In situ compatibilization by reactive extrusion
DATE：2021/3/31 8:39:21 / READ： / SOURCE：This station
In situ compatibilization by reactive extrusion
Hollow board production line www.handern.comReactive extrusion is used for in-situ Compatibilization of polymer blends. In the process of reactive extrusion, part of macromolecular chains of polymer can be broken to form small segments or graft copolymers, which promotes the compatibility between components and improves the performance of materials.
(1) Effect of reactive extrusion parameters on properties of blends
1. With the increase of feeding speed (V) and screw speed: V, the residence time of materials in the barrel decreases, so the grafting rate of polymer functionalized by free root reaction decreases, and the amount of copolymer formed by interfacial interaction decreases, which eventually leads to the decrease of impact strength and elongation at break of the blends; if V decreases, the opposite is true.
With the increase of screw speed, the residence time of the material in the barrel decreases, and the impact strength and elongation at break of the blend decrease; with the decrease of screw speed, the shear force decreases, so the shear degradation of the material decreases, the residence time of the material increases, the final crosslinking degree increases, and the viscosity of the material increases.
Specific flow rate (Q / N) and length diameter ratio (L / D): Q / N is used to measure the amount of material that can be extruded by the screw of twin-screw extruder every rotation, and the change of its value mainly affects the residence time of material in the barrel and the blending strength of material. With the increase of L / D, the residence time of materials in the barrel increases, which is conducive to the full mixing of materials, and the properties of the blends are also enhanced.
3. The ratio of extrusion temperature and screw speed: high extrusion temperature, fast decomposition of initiator, fast graft reaction, screw speed can be increased correspondingly; otherwise, it is the opposite. If the temperature is too high, the initiator will decompose and produce bubbles, which will change the color of the material; if the temperature is too low, the melt will break easily. Hollow board production line www.handern.com
4 Effect of the position of devolatilization section: the position of devolatilization section is very important for compatibilizing immiscible polymer blends in situ by one-step method. When the devolatilization section is designed between the solid conveying section and the melting section, and the length of the devolatilization section is appropriately increased, the residual monomers can be eliminated before the polymer with functional groups is mixed. For example, PBT, the impact strength and elongation at break of the blends are 15-20 times higher than those of the blends without residual monomers.
(2) Viscosity ratio of dispersed phase to continuous phase
The results show that the viscosity ratio of dispersed phase to continuous phase increases, and the particle size of dispersed phase increases. The effect of viscosity ratio on the phase distribution is much greater than that of viscosity ratio.
(3) Effect of the affinity of blending component and compatibilizer on the particle size of dispersed phase
When the polymer component with high affinity to compatibilizer is continuous phase, the average number and diameter of dispersed phases modified by two-step method is smaller than that by one-step method; when the polymer component with low affinity to compatibilizer is continuous phase, the average number and diameter of dispersed phases modified by one-step method is smaller than that by two-step method. Hollow board production line www.handern.com
(4) Effect of properties and dosage of reactive compatibilizer and crosslinker on blending effect
Most polymers are incompatible, and the compatibility can be changed by adding six compatibilizers. Different compatibilizers have different compatibilizing effects on the same blend system. AA, Ma and GMA are used to compatibilize PP / PBT respectively. The results show that GMA has good compatibilizing effect. Under the optimal GMA concentration and process conditions, the elongation and impact strength of the blends are 15-20 times higher than those of the non Compatibilized Blends. Because ppgaa interacts with BT by hydrogen bond, the interaction force is relatively weak; PP.gMA With PR_ The OH reaction is reversible. With the increase of temperature, the reaction is in the direction of PMA. The - c0oh reaction of PP ggma and PBT is also reversible, but with the increase of temperature, the reaction is in the direction of product.
The concentration of the compatibilizer is not higher than that of the best compatibilizer. The optimum concentration of compatibilizer is 5%. When the concentration is more than 5%, the particle size and torque of dispersed phase have no obvious change. For some blends, such as PO / PA, flocculation occurs when the concentration of compatibilizer is too high. Appropriate amount of multi-functional crosslinking agent was added to the blend system to promote the interphase adhesion, hinder the chain cracking caused by the presence of peroxide initiator, improve the crosslinking efficiency of the blend components, and greatly improve the mechanical properties and melt flow properties of the blend system.
(5) Effect of initiator on reactive extrusion blending
The concentration of initiator has a great influence on the modification effect of reactive extrusion. When the concentration of DCP is low, the grafting reaction is dominant; on the contrary, the cross-linking reaction is dominant. For example, HDPE is easy to produce self crosslinking reaction, which leads to melt rupture and the extrusion process can not be carried out normally.
(6) Effect of feeding method on blending effect of reactive extrusion
There are two ways to add polymer to extruder. 1. Add the polymer, the auxiliary agent and the polymer with other functional groups into a feed port at the same time; 2. Add the polymer and the auxiliary agent into the first feed port and the polymer with functional groups into the second feed port. The results show that the properties of the first polymer blend are inferior to those of the second. For example, PP / PBT = 70 / 30 (mass ratio) blends, the impact strength of the two methods is 6 times that of the first method. In the first way, the presence of PBT dilutes the concentration of gmapp, which slows down the reaction between GMA and PP and reduces the efficiency. Moreover, there is a side reaction between GMA and PBT, which is faster than PP-g-GMA due to the good fluidity of PBT.
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