In the secondary utilization of thermosetting, cross-linking and multi-functional waste plastics, the first thing to be solved is reverse plasticity, and secondly, it must be reasonably matched, and there must be process conditions. Generally, there are several methods for preparing engineering plastics from waste plastics:
First, the compatibility of engineering plastics
The compatibility of plastics is similar to that of general-purpose recycled plastics. Engineering plastics also need to consider compatibility issues, except that engineering plastics are heterogeneous multi-component blends. For example, its melt is often compounded by general-purpose plastics, thermoset plastics, and multifunctional plastics, so thermal compatibility is extremely important.
Second, the basic principles of high performance engineering plastic formula design
1. Selection of main materials
The main material should meet the requirements of new products in terms of appearance and mechanical properties. The wells make the composition of recycled plastic components as consistent as possible with the products produced. The material selection can be referred to the raw material formula.
2. Choice of functional plastics
Functional plastics require a choice when the host material does not have the functionality required by the product. It should generally have the outstanding features required by the product. For example: flame retardancy of PPS; conductivity of PPY; barrier property of PVDC; thermal insulation of PBI; wear resistance of silicone. The choice of this component should not only take into account its compatibility with the main component, but also the compatibility of the filler.
3. Soft Filling Components Soft filling is only a phase component, usually referred to as compatibilizers, softeners such as: PVC, PE, PP, HIPS, PET, PC, Pa, PMMa, EVOH, PVDC, and rubber. And elastomers. Adding soft filling not only helps toughen, anti-stick, improve elasticity, but also facilitates processing heat stability. The choice and amount of soft fill depends on the properties of the primary builder. Generally, high-performance plastics should be used as the main body, and should be added when general-purpose plastics are the main body.
4. Selection of processing modifiers
The processing aids are mainly modified in functional plastics without affecting the strength and functionality of the modified plastics. Among them, the recovery of PPS, LCP, fusible PI, PVDC can achieve the purpose of improving the fluidity of recycled plastics, and can also improve the strength of modified plastics.
5. Selection of other additives
Other additives can be divided into two parts: improving processability and improving function. Among them, heat stabilizers and co-mixers are components that must be added. For example, paraffin oil, dichloroethylene, and polychlorotrifluoroethylene are commonly used as stabilizers in PTFE modification; LMWPS and chlorinated paraffin are commonly used as stabilizers in PPS processing; and PaR is commonly used as stabilizer in triphenyl phosphite. PSF processing commonly uses alkylbenzenes and diphenyl phosphates as stabilizers.
Third, the basic principles of formula composition
1. Crosslinked plastics are generally continuous phase crosslinked plastics which are often olefinic polymers. The use of large doses of peroxygen compounds increases their fluidity, so their mutual compatibility is easily expressed as a continuous phase in a low molecular distribution state. And the operation is very convenient.
2. High-performance plastics are generally functional additives. High-performance plastic recyclates are difficult to melt, but they are also easily depolymerized under DCP catalysis. This forms a co-degradation system that not only easily disperses in the continuous phase, but also forms Chemical grafting (ie, formation of entangled crosslinks). This is also because the high-performance recycled plastics have less resources and therefore can only be used as functional additives.
3. Thermoset plastics are generally filler components. Because thermoset plastics are highly filled, they are compatible with alternative fillers. Thermoset plastics are also suitable for alternative fillers due to their low recycling price, good overall performance and low activity. The reinforcement and impact resistance of thermosetting plastic composite recycled plastics are also basically combined with rigid modification requirements.
Fourth, high performance recycling plastic modification process
Process for high performance recycled plastic modified high functional composites The homogeneous quality of recycled plastics and other components depends not only on the scientific formulation but also on the rational process. Among them, it is very important to refine the particle size of recycled plastic and granulation under high pressure conditions. Generally, the following processes should be used.
1. The shrinking process uses three crushers with different mesh openings, the first process is shaping and purifying; the second process is secondary shrinkage and drainage; the third process is refining milling. The particle diameters were 50 mm, 20 mm, and 0.5 mm, respectively.
2. The mixing process uses a kneading machine with a speed of 800 r/min to control the material temperature to 100 ° C and premix the formulation. The first step is to mix the raw materials, filler and coupling agent, stop, wait for the temperature of the material to drop to 40 ° C, add hydrocarbon and ester additives, dispersant, temperature control 80 ° C, stir for about 30 min, discharge can be.
3. The granulation process selects the 65H type co-rotating twin-screw extruder (L/D 1:38) for granulation, and the temperature is controlled at 160-360 °C to complete the composite granulation.
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