1. A low-odor high-crystallization ultrahigh-fluidity polypropylene is characterized in that,

the paint comprises the following components in percentage by mass:

wherein:

the polypropylene resin is any one or a mixture of several polypropylene resins, and the polypropylene resin is at least one selected from the group consisting of homo-polypropylene, random co-polypropylene and impact co-polypropylene.

2. The low-odor high-crystalline ultrahigh-flowability polypropylene as claimed in claim 1, wherein said polypropylene resin has a melt index of 0.5 to 400g/10 min.

3. The low-odor high-crystalline ultrahigh-flowability polypropylene as claimed in claim 1 or 2, wherein said radical type initiator is an organic peroxide type initiator having a general structural formula of R-O-H or R-O-R, wherein R is an alkyl or acyl organic group;

the antioxidant is any one or a mixture of hindered phenol antioxidant and phosphite antioxidant.

4. The low-odor high-crystalline ultrahigh-flowability polypropylene as claimed in claim 3,

the organic peroxide initiator is any one of di-tert-butyl peroxide, tert-butyl hydroperoxide, 2, 5-dimethyl-2, 5-bis (tert-butyl peroxide) hexane, 3,6, 9-triethyl-3, 6, 9-trimethyl-1, 4, 7-triperoxonane;

the antioxidant is one or a mixture of two of tetra [ beta- (3, 5-di-tert-butyl-4-hydroxyphenyl) propionic acid ] pentaerythritol ester and tris (2, 4-di-tert-butylphenyl) phosphite.

5. The low-odor high-crystalline ultrahigh-flowability polypropylene as claimed in claim 1 or 2,

the compound high-crystallization nucleating agent is a mixture of HPN-715 (2-methylene- (4, 6-di-tert-butylphenyl phosphate) basic aluminum) and M1128 (magnesium carbonate) nucleating agent; and the mass ratio of the HPN-715 to the M1128 is (1-1.5): 1.

6. a preparation method of low-odor high-crystallization ultrahigh-fluidity polypropylene is characterized by comprising the following steps:

s1, mixing HPN-715 (2-methylene- (4, 6-di-tert-butylphenyl phosphoric acid) basic aluminum) and M1128 (magnesium carbonate) according to a certain proportion to form a compound high-crystallization nucleating agent, uniformly mixing an antioxidant, the compound high-crystallization nucleating agent and polypropylene resin through a high-speed stirring mixer to form a mixture, and feeding the mixture into a double-screw extruder from an intermediate hopper through a precision metering pump;

s2, adding the free radical initiator into an extruder from an intermediate hopper through a precision metering pump; under the actions of a free radical initiator, high-temperature melting and screw shearing, polypropylene resin generates a free radical degradation reaction, the molecular weight is changed from high to low, and the melt index is changed from low to high; the melt after reaction flows out of the die head of the extruder; solidifying into strips under the traction of a granulator, cooling and forming in a water tank, blowing and drying by a high-efficiency dewatering device, granulating by the granulator, and packaging after removing water vapor and micromolecular gas in a degassing bin.

7. The production method according to claim 6,

the extruder adopts a double-screw extruder; the length-diameter ratio of the double-screw extruder is 65-95; the temperature of the barrel of the extruder is 175-260 ℃; the rotation speed of the screw is set to 100-500 rpm.

8. The production method according to claim 6,

the degassing bin is characterized in that the original two degassing bins of the parallel cylinder A, B are changed into series connection, the material retention time of the degassing bin A is 45min, the degassing temperature is set to be 65-70 ℃, the material retention time of the degassing bin B is 30min, and the degassing temperature is set to be 55-60 ℃.

Background

The ultra-high fluidity polypropylene generally refers to a polypropylene material with an extremely high melt index (MFR ≧ 1000g/10min), which is commonly used as a main raw material for melt-blown nonwoven fabrics. At present, there are two main processes for preparing the raw materials at home. One is that the metallocene catalyst hydrogen regulation method is adopted to directly polymerize the ultrahigh fluidity polypropylene, the molecular weight distribution of the material obtained by the method is narrow, but the cost price of the catalyst is high, the polymerization process is difficult to control, the product price is high, the yield is limited, and the acceptance of downstream customers is not high; the process is characterized in that a peroxide free radical initiator is added into the conventional polypropylene, and the ultra-high fluidity polypropylene is obtained by initiating a degradation reaction of controllable free radical molecular chain breakage, so that the process is low in production cost, accurate and adjustable in melt index, narrow in molecular weight distribution, and suitable for melt-blown non-woven fabric production process, and the process is mostly adopted in the production of the conventional ultra-high fluidity polypropylene.

The demand for protective articles such as medical KN95 masks and protective clothing is rapidly increasing. The core material applied to the medical KN95 mask and the protective clothing is a non-woven fabric material, namely, the non-woven fabric is produced by a non-woven fabric melt-blowing process which is produced by adopting raw materials such as ultra-high fluidity polypropylene granules and the like through a continuous one-step method of high-temperature melting, spinning, line laying and hot-pressing coiling. People have higher and higher requirements on the filtering performance of the mask, and the filtering performance of the mask is required to reach more than 95%. The middle layer of the mask is made of melt-blown non-woven fabrics, and the melt-blown non-woven fabrics are subjected to electret treatment and have static charges and can adsorb bacteria, viruses and PM2.5 particles in the air. The electrostatic charge content and the duration of the electrostatic charge on the meltblown nonwoven are particularly important. The ultrahigh fluidity polypropylene is used as an important raw material of a non-woven fabric product, and the crystallization performance has an important influence on the electret treatment of the melt-blown non-woven fabric. Crystallinity is an important parameter of crystalline polymers, and has an important influence on the physical and mechanical properties of materials. Factors affecting the crystallinity include the regularity of polypropylene, nucleating agents, etc., but the main role is regularity. The higher the regularity and crystallinity of the material, the better the stability of space charge and the stronger the crystallization ability. The regularity of the resin is generally greatly influenced by a catalyst and production process conditions, the regularity difference between the same type of ex-factory polypropylene (PP) resin is not large, but the crystallinity difference is sometimes large. Research shows that the nucleating agent has obvious influence on the crystallization behavior of PP, and generally, the nucleating agent can increase the crystallization temperature of PP, increase the crystallinity and accelerate the crystallization rate. The effect of nucleating agents is generally evaluated by increasing the crystallization temperature, the more the PP is increased, the more effective the nucleation. When the nucleating agent leads PP to nucleate and crystallize at higher temperature to form high-perfection crystals, the stability of space charge of the material can be improved to a certain extent.

As a respiratory protection product closely related to human health, the product is not toxic, tasteless and irritant and is closely related to the health and comfort of people. In the prior art, the ultra-high fluidity polypropylene product produced by the polypropylene degradation induced by the peroxide free radical initiator contains more initiator residues and micromolecular by-products formed by the free radical degradation reaction, so that the Volatile Organic Compound (VOC) content of the product is higher, and the respiratory protection product carrying a large amount of organic micromolecules and aromatic substances is inevitably absorbed into the body in the using process of consumers to cause discomfort of the users.

With the increasing demand of people, the demand of low-odor, high-crystallization and ultrahigh-flow polypropylene raw materials is increasing.

Chinese patent application CN103571039B discloses a high-melt index polypropylene composition and a preparation method thereof, wherein polypropylene, peroxide master batches and nucleating agent master batches are mixed and extruded in a double-screw extruder for melting granulation to prepare high-melt index and high-performance polypropylene resin, but the method needs three double-screw granulation processes in order to obtain the final product material, thereby wasting time and labor, having higher energy and material consumption and higher product processing cost. Chinese patent application CN1314745C discloses a method for preparing high-fluidity polypropylene, which comprises the steps of adding powdery polypropylene and peroxide chemical degradation agent into a reaction kettle with a stirrer to prepare polypropylene with a melt index of 40-3000g/10min through solid-phase degradation reaction, but the product obtained by the method has poor melt index controllability, wider molecular weight distribution and more chemical degradation agent residue, influences the subsequent downstream customer processing production, and has larger smell. Chinese patent application CN1876708A discloses a special material for ultrahigh flow polypropylene melt-blown nonwoven fabric; chinese patent application CN104589523A discloses a production method and production equipment for polypropylene melt-blown non-woven fabric, wherein polypropylene and peroxide master batches are blended in a double-screw extruder, and are extruded and melted for granulation at one time to prepare high-melt-index and high-performance polypropylene resin. Chinese patent application CN109503935A discloses a low-odor high-transparency ultrahigh-fluidity polypropylene and a preparation method thereof, and the method is characterized in that on the basis of the former two patents, a transparent nucleating agent is added, so that the transparency of resin is improved, and the production of a transparent mask is facilitated.

None of the above patent documents suggests a complete and effective method for obtaining a polypropylene material having reduced odor and volatile components and improved resin crystallinity. In addition, people have great demands on the melt-blown fabric with high filterability and low odor, so that the low-odor high-crystalline polypropylene has wide market prospect. Domestic enterprises have not developed the polypropylene with ultrahigh fluidity, high crystallization and low odor. Therefore, there is a need for a method for preparing low-odor high-crystallization ultrahigh-flowability polypropylene which can simultaneously combine the characteristics of high crystallization, low odor, high melt index and low ash content.

Disclosure of Invention

In view of the above-mentioned deficiencies in the prior art, the present invention provides an ultrahigh-fluidity polypropylene having the significant advantages of low odor, low volatility, narrow molecular weight distribution, low ash content, high crystallinity, etc., and a preparation method thereof.

In order to provide the low-odor high-crystallization ultrahigh-fluidity polypropylene, the invention adopts the following technical scheme:

[1] the low-odor high-transparency ultrahigh-fluidity polypropylene comprises the following components in percentage by mass:

wherein:

the polypropylene resin is any one or a mixture of several polypropylene resins, and the polypropylene resin is at least one selected from the group consisting of homo-polypropylene, random co-polypropylene and impact co-polypropylene.

In the technical scheme, the initiator can effectively improve the fluidity of the PP resin, but because the activity of free radicals is strong, more active centers are easily induced to be generated on PP molecular chains, and under the action of shear heat, the active centers can further generate free radicals, so that the PP molecular chains are further thermally degraded, and because the polypropylene material is extremely easy to age, an antioxidant is added in the production and processing process, so that the stability of the melt index of the polypropylene can be improved.

In the technical scheme, a specially-made compound high-crystallization nucleating agent is added into polypropylene resin, and the nucleating agent is a compound of HPN-715 and M1128. On one hand, the nucleating agent can play a role of a crystal nucleus in the polypropylene, so that polypropylene molecular chains are crystallized around the crystal nucleus formed by the nucleating agent at a higher temperature, thereby reducing the size of spherulites, increasing the spherulites in unit area, and increasing the crystallinity to generate fine and uniformly distributed spherulites. On the other hand, the compound of the nucleating agent can improve the crystallization temperature of PP, increase the crystallinity of PP, accelerate the crystallization rate, form more spherulites in a shorter cooling time, improve the crystallinity and be beneficial to the stability of electrostatic charge of melt-blown cloth.

[2] The low-odor high-crystalline ultrahigh-flowability polypropylene according to [1], wherein the melt index of the polypropylene resin is 0.5 to 400g/10 min.

[3] The low-odor high-crystalline ultrahigh-flowability polypropylene according to [1], wherein the radical initiator is an organic peroxide initiator having a general structural formula of R-O-O-H or R-O-O-R, wherein R is an alkyl or acyl organic group, and R is preferably an alkyl or acyl group having 1 to 20 carbon atoms;

the antioxidant is one or a mixture of hindered phenol antioxidant and phosphite antioxidant.

[4] The low-odor high-crystalline ultrahigh-flowability polypropylene as described in [3], wherein the organic peroxide-based initiator is any one of di-t-butyl peroxide, t-butyl hydroperoxide, 2, 5-dimethyl-2, 5-bis (t-butyl peroxide) hexane, 3,6, 9-triethyl-3, 6, 9-trimethyl-1, 4, 7-triperoxonane;

the antioxidant is one or a mixture of two of tetra [ beta- (3, 5-di-tert-butyl-4-hydroxyphenyl) propionic acid ] pentaerythritol ester and tris (2, 4-di-tert-butylphenyl) phosphite.

[5] The low-odor high-crystalline ultrahigh-flowability polypropylene according to [1], wherein the compounded high-crystallization nucleating agent is a mixture of HPN-715 (2-methylene- (4, 6-di-tert-butylphenyl phosphoric acid) basic aluminum) and M1128 (magnesium carbonate) nucleating agents; and the mass ratio of the HPN-715 to the M1128 is (1-1.5): 1.

[6] A method for preparing a low-odor, high-crystalline, ultra-high-flow polypropylene, said method comprising the steps of:

s1, firstly, mixing HPN-715 (2-methylene- (4, 6-di-tert-butylphenyl phosphate) basic aluminum) and M1128 (magnesium carbonate) nucleating agent according to a certain proportion to form a compound high-crystallization nucleating agent, then uniformly mixing the antioxidant, the compound high-crystallization nucleating agent and the polypropylene resin through a high-speed stirring mixer to form a mixture, and putting the mixture into a double-screw extruder from a middle hopper through a precision metering pump;

s2, adding the solid organic peroxide initiator into an extruder from a middle hopper through a precision metering pump; under the action of an organic peroxide initiator, high-temperature melting and screw shearing, the polypropylene resin generates a free radical degradation reaction, the molecular weight is changed from high to low, and the melting index is changed from low to high; the melt after reaction flows out from the die head of the extruder; solidifying into strips under the traction of a granulator, cooling and forming in a water tank, blowing and drying by a high-efficiency dewatering device, granulating by the granulator, and packaging after removing water vapor and micromolecular gas in a degassing bin.

[7] The production method according to [6], wherein the extruder is a twin-screw extruder; the length-diameter ratio of the double-screw extruder is 65-95; the temperature of the barrel of the extruder is 175-260 ℃; the rotation speed of the screw is set to 100-500 rpm.

[8] According to the preparation method described in the item [6], the degassing bin is formed by changing the original two degassing bins of the parallel cylinder A, B into series connection, the material retention time of the degassing bin A is 45min, the degassing temperature is set to be 65-70 ℃, the material retention time of the degassing bin B is 30min, and the degassing temperature is set to be 55-60 ℃.

In conclusion, the invention provides the ultra-high fluidity polypropylene with a brand-new formula, and the uniform and controllable molecular weight distribution and processing fluidity are realized through the synergistic effect of the compound high-crystallization nucleating agent, the hyperoxidant, the lubricant and the polypropylene, so that the low-odor high-crystallization ultra-high fluidity polypropylene is finally obtained. The invention also provides an operation method for reducing the odor of the high-crystalline ultrahigh-fluidity polypropylene, which can further reduce the odor and volatile matters in the product on the basis of a brand new formula, can be successfully prepared by a one-step method, is convenient for mass popularization and production in factories, greatly solves the problem of small molecule residue in the product, improves the crystallinity of the product, is beneficial to the subsequent main electret treatment process of non-woven fabric manufacturing enterprises and the problem of odor residue, simplifies the post-treatment process of the non-woven fabric enterprises, and is greatly beneficial to the health protection of people.

Detailed Description

The first embodiment is as follows:

80kg of polypropylene powder (MFR is 0.5g/10min), 0.02kg of antioxidant 1010 (pentaerythritol tetrakis [ beta- (3, 5-di-tert-butyl-4-hydroxyphenyl) propionate), 0.03kg of antioxidant 168 (tris (2, 4-di-tert-butylphenyl) phosphite), 0.04kg of HPN-715 and 0.04kg of M1128 are mixed uniformly in a mixer, and the mixture is weighed into an intermediate hopper by a No. 1 weight loss scale; 19.87kg of a free radical initiator (di-tert-butyl dipentaperoxide (2, 5-dimethyl-2, 5-bis (tert-butyl peroxide)) as a free radical initiator was weighed into an intermediate hopper by a 2# loss weight scale; setting the rotating speed of the extruder to be 350 revolutions per minute, setting the total feeding speed of the weightlessness scale to be 450kg/h, setting the feeding proportion of the 1# weightlessness scale and the 2# weightlessness scale to be 80.13%/19.87%, and feeding materials to the extruder through an intermediate hopper; under the action of an organic peroxide initiator, high-temperature melting and screw shearing, polypropylene generates a free radical degradation reaction, the molecular weight is changed from high to low, and the melting index is changed from low to high; and extruding the resin by a double-screw extruder, bracing, cooling, granulating and drying to obtain the product. The product particles pass through a degassing bin connected in parallel with A, B, the retention time of the material in the degassing bin A is 45min, and the degassing temperature is set to be 65 ℃. And the material retention time of the degassing bin B is 30min, the degassing temperature is set to be 55 ℃, and the moisture and low-boiling-point micromolecular organic matters contained in the surface layer of the particles are carried out by hot air flow, so that the aims of drying and reducing odor are fulfilled.

Example two:

87.42kg of polypropylene powder (MFR is 1.2g/10min), 0.01kg of antioxidant 1010, 0.02kg of antioxidant 168, 0.03kg of HPN-715 and 0.02kg of M1128 are mixed uniformly in a mixer, and the mixture is weighed and put into an intermediate hopper from a No. 1 weight loss scale; adding 12.5kg of the free radical type initiator into an intermediate hopper by a No. 2 weight loss scale by using di-penta-di-tert-butyl peroxide as the free radical type initiator; setting the rotating speed of the extruder to be 350 revolutions per minute, setting the total blanking speed of the loss-weight scale to be 450kg/h, setting the feeding proportion of the 1# loss-weight scale and the 2# loss-weight scale hopper to be 87.5%/12.5%, and feeding materials to the extruder through the intermediate hopper; under the action of an organic peroxide initiator, high-temperature melting and screw shearing, polypropylene generates a free radical degradation reaction, the molecular weight is changed from high to low, and the melting index is changed from low to high; and extruding the resin by a double-screw extruder, bracing, cooling, granulating and drying to obtain the product. The product particles pass through a degassing bin connected in parallel with A, B, the retention time of the material in the degassing bin A is 45min, and the degassing temperature is set to be 70 ℃. And the material retention time of the degassing bin B is 30min, the degassing temperature is set to be 60 ℃, and both the water contained in the particle surface layer and the low-boiling-point micromolecule organic matter can be brought out by hot air flow, so that the aims of drying and reducing odor are fulfilled.

Example three:

89.56kg of polypropylene powder (MFR is 3.0g/10min), 0.03kg of antioxidant 1010, 0.01kg of antioxidant 168, 0.03kg of HPN-715 and 0.02kg of M1128 are mixed uniformly in a mixer, and the mixture is weighed and put into an intermediate hopper from a No. 1 weight loss scale; 10.35kg of the free radical initiator is weighed by a 2# weight loss and is put into an intermediate hopper by using di-penta-di-tert-butyl peroxide as the free radical initiator; setting the rotating speed of the extruder to be 350 revolutions per minute, setting the total blanking speed of the loss-weight scale to be 450kg/h, setting the feeding proportion of the 1# loss-weight scale and the 2# loss-weight scale hopper to be 89.65%/10.35%, and feeding materials to the extruder through the intermediate hopper; polypropylene generates free radical degradation reaction under the action of organic peroxide initiator, high-temperature melting and screw shearing, the molecular weight is changed from high to low, and the melting index is changed from low to high; and extruding the resin by a double-screw extruder, bracing, cooling, granulating and drying to obtain the product. The product particles pass through a degassing bin connected in parallel with A, B, the retention time of the material in the degassing bin A is 45min, and the degassing temperature is set to be 70 ℃. And the material retention time of the degassing bin B is 30min, the degassing temperature is set to be 55 ℃, and both the water contained in the particle surface layer and the low-boiling-point micromolecule organic matter can be brought out by hot air flow, so that the aims of drying and reducing odor are fulfilled.

Example four:

91.55kg of polypropylene powder (MFR is 10g/10min), 0.02kg of antioxidant 1010, 0.02kg of antioxidant 168, 0.03kg of HPN-715 and 0.03kg of M1128 are mixed uniformly in a mixer, and the mixture is weighed and put into an intermediate hopper from a No. 1 weight loss scale; 7.45kg of the free radical initiator is weighed by 2# weight loss and is put into an intermediate hopper by using di-penta-di-tert-butyl peroxide as the free radical initiator; setting the rotating speed of the extruder to be 350 revolutions per minute, setting the total blanking speed of the loss-weight scale to be 450kg/h, setting the feeding proportion of the 1# loss-weight scale and the 2# loss-weight scale hopper to be 92.55%/7.45%, and feeding materials to the extruder through the intermediate hopper; under the action of an organic peroxide initiator, high-temperature melting and screw shearing, polypropylene generates a free radical degradation reaction, the molecular weight is changed from high to low, and the melting index is changed from low to high; and extruding the resin by a double-screw extruder, bracing, cooling, granulating and drying to obtain the product. The product particles pass through a degassing bin connected in parallel with A, B, the retention time of the material in the degassing bin A is 45min, and the degassing temperature is set to be 70 ℃. And the material retention time of the degassing bin B is 30min, the degassing temperature is set to be 55 ℃, and both the water contained in the particle surface layer and the low-boiling-point micromolecule organic matter can be brought out by hot air flow, so that the aims of drying and reducing odor are fulfilled.

Example five:

mixing 94.11kg of polypropylene powder (MFR is 30g/10min), 0.02kg of antioxidant 1010, 0.02kg of antioxidant 168, 0.02kg of HPN-715 and 0.02kg of M1128 in a mixer uniformly, and weighing from a No. 1 weight loss and putting into an intermediate hopper; 5.8kg of the free radical type initiator is put into an intermediate hopper by a No. 2 weight loss scale by using di-penta-di-tert-butyl peroxide as the free radical type initiator; setting the rotating speed of the extruder to be 350 revolutions per minute, setting the total blanking speed of the weightlessness scale to be 450kg/h, setting the feeding proportion of the 1# weightlessness scale and the 2# weightlessness scale hopper to be 94.2%/5.8%, and feeding materials to the extruder through the intermediate hopper; under the action of an organic peroxide initiator, high-temperature melting and screw shearing, polypropylene generates a free radical degradation reaction, the molecular weight is changed from high to low, and the melting index is changed from low to high; and extruding the resin by a double-screw extruder, bracing, cooling, granulating and drying to obtain the product. The product particles pass through a parallel A, B degassing bin, the retention time of the material in the degassing bin A is 45min, and the degassing temperature is set to be 70 ℃. And the material retention time of the degassing bin B is 30min, the degassing temperature is set to be 60 ℃, and the moisture and low-boiling-point micromolecule organic matters contained in the surface layer of the particles are carried out by hot air flow, so that the aims of drying and reducing odor are fulfilled.

Example six:

96.33kg of polypropylene powder (MFR is 60g/10min), 0.02kg of antioxidant 1010, 0.03kg of antioxidant 168, 0.01kg of HPN-715 and 0.01kg of M1128 are mixed uniformly in a mixer, and the mixture is weighed and put into an intermediate hopper from a No. 1 weight loss scale; 3.6kg of the free radical type initiator is put into an intermediate hopper by a No. 2 weight loss scale by using di-penta-di-tert-butyl peroxide as the free radical type initiator; setting the rotating speed of the extruder to be 350 revolutions per minute, setting the total blanking speed of the weightlessness scale to be 450kg/h, setting the feeding proportion of the 1# weightlessness scale and the 2# weightlessness scale hopper to be 96.4%/3.6%, and feeding materials to the extruder through the intermediate hopper; under the action of an organic peroxide initiator, high-temperature melting and screw shearing, polypropylene generates a free radical degradation reaction, the molecular weight is changed from high to low, and the melting index is changed from low to high; and extruding the resin by a double-screw extruder, bracing, cooling, granulating and drying to obtain the product. The product particles pass through a parallel A, B degassing bin, the material retention time of the degassing bin A is 45min, and the degassing temperature is set to be 65-70 ℃. And B, the material retention time of the degassing bin is 30min, the degassing temperature is set to be 55-60 ℃, and the moisture and low-boiling-point micromolecule organic matters contained in the surface layer of the particles can be brought out by hot air flow, so that the purposes of drying and reducing the smell are achieved.

Example seven:

98.67kg of polypropylene powder (MFR 100g/10min), 0.02kg of antioxidant 1010, 0.03kg of antioxidant 168, 0.04kg of HPN-715 and 0.04kg of M1128 are mixed uniformly in a mixer, and the mixture is weighed and put into an intermediate hopper from a No. 1 weight loss scale; the free radical type initiator is di-penta-peroxide di-tert-butyl, and 1.2kg of the free radical type initiator is weighed by 2# weight loss and is put into an intermediate hopper; setting the rotating speed of the extruder to be 350 revolutions per minute, setting the total blanking speed of the weightlessness scale to be 450kg/h, setting the feeding proportion of the 1# weightlessness scale and the 2# weightlessness scale hopper to be 98.8%/1.2%, and feeding materials to the extruder through the intermediate hopper; under the action of an organic peroxide initiator, high-temperature melting and screw shearing, polypropylene generates a free radical degradation reaction, the molecular weight is changed from high to low, and the melting index is changed from low to high; and extruding the resin by a double-screw extruder, bracing, cooling, granulating and drying to obtain the product. The product particles pass through a parallel A, B degassing bin, the material retention time of the degassing bin A is 45min, and the degassing temperature is set to be 65-70 ℃. And B, the material retention time of the degassing bin is 30min, the degassing temperature is set to be 55-60 ℃, and the moisture and low-boiling-point micromolecule organic matters contained in the surface layer of the particles can be brought out by hot air flow, so that the purposes of drying and reducing the smell are achieved.

Example eight:

99.4kg of polypropylene powder (MFR is 400g/10min), 0.01kg of antioxidant 1010, 0.01kg of antioxidant 168, 0.01kg of HPN-715 and 0.01kg of M1128 are mixed uniformly in a mixer, and are weighed and put into an intermediate hopper from a No. 1 weight loss scale; 0.2kg of the free radical type initiator is put into an intermediate hopper by a No. 2 weight loss scale by using di-penta-di-tert-butyl peroxide as the free radical type initiator; setting the rotating speed of the extruder to be 350 revolutions per minute, setting the total blanking speed of the weightlessness scale to be 450kg/h, setting the feeding proportion of the 1# weightlessness scale and the 2# weightlessness scale hopper to be 99.8%/0.2%, and feeding materials to the extruder through the intermediate hopper; under the action of an organic peroxide initiator, high-temperature melting and screw shearing, polypropylene generates a free radical degradation reaction, the molecular weight is changed from high to low, and the melting index is changed from low to high; and extruding the resin by a double-screw extruder, bracing, cooling, granulating and drying to obtain the product. The product particles pass through a parallel A, B degassing bin, the material retention time of the degassing bin A is 45min, and the degassing temperature is set to be 65-70 ℃. And B, the material retention time of the degassing bin is 30min, the degassing temperature is set to be 55-60 ℃, and the moisture and low-boiling-point micromolecule organic matters contained in the surface layer of the particles can be brought out by hot air flow, so that the purposes of drying and reducing the smell are achieved.

Comparative example one:

mixing 92.48kg of polypropylene powder (MFR is 10g/10min), 0.01kg of antioxidant 1010 and 0.01kg of antioxidant 168 uniformly in a mixer, and weighing from a No. 1 weight loss scale and putting into an intermediate hopper; 7.5kg of the free radical type initiator is weighed by 2# weight loss and put into an intermediate hopper by using di-penta-di-tert-butyl peroxide as the free radical type initiator; setting the rotating speed of the extruder to be 350 revolutions per minute, setting the total blanking speed of the weightlessness scale to be 450kg/h, setting the feeding proportion of the 1# weightlessness scale and the 2# weightlessness scale hopper to be 92.5%/7.5%, and feeding materials to the extruder through the intermediate hopper; under the action of an organic peroxide initiator, high-temperature melting and screw shearing, polypropylene generates a free radical degradation reaction, the molecular weight is changed from high to low, and the melting index is changed from low to high; and extruding the resin by a double-screw extruder, drawing strips, cooling, granulating and drying to obtain the product. The product particles pass through a degassing bin A, B connected in series, the retention time of the material in the degassing bin A is 30min, and the degassing temperature is set to be 65 ℃. And the material retention time of the degassing bin B is 30min, the degassing temperature is set to be 65 ℃, and the moisture and low-boiling-point micromolecule organic matters contained in the surface layer of the particles are carried out by hot air flow, so that the aims of drying and reducing the smell are fulfilled.

TABLE 1 results of performance testing of finished products obtained in examples and comparative examples

It can be seen from table 1 that the initiator addition, PP raw resin, nucleating agent, antioxidant and degassing process parameters all have different degrees of influence on the melt index, molecular weight distribution, volatile matter, isotacticity, crystallinity and other properties of the product. The Melt Flow Rate (MFR) characterizes the fluidity of the material, the larger the melt flow rate, the better the fluidity of the material, and the melt flow rate is determined by the standard of the national standard GBT 3682-2000 determination of the mass flow rate and the volume flow rate of the thermoplastic melt. The volatile components represent the odor size of the material, the lower the volatile components indicate the smaller the odor, and the volatile components are determined by the standard of the national standard GBT 2914-2008 determination of the volatile matters (including water) of the plastic vinyl chloride homopolymerization and copolymerization resin. The isotacticity represents the structural regularity of molecular chains of the material, generally speaking, the higher the isotacticity is, the better the crystallization performance is, the isotacticity refers to the weight percentage of an isotactic polymer, and the determination method comprises the following steps: and refluxing and extracting for 6-24 h by using boiling n-heptane, and dissolving the mass percentage of the residue after the random polymer and the low molecular weight polymer are dissolved. The molecular weight distribution index is the ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn) of the material, the smaller the molecular weight distribution index, the better for a fiber grade crystalline material;

according to the indexes, for PP raw materials with different melt indexes, to reach a polypropylene material with an extremely high melt index (MFR is more than or equal to 1000g/10min), the addition amount of the initiator needs to be different, but the crystallinity of the PP resin added with the nucleating agent is greatly improved, and the crystallinity of the polypropylene resin is also increased along with the increase of the addition amount of the nucleating agent; by optimizing the operating conditions of the degassing bin, the content of volatile components can be effectively improved, the odor is reduced, and the increasingly high performance requirements of customers on the ultrahigh-flow polypropylene raw material are met.