Production line of polypropylene and polyethylene blended hollow grid plate
DATE：2021/6/21 8:34:41 / READ： / SOURCE：This station
Production line of polypropylene and polyethylene blended hollow grid plate
The modification of PP with plastic as toughening material has been studied earlier, and the more successful example is PP / PE system. PP is a kind of high-quality polymer, which produces larger pellets, which is the main reason why PP is easy to crack and has low impact property. The impact property of PP can be improved by making the PP product fine. In PP / PE blends, PP and PE are crystalline polymers. They do not form eutectic, but crystallize separately. However, there are five constraints between PP crystal and PE crystal, which can destroy the spherulite structure of PP. PP spherulite is divided into flakes by PE, which makes PP more difficult to be spherulite. With the increase of PE content, the segmentation becomes more and more significant, and PP crystal is further refined. The impact strength of PP increases with the decrease of crystal time. Through the study of PP / LLDPE BLEND system, the following rules are obtained: hollow grid plate production line www.handern.comThe impact strength of PP at room temperature can be improved by different types of PE, but the difference is very obvious. For PP / HDPE blends, when the mass fraction of HDPE is less than 60%, the strength of the blends is basically unchanged; When the mass fraction of HDPE is higher than 60%, the impact strength of the blends increases. For PP / up: blends, only when the mass fraction of LDPE is higher than 60%, the impact strength can be greatly improved. For PP / LLDPE Blends, when the mass fraction of LLDPE is more than 40%, the impact strength of PP / LLDPE Blends increases obviously; The toughening effect of LLDPE was the best. When the mass ratio of PP / LLDPE is 30 / 70, the impact strength of the blends is 23.2kj/m, which is 20 times higher than that of pure PP, while the impact strength of PP / HDPE and PP / LDPE Blends is only about 5kj / m under the same conditions. This further shows that the amount of LLDPE is the least when the impact strength is the same, which means that the rigidity of PP can be maintained more; At the same dosage, LLDPE modified PP has the best impact strength, which makes the material obtain better toughness. Hollow grid plate production line www.handern.com
The impact strength of the sample mixed by twin-screw extruder is the highest, and that of the sample by direct injection is the worst. Because the effective length of the screw of the injection machine is smaller than that of the extruder, the shear mixing effect is small and the effect is poor. Under different mixing methods, the impact properties of the materials show the same rule, that is, the mass of LLDPE starts from 40%, and the impact strength increases greatly with the increase of LLDPE content; The results show that the mixing method has an effect on the impact properties of the blends, but the law remains unchanged. Hollow grid plate production line www.handern.com
When the mass fraction of LLDPE is less than 50%, the impact fracture surface of PP / LLDPE Blends is smooth and flat, showing typical brittle fracture characteristics; When the mass fraction of LLDPE is more than 50%, the fracture surface of the material is characterized by ductile fracture, filaments, uneven fracture surface, tearing marks, and the interface between the two phases tends to be blurred. At this time, the yield strength of the material increases rapidly; When the content of LLDPE is increased to 70%, it can be clearly seen that PP interweaves into a net, so the material has a high impact strength on the macro level. The size of pure PP balls is very large, and the interface between balls is clear, so the impact performance of PP is very poor. In contrast, LLDPE is very fine, and the interface between crystals is also very fuzzy, so its impact performance is very good. The difference of crystalline morphology between PP and LLDPE is caused by the different crystallization rates of PP and LLDPE: the crystallization rate of PP is slow (3.3x10'nm / 5), the crystal growth is larger, and the connection between the products is less, so the interface between the products is clear; while the crystallization rate of LLDPE is very fast (8.3x10 nm / s), the crystal is small, and the connection between the crystals is more, so the interface between the crystals is blurred. When LLDPE was added to PP, the spherulite size of PP decreased obviously, and the interface between the crystals became blurred, which was beneficial to improve the impact properties of the material. With the increase of LLDPE content, PP spherulites further decrease. When the mass fraction of LL-DPE reaches 70%, PP crystals have been divided into broken crystals, and the interface between crystals disappears completely, which is mixed with LLDPE and difficult to distinguish. Therefore, the impact strength of the blends is very high and it is not easy to be broken. It shows that the addition of LLDPE refines the spherulites of PP and increases the connection between the crystals, which is another important reason for the improvement of the toughness of PP blends. Hollow grid plate production line www.handern.com
The effect of LLDPE content on the properties of blends decreased with the increase of LLDPE content, but the elongation at break increased gradually, and showed a good linear relationship. With the increase of LLDPE content, the Vicat softening point of the blends decreases. When the mass fraction of LLDPE is 40% ~ 60%, the Vicat softening point of the blends is still close to 120c. With the increase of LLDPE content, the impact strength increases, while the tensile yield strength, tensile modulus and Vicat softening point decrease. In the LLDPE based system, when the material is impacted, not only the LLDPE phase consumes a lot of energy and improves the toughness of the material, but also because of the insertion, segmentation and refinement of PP spherulites by LLDPE, the size of PP crystals decreases and the connection between crystals increases, which improves the impact strength of the material. In PP / LLDPE Blends, when the mass fraction of LLDPE is 40% ~ 70%, the interpenetrating network structure is gradually formed, which has the characteristics of rigidity and toughness. Hollow grid plate production line www.handern.com
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