Process for the preparation of a flame retardant lldpe with good processability

Abstract

The application discloses a preparation method of a flame-retardant LLDPE with good processability, and comprises the following steps: step (1), crushing LLDPE raw materials to obtain LLDPE raw material powder; step (2), uniformly mixing flaky magnesium hydroxide into the LLDPE raw material powder to obtain mixed raw material powder; and step (3), adding the mixed raw material powder into a double-screw extruder to perform granulation to obtain the flame-retardant LLDPE. The application can solve the problem that the existing LLDPE material has poor processability after adding inorganic flame retardants.

Description

Technical Field

[0001] This invention relates to the field of linear low-density polyethylene (LLDPE) processing technology. Specifically, it relates to a method for preparing flame-retardant LLDPE with good processing properties. Background Technology

[0002] Linear low-density polyethylene (LLDPE), as a polymer with excellent processing and performance properties, has significant application value in many fields. However, LLDPE's low ignition point poses a considerable safety hazard. Adding flame retardants during LLDPE processing is an important way to solve this problem. However, the addition of flame retardants has a significant impact on its flow properties during processing, especially the destructive effect of the addition of inorganic flame retardants. Furthermore, the poor compatibility between oleophilic LLDPE materials and hydrophilic magnesium hydroxide flame retardants inevitably leads to changes in the flow properties of LLDPE with added inorganic flame retardants during processing, which will inevitably affect the morphology and performance of the finished product. Summary of the Invention

[0003] Therefore, the technical problem to be solved by the present invention is to provide a method for preparing flame-retardant LLDPE with good processing performance, so as to solve the problem that the existing LLDPE materials have poor processing performance after the addition of inorganic flame retardants.

[0004] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0005] A method for preparing flame-retardant LLDPE with good processing properties includes the following steps:

[0006] Step (1): Crush the LLDPE raw material to obtain LLDPE raw material powder;

[0007] Step (2): Add flake magnesium hydroxide to LLDPE raw material powder and mix evenly to obtain mixed raw material powder;

[0008] Step (3): Add the mixed raw material powder into a twin-screw extruder for granulation to obtain flame-retardant LLDPE.

[0009] In the above-mentioned method for preparing flame-retardant LLDPE with good processing properties, in step (1), the degree of polymerization of the LLDPE raw material is 1000-1200, and the density is 0.91-0.93 g / cm³. 2 .

[0010] In the preparation method of the flame-retardant LLDPE with good processing performance, in step (1), the LLDPE raw material is produced by China Petroleum & Chemical Corporation Maoming Branch.

[0011] In the above-mentioned method for preparing flame-retardant LLDPE with good processing performance, in step (1), the LLDPE raw material powder is passed through an 800-mesh sieve.

[0012] In the above-mentioned method for preparing flame-retardant LLDPE with good processing performance, in step (2), the mass of flake magnesium hydroxide is 5 to 40% of the mass of LLDPE raw material powder.

[0013] In the above-mentioned method for preparing flame-retardant LLDPE with good processing performance, in step (2), the mass of flake magnesium hydroxide is 10-25% of the mass of LLDPE raw material powder.

[0014] In the above-mentioned method for preparing flame-retardant LLDPE with good processing performance, in step (3), the granulation temperature is 160-175℃ and the pressure is 10-30Pa.

[0015] In the above-mentioned method for preparing flame-retardant LLDPE with good processing performance, in step (3), the granulation temperature is 171℃ and the pressure is 24.4Pa.

[0016] The preparation method of the above-mentioned flame-retardant LLDPE with good processing properties, and the preparation method of flake magnesium hydroxide are as follows:

[0017] The preheated magnesium chloride solution was added dropwise to the preheated sodium hydroxide solution while stirring. After the addition was complete, stirring was continued and the solution was kept warm to allow for precipitation. After the reaction was complete, liquid-solid separation was performed. The separated solid was washed, dried, and pulverized to obtain flake magnesium hydroxide.

[0018] The above-mentioned method for preparing flame-retardant LLDPE with good processing properties involves the following steps: the concentration of magnesium chloride in the magnesium chloride solution is 0.75 mol / L, and PEG12000 is added to the magnesium chloride solution at a dosage of 1.1 g per mol of magnesium chloride; the concentration of sodium hydroxide solution is 1.0 mol / L; the preheating temperature of both the magnesium chloride and sodium hydroxide solutions is uniformly 30℃; the dropping rate of the magnesium chloride solution is 2 mL / min; the stirring speed is 700 rpm; the holding temperature is 30℃; during washing, the material is first washed once with water, and then twice with anhydrous ethanol; the drying temperature is 60℃; the drying time is 7 h; and the particle size of the flake magnesium hydroxide is 100–300 nm. This invention employs a homogeneous precipitation method, in which a magnesium chloride solution of a specific concentration is added dropwise to an alkaline solution of a specific concentration to induce a precipitation reaction. By adding a specific amount of PEG12000 to the magnesium chloride solution and controlling process parameters such as the dropwise addition rate, stirring speed during the precipitation reaction, and precipitation reaction temperature, magnesium hydroxide with a plate-like structure is prepared. This magnesium hydroxide has a regular structure, fine and uniform particles. The method for preparing plate-like magnesium hydroxide of this invention only requires low-temperature conditions to obtain ideal magnesium hydroxide, and the hydrothermal treatment time is short, resulting in low production costs.

[0019] The technical solution of the present invention achieves the following beneficial technical effects:

[0020] This invention adds self-made flake magnesium hydroxide as an inorganic flame retardant to LLDPE. By controlling the particle size of LLDPE and flake magnesium hydroxide, the two are mixed uniformly in a specific ratio. The temperature and pressure during the processing are also controlled to prepare flame-retardant LLDPE with uniformly dispersed magnesium hydroxide. Compared with commercially available spherical magnesium hydroxide, the self-made flake magnesium hydroxide of this invention has a regular structure, fine and uniform particles. The flame-retardant LLDPE prepared using it as a flame retardant with the processing technology of this invention not only has ideal flame retardancy but also excellent processability. Furthermore, the flake magnesium hydroxide has little impact on the processing performance of flame-retardant LLDPE. Attached Figure Description

[0021] Figure 1 Melt flow rate diagrams of LLDPE under different temperatures and pressures in embodiments of the present invention;

[0022] Figure 2a Apparent image of a segment of LLDPE in an embodiment of the present invention (169°C, 12.4 Pa);

[0023] Figure 2b Apparent image of a segment of LLDPE in an embodiment of the present invention (171°C, 16.4 Pa);

[0024] Figure 2cApparent image of a segment of LLDPE in an embodiment of the present invention (170°C, 12.4 Pa);

[0025] Figure 2d Apparent image of a segment of LLDPE in an embodiment of the present invention (171°C, 18.4 Pa);

[0026] Figure 2e Apparent image of a segment of LLDPE in an embodiment of the present invention (171°C, 12.4 Pa);

[0027] Figure 2f Apparent image of a segment of LLDPE in an embodiment of the present invention (171°C, 24.4 Pa);

[0028] Figure 2g Apparent image of a segment of LLDPE in an embodiment of the present invention (172°C, 12.4 Pa);

[0029] Figure 2h Apparent image of a segment of LLDPE in an embodiment of the present invention (171°C, 26.4 Pa);

[0030] Figure 3a The LLDPE melt flow rate after adding magnesium hydroxide groups a1 to a6 in the embodiments of the present invention;

[0031] Figure 3b In the embodiments of the present invention, the melt flow rate of LLDPE after adding magnesium hydroxide groups b1 to b6;

[0032] Figure 3c The LLDPE melt flow rate after adding magnesium hydroxide groups c1 to c6 in the embodiments of the present invention;

[0033] Figure 4a Appearance of LLDPE segments after adding 5% magnesium hydroxide in an embodiment of the present invention;

[0034] Figure 4b Appearance of LLDPE segments after adding 10% magnesium hydroxide in an embodiment of the present invention;

[0035] Figure 4c Appearance of LLDPE segments after adding 15% magnesium hydroxide in an embodiment of the present invention;

[0036] Figure 4d Appearance of LLDPE segments after adding 20% ​​magnesium hydroxide in an embodiment of the present invention;

[0037] Figure 4e Appearance of LLDPE segments after adding 25% magnesium hydroxide in an embodiment of the present invention;

[0038] Figure 4f Appearance of LLDPE segments after adding 30% magnesium hydroxide in an embodiment of the present invention;

[0039] Figure 4g Appearance of LLDPE segments after adding 35% magnesium hydroxide in an embodiment of the present invention;

[0040] Figure 4h Appearance of LLDPE segments after adding 40% magnesium hydroxide in an embodiment of the present invention;

[0041] Figure 5a Appearance of LLDPE segments after adding a1 magnesium hydroxide in an embodiment of the present invention;

[0042] Figure 5b Appearance of LLDPE segments after adding a6 magnesium hydroxide in an embodiment of the present invention;

[0043] Figure 5c Appearance of LLDPE segments after adding magnesium hydroxide (b1) in an embodiment of the present invention;

[0044] Figure 5d Appearance of LLDPE segments after adding magnesium hydroxide (b6) in an embodiment of the present invention;

[0045] Figure 5e Appearance of LLDPE segments after adding c1 magnesium hydroxide in an embodiment of the present invention;

[0046] Figure 5f Appearance of LLDPE segments after adding C6 magnesium hydroxide in an embodiment of the present invention;

[0047] Figure 6 The melt flow rates of LLDPE with magnesium hydroxide of different morphologies added in the embodiments of the present invention;

[0048] Figure 7a , Figure 7c and Figure 7e The images show the appearance of LLDPE segments with 5%, 15%, and 25% magnesium hydroxide flakes in the embodiments of the present invention, respectively.

[0049] Figure 7b , Figure 7d and Figure 7f The images show the appearance of LLDPE segments with 5%, 15%, and 25% magnesium hydroxide added in the embodiments of the present invention, respectively.

[0050] Figure 8 and Figure 9 The diagrams and schematic diagrams are respectively of the XNR-400B melt flow rate meter in the embodiments of the present invention. Detailed Implementation

[0051] 1. Preparation of magnesium hydroxide and flame-retardant LLDPE

[0052] 1.1 Preparation of Magnesium Hydroxide

[0053] In this embodiment, magnesium hydroxide was prepared using a homogeneous method. Magnesium hydroxide flame retardant was prepared by reacting sodium hydroxide with magnesium chloride hexahydrate, and then added to the LLDPE matrix material. The experimental procedure is as follows.

[0054] The specific steps for preparing magnesium hydroxide are as follows:

[0055] 1) Turn on the digital display constant temperature stirring and circulating water tank and set the temperature to the required temperature of 30℃;

[0056] 2) Take a certain amount of high-concentration magnesium chloride solution and sodium hydroxide solution and dilute them to the required concentrations, i.e., the concentration of magnesium chloride in the magnesium chloride solution is 0.75 mol / L, and add PEG12000 to the magnesium chloride solution, with 1.1 g of PEG12000 used per mol of magnesium chloride; the concentration of the sodium hydroxide solution is 1.0 mol / L.

[0057] 3) Transfer the prepared sodium hydroxide solution to a three-necked flask in a constant temperature water bath, and at the same time preheat the prepared magnesium chloride solution to 30°C;

[0058] 4) Turn on the digital display mixer and adjust it to the desired speed of 700 rpm;

[0059] 5) After keeping warm for 30 minutes, slowly add the magnesium chloride solution dropwise to the sodium hydroxide solution at a rate of 2 mL / min.

[0060] 6) After the dripping is complete, keep warm for another 30 minutes;

[0061] 7) Use a centrifuge to separate the solid and liquid, then wash the separated solid once with water and twice with anhydrous ethanol;

[0062] 8) Finally, the obtained solid precipitate was transferred to a petri dish and placed in an electric heating drying oven to dry at 60°C for 7 hours to obtain magnesium hydroxide powder. The particle size of the flake magnesium hydroxide was 100-300 nm.

[0063] 1.2 Preparation of Flame-Retardant LLDPE

[0064] The preparation method of flame-retardant LLDPE includes the following steps:

[0065] Step (1): Crush the LLDPE raw material to obtain LLDPE raw material powder; the degree of polymerization of the LLDPE raw material is 1000-1200, and the density is 0.91-0.93 g / cm³. 2 The LLDPE raw material was produced by China Petroleum & Chemical Corporation Maoming Branch; the LLDPE raw material powder passed through an 800-mesh sieve.

[0066] Step (2): Add the flake magnesium hydroxide prepared in this embodiment to the LLDPE raw material powder and mix evenly to obtain a mixed raw material powder;

[0067] Step (3): Add the mixed raw material powder into a twin-screw extruder for granulation to obtain flame-retardant LLDPE.

[0068] 2. Characterization of magnesium hydroxide

[0069] The morphology of magnesium hydroxide prepared in this example and commercially available magnesium hydroxide was observed using SEM. Since it was a powder, it was first diluted in ethanol, then dried and prepared into slides for observation.

[0070] 3. Flow performance testing

[0071] Melt flow rate refers to the mass or volume of melt passing through a standard die per 10 minutes under a certain temperature and load, and it best characterizes the flow properties of polymer materials. This example investigates the effect of magnesium hydroxide addition on the flow properties of LLDPE by examining its melt flow rate and finished product morphology. An XNR-400B melt flow rate meter was used (see simplified diagram). Figure 8 (As shown) The flow properties of the matrix material were tested. The specific testing procedure is as follows:

[0072] 1) First, weigh and package the prepared flame-retardant LLDPE samples in plastic sealed bags, 4g per bag, to facilitate the smooth conduct of the test;

[0073] 2) Adjust the equipment level, install the die, scraper, and prepare supplies;

[0074] 3) Turn on the machine, set the parameters, adjust to the required temperature, and wait for the instrument to heat up to the required temperature. After maintaining the temperature for 15 minutes, quickly add the weighed sample into the barrel (Note: It is best to complete this within 20 seconds).

[0075] 4) After keeping it warm for about 5 minutes, perform a pre-cut. Observe the outflowing sample and measure it after confirming that there are no air bubbles.

[0076] 5) Data collection is based on the formula MRF(θ,m) nom )=t ref Calculations are performed using *m / t to arrive at the conclusion; in the formula, MRF(θ,m) nom ) — Melt flow rate, g / 600s; θ — Test temperature, in °C; m nom —Nominal load, in kg; t ref —Reference time, in seconds (600 seconds); m—Average mass of the cut, in grams; t—Time interval between cuts, in seconds.

[0077] 4. Selection of optimal flow properties for LLDPE

[0078] Temperature and pressure are the main influencing factors for the melt flow rate of thermoplastic polymers. This is primarily because the main polymer material consists of very long polymer chains, and processing is mainly carried out in the viscous flow state of the polymer material. During processing in the viscous flow state, the polymer chains within the polymer material form a network structure that is entangled together. Through intermolecular forces or geometric phase junctions, under certain temperature and pressure conditions, this entangled network structure disintegrates, causing relative displacement of the polymer chain structure from the chain ends, resulting in flow and product formation. For LLDPE, which is widely used in the market, different synthesis methods produce LLDPE with different polymer chain segment structures and degrees of polymerization. Therefore, it is necessary to investigate the melt flow rate of LLDPE without the addition of any magnesium hydroxide flame retardant from the perspective of temperature and pressure.

[0079] like Figure 1 As shown, the melt flow rate of LLDPE was measured under constant temperature and constant pressure. By comparing the melt flow rates under different combinations of temperature and pressure, the results were obtained. Figure 1 ) and the appearance morphology of LLDPE cut ( Figures 2a to 2h To determine the most suitable temperature and pressure.

[0080] like Figure 1 As shown, under the same pressure, when a certain temperature is reached, the melt flow rate increases with increasing temperature. This is because when the temperature reaches the minimum processing temperature of LLDPE, the polymer chain segments inside the LLDPE begin to move, causing the entire melt to be in a flowing state. As the temperature continues to rise, the bonding performance between polymer molecular chains gradually weakens, and the distance between adjacent molecules increases with the temperature. The intermolecular forces also decrease accordingly, thus improving the melt's fluidity. Under a certain pressure, the mass of LLDPE flowing out of the die in the same amount of time continuously increases, leading to an increase in the melt flow rate. Higher temperatures result in better melt fluidity, but this does not necessarily mean better processing performance, because when the temperature reaches a certain high level, the LLDPE being in a fluid state is not conducive to molding.

[0081] Also in Figure 1As can be seen, at the same temperature, the melt flow rate increases with increasing pressure. This is because regardless of the processing technology used to prepare LLDPE products, the final LLDPE material contains varying degrees of gaps between molecules and molecular chains, referred to as free volumes. When LLDPE is in a viscous flow state, these free volumes give the molecules significant compressibility, thus becoming a significant factor affecting processing performance during molding. When LLDPE is in a viscous flow state, these highly compressible gaps gradually decrease with increasing pressure during processing, improving the melt flow properties of LLDPE. The mass of LLDPE flowing from the die within the same time frame at a given temperature continuously increases, leading to an increase in the melt flow rate. Higher pressure results in better melt flowability, but this does not necessarily mean better processing performance. When the pressure reaches a certain level, the molecular chain segments of LLDPE move too fast, and the melt tends to accumulate, producing large pores. This makes it difficult to obtain uniform film products. Furthermore, excessive pressure also places excessive demands on the equipment, which is counterproductive.

[0082] refer to Figures 2a to 2h The appearance of LLDPE segments is easily observed; significant differences exist under different pressures and temperatures. Comparing the four segments in the first column, taken at the same pressure but different temperatures, it's clear that as temperature increases, the aspect ratio and surface smoothness of the segments continuously increase. However, faster melt flow results in a noticeable increase in air bubbles. Segments taken at 171℃ have relatively fewer air bubbles and a relatively consistent aspect ratio; therefore, 171℃ is considered a suitable temperature. Comparing the four segments in the second column, taken at the same temperature but different pressures, it's evident that as pressure increases, the aspect ratio and surface smoothness of the segments also continuously increase. However, faster melt flow again results in a noticeable increase in air bubbles.

[0083] exist Figure 1 , Figures 2a to 2h Based on this, and considering the compatibility between magnesium hydroxide and LLDPE, a process condition with a temperature of 171℃ and a pressure of 24.4Pa was selected, which has a relatively fast melt flow rate, a relatively smooth surface, and a certain amount of bubble porosity.

[0084] 5. Effect of magnesium hydroxide addition on the flow properties of LLDPE

[0085] 5.1 Effect of adding flake magnesium hydroxide on the flow properties of LLDPE

[0086] As previously analyzed, under conditions of 171℃ and 24.4Pa, the melt flow rate of LLDPE is 8.1 g / 10 min. The surface smoothness and bubble count of the cut segments are relatively good. Under these conditions, flake magnesium hydroxide was added, and the flow properties of LLDPE were measured. Figures 3a to 3c Meanwhile, observe the appearance of the segments after their addition. Figures 4a to 4h .

[0087] Figures 3a to 3c Overall, it can be seen that with the addition of flake magnesium hydroxide, the melt flow rate of LLDPE decreases continuously with the increase of its content, which means that its flow performance gradually deteriorates. However, in terms of the entire change process, the relationship between the increase of magnesium hydroxide content and the decrease of melt flow rate is not a simple linear one. As can be seen from the figure, when the magnesium hydroxide content increases from about 5% to about 30%, the decrease in melt flow rate is very rapid, from about 8 g / 10 min to about 3 g / 10 min. When the magnesium hydroxide content increases from about 30% to about 50%, the decrease in melt flow rate is relatively gradual, from about 3 g / 10 min to about 2 g / 10 min. The relationship between the two is obviously non-linear. When the content of magnesium hydroxide is less than 30%, its increase has a significant impact on the chain segment movement between LLDPE molecules. This is because under the process conditions of 171℃ and 24.4Pa, magnesium hydroxide is almost still in solid form, but this does not prevent it from absorbing heat. This leads to a reduction in the heat received by the surrounding LLDPE, and the movement of the molecular chain ends is hindered. On the other hand, the addition of magnesium hydroxide also occupies a certain amount of space, so the space for the free-moving molecular chain segments of LLDPE is relatively less. Under the combined influence of these two factors, the melt flow rate of LLDPE will be significantly reduced. When the magnesium hydroxide content exceeds 30%, its influence on the chain segment movement between LLDPE molecules weakens with increasing content. This is because, with further increases in magnesium hydroxide content, the agglomeration effect of magnesium hydroxide becomes more pronounced under process conditions of 171℃ and 24.4Pa, reducing its effective heat absorption rate. The tighter intermolecular bonds prevent the heat and space available for LLDPE chain segment movement from increasing rapidly with increasing content. This slows down the decrease in LLDPE melt rate to some extent. This trend aligns with the exponential law proposed by Ostwald and Dewade, which states that the flow properties of plastic materials are non-linearly related to the amount of flame retardant added.

[0088] Figure 3a , Figure 3b , Figure 3c It can be seen that although both are flake-shaped magnesium hydroxide, the effects on the melt flow rate of LLDPE are different when the same amount is added. Figure 3a , Figure 3b It can be seen that the melt flow rate of LLDPE with the addition of the a3 group of flake-shaped magnesium hydroxide flame retardants is slightly better than that of the other groups. The a3 group of flake-shaped magnesium hydroxide has a relatively small and regular shape with clear boundaries. When added to the LLDPE matrix material, it is less likely to agglomerate and is easily dispersed within the matrix material. Under the same processing conditions, its resistance to the movement of polymer chain ends in the melt is relatively balanced, resulting in a relatively balanced space for movement throughout the melt. There is no significant polar hindrance, making the overall flowability of the system more uniform, and its impact on the melt flow index is relatively small. Therefore, the melt flow index of LLDPE with the addition of a3 group of magnesium hydroxide is relatively higher. Figure 3c Since the added C4 group of flake magnesium hydroxide is better than the a3 group of flake magnesium hydroxide in terms of both regularity and boundary, its effect on the melt flow rate of LLDPE is smaller.

[0089] All three sets of figures show that as the regularity and boundaries of the flake magnesium hydroxide become more blurred, its impact on the melt flow index of LLDPE becomes greater.

[0090] Figures 4a to 4h This is an appearance diagram of LLDPE segments with added a1-type flake magnesium hydroxide. As can be seen from the figure, the appearance of LLDPE changes significantly with the increase of magnesium hydroxide content. As the magnesium hydroxide content increases, the cut LLDPE gradually changes from transparent to milky white, and the surface smoothness gradually deteriorates. When the content reaches 40%, protrusions on the cut surface are visible to the naked eye. However, while the internal air bubbles appear to be gradually decreasing as seen in the image, this is not the case. When the magnesium hydroxide content is below 30%, the air bubble does decrease to some extent with increasing magnesium hydroxide content. This is because LLDPE without added magnesium hydroxide already has a certain amount of air bubbles under the selected process conditions. As the magnesium hydroxide content increases, the air bubbles are gradually filled by magnesium hydroxide, as magnesium hydroxide acts as both a flame retardant and a filler. When the magnesium hydroxide content is greater than 30%, the agglomeration effect becomes significant, and the gaps between molecules continuously increase, leading to a gradual increase in air bubbles, although this is not visible on the surface. This is due to the matrix tending towards a milky white color, and its transformation trend is similar to... Figures 3a to 3cThis is consistent with the observation that when the magnesium hydroxide content is less than or equal to 20%, the melt flow rate changes significantly, and the morphology of the cut also changes significantly. When the magnesium hydroxide content is between 20% and 40%, the melt flow rate changes less, and the morphology of the cut segment also changes relatively little.

[0091] Figures 5a to 5f Figure 4 shows the appearance of LLDPE segments with 20% different flake-shaped magnesium hydroxide. A1, A6, B1, B6, C1, and C6 represent the types of magnesium hydroxide added. As can be seen from Figure 4, although the morphology of the added magnesium hydroxide varies slightly, the LLDPE segments at the same addition amount are generally similar. This is because although the flake structure of the added magnesium hydroxide differs, at the same addition amount, their resistance to the molecular chain movement of the polymer in the melt is roughly the same. Therefore, even though the flakes differ, the movement trend in each melt is generally the same, and there is no significant difference in resistance. This makes the overall fluidity of each melt system relatively similar, and thus the impact on the melt flow index is relatively similar, resulting in a generally similar appearance of the segments. However, there are still differences. Comparing groups A1 and C6, the aspect ratio of the segments is noticeably different; the former has a slightly larger aspect ratio than the latter. This is related to… Figures 3a to 3c The difference in melt flow rate between a1 and c6 corresponds to the difference in melt flow rate, which shows that the morphology of the flame retardant magnesium hydroxide has a certain influence on the melt flow rate of LLDPE.

[0092] Therefore, as the content of magnesium hydroxide in the flame retardant increases, its flame retardant performance inevitably improves. However, the experiments above show that its melt flow properties gradually decrease, and the surface morphology of the LLDPE segments also undergoes significant changes. This has a considerable impact on the processing and molding of the original matrix and necessitates new changes to the product's process conditions. Therefore, while improving its flame retardant performance, the amount of magnesium hydroxide added should not be too large to ensure its original melt flowability.

[0093] 5.2 Effect of the amount of magnesium hydroxide with different morphologies on the properties of LLDPE

[0094] Spherical magnesium hydroxide is also a widely used flame retardant. LLDPE with the same morphology but different sizes will have different melt flow rates. This example uses self-prepared B4 type flake magnesium hydroxide, with a particle size similar to commercially available spherical magnesium hydroxide, for comparison. Figure 6The effect of adding magnesium hydroxide sample b4 (“flake” in the figure) and globular-flower-like magnesium hydroxide (“globular-flower-like” in the figure) on the melt rheological properties of LLDPE is shown. Figures 7a to 7f The appearance morphology of LLDPE segments.

[0095] like Figure 6 Overall, it can be seen that the melt flow rate of LLDPE decreases continuously with the increase of its content, whether in flake or spherical form, indicating a gradual deterioration in its flow properties. Similarly, the relationship between the amount of spherical magnesium hydroxide added and the melt flow rate of LLDPE is not a simple linear one. However, as shown in the figure, when the magnesium hydroxide content is around 25%, the flow rates of both types on the LLDPE matrix are roughly the same. But when the magnesium hydroxide content is below 25%, the flow rate of flake magnesium hydroxide on the LLDPE matrix is ​​relatively lower, while when the addition amount is greater than 25%, the flow rate of spherical magnesium hydroxide on the LLDPE matrix is ​​relatively lower. The main reason is that under these process conditions, the agglomeration degree of globular magnesium hydroxide is higher than that of flake magnesium hydroxide. When its addition amount is less than 25%, with the increase of the addition amount, due to the higher agglomeration degree of globular magnesium hydroxide, the movement of the molecular chain ends of the polymer material becomes more uneven, and the resistance to melt flow is greater. At this time, its main role is the force of molecular chain end movement. As the magnesium hydroxide content increases, the decrease in melt flow rate will inevitably become more obvious. However, when the content is greater than 25%, although the agglomeration degree of globular magnesium hydroxide is higher, its contact area with the molecular chain ends of LLDPE is larger than that of flake magnesium hydroxide. That is, the gap for free movement of molecular chain ends is relatively large, and its fluidity is better. At this time, the volume of free radicals moving at the molecular chain ends plays a major role. Therefore, the effect of globular magnesium hydroxide on the flow rate of LLDPE matrix is ​​small.

[0096] like Figure 7a , Figure 7c and Figure 7e The samples were cut from LLDPE containing 5%, 15%, and 25% flake magnesium hydroxide, respectively. Figure 7b , Figure 7d and Figure 7fThe figures represent cuts of LLDPE containing 5%, 15%, and 25% granulated magnesium hydroxide, respectively. As can be seen from the figures, when the same type of granulated magnesium hydroxide was added to the LLDPE cuts, the appearance of the cuts changed significantly with increasing magnesium hydroxide content. The trend was similar to that of LLDPE cuts containing flake magnesium hydroxide, only the degree of change differed slightly. More noticeably, when the addition amount was less than 25%, the LLDPE cuts with the same amount of granulated magnesium hydroxide were not as smooth as those with flake magnesium hydroxide, and their transparency was also somewhat inferior. When the addition amount was greater than 25%, the LLDPE cuts with the same amount of granulated magnesium hydroxide had a smoother appearance than those with flake magnesium hydroxide, and the milky white gradient was slower. This is related to… Figure 6 The melt flow rates of the obtained LLDPE with different morphologies and dosages were consistent.

[0097] The effect of both flake and bulbous magnesium hydroxide on the melt flow rate of LLDPE gradually increases with the increase of its addition amount. However, when the addition amount is less than 25%, the effect of bulbous magnesium hydroxide is greater, but when the addition amount is greater than 25%, the effect of flake magnesium hydroxide on the melt flow rate of LLDPE is greater.

[0098] The results of this embodiment indicate that:

[0099] 1) The melt flow rate of LLDPE is different under different pressures and temperatures, and the melt flow rate of LLDPE also increases with the increase of temperature and pressure. However, the bubble pores at the cut ends also change with the increase of temperature and pressure. The results show that a higher melt flow rate does not necessarily mean better material processing and molding performance. The cut ends obtained at a temperature of 171℃ and a pressure of 18.4Pa are relatively good. However, in subsequent experiments, it was found that the addition of flame retardant inevitably affects the melt flowability. Therefore, the process parameters of 171℃ and 24.4Pa were selected in subsequent experiments.

[0100] 2) When the flake magnesium hydroxide prepared in this embodiment is added, its morphology and amount have different effects on the melt flow rate of LLDPE. The main effect is on the amount added. As the amount of flake magnesium hydroxide added increases, the melt flow rate of LLDPE gradually decreases. The degree of influence varies greatly when the amount added is less than 20%, and the trend of influence weakens significantly after reaching 20%. The regularity of the flakes also has a certain influence. The more regular the flakes are, the smaller the influence on the melt flow rate of LLDPE.

[0101] 3) Magnesium hydroxide with different morphologies has different effects on the melt flow rate of LLDPE. Compared with spherical magnesium hydroxide, although both spherical and flake magnesium hydroxide gradually decrease the melt flow rate of LLDPE with increasing addition, the degree of influence is different. When the addition amount is less than 25%, spherical magnesium hydroxide has a greater influence, but when the addition amount is greater than 25%, flake magnesium hydroxide has a greater influence on the melt flow rate of LLDPE.

[0102] In addition to the melt flow rate and viscosity of LLDPE, this embodiment also comprehensively considered the flame retardancy of LLDPE after adding magnesium hydroxide. The results showed that when the addition amount was 25%, the flame retardant effect of LLDPE with the flake magnesium hydroxide prepared in this embodiment reached a relatively ideal state, and was superior to that with commercially available flower-shaped magnesium hydroxide. Therefore, the amount of flake magnesium hydroxide prepared in this embodiment was controlled within the range of less than or equal to 25%. Compared with commercially available flower-shaped magnesium hydroxide, adding the flake magnesium hydroxide prepared in this embodiment as a flame retardant to LLDPE allows magnesium hydroxide to achieve an ideal flame retardant effect with a smaller dosage, and can effectively reduce the impact of the addition of flame retardant on the processing and molding properties of LLDPE.

Claims

1. A method for preparing flame-retardant LLDPE with good processing properties, characterized in that, Includes the following steps: Step (1): Crush the LLDPE raw material to obtain LLDPE raw material powder; Step (2): Add flake magnesium hydroxide to LLDPE raw material powder and mix evenly to obtain mixed raw material powder; Step (3): Add the mixed raw material powder into a twin-screw extruder for granulation to obtain flame-retardant LLDPE; In step (2), the mass of the flake magnesium hydroxide is 5-40% of the mass of the LLDPE raw material powder; The preparation method of flake magnesium hydroxide is as follows: The preheated magnesium chloride solution was added dropwise to the preheated sodium hydroxide solution while stirring. After the addition was complete, stirring was continued and the solution was kept warm to carry out the precipitation reaction. After the reaction was completed, liquid-solid separation was performed. The separated solid was washed, dried and pulverized to obtain flake magnesium hydroxide. The magnesium chloride solution contained 0.75 mol / L magnesium chloride and PEG12000 was added to it at a dosage of 1.1 g per mol of magnesium chloride. The sodium hydroxide solution contained 1.0 mol / L sodium hydroxide. The preheating temperature for both the magnesium chloride and sodium hydroxide solutions was 30℃. The dropping rate of the magnesium chloride solution was 2 mL / min. The stirring speed was 700 rpm, and the holding temperature was 30℃. During washing, the solution was first washed with water and then twice with anhydrous ethanol. The drying temperature was 60℃, and the drying time was 7 h. The particle size of the flake magnesium hydroxide was 100–300 nm.

2. The method for preparing flame-retardant LLDPE with good processing properties according to claim 1, characterized in that, In step (1), the degree of polymerization of the LLDPE raw material is 1000–1200, and the density is 0.91–0.93 g / cm³. 2 .

3. The method for preparing flame-retardant LLDPE with good processing properties according to claim 1, characterized in that, In step (1), the LLDPE raw material powder is passed through an 800-mesh sieve.

4. The method for preparing flame-retardant LLDPE with good processing properties according to claim 1, characterized in that, In step (2), the mass of the flake magnesium hydroxide is 10-25% of the mass of the LLDPE raw material powder.

5. The method for preparing flame-retardant LLDPE with good processing properties according to claim 1, characterized in that, In step (3), the temperature is 160-175℃ and the pressure is 10-30Pa.

6. The method for preparing flame-retardant LLDPE with good processing properties according to claim 5, characterized in that, In step (3), the temperature is 171℃ and the pressure is 24.4Pa.

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