Modification method for improving granulation melt index and whiteness of regenerated plastic

Abstract

The invention belongs to the technical field of reprocessed plastic modification, and particularly discloses a modification method for improving the granulation melt index and whiteness of reprocessed plastics, through control of a specially-made modifier formula, an adding sequence, pretreatment of waste PP plastics, annealing treatment after granulation and the like, the whiteness and melt index of reprocessed PP plastic particles can be synchronously improved, and the yield of the reprocessed plastics is improved. The mechanical strength and toughness are ensured, and the effect is very good.

Description

Technical Field

[0001] The invention relates to the technical field of recycled plastics, and in particular to a modification method for improving the granulation melt index and whiteness of recycled plastics. Background Art

[0002] The melt index of plastic (also known as melt flow rate) is used to describe the ability of plastic to melt and flow after heating, that is, the fluidity of the melt. Improving the melt index can improve the fluidity of recycled plastic-related products and reduce the shrinkage of the product. However, recycled plastics may degrade to a certain extent during the recycling process, or be mixed with different types of plastics / added with various additives, etc., which will reduce their melt index, thereby affecting the application scope, product performance, market value, etc. of recycled plastics. In the prior art, the melt index of recycled plastics is mainly improved by adding PE paraffin, plasticizer RQT-P-1 or using polypropylene flow enhancer. However, the use of the aforementioned plasticizers will reduce the mechanical strength and durability of plastics, and plasticizers also pose certain environmental pollution and health risks.

[0003] The whiteness of recycled plastic particles is an important indicator for measuring the quality of recycled plastics, especially in applications that require high whiteness products. In practical applications, it is difficult for recycled plastics to meet product whiteness requirements due to the aging and degradation of waste plastic products and the poor removal of pollutants during recycling and regeneration. In the prior art, whiteness is mainly improved by efficient cleaning to remove impurities and stains carried by waste plastics and adding optical brighteners. However, the addition of brighteners will affect the fluidity and formability of plastics during processing.

[0004] Therefore, the existing technology cannot simultaneously improve the melt index and whiteness of recycled plastic particles. Summary of the invention

[0005] In view of the deficiencies in the above-mentioned prior art, the object of the present invention is to provide a modification method for improving the melt index and whiteness of recycled plastic granulation, so as to ensure that the modifier can be evenly dispersed in the recycled PP particles, and improve the whiteness and melt index of the recycled PP particles while ensuring their mechanical properties.

[0006] To achieve the above purpose, the technical solution adopted by the present invention is as follows: A modification method for improving the melt index and whiteness of recycled plastic granulation is characterized by being achieved through the following steps: Step 1. Modifier preparation: Determine the formula of the modifier, which is composed of 30%-35% titanium dioxide, 20%-30% nano calcium carbonate powder, 15%-20% whitening powder, 8%-15% putty powder (talcum powder 200 mesh, glass fiber), 8%-15% PE paraffin, 3%-10% maleic anhydride grafted PP, and 3%-10% calcium stearate; Titanium dioxide is a white pigment that can significantly improve the whiteness and light and heat stability of PP plastics, and can improve mechanical properties, etc. However, titanium dioxide has poor compatibility with PP, and the addition of titanium dioxide will cause it to be unevenly dispersed in PP. In order to increase the compatibility of titanium dioxide with PP, maleic anhydride is added to graft PP to enhance the compatibility between titanium dioxide and PP, which is conducive to the dispersion of titanium dioxide in PP. Calcium stearate is a commonly used stabilizer and lubricant that can reduce the viscosity of PP when it is melted, improve fluidity and increase the gloss of the final product, etc. However, the addition of calcium stearate will reduce the toughness and strength of PP products. For this reason, a certain proportion of nano calcium carbonate powder and putty powder are added to effectively improve the toughness of the final product. After many failed tests, the inventor finally determined the formula of the above modifier. The whiteness and melt index of the regenerated particles modified by the above formula are not significantly different from those of the new material.

[0007] Step 2: Pretreatment of waste PP plastics: The collected waste PP plastics are routinely crushed, cleaned and impurity-removed, and then crushed to 60-80 mesh, and then irradiated with an electron beam for 2-6 hours; Although the waste PP plastics have been effectively cleaned and impurities removed, the waste PP plastics themselves may be made of modified particles, and their melt index is affected due to cross-linking and other reasons between the molecular structures. The inventors found in the experiment that electron beam irradiation after the waste plastics are crushed to a certain mesh size can effectively enhance their compatibility with the modifier, so that the plastic particles and the modifier can be evenly dispersed, ensuring the whiteness and melt index improvement effect.

[0008] Step 3, equipment preparation: improve the original melt extrusion equipment, specifically, add a first automatic feeding device, a second automatic feeding device, and a third automatic feeding device in sequence along the feeding direction of the feed section of the melt extrusion equipment, each automatic feeding device includes a hopper with a sealing cover, a quantitative feeding mechanism, and a dispersion pipeline, and a dispersion stirring retention chamber is fixedly connected to the discharge port of the dispersion pipeline, and a stirring assembly is fixedly connected in each dispersion stirring retention chamber, and the dispersion stirring retention chamber of the automatic feeding device located in front of the two adjacent automatic feeding devices is connected and communicated with the feeding end of the dispersion pipeline of the automatic feeding device located in the back; The existing melt extrusion equipment has only one feed port in the feed section for adding waste PP crushed materials and modifiers. If the modifier and waste PP crushed materials are evenly mixed directly outside the equipment, the dispersion effect is obviously poor during the feeding process due to different specific gravities and compatibility issues. Therefore, the inventor improved the equipment, adding certain components of the modifier in batches, and evenly stirring in a hot environment after each addition, thereby effectively improving the dispersion effect and ensuring the uniformity of the whiteness and melt index of the final product particles.

[0009] Step 4, melt granulation: first, all the titanium dioxide in the modifier is mixed with the maleic anhydride grafted PP in the hopper of the first automatic feeding device to obtain a mixture A, and the mixture A is fed into the corresponding dispersion pipe through the quantitative feeding mechanism of the first automatic feeding device. At the same time, the waste PP plastic particles are fed into the dispersion pipe of the first automatic feeding device, and after being evenly mixed, they enter the second automatic feeding device; when there is material entering the dispersion pipe of the second automatic feeding device, a mixture B of putty powder, nano calcium carbonate powder and calcium stearate is added to the corresponding dispersion pipe through the quantitative feeding mechanism of the second automatic feeding device, and after being evenly mixed, it is fed into the third automatic feeding device; when there is material entering the dispersion pipe of the third automatic feeding device, a mixture C of whitening powder and PE paraffin is added to the dispersion pipe of the third automatic feeding device through the quantitative feeding mechanism of the third automatic feeding device; and then melt granulation is performed in a conventional manner; This aspect is similar to step 3. If the modifier is mixed first and then mixed with the waste PP crushed material, separation is likely to occur in the subsequent feeding section, extrusion section, etc., resulting in poor dispersion effect, affecting the uniform distribution of the components in the subsequent melting and extrusion process, and further affecting the uniformity of product quality. The present invention adds some components of the modifier in sequence, which can effectively promote uniform dispersion between the components and make the final modification effect better.

[0010] Step 5, annealing after granulation: put the conventional granulated particles into annealing equipment for annealing, control the annealing temperature to 110℃-160℃, the time to 3-5h, the atmosphere to be inert atmosphere, and naturally cool to room temperature after annealing; Annealing treatment can effectively improve the reprocessing performance of product particles, especially the fluidity and toughness of product particles during reprocessing, and expand the application range of product particles.

[0011] Furthermore, the specific ingredients of the putty powder in the above step 1 are talcum powder 200 mesh, glass fiber, acrylic emulsion (specifically, silicon-modified acrylic emulsion or polyurethane-modified acrylic emulsion or butyl acrylate, etc.) in a weight ratio of 100-300:3-8:5-6. The addition of putty powder with a suitable formula can improve the mechanical strength and toughness of waste PP plastics, and also have a certain improvement effect on the fluidity of waste PP.

[0012] Furthermore, in the above step 2, the electron beam energy during electron beam irradiation is 1-3 MeV and the irradiation is performed in a vacuum environment or an inert atmosphere.

[0013] Furthermore, in the above step three, the discharge port at the bottom of the hopper of each automatic feeding device is connected to the feed port of the quantitative feeding mechanism and the two are interconnected, the discharge port of the quantitative feeding mechanism is connected to the dispersion pipe and the two are interconnected, the dispersion pipe is inclined and a stirring spiral blade is arranged in the dispersion pipe, and the stirring spiral blade is driven by a servo motor fixed on the outer wall of the lower end of the dispersion pipe; a discharge port is opened at the bottom of the lower end of the dispersion pipe, and the discharge port is fixedly connected to the dispersion stirring retention chamber; the outer shell of the dispersion stirring retention chamber is made of thermal insulation material, and a plurality of electric heating plates are fixedly connected to the inner wall of the dispersion stirring retention chamber.

[0014] Furthermore, in the above step four, in the automatic feeding device for adding the titanium dioxide and maleic anhydride grafted PP mixture A, its dispersion stirring retention chamber is heated to 80-150°C before feeding; in the automatic feeding device for adding the mixture B of putty powder, nano calcium carbonate powder and calcium stearate, its dispersion stirring retention chamber is heated to 50-80°C before feeding; in the automatic feeding device for adding the mixture C of whitening powder and PE paraffin, its dispersion stirring retention chamber is heated to 50-80°C before feeding.

[0015] Compared with the prior art, the present invention has the following beneficial effects: 1. The present invention can simultaneously improve the whiteness and melt index of recycled PP plastic particles while ensuring their mechanical strength and toughness through the control of special modifier formula, addition order, pretreatment of waste PP plastics, annealing treatment after granulation, etc., and the effect is very good; 2. The present invention improves the structure of the feed section of the melt granulation equipment, which can meet the control of the order of adding the modifier and effectively and evenly disperse the modifier and the waste plastic particles, thereby providing the most critical technical control point for the melt index and whiteness uniformity of the final product particles, and realizing automatic and uniform feeding, preventing the hot air in the melting process from injuring the workers and effectively preventing the outside air from entering the melting equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a schematic diagram of the structure of the feed section of the melt granulation equipment of the present invention; Figure 2 It is a schematic diagram of the structure of three automatic feeding devices of the present invention; Among them, 1. a first automatic feeding device, 11. a first hopper, 12. a first quantitative unloading mechanism, 13. a first dispersing pipeline, 14. a first stirring spiral blade, 15. a first servo motor, 16. a first dispersing stirring retention chamber, 17. a first stirring component, 18. a first electric heating plate; 2. a second automatic feeding device, 21. a second hopper, 22. a second quantitative unloading mechanism, 23. a second dispersing pipeline, 24. a second stirring spiral blade, 25. a second servo motor, 26. a second dispersing stirring retention chamber, 27. a second stirring component, 28. a second electric heating plate; 3. a third automatic feeding device, 31. a third hopper, 32. a third quantitative unloading mechanism, 33. a third dispersing pipeline, 34. a third stirring spiral blade, 35. a third servo motor, 36. a third dispersing stirring retention chamber, 37. a third stirring component, 38. a third electric heating plate; 4. an oblique pipeline, 5. a plastic grinding machine, 6. a crushed plastic conveying mechanism. DETAILED DESCRIPTION

[0017] The present invention will now be further described with reference to the accompanying drawings and specific embodiments. Parts not described in detail below are based on the prior art in the art.

[0018] The purpose of the improvement of the equipment part in the present invention is to promote the uniform dispersion of the components. Whether the modifier is fully dispersed with the waste PP particles directly affects the melt index and whiteness uniformity of the final product particles, which is the core technical point of the present invention. According to the conventional design, the components are uniformly stirred before the melt granulation equipment, and then added to the feed end of the melt granulation equipment. In this way, during the feeding process, due to the different specific gravity of each substance and compatibility problems, the components of the modifier and the waste PP particles are easily separated and uneven, which ultimately leads to uneven whiteness of the granulated particles and poor melt index modification effect. The present invention transforms the feed section of the existing melt granulation equipment, adds certain components of the modifier in batches, and uniformly disperses them during the addition process and disperses them again under heating, effectively promoting the compatibility and uniform mixing of the components. At the same time, the improved feed section structure of the melt granulation equipment can realize the removal of moisture from certain components (such as acrylic emulsion, etc.) to prevent quality problems such as bubbles in the granulated particles.

[0019] Embodiment 1 The modification method for improving the melt index and whiteness of recycled plastic granulation in this embodiment is specifically achieved through the following steps: Step 1. Modifier preparation: Determine the formula of the modifier, which is composed of 30% titanium dioxide, 20% nano calcium carbonate powder, 15% whitening powder, 10% putty powder (talcum powder 200 mesh, glass fiber, polyurethane modified acrylic emulsion mixed in a weight ratio of 150:3:5), 8% PE paraffin, 10% maleic anhydride grafted PP, and 7% calcium stearate; the amount of the modifier is 8% of the total weight of the waste PP plastic particles; Step 2: Pretreatment of waste PP plastics: The collected waste PP plastics are routinely crushed, cleaned and impurity-removed, and then crushed to 60-80 mesh, and then irradiated with an electron beam for 6 hours, with an electron beam energy of 3MeV and irradiation in a vacuum environment; Step 3, equipment preparation: improve the original melt extrusion equipment, specifically, add three automatic feeding devices in sequence along the feeding direction of the melt extrusion equipment on the feeding section, namely, a first automatic feeding device 1, a second automatic feeding device 2, and a third automatic feeding device 3. The first automatic feeding device 1 includes a first hopper 11 with a sealing cover (the sealing cover is hinged at the top inlet of the hopper, and the first hopper 11 is connected with a stirring mechanism in a conventional manner), a first quantitative feeding mechanism 12 (such as a spiral quantitative feeder in the prior art), and a first dispersion pipeline 13, wherein the feeding port of the first dispersion pipeline 13 is connected to the discharge port of a plastic grinder 5 (a conventional plastic grinder), the feeding hopper of the plastic grinder 5 is connected to a crushed plastic conveying mechanism 6 (a conventional belt conveying mechanism), and the bottom discharge port of the first hopper 11 is connected to the first quantitative feeding mechanism 12 The first quantitative feeding mechanism 12 has a feeding port connected to the first dispersing pipe 13 and the two are connected. The first dispersing pipe 13 is tilted and a first stirring spiral blade 14 is arranged in the first dispersing pipe 13. The first stirring spiral blade 14 is driven by a first servo motor 15 fixed on the outer wall of the lower end of the first dispersing pipe 13; a discharging port is provided at the bottom of the lower end of the first dispersing pipe 13, and a first dispersing stirring retention chamber 16 is fixedly connected to the discharging port. A first stirring assembly 17 (mainly composed of a rotating shaft and stirring blades fixedly connected to different heights of the rotating shaft, and the rotating shaft is driven by an independent servo motor) is fixedly connected in the first dispersing stirring retention chamber 16. The outer shell of the first dispersing stirring retention chamber 16 is made of heat-insulating material, and a plurality of first electric heating plates 18 are fixedly connected to the inner wall of the first dispersing stirring retention chamber 16. The specific structures of the second automatic feeding device 2 and the third automatic feeding device 3 are substantially the same as those of the first automatic feeding device 1 (the second automatic feeding device 2 includes a second hopper 21, a second quantitative feeding mechanism 22, a second dispersion pipeline 23, a second stirring spiral blade 24, a second servo motor 25, a second dispersion stirring retention chamber 26, a second stirring assembly 27, and a second electric heating plate 28; the third automatic feeding device 3 includes a third hopper 31, a third quantitative feeding mechanism 32, a third dispersion pipeline 33, a third stirring spiral blade 34, a third servo motor 35, a third dispersion stirring retention chamber 36, a third stirring assembly 27, and a second electric heating plate 28. The mixing assembly 37 and the third electric heating plate 38 are provided, except that the high-end feed port of the second dispersing pipe 23 of the second automatic feeding device 2 is fixedly connected to the discharge port opened at the bottom of one side of the first dispersing stirring retention chamber 16 of the first automatic feeding device 1, the high-end feed port of the third dispersing pipe 33 of the third automatic feeding device 3 is fixedly connected to the discharge port opened at the bottom of one side of the second dispersing stirring retention chamber 26 of the second automatic feeding device 2, the discharge port opened at the bottom of one side of the third dispersing stirring retention chamber 36 of the third automatic feeding device 3 is fixedly connected to the oblique pipe 4, and the discharge end of the oblique pipe 4 is fixedly connected to the melting extrusion section of the granulation melting equipment; Step 4, melt granulation: first, all the titanium dioxide in the modifier and the maleic anhydride grafted PP are mixed evenly in the first hopper 11, and are uniformly added to the first dispersion pipe 13 through the first quantitative feeding mechanism 12 of the first automatic feeding device 1. At the same time, the pre-treated waste PP plastic particles are uniformly added to the high end of the first dispersion pipe 13 of the first automatic feeding device 1 through the discharge port of the plastic grinder. The first dispersion stirring retention chamber 16 of the first automatic feeding device 1 turns on its electric heating plate before feeding to heat the dispersion stirring retention chamber to about 80-100°C; when material enters the second dispersion pipe 23 of the second automatic feeding device 2, through The second quantitative feeding mechanism 22 of the second automatic feeding device 2 uniformly adds a mixture B of putty powder, nano calcium carbonate powder and calcium stearate (the three are uniformly mixed in the second hopper 21 in advance), and the second dispersion stirring retention chamber 26 of the second automatic feeding device 2 is preheated to 80°C before feeding; when the dispersion pipeline 33 of the third automatic feeding device 3 has materials entering, the quantitative feeding mechanism 32 of the third automatic feeding device 3 uniformly adds a mixture C of whitening powder and PE paraffin (the whitening powder and PE paraffin are uniformly mixed in the third hopper 31 in advance); finally, the mixture enters the melt extrusion section of the melt granulation equipment through the oblique pipeline 4 for conventional melt granulation; Step 5, annealing after granulation: put the conventional granulated particles into annealing equipment for annealing, control the annealing temperature to 110°C-120°C, the time to 5h, the atmosphere to be an inert atmosphere, and naturally cool to room temperature after annealing.

[0020] Comparative Example 1 (Conventional modifier) Step 1: Preparation of modifier, specifically 50% titanium dioxide and 50% PE paraffin, the amount of modifier used is 8% of the total weight of waste PP plastic particles; Step 2: Pretreatment of waste PP plastics: The collected waste PP plastics are routinely crushed, cleaned and impurity-removed, and then crushed to 60-80 mesh, and then irradiated with an electron beam for 6 hours, with an electron beam energy of 3MeV and irradiation in a vacuum environment; Step 3: Equipment preparation: This step is the same as step 3 of Example 1; Step 4, melt granulation: first, all the titanium dioxide in the modifier is uniformly added to the first dispersion pipe 13 thereof through the first quantitative unloading mechanism 12 of the first automatic feeding device 1, and the pretreated waste PP plastic particles are uniformly added to the high end of the first dispersion pipe 13 of the first automatic feeding device 1 at the same time, and the first dispersion stirring retention chamber 16 of the first automatic feeding device 1 is heated to about 80°C before feeding; when the second dispersion pipe 23 of the second automatic feeding device 2 has material entering, PE paraffin is uniformly added through the second quantitative unloading mechanism 22 of the second automatic feeding device 2, and the second dispersion stirring retention chamber 26 of the second automatic feeding device 2 is heated to 80°C before feeding; and then enters the melt extrusion section of the melt granulation equipment through the third dispersion pipe 33, the third dispersion stirring retention chamber 36 (the third dispersion stirring retention chamber 36 is turned on and heated to 80°C when feeding in the third dispersion pipe) and the oblique pipe 4 of the third automatic feeding device 3, and conventional granulation is carried out; Step 5, annealing after granulation: put the conventional granulated particles into annealing equipment for annealing, control the annealing temperature to 110°C-120°C, the time to 5h, the atmosphere to be an inert atmosphere, and naturally cool to room temperature after annealing.

[0021] Comparative Example 2 (without irradiation) Step 1. Modifier preparation: Determine the formula of the modifier, which is composed of 30% titanium dioxide, 20% nano calcium carbonate powder, 15% whitening powder, 10% putty powder (talcum powder 200 mesh, glass fiber, polyurethane modified acrylic emulsion mixed in a weight ratio of 150:3:5), 8% PE paraffin, 10% maleic anhydride grafted PP, and 7% calcium stearate; the amount of the modifier is 8% of the total weight of the waste PP plastic particles; Step 2: Pretreatment of waste PP plastics: conventionally crush, clean and remove impurities from the collected waste PP plastics; Step 3 to step 5: the same as step 3 to step 5 of embodiment 1 respectively.

[0022] Comparative Example 3 (all modifiers added at once) Step 1: Modifier preparation: Determine the formula of the modifier, which is composed of 30% titanium dioxide, 20% nano calcium carbonate powder, 15% whitening powder, 10% putty powder (talcum powder 200 mesh, glass fiber), 8% PE paraffin, 10% maleic anhydride grafted PP, and 7% calcium stearate; the amount of the modifier is 8% of the total weight of the waste PP plastic particles; Step 2: Pretreatment of waste PP plastics: The collected waste PP plastics are routinely crushed, cleaned and impurity-removed, then crushed to 60-80 mesh, and then irradiated with an electron beam for 6 hours; Step 3: After the modifier is fully mixed, the pretreated waste PP particles are added through the feed section of a conventional melt granulation equipment to perform melt granulation; Step 4: Place the conventionally granulated particles into an annealing device for annealing, control the annealing temperature to be 110°C-120°C, the time to be 5 hours, the atmosphere to be an inert atmosphere, and naturally cool to room temperature after annealing.

[0023] Comparative Example 4 (without annealing) Step 1: Selection and preparation of modifier: Determine the formula of the modifier, which is composed of 30% titanium dioxide, 20% nano calcium carbonate powder, 15% whitening powder, 10% putty powder (talcum powder 200 mesh, glass fiber), 8% PE paraffin, 10% maleic anhydride grafted PP, and 7% calcium stearate; the amount of modifier is 8% of the total weight of waste PP plastic particles; Step 2: Pretreatment of waste PP plastics: The collected waste PP plastics are routinely crushed, cleaned and impurity-removed, then crushed to 60-80 mesh, and then irradiated with an electron beam for 6 hours; Step 3, equipment preparation: improve the original melt extrusion equipment, specifically, add three automatic feeding devices in sequence along the feeding direction of the melt extrusion equipment on the feeding section, namely, a first automatic feeding device 1, a second automatic feeding device 2, and a third automatic feeding device 3. The first automatic feeding device 1 includes a first hopper 11 with a sealing cover (the sealing cover is hinged at the top inlet of the hopper, and the first hopper 11 is connected with a stirring mechanism in a conventional manner), a first quantitative feeding mechanism 12 (such as a spiral quantitative feeder in the prior art), and a first dispersion pipeline 13, wherein the feeding port of the first dispersion pipeline 13 is connected to the discharge port of a plastic grinder 5 (a conventional plastic grinder), the feeding hopper of the plastic grinder 5 is connected to a crushed plastic conveying mechanism 6 (a conventional belt conveying mechanism), and the bottom discharge port of the first hopper 11 is connected to the first quantitative feeding mechanism 12 The first quantitative feeding mechanism 12 has a feeding port connected to the first dispersing pipe 13 and the two are connected. The first dispersing pipe 13 is tilted and a first stirring spiral blade 14 is arranged in the first dispersing pipe 13. The first stirring spiral blade 14 is driven by a first servo motor 15 fixed on the outer wall of the lower end of the first dispersing pipe 13; a discharging port is provided at the bottom of the lower end of the first dispersing pipe 13, and a first dispersing stirring retention chamber 16 is fixedly connected to the discharging port. A first stirring assembly 17 (mainly composed of a rotating shaft and stirring blades fixedly connected to different heights of the rotating shaft, and the rotating shaft is driven by an independent servo motor) is fixedly connected in the first dispersing stirring retention chamber 16. The outer shell of the first dispersing stirring retention chamber 16 is made of heat-insulating material, and a plurality of first electric heating plates 18 are fixedly connected to the inner wall of the first dispersing stirring retention chamber 16. The specific structures of the second automatic feeding device 2 and the third automatic feeding device 3 are substantially the same as those of the first automatic feeding device 1 (the second automatic feeding device 2 includes a second hopper 21, a second quantitative feeding mechanism 22, a second dispersion pipeline 23, a second stirring spiral blade 24, a second servo motor 25, a second dispersion stirring retention chamber 26, a second stirring assembly 27, and a second electric heating plate 28; the third automatic feeding device 3 includes a third hopper 31, a third quantitative feeding mechanism 32, a third dispersion pipeline 33, a third stirring spiral blade 34, a third servo motor 35, a third dispersion stirring retention chamber 36, a third stirring assembly 27, and a second electric heating plate 28. The mixing assembly 37 and the third electric heating plate 38 are provided, except that the high-end feed port of the second dispersing pipe 23 of the second automatic feeding device 2 is fixedly connected to the discharge port opened at the bottom of one side of the first dispersing stirring retention chamber 16 of the first automatic feeding device 1, the high-end feed port of the third dispersing pipe 33 of the third automatic feeding device 3 is fixedly connected to the discharge port opened at the bottom of one side of the second dispersing stirring retention chamber 26 of the second automatic feeding device 2, the discharge port opened at the bottom of one side of the third dispersing stirring retention chamber 36 of the third automatic feeding device 3 is fixedly connected to the oblique pipe 4, and the discharge end of the oblique pipe 4 is fixedly connected to the melting extrusion section of the granulation melting equipment; Step 4, melt granulation: first, all the titanium dioxide in the modifier and the maleic anhydride grafted PP are mixed evenly in the first hopper 11, and are uniformly added to the first dispersion pipe 13 through the first quantitative feeding mechanism 12 of the first automatic feeding device 1. At the same time, the pre-treated waste PP plastic particles are uniformly added to the high end of the first dispersion pipe 13 of the first automatic feeding device 1 through the discharge port of the plastic grinder. The first dispersion stirring retention chamber 16 of the first automatic feeding device 1 turns on its electric heating plate before feeding to heat the dispersion stirring retention chamber to about 80-100°C; when material enters the second dispersion pipe 23 of the second automatic feeding device 2, through The second quantitative unloading mechanism 22 of the second automatic feeding device 2 uniformly adds a mixture B of putty powder, nano calcium carbonate powder and calcium stearate (the three are mixed uniformly in the second hopper 21 in advance), and the second dispersing stirring retention chamber 26 of the second automatic feeding device 2 is preheated to 80°C before feeding; when material enters the dispersing pipe 33 of the third automatic feeding device 3, the quantitative unloading mechanism 32 of the third automatic feeding device 3 uniformly adds a mixture C of whitening powder and PE paraffin (the whitening powder and PE paraffin are mixed uniformly in the third hopper 31 in advance); finally, the material enters the melt extrusion section of the melt granulation equipment through the oblique pipe 4 for conventional melt granulation.

[0024] The plastic particles obtained in the above Example 1 and Comparative Examples 1 to 4 were subjected to quality inspection, wherein the melt flow rate detection method complies with the national standard GB / T 3682.1-2018, and the tensile strength and elongation at break detection methods comply with the national standard GB / T 1040-2018. The specific quality inspection results are shown in Table 1 below: Table 1:

[0025] As can be seen from Table 1 above, the plastic particles of Example 1 of the present invention have uniform color in appearance, and their melt flow rate, tensile strength, and elongation at break are all in compliance with national standards, especially the melt flow rate is preferred in the standard (the technical requirements in the standard are 7-11). Comparing Example 1 with Comparative Examples 1 to 4, and comparing Comparative Examples 1 to 4 with each other, it can be seen that the modifier formula and the method of adding the modifier have a significant effect on the appearance and melt flow rate of the product plastic, the modifier formula has a significant effect on the tensile strength and elongation at break of the product plastic, and whether annealing after granulation has a significant effect on the tensile strength and elongation at break of the product plastic. Judging from the influence of appearance alone, whether the modifier is added at one time > the formula of the modifier > whether it is irradiated > whether it is annealed; judging from the influence of melt flow rate alone, the formula of the modifier > whether the modifier is added at one time > whether it is annealed > whether it is irradiated; judging from the influence of tensile strength alone, the formula of the modifier > whether it is annealed > whether the modifier is added at one time > whether it is irradiated; judging from the influence of elongation at break alone, the formula of the modifier > whether it is annealed > whether the modifier is added at one time > whether it is irradiated. Therefore, in order to comprehensively improve the whiteness and melt index of the product plastic, in order to ensure the tensile strength and elongation at break of the product plastic, the formula of the modifier, whether the modifier is added at one time, and whether it is annealed are all crucial factors.

Claims

1. A modification method for improving the melt index and whiteness of recycled plastic granulation, characterized in that: This is accomplished by: Step 1. Modifier preparation: Determine the formula of the modifier, which is specifically prepared from the following raw materials in percentage by weight: titanium dioxide 30%-35%, nano calcium carbonate powder 20%-30%, whitening powder 15%-20%, putty powder 8%-15%, PE paraffin 8%-15%, maleic anhydride grafted PP 3%-10%, calcium stearate 3%-10%; Step 2: Pretreatment of waste PP plastics: The collected waste PP plastics are routinely crushed, cleaned and impurity-removed, and then crushed to 60-80 mesh, and then irradiated with an electron beam for 2-6 hours; Step 3, equipment preparation: improve the original melt extrusion equipment, specifically, add a first automatic feeding device, a second automatic feeding device, and a third automatic feeding device in sequence along the feeding direction of the feed section of the melt extrusion equipment, each automatic feeding device includes a hopper with a sealing cover, a quantitative feeding mechanism, and a dispersion pipeline, and a dispersion stirring retention chamber is fixedly connected to the discharge port of the dispersion pipeline, and a stirring assembly is fixedly connected in each dispersion stirring retention chamber, and the dispersion stirring retention chamber of the automatic feeding device located in front of the two adjacent automatic feeding devices is connected and communicated with the feeding end of the dispersion pipeline of the automatic feeding device located in the back; Step 4, melt granulation: first, all the titanium dioxide in the modifier is mixed with the maleic anhydride grafted PP in the hopper of the first automatic feeding device to obtain a mixture A, and the mixture A is fed into the corresponding dispersion pipe through the quantitative feeding mechanism of the first automatic feeding device. At the same time, the waste PP plastic particles are fed into the dispersion pipe of the first automatic feeding device, and after being evenly mixed, they enter the second automatic feeding device; when there is material entering the dispersion pipe of the second automatic feeding device, a mixture B of putty powder, nano calcium carbonate powder and calcium stearate is added to the corresponding dispersion pipe through the quantitative feeding mechanism of the second automatic feeding device, and after being evenly mixed, it is fed into the third automatic feeding device; when there is material entering the dispersion pipe of the third automatic feeding device, a mixture C of whitening powder and PE paraffin is added to the dispersion pipe of the third automatic feeding device through the quantitative feeding mechanism of the third automatic feeding device; and then melt granulation is performed in a conventional manner; Step 5: Annealing after granulation: put the conventional granulated particles into annealing equipment for annealing, control the annealing temperature to 110°C-160°C, the time to 3-5h, the atmosphere to be inert atmosphere, and naturally cool to room temperature after annealing.

2. The modification method for improving the melt index and whiteness of recycled plastic granulation according to claim 1, characterized in that: The putty powder in the above step 1 is prepared from talcum powder 200 mesh, glass fiber, and acrylic emulsion according to a weight ratio of 100-300:3-8:5-6.

3. The modification method for improving the melt index and whiteness of recycled plastic granulation according to claim 1, characterized in that: In the above step 2, the electron beam energy of the electron beam irradiation is 1-3 MeV and the irradiation is performed in a vacuum environment or an inert atmosphere.

4. The modification method for improving the melt index and whiteness of recycled plastic granulation according to claim 1, 2 or 3, characterized in that: In the above step three, the discharge port at the bottom of the hopper of each automatic feeding device is connected to the feed port of the quantitative feeding mechanism and the two are interconnected, the discharge port of the quantitative feeding mechanism is connected to the dispersion pipe and the two are interconnected, the dispersion pipe is inclined and a stirring spiral blade is arranged in the dispersion pipe, and the stirring spiral blade is driven by a servo motor fixed on the outer wall of the lower end of the dispersion pipe; a discharge port is opened at the bottom of the lower end of the dispersion pipe, and the discharge port is fixedly connected to the dispersion stirring retention chamber; the outer shell of the dispersion stirring retention chamber is made of thermal insulation material, and a plurality of electric heating plates are fixedly connected to the inner wall of the dispersion stirring retention chamber.

5. The modification method for improving the melt index and whiteness of recycled plastic granulation according to claim 4, characterized in that: In the above step four, in the automatic feeding device for adding the mixture A of titanium dioxide and maleic anhydride grafted PP, the dispersion stirring retention chamber is heated to 80-150°C before feeding; in the automatic feeding device for adding the mixture B of putty powder, nano calcium carbonate powder and calcium stearate, the dispersion stirring retention chamber is heated to 50-80°C before feeding; in the automatic feeding device for adding the mixture C of whitening powder and PE paraffin, the dispersion stirring retention chamber is heated to 50-80°C before feeding.

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