A method for preparing flake magnesium hydroxide to improve the processing properties of LLDPE

Abstract

This invention discloses a method for preparing flake magnesium hydroxide to improve the processing performance of LLDPE, comprising the following steps: Step (1) preparing a magnesium chloride solution and an alkaline solution; Step (2) preheating the magnesium chloride solution and the alkaline solution respectively; Step (3) adding the preheated magnesium chloride solution dropwise to the preheated alkaline solution while stirring; Step (4) continuing to stir and keep warm after the dropwise addition to carry out a precipitation reaction, and separating the solid and liquid using a centrifuge after the reaction is completed; Step (5) washing and drying the separated solid to obtain flake magnesium hydroxide that improves the processing performance of LLDPE. This invention can solve the problem that the existing magnesium hydroxide is added to LLDPE as a flame retardant with excessive filler content, which affects its processing and molding performance.

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 flake magnesium hydroxide to improve the processing performance of LLDPE. Background Technology

[0002] Among the many polymer materials, linear low-density polyethylene (LLDPE), which was industrially produced by Union Carbide in the 1970s, quickly penetrated the traditional low-density polyethylene (LDPE) market due to its excellent processing and use performance and low cost. It also rapidly replaced LDPE in many fields, becoming the main material for processing films, molding, pipes, and wires and cables.

[0003] However, both traditional polyethylene materials and the later, higher-performance linear low-density polyethylene have a fatal flaw: a low ignition point. This greatly limits their application range and poses significant safety hazards during normal use. Therefore, flame retardants are typically added to achieve better flame-retardant effects. Consequently, research on flame retardants has developed rapidly, evolving from the initial halogen-based systems to phosphorus-based, intumescent, inorganic, and synergistic flame retardant systems in a short period.

[0004] Magnesium hydroxide (MH) stands out due to its excellent properties such as flame retardancy, smoke suppression, acid resistance, filler compatibility, non-toxicity, and good thermal stability, and has been widely used in LLDPE materials, becoming a new generation of green and environmentally friendly inorganic flame retardants. However, as an environmentally friendly halogen-free flame retardant, magnesium hydroxide has a high filler content and poor compatibility with polymer materials. Therefore, it is essential to prepare a magnesium hydroxide that can improve flame retardancy while minimizing its impact on the molding performance of LLDPE. Summary of the Invention

[0005] Therefore, the technical problem to be solved by the present invention is to provide a method for preparing flake magnesium hydroxide to improve the processing performance of LLDPE, so as to solve the problem that the existing magnesium hydroxide is added to LLDPE as a flame retardant with excessive filling amount and affects its processing and molding performance.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0007] A method for preparing flake magnesium hydroxide to improve the processing properties of LLDPE includes the following steps:

[0008] Step (1): Prepare magnesium chloride solution and alkaline solution;

[0009] Step (2): Preheat the magnesium chloride solution and the alkaline solution separately;

[0010] Step (3): Add preheated magnesium chloride solution dropwise to the preheated alkaline solution while stirring;

[0011] Step (4): After the addition is complete, continue stirring and keep warm to carry out the precipitation reaction. After the reaction is complete, use a centrifuge to separate the solid and liquid.

[0012] Step (5): Wash and dry the separated solids to obtain flake magnesium hydroxide that improves the processing performance of LLDPE.

[0013] In the above-mentioned method for preparing flake magnesium hydroxide to improve the processing performance of LLDPE, in step (1), the alkaline solution is a sodium hydroxide solution; when preparing the magnesium chloride solution, PEG12000 is added and dispersed evenly.

[0014] In the above-mentioned method for preparing flake magnesium hydroxide to improve the processing performance of LLDPE, in step (1), the concentration of magnesium chloride in the magnesium chloride solution is 0.25-1.5 mol / L, and the amount of PEG12000 used per mol of magnesium chloride is 1.0-1.2 g; the concentration of sodium hydroxide solution is 0.25-1.5 mol / L.

[0015] In the above-mentioned method for preparing flake magnesium hydroxide to improve the processing performance of LLDPE, in step (1), the concentration of magnesium chloride in the magnesium chloride solution is 0.75 mol / L, and the amount of PEG12000 used per 1 mol of magnesium chloride is 1.1 g; the concentration of sodium hydroxide solution is 1.0 mol / L.

[0016] The above-mentioned method for preparing flake magnesium hydroxide to improve the processing performance of LLDPE is characterized in that, in step (2), both the magnesium chloride solution and the alkaline solution are preheated to 30-35°C.

[0017] In the above method for preparing flake magnesium hydroxide to improve the processing performance of LLDPE, in step (3), the dropping speed is 1-2 mL / min, the stirring speed is 500-800 rpm, and the temperature is maintained at 30-35℃ in a constant temperature water bath during dropping.

[0018] In the above method for preparing flake magnesium hydroxide to improve the processing performance of LLDPE, in step (3), the dropping speed is 2 mL / min, the stirring speed is 700 rpm, and the temperature is maintained at 30℃ in a constant temperature water bath during dropping.

[0019] In the above method for preparing flake magnesium hydroxide to improve the processing performance of LLDPE, in step (4), the stirring speed is 500-800 rpm; the holding temperature is 30-35℃; and the holding time is 30-40 min.

[0020] In the above-mentioned method for preparing flake magnesium hydroxide to improve the processing performance of LLDPE, the washing method in step (5) is as follows: first wash with water once, then wash twice with anhydrous ethanol; the drying temperature is 55-65℃, and the drying time is 6-8h.

[0021] In the above-mentioned method for preparing flake magnesium hydroxide to improve the processing performance of LLDPE, in step (1), the alkaline solution is a sodium hydroxide solution with a concentration of 1.0 mol / L, the magnesium chloride solution has a magnesium chloride concentration of 0.75 mol / L, and the amount of PEG12000 used per 1 mol of magnesium chloride is 1.1 g.

[0022] In step (2), both the magnesium chloride solution and the alkaline solution are preheated to 30°C.

[0023] In step (3), the dropping rate is 2 mL / min, the stirring speed is 700 rpm, and the temperature is maintained at 30℃ in a constant temperature water bath during the dropping process.

[0024] In step (4), the stirring speed is 700 rpm; the holding temperature is 30℃ and the holding time is 30 min.

[0025] In step (5), the washing method is as follows: first wash with water once, then wash twice with anhydrous ethanol; the drying temperature is 60℃ and the drying time is 7h.

[0026] The technical solution of the present invention achieves the following beneficial technical effects:

[0027] 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. Magnesium hydroxide with a lamellar structure is prepared 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 temperature. This magnesium hydroxide has a regular structure, fine and uniform particles. The method for preparing the lamellar 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. Compared with commercially available flower-shaped magnesium hydroxide, adding the lamellar magnesium hydroxide prepared by this invention as a flame retardant to LLDPE allows for flame retardant effects with a small dosage, and effectively reduces the impact of flame retardant addition on the processing and molding properties of LLDPE. Attached Figure Description

[0028] Figure 1 X-ray diffraction pattern of magnesium hydroxide prepared in the embodiments of the present invention;

[0029] Figure 2a Microscopic morphology of magnesium hydroxide in group A3 of this invention;

[0030] Figure 2b Microscopic morphology of magnesium hydroxide in group A1 of the present invention;

[0031] Figure 2c Microscopic morphology of magnesium hydroxide in group B2 of this invention;

[0032] Figure 2d Microscopic morphology of magnesium hydroxide in group B4 of this invention;

[0033] Figure 2e Microscopic morphology of magnesium hydroxide in group C5 in this embodiment of the invention;

[0034] Figure 2f Microscopic morphology of magnesium hydroxide in group C6 in this embodiment of the invention;

[0035] Figures 3a1 to 3a6 SEM images of magnesium hydroxide in groups A1-A6 of this invention;

[0036] Figures 3b1 to 3b6 SEM images of magnesium hydroxide in groups B1-B6 of this invention;

[0037] Figures 3c1 to 3c6 SEM images of magnesium hydroxide in groups C1-C6 of this invention;

[0038] Figure 4a The flow properties of LLDPE with added magnesium hydroxide (groups A1-A6) in the embodiments of the present invention;

[0039] Figure 4b The flow properties of LLDPE with added magnesium hydroxide (groups B1-B6) in the embodiments of the present invention;

[0040] Figure 4c The flow properties of LLDPE with added C1-C6 group magnesium hydroxide in the embodiments of the present invention;

[0041] Figure 5a Appearance of LLDPE segments with 30% A1 group magnesium hydroxide added in an embodiment of the present invention;

[0042] Figure 5b Appearance of LLDPE segments with 30% A6 group magnesium hydroxide added in an embodiment of the present invention;

[0043] Figure 5c Appearance of LLDPE segments with 30% B1 group magnesium hydroxide added in an embodiment of the present invention;

[0044] Figure 5d Appearance of LLDPE segments with 30% B6 group magnesium hydroxide added in an embodiment of the present invention;

[0045] Figure 5eAppearance of LLDPE segments with 30% C1 group magnesium hydroxide added in this embodiment of the invention;

[0046] Figure 5f Appearance of LLDPE segments with 30% C6 magnesium hydroxide added in this embodiment of the invention; Figure 6 The addition of magnesium hydroxide group B4 and flower-shaped magnesium hydroxide in the embodiments of the present invention affects the rheological properties of LLDPE melt;

[0047] Figure 7a , Figure 7c and Figure 7e The images show the cut appearance of LLDPE with added 5%, 15%, and 25% flake magnesium hydroxide, respectively.

[0048] Figure 7b ,and Figure 7d and Figure 7f The images show the cut appearance of LLDPE with added 5%, 15%, and 25% flower-shaped magnesium hydroxide, respectively.

[0049] Figure 8 The effect of adding magnesium hydroxide in group B4 and spherical magnesium hydroxide on the melt viscosity of LLDPE in the embodiments of the present invention. Detailed Implementation

[0050] 1. Preparation of magnesium hydroxide powder

[0051] This embodiment uses a homogeneous method to prepare magnesium hydroxide. Flame retardant magnesium hydroxide is prepared by reacting sodium hydroxide (Tianjin Beilian Fine Chemicals Development Co., Ltd., analytical grade) with magnesium chloride hexahydrate (Tianjin Beilian Fine Chemicals Development Co., Ltd., analytical grade). The magnesium hydroxide powders prepared under different conditions are numbered as shown in Tables 1 and 2. Due to factors such as conditions, magnesium hydroxide is further divided into three groups according to the process conditions, denoted as Group A, Group B, and Group C.

[0052] Table 1. Numbering of magnesium hydroxide samples prepared at different concentrations

[0053]

[0054] Table 2. Numbering of magnesium hydroxide powder prepared by different dropping methods

[0055]

[0056] The matrix material LLDPE used in this embodiment is produced by China Petrochemical Corporation Guangzhou Branch, and the magnesium hydroxide purchased is produced by Tianjin Fuchen Chemical Reagent Factory.

[0057] 2. Evaluation Test Methods for Magnesium Hydroxide

[0058] The phase composition of the product was determined using a D / MAX-2500 / PC XRD, and the morphology of the magnesium hydroxide product was determined using a Zeiss JME-2010 atomic absorption spectrometer. The morphology of the self-made and purchased magnesium hydroxide was observed using a TESCAN Mira3 LMH scanning electron microscope (SEM). The melt flow rate of the matrix material was tested using an XNR-400B melt flow rate meter, and the rheological properties of the material were tested using an XLY-II rheometer.

[0059] 3. Experimental Results and Analysis

[0060] 3.1 XRD analysis of magnesium hydroxide

[0061] Figure 1 Table 3 shows the X-ray diffraction patterns of magnesium hydroxide samples A1 and B1, and compares the X-ray diffraction values ​​of magnesium hydroxide with the standard values. The data comparison in Table 3 shows that the eight strong peaks of each sample correspond perfectly with the standard card for magnesium hydroxide. The table also shows that the interplanar spacing d and relative intensity I of the product maintain a high degree of similarity to the standard values, indicating that the powder prepared in the experiment is indeed magnesium hydroxide.

[0062] Table 3 Comparison of X-ray diffraction values ​​of reaction products with JCDPS card standard values

[0063]

[0064] 3.2 Morphological analysis of magnesium hydroxide

[0065] from Figures 2a to 2f It can be seen that the magnesium hydroxide produced under different process conditions is mostly in the form of flakes, but the shape, size, and agglomeration vary due to different reaction conditions. Figure 2a and Figure 2b The images show the shapes of the products at different magnesium chloride concentrations. It can be seen that as the magnesium chloride concentration increases, the area of ​​the flakes increases, and the aggregation phenomenon intensifies. Figure 2a For sample A3, it can be seen that the size of the flakes is about 5um × 10um, and there are even smaller ones, but they are dispersed very uniformly. Figure 2b Corresponding to sample A1, it can be seen that they are all aggregated together. Figure 2c Corresponding to sample B2, it can be seen that its sheet-like dimensions are approximately 5µm × 5µm, showing a trend towards becoming more spherical. Figure 2d The figure corresponds to sample B4, and it can be seen that it is quite consistent with A1 in all aspects. Figure 2e and Figure 2f The figures correspond to samples C5 and C6. It can be seen that the size of the flakes in both samples is less than 1 μm × 1 μm, the boundaries are relatively blurred, and the aggregation is quite severe.

[0066] Figures 3a1 to 3c6 These are SEM images of magnesium hydroxide samples prepared using different processes. Figures 3a1-3a6 Corresponding to samples A1-A6, the morphology of the samples in the figure shows that the concentration of magnesium chloride has a significant impact on the morphology of magnesium hydroxide. As can be seen from the figure, although the generated magnesium hydroxide largely exhibits irregular agglomerates of varying degrees when the magnesium chloride concentration is different, the morphology of the reaction product varies greatly due to the different concentrations of the main reactant, sodium hydroxide. The degree of agglomeration of the product also varies considerably, ultimately leading to differences in the regularity of the morphology. Figure 3a3 It can be seen that when the concentration of magnesium chloride is 0.75 mol / L, the flakes of magnesium hydroxide are very clear, the boundaries are also very clear, the morphology is to a certain extent regular, and the flakes are also very uniform. Figures 3b1 to 3b6 Corresponding to samples B1-B6. As shown in the figure, the concentration of sodium hydroxide significantly affects the degree of aggregation of the product magnesium hydroxide, and also results in considerable differences in the regularity of its morphology. When the concentration of sodium hydroxide is 1 mol / L, the flakes of magnesium hydroxide are relatively obvious and uniform, with relatively clear boundaries, and the morphology is relatively regular to a certain extent. Figure 3b4 As shown.

[0067] The magnesium chloride solution concentration was 0.75 mol / L (PEG12000 dispersant was added to the magnesium chloride solution, with 1.1 g of PEG12000 used per mol of magnesium chloride), the sodium hydroxide solution concentration was 1 mol / L, the stirring speed was 700 rpm, the precipitation time was 30 min, and the temperature was maintained at 30℃ in a constant temperature water bath. The washing method consisted of a first water wash, followed by two washes with anhydrous ethanol, and drying in a hot air drying oven at 60℃ for 7 hours. The morphology of the magnesium hydroxide prepared by groups C1-C6 is as follows. Figures 3c1 to 3c6 As shown.

[0068] As shown in the figure, as the dropping rate decreases, the magnesium hydroxide flakes tend to be more uniform and fine, but the boundaries become increasingly blurred, and the morphology is affected to some extent. Considering actual industrial production, increasing the dropping time means increasing the overall production process time and thus increasing production costs. However, to achieve the best cost-effectiveness, production costs are unlikely to increase significantly for such minor differences, especially when meeting product quality requirements. Therefore, the intermediate dropping rate is defined as the optimal dropping rate. Furthermore, comparing C1 and C2, C3 and C4, and C5 and C6 shows that the different dropping order also has some impact on the flake-like magnesium hydroxide product. It is quite obvious that, compared to the reverse-addition of C2, C4, and C6, the magnesium hydroxide flakes in the images of forward-addition of C1, C3, and C5 are more uniform and smaller, with clearer boundaries and a more regular morphology. Therefore, under the same conditions, reverse-addition may be more likely to produce more regular, smaller, and more uniform flakes of magnesium hydroxide.

[0069] 3.3 Effect of magnesium hydroxide addition on LLDPE flow properties

[0070] At a temperature of 171℃ and a pressure of 24.4 Pa, the melt flow rate of LLDPE was 8.102 g / 10 min. The surface smoothness and bubble structure of the cut segments were relatively good. Under these conditions, flake magnesium hydroxide was added, and the flow properties of LLDPE were measured. Figures 4a to 4c As shown, observe the appearance of the segment after its addition, as shown below. Figures 5a to 5f As shown.

[0071] like Figures 4a to 4cOverall, 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 in melt flow rate is not a simple linear one. As shown in 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, a reduction of 62.5%. 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, a reduction of about 50%. The relationship between the two is clearly 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, thus hindering the movement of the molecular chain ends. On the other hand, the addition of magnesium hydroxide also occupies a certain amount of space, making the space for the free-moving molecular chain segments of LLDPE relatively small. 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.

[0072] Compare Figure 4a , Figure 4b , Figure 4c The three figures show that although flake magnesium hydroxide is added in all cases, the effect on the melt flow rate of LLDPE differs at the same addition amount. When the addition amount is 5%, Figure 4a The melt flow rate decreased from approximately 8 g / 10 min to 7.73 g / 10 min, a reduction of approximately 3.4%. Figure 4bThe melt flow rate decreased from approximately 8 g / 10 min to 7.75 g / 10 min, a reduction of approximately 3.1%. Figure 4c The melt flow rate decreased from approximately 8 g / 10 min to 7.8 g / 10 min, a reduction of approximately 2.5%; when the addition amount was approximately 40%, Figure 4a The melt flow rate decreased from approximately 2.95 g / 10 min to 2.35 g / 10 min, a reduction of approximately 20.33%. Figure 4b The melt flow rate decreased from approximately 2.95 g / 10 min to 2.35 g / 10 min, a reduction of approximately 20.33%. Figure 4c The melt flow rate decreased from approximately 2.95 g / 10 min to 2.75 g / 10 min, a reduction of about 6.8%. This shows that, at the same addition amount, different morphologies of magnesium hydroxide affect the melt flow rate of LLDPE differently, with the third graph showing a relatively smaller decrease. Figure 4a and Figure 4b It can be seen that the melt flow rate of LLDPE with the addition of 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 magnesium hydroxide is relatively higher. Figure 4c Because the added C4 group of flake magnesium hydroxide is better than the A3 group in terms of both regularity and boundary characteristics, its impact on the melt flow rate of LLDPE is relatively small. Similarly, all three sets of figures show that as the regularity and boundary of the flake magnesium hydroxide become more blurred, its impact on the melt flow index of LLDPE becomes greater.

[0073] Figures 5a to 5f These are appearance images of segments of LLDPE with different magnesium hydroxide samples having 30% added. Figures 5a to 5fAs can be seen, although the morphology of the added magnesium hydroxide varies slightly, the LLDPE segments are generally similar at the same addition amount. This is because, although the lamellar 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 lamellar structure differs, the movement trend in each melt is generally the same, and there is no significant difference in resistance, making the overall fluidity of each melt system relatively similar. Thus, its effect on the melt flow index is relatively similar, resulting in roughly similar appearances of the cut segments. However, there are still some differences. Comparing groups A1 and C6, the aspect ratio of the segments is noticeably different, with the former having a slightly larger ratio than the latter. This is related to... Figures 4a to 4c 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.

[0074] 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 in order to maintain its original melt flowability.

[0075] 3.4 Effect of the amount of magnesium hydroxide with different morphologies on the properties of LLDPE

[0076] Besides the flake-like morphology prepared in this example, the flame retardant magnesium hydroxide also exhibits the more common spherical shape, which is widely used in the market. As shown in section 3.3, even with the same morphology, differences in shape and size result in different melt flow rates for LLDPE. Therefore, research on different morphologies is also necessary. For comparison, we selected self-prepared B4 type flake-like magnesium hydroxide, whose particle size is not significantly different from commercially available spherical magnesium hydroxide. Figure 6 The 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.

[0077] like Figure 6Overall, it can be seen that with the addition of flake or flower-shaped magnesium hydroxide, the melt flow rate of LLDPE decreases continuously with the increase of its content. When the addition amount increases from 5% to 40%, the melt flow rate decreases from about 8g / 10min to about 3g / 10min, which means that its flow properties are gradually deteriorating. Similarly, the relationship between the amount of flower-shaped magnesium hydroxide added and the melt flow rate of LLDPE is not a simple linear one. However, as shown in the graph, when the addition amount is 5%, the melt flow rate of flake magnesium hydroxide is 8.03 g / 10 min, and the melt flow rate of spherical magnesium hydroxide is 7.72 g / 10 min. When the addition amount is 25%, the melt flow rate of flake magnesium hydroxide is 3.30 g / 10 min, and the melt flow rate of spherical magnesium hydroxide is 3.35 g / 10 min. When the addition amount is 40%, the melt flow rate of flake magnesium hydroxide is 2.95 g / 10 min, and the melt flow rate of spherical magnesium hydroxide is 3.05 g / 10 min. When the magnesium hydroxide addition amount is around 25%, the flow rates of both flake and spherical magnesium hydroxide on the LLDPE matrix are similar. Therefore, when the magnesium hydroxide content is below 25%, the flow rate of flake magnesium hydroxide on the LLDPE matrix is ​​relatively low, but when its addition amount is greater than 25%, the flow rate of spherical magnesium hydroxide on the LLDPE matrix is ​​relatively low. The main reason is that the agglomeration degree of globular magnesium hydroxide under these process conditions 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, it hinders the movement of the molecular chain ends of the polymer material more unevenly, and the resistance to melt flow is greater. At this time, its main role is the force of molecular chain end movement. Therefore, with the increase of magnesium hydroxide content, the decrease in melt flow rate will inevitably be 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 larger, so its fluidity is better. At this time, its main role is the volume of free radicals moving at the molecular chain ends. Therefore, globular magnesium hydroxide has a smaller impact on the flow rate of LLDPE matrix.

[0078] like Figures 7a to 7f As shown, Figure 7a , Figure 7c , Figure 7e The samples were cut from LLDPE containing 5%, 15%, and 25% flake magnesium hydroxide, respectively. Figure 7b ,and Figure 7d and Figure 7fThe figures represent cuts of LLDPE with added 5%, 15%, and 25% globular magnesium hydroxide, respectively. When the same type of globular LLDPE was added, the appearance of the cut LLDPE changed significantly with increasing magnesium hydroxide content. The trend was similar to that of the LLDPE segments with added flake magnesium hydroxide in the first column, only the degree of change differed slightly. More noticeably, when the addition amount was less than 25%, the LLDPE segments with the same amount of globular magnesium hydroxide were not as smooth as those with added flake magnesium hydroxide, and their transparency was also somewhat inferior. When the addition amount was greater than 25%, the LLDPE segments with the same amount of globular magnesium hydroxide had a smoother appearance than those with added 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.

[0079] 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.

[0080] 3.5 Effect of adding magnesium hydroxide with different morphologies on the viscosity of LLDPE

[0081] For spherical magnesium hydroxide, its effect on the viscosity of LLDPE matrix material differs somewhat from that of flake magnesium hydroxide. A self-made flake magnesium hydroxide sample B4, with a particle size not significantly different from commercially available spherical magnesium hydroxide, was selected for comparison. Figure 8 The figure shows the effect of adding magnesium hydroxide with different morphologies on the viscosity of the matrix material. "globular-flower-like" represents globular magnesium hydroxide, and "flake" represents flake magnesium hydroxide sample B4.

[0082] Figure 8The figure shows the viscosity change when flake-shaped and spherical magnesium hydroxide of similar particle size are added to an LLDPE matrix material at 175℃ and 5MPa, with increasing addition amount. As can be seen from the figure, the viscosity of the LLDPE matrix material increases with the addition of magnesium hydroxide, but the magnitude of the increase differs. When the addition amount is less than 25%, the spherical magnesium hydroxide has a greater impact on viscosity; when the addition amount is greater than 25%, the spherical magnesium hydroxide has a smaller impact on viscosity than the flake-shaped magnesium hydroxide. However, as the content increases, the effects of both on viscosity tend to converge. The reason for this trend is that, compared to flake magnesium hydroxide, small-particle, spherical magnesium hydroxide is more likely to integrate into the intermolecular gaps of LLDPE. At the same content, its surface area in contact with LLDPE is larger, leading to enhanced polar forces between the two. When the addition amount is less than about 25%, the polar forces between molecules play a dominant role, resulting in an excessive increase in viscosity. However, when the addition amount exceeds about 25%, due to the increased addition amount, compared to flake magnesium hydroxide, spherical magnesium hydroxide is more likely to agglomerate due to the surface polarity. At this time, under the same addition amount, the polar forces between molecules will decrease, resulting in a smaller effect on viscosity.

[0083] When the addition amount reaches about 25%, the effects of the two types of magnesium hydroxide on viscosity tend to be the same. The main reason for this phenomenon is the existence of polarity between magnesium hydroxide molecules and LLDPE molecules. Due to the large polarity between the two molecules, when the addition amount is within a certain range, the addition of magnesium hydroxide has a significant effect on the intermolecular forces of LLDPE. However, when it reaches a certain amount, the polar forces between molecules lead to an intensification of magnesium hydroxide agglomeration. As the agglomeration of magnesium hydroxide intensifies, whether it is flake-shaped or flower-shaped strong magnesium oxide, its effective surface area will tend to be consistent, and the shape and particle size of the agglomerated particles will also tend to be consistent. This reduces the intermolecular gaps of LLDPE to a minimum and weakens the mobility of the molecular chain ends to a minimum, thus making its effect on viscosity approach a constant value.

[0084] This embodiment uses a homogeneous precipitation method to prepare magnesium hydroxide. The prepared flake-shaped magnesium hydroxide and commercially available flower-shaped magnesium hydroxide are added to an LLDPE matrix material. Changes in melt flow rate and viscosity are used to study the alterations in the LLDPE rheological properties. The conclusions are as follows:

[0085] 1) When preparing magnesium hydroxide by homogeneous precipitation, it was found that the concentration of reactants had a significant impact on the formation of the flakes, and the dropping method also had a significant impact on the formation of the flakes. As the concentration of the reactants sodium hydroxide and magnesium chloride increased, the magnesium hydroxide product gradually became larger and clearer. Choosing an appropriate dropping rate and forward dropping resulted in relatively clear and regular magnesium hydroxide flakes.

[0086] 2) The morphology and amount of magnesium hydroxide also have different effects on the melt flow rate of LLDPE. The main effect is on the amount of magnesium hydroxide added. When the amount of magnesium hydroxide added is less than 20%, the melt flow rate decreases from 8 g / 10 min to about 4 g / 10 min as the amount of magnesium hydroxide added increases. When the content of magnesium hydroxide increases from 20% to 40%, the melt flow rate decreases from 4 g / 10 min to about 3 g / 10 min. The decrease is not linear with the amount of magnesium hydroxide added. When the amount of spherical magnesium hydroxide added is less than 25%, the melt flow rate changes more significantly. After reaching 25%, the influence trend weakens significantly, and the effects of both on the melt flow rate tend to be consistent as the amount of magnesium hydroxide added increases. The regularity of the flakes also has a certain impact on the melt flow rate. The more regular the flakes are, the smaller the impact on the melt flow rate of LLDPE.

[0087] 3) The amount and morphology of magnesium hydroxide also affect the viscosity of the LLDPE matrix material to varying degrees. The main effect is on the amount added. As the amount of flake magnesium hydroxide increases, the viscosity of the LLDPE matrix continuously increases. When the addition amount is less than 25%, the spherical magnesium hydroxide has a greater impact on the LLDPE matrix material than the flake magnesium hydroxide. However, when the addition amount exceeds 25%, the flake magnesium hydroxide has a greater impact. With increasing content, the effects of both eventually tend to be equal. The regularity of the flakes also has a certain influence; the more regular the flakes, the greater the impact on the viscosity of the LLDPE matrix material.

[0088] 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 spherical 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%.

Claims

1. A method for preparing flake magnesium hydroxide to improve the processing properties of LLDPE, characterized in that, Includes the following steps: Step (1): Prepare magnesium chloride solution and alkaline solution; the alkaline solution is sodium hydroxide solution; when preparing magnesium chloride solution, add PEG12000 and disperse evenly; the concentration of magnesium chloride in magnesium chloride solution is 0.25-1.5 mol / L, and the amount of PEG12000 used per mol of magnesium chloride is 1.0-1.2 g; the concentration of sodium hydroxide solution is 0.25-1.5 mol / L. Step (2): Preheat the magnesium chloride solution and the alkaline solution separately; Step (3): Add the preheated magnesium chloride solution dropwise to the preheated alkaline solution while stirring; the dropping rate is 1-2 mL / min, the stirring speed during the dropping is 500-800 rpm; the constant temperature water bath is kept at 30-35℃ during the dropping; Step (4): After the addition is complete, continue stirring and keep warm to carry out the precipitation reaction. After the reaction is complete, use a centrifuge to separate the solid and liquid. Continue stirring at a speed of 500-800 rpm. Keep warm at 30-35℃ for 30-40 min. Step (5): Wash and dry the separated solids to obtain flake magnesium hydroxide that improves the processing performance of LLDPE.

2. The method for preparing flake magnesium hydroxide to improve the processing performance of LLDPE according to claim 1, characterized in that, In step (1), the concentration of magnesium chloride in the magnesium chloride solution is 0.75 mol / L, and the amount of PEG12000 used per 1 mol of magnesium chloride is 1.1 g; the concentration of sodium hydroxide solution is 1.0 mol / L.

3. The method for preparing flake magnesium hydroxide to improve the processing performance of LLDPE according to claim 1, characterized in that, In step (2), both the magnesium chloride solution and the alkaline solution are preheated to 30-35°C.

4. The method for preparing flake magnesium hydroxide to improve the processing performance of LLDPE according to claim 1, characterized in that, In step (3), the dropping speed is 2 mL / min, the stirring speed during dropping is 700 rpm, and the constant temperature water bath is maintained at 30℃ during dropping.

5. The method for preparing flake magnesium hydroxide to improve the processing performance of LLDPE according to claim 1, characterized in that, In step (5), the washing method is as follows: first wash with water once, then wash twice with anhydrous ethanol; the drying temperature is 55-65℃, and the drying time is 6-8h.

6. The method for preparing flake magnesium hydroxide to improve the processing performance of LLDPE according to claim 1, characterized in that, In step (1), the alkaline solution is a sodium hydroxide solution with a concentration of 1.0 mol / L, the magnesium chloride solution has a magnesium chloride concentration of 0.75 mol / L, and the amount of PEG12000 used per 1 mol of magnesium chloride is 1.1 g. In step (2), both the magnesium chloride solution and the alkaline solution are preheated to 30°C. In step (3), the dropping rate is 2 mL / min, the stirring speed is 700 rpm, and the temperature is maintained at 30℃ in a constant temperature water bath during the dropping process. In step (4), the stirring speed is 700 rpm; the holding temperature is 30℃ and the holding time is 30 min. In step (5), the washing method is as follows: first wash with water once, then wash twice with anhydrous ethanol; the drying temperature is 60℃ and the drying time is 7h.

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