Text/Meteor Polymer NOVA
Industrial methods for preparing polymer blends include melt blending, solution blending, and latex blending. Mixtures of rubber and plastic are usually produced by melt blending technology. Mixing different polymers is convenient and economical by melt blending. Various mixing equipment can be used, such as open mills, internal mixers, and various types of twin screw extruders. is carried out in an extruder, among which open mill stirring will cause oxidative degradation due to opening, internal mixer is a batch mixer, and twin screw extruder is a continuous mixer.
1. Copolymer preparation by a simple melt mixing method
Simple mixing of rubber and plastic can be carried out at a temperature above melting point or softening point of plastic, and at a certain speed, components are mixed in an internal mixer for a certain period of time. and mixing time depends on equipment model and total amount of mixed materials. The correct mixing temperature is determined by nature of plastic or polymeric material, but temperature must be high enough to keep plastic in a liquid molten state for mixing. At same time, to avoid occurrence of oxidative degradation, the temperature should be as low as possible. The blended mixture is milled or granulated for extrusion, injection molding, hot calendering, etc. The table below lists typical melting points for some specific blends.
2. Mixes of moderately vulcanized rubber and plastic
When EPDM is mixed with a polyolefin resin such as polypropylene, rubber will be slightly cross-linked under action of organic peroxide, and mixing temperature and time should be chosen to ensure good melt flow, so as to achieve highest degree of homogeneous mixing and partial vulcanization of rubber significantly improved properties of residual deformation of mixture. The disadvantage of vulcanizing rubber before blending with polyolefin is that blend will contain larger rubber particles.
3. Preparation of mixtures by dynamic vulcanization
Dynamic vulcanization is a rubber vulcanization process in which rubber and plastic are mixed to a homogeneous state when mixture is mixed in a mixer. The mixing process developed by Gessler in 1962, called "dynamic vulcanization method", he prepared a rubber-plastic mixture containing a small amount of vulcanizate. In 1963, Fischer used his unique understanding of dynamic vulcanization to prepare compounds containing varying amounts of partially vulcanized rubber. In presence of polypropylene, if organic peroxides are used to crosslink rubber, polypropylene will be damaged to a greater extent and degradation will be severe. In 1978, Koran and his team discovered that high-strength EPDM/PP elastic blends could be obtained by dynamic vulcanization if no peroxide vulcanizing agent was used. If plastic phase reaches a certain proportion in molten state, mixture can be processed as a thermoplastic. It is very important to mix rubber and plastic well before starting vulcanization, during this period and for a period of time after completion of vulcanization reaction, mixing must be carried out continuously. Plasticizers or filler oils can be used to increase volume of rubber phase. In molten state, plasticizer simultaneously increases volume of rubber and plastic phases. If plastic is a crystalline polymer such as polypropylene, when material crystallizes, plasticizer or filler oil is forced to precipitate out of plastic phase and into rubber phase, so plasticizer acts as a processing aid in molten state and acts as a softener at temperature of use.
In late 1980s, this process was used by industry to produce a large number of new thermoplastic elastomers, which played an important role in promotion.
The dynamic vulcanization method has been applied to many rubber and plastic mixing systems. It is recommended to use a special stage of dispersing fine rubber particles in a small amount of plastic to ensure an ideal elastic mixture of rubber and plastic.
First, it is a simple mixing, melting and mixing of rubber and plastic in same wayat once, and then adding vulcanizing agent after mixture is completely melted and mixed, and starting vulcanization reaction during continuous mixing, higher vulcanization rate, mixing degree should also be more aggressive to ensure good workability of final mixture. When mixing torque or power curve reaches its maximum value, continue mixing for a certain period of time to improve processing performance of mixture. During this period, the mixing torque or mixing power may decrease. The pellets are used for extrusion, injection molding, calendering. , etc.