization liquid of vinyl chloride, a mixed suspending agent composed of 1%~99.9% water-soluble MC and 99%~1% hydroxyethyl cellulose is added in an amount of 0.04%~0.25%, and the uniform granular product obtained has no “fish eyes.” MC (15mPa·s) and polyvinyl alcohol can also be mixed and used. The resulting polyvinyl chloride has a uniform particle size distribution, 46.8% passes through a 50-100 mesh sieve, and the apparent bulk density is 10kg/m³.
The use of MC in the suspension polymerization liquid of vinyl chloride significantly enhances the plasticizer absorption of the resulting polyvinyl chloride. For instance, when MC with a viscosity of ≤100 mPa·s and ≥400 mPa·s are mixed in a 1:1 ratio and used in the suspension polymerization liquid of vinyl chloride, the plasticizer absorption of the resulting polyvinyl chloride is 30%, with an absorption time of 10 minutes, and 100% passing through a 0.25mm sieve. However, when only MC with higher viscosity is used, the absorption is below 42.3%. When MC with a viscosity of ≤100 mPa·s and ≥400 mPa·s are mixed in a 75:25 ratio and used in the suspension polymerization liquid of vinyl chloride, the yield is 100% (>60 mesh), the plasticizer absorption is 31.9%, and the gel time is 16 minutes. If only 15 mPa·s MC is used, the yield is 56.5% and the plasticizer absorption is 18.5%.
In the suspension polymerization of vinyl chloride, if MC and copolymers of maleic anhydride and α-olefin (C₆~Czo) are used as mixed suspension agents, the drying time of the obtained polyvinyl chloride is only 144s, and 99% and 31% can pass through 0.177mm and 0.105mm sieves respectively. In comparison, the drying time of using only polyvinyl alcohol as a suspension agent is 234s.
Adding 0.0001%~1% MC can improve its thermal stability when synthesizing polyvinylidene fluoride. The coating film formed by model casting or coating preparation will not change color after baking.
MC’s versatility extends beyond specific polymers. It can be effectively used in the polymerization or copolymerization of various resins. For instance, when a small amount of MC and piperidine (aza cyclohexane) is added to the polyacrylaldehyde polymerization solution, it produces colorless and uniform spherical polyacrylaldehyde. Similarly, in the suspension copolymer of vinyl chloride and vinyl acetate, the inclusion of a small amount of MC as a suspending agent leads to the production of a copolymer with excellent light resistance and transparency. In the suspension copolymer of vinyl acetate and crotonic acid, the addition of a small amount of MC (<500mPa·s) results in the production of a stable 0.5-1mm granular copolymer.
MC, a versatile compound, can be grafted with a variety of other monomers. For instance, in an aqueous solution containing ammonium persulfate, MC can be grafted with vinyl acetate. The resulting product can then be extracted with acetone or dimethylformamide, and precipitated in water, showcasing the adaptability of MC in different chemical processes.
MC has good film-forming properties. Alkali-soluble MC (DS=0.2~0.7) can be dissolved in an alkaline solution with a resin plasticizer to prepare a base or film. For example, 100 parts of MC alkaline solution and 7.5 parts of polyethylene glycol with molecular weights of 4000 and 200 are mixed. After filtering, a slurry with a viscosity of 5140mPa·s at 20°C is obtained. After extrusion, it is passed through an 11.4% sulfuric acid bath and then rinsed with a 7% NaHCO₃ aqueous solution at 60°C, wound on a drum, and dried at 150°C for 40 minutes to obtain a solid and flexible film.
MC can be added to the components of various synthetic resin foam materials. For example, adding MC to a polyvinyl alcohol aqueous solution and formaldehyde to solidify it in an acidic catalyst can produce a porous foam material with excellent physical and mechanical properties. A small amount of MC and azodicarbonamide is formulated into a polyethylene foaming component and extruded in an extruder to form a foam material that can encapsulate copper wires. Each component is evenly deposited on the extruder wall, and the thickness of the film formed is not significantly different.
