Hydrophobic emulsion coated plant fiber foam material with low moisture absorption rate and preparation method of hydrophobic emulsion coated plant fiber foam material

Abstract

The invention discloses a preparation method of a hydrophobic emulsion coated plant fiber foam material with low moisture absorption rate. The preparation method comprises the following steps: step 1, uniformly mixing defibered plant fibers, a hydrophobic modifier, an emulsifier and water to obtain a plant fiber emulsion; step 2, uniformly mixing the defibered plant fibers, a cross-linking agent and other auxiliaries, and heating and foaming to obtain an intermediate product; and step 3, coating the plant fiber emulsion prepared in the step 1 on the surface of the intermediate product prepared in the step 2, and then performing high-temperature drying to obtain the hydrophobic emulsion coated plant fiber foam material with low moisture absorption rate. The density of the plant fiber foam material prepared by the invention is less than or equal to 85 kg / m < 3 >; the saturated moisture absorption rate after 24 hours is less than or equal to 8 percent, and the saturated moisture absorption rate after 72 hours is less than or equal to 15 percent; under the humidity conditions of 85% RH and 50% RH, the change of 50% strain compression strength is not greater than 35%; the method is expected to be widely applied to the packaging field of packaging materials, especially high-end electronic equipment.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of foamed materials, and in particular to a low-hygroscopicity plant fiber foamed material coated with a hydrophobic emulsion and a preparation method thereof. BACKGROUND

[0002] Currently, the widely used cushioning materials in packaging are mainly foamed polystyrene (EPS), foamed polypropylene (EPP), foamed polyurethane (PU), ethylene-vinyl acetate copolymer (EVA), paper pulp molding and honeycomb paperboard, etc. Among them, EPS, EPP, PU and EVA are mainly petroleum-based foamed materials, which are low in cost but difficult to degrade, causing serious harm to the living environment of human beings and the entire ecological system. The main raw material of paper pulp molding and honeycomb paperboard is plant fiber, which can be naturally degraded, but it is brittle, has a large specific gravity, poor resilience and small cushioning coefficient, limiting its application in packaging.

[0003] Plant fiber foamed material is different from paper pulp molding and honeycomb paperboard. It uses plant fiber as raw material, adds adhesives, plasticizers and other additives, and forms micron or millimeter level hole structure inside the material through physical foaming or chemical foaming, thus having good cushioning performance. Plant fiber foamed material has both natural degradability and cushioning performance, and is a green cushioning material with broad development prospects.

[0004] However, one important reason limiting the application of plant fiber foamed material is its high hygroscopicity, and the loss of cushioning performance caused by high hygroscopicity. The high hygroscopicity of plant fiber foamed material is derived from the hydrophilicity of plant fiber, adhesives, plasticizers and other components. Hydroxyl, carboxyl and other groups on the surface form hydrogen bonds with water molecules, which easily adsorb water molecules, and the hygroscopicity can be as high as 20%-30%. On the other hand, unlike the dense structure of paper pulp molding products, the micron or millimeter level holes on the surface of plant fiber foamed material provide a convenient channel for the entry and diffusion of water molecules, which can fully contact the hydrophilic groups inside the plant fiber foamed material, thus significantly increasing the hygroscopicity. Under different humidity conditions, plant fiber foamed material releases water to the outside or absorbs water from the outside until equilibrium is reached. Water molecules are good plasticizers, and after absorbing water, plant fiber swells, and slippage occurs between plant fibers, resulting in a decrease in compressive strength and loss of cushioning performance. The high hygroscopicity of plant fiber foamed material limits its application, especially in scenes with large humidity changes, such as plum rain season or transnational sea transportation. High hygroscopicity also affects the application of plant fiber foamed material in high-end electronic device packaging.

[0005] The waterproof agents widely used in the field of pulp molding at present, such as acrylic waterproof agent, fluorocarbon waterproof agent or wax emulsion, etc., have unsatisfactory anti-wetting effect on plant fiber foam materials, mainly because the porous surface of the plant fiber foam material affects the film forming effect of the waterproof agent. SUMMARY

[0006] In view of the deficiencies of the prior art, the application discloses a preparation method of a low-hygroscopic plant fiber foam material coated with a hydrophobic emulsion, and the prepared plant fiber foam material has excellent cushioning performance and extremely low hygroscopicity, and also has stable compression strength under different humidity conditions, and can be used as high-end packaging material.

[0007] The specific technical scheme is as follows:

[0008] A preparation method of a low-hygroscopic plant fiber foam material coated with a hydrophobic emulsion, comprising the following steps:

[0009] Step one, mixing and uniformly distributing the defibered plant fiber, hydrophobic modifier, emulsifier and water to obtain a plant fiber emulsion;

[0010] Step two, mixing and uniformly distributing the defibered plant fiber, crosslinking agent and other additives, and then heating and foaming to obtain an intermediate product;

[0011] Step three, coating the plant fiber emulsion prepared in step one on the surface of the intermediate product prepared in step two, and then drying at high temperature to obtain the low-hygroscopic plant fiber foam material coated with the hydrophobic emulsion.

[0012] The preparation method disclosed by the application first uses plant fiber as raw material, and then prepares a plant fiber emulsion after hydrophobic modification; and then coats the plant fiber emulsion on the surface of the foamed plant fiber material as a coating layer, and finally obtains the final product after drying. The plant fiber foam material prepared by the process has excellent cushioning performance, high 50% strain compression strength and extremely low hygroscopicity, and also has stable compression strength under different humidity conditions.

[0013] It is found through experiments that if the defibered plant fiber is directly blended with the hydrophobic modifier and other additives, and then heated and foamed without the step of coating the plant fiber emulsion, the strain compression strength of the prepared plant fiber foam material under different humidity conditions changes dramatically, and the hygroscopicity is also not ideal.

[0014] In step one,

[0015] The plant fiber is selected from one or more of conifer pulp fiber, broadleaf wood pulp fiber, bamboo pulp fiber, sugarcane pulp fiber and straw pulp fiber.

[0016] Preferably, the plant fiber needs to be defibered before use, and the defibered process is specifically as follows:

[0017] The plant fibers are dispersed in water by mechanical stirring, and then are subjected to dewatering treatment to obtain the defibrated plant fibers.

[0018] In step one:

[0019] The hydrophobic modifier is selected from one or more of liquid paraffin, naphthenic oil, PE wax, LDPE wax, HDPE wax, LLDPE wax, nano-silicon dioxide, nano-calcium carbonate, nano-silicon powder.

[0020] Preferably, the selection of the composite hydrophobic modifier can further reduce the moisture absorption rate of the plant fiber foam material.

[0021] Such as a mixture of liquid paraffin and high molecular wax, or liquid paraffin and nano-particles, or naphthenic oil and high molecular wax, or naphthenic oil and nano-particles, or liquid paraffin and high molecular wax and nano-particles, or naphthenic oil and high molecular wax and nano-particles, and the like.

[0022] The emulsifier is selected from one or more of glyceryl monooleate, glyceryl monostearate, glyceryl monolaurate, polyglyceryl-3 disiloxane dimethicone, PEG-10 dimethicone, PEG-9 dimethicone, C12-C20 fatty alcohol.

[0023] Preferably:

[0024] The mass ratio of the defibrated plant fibers, the hydrophobic modifier, the emulsifier and water is 100: (20-150): (5-30): (100-200) based on the dry weight of the defibrated plant fibers.

[0025] It is found through experiments that when the mass ratio of the defibrated plant fibers and the hydrophobic modifier is 100: (20-150), the plant fiber foam material can be well coated by the hydrophobic oil film, and the moisture absorption rate is significantly reduced. If the mass ratio is too large (such as 100:10), the moisture absorption rate is not significantly reduced.

[0026] Preferably, the mass ratio of the defibrated plant fibers and the hydrophobic modifier is 100: (30-90); further preferably, the mass ratio is 100:70.

[0027] In step one, the raw materials are mixed by mechanical ball milling.

[0028] Preferably, the rotation speed of the mechanical ball milling is 1000-1400 rpm.

[0029] In step two:

[0030] In the present application, the crosslinking agent is selected from blocked polyurethane, and after the plant fiber foam material is formed, high temperature treatment is carried out to unblock the isocyanate functional group, and the isocyanate functional group is reacted with the hydroxyl group on the plant fiber and the adhesive again, so as to cure and crosslink, thereby overcoming the defects that the general polyurethane is easily interfered by water molecules in the aqueous system, and the foaming ratio of the plant fiber foam material is affected after curing and crosslinking, and the compression strength of the plant fiber foam material under high humidity conditions is improved through post curing and crosslinking.

[0031] Preferably, the crosslinking agent is selected from one or more of oxime blocked waterborne polyurethane, nitrogen-containing heterocyclic compound blocked waterborne polyurethane, alcohol blocked waterborne polyurethane, phenol blocked waterborne polyurethane, and ester blocked waterborne polyurethane.

[0032] The oxime blocked waterborne polyurethane is selected from methyl ethyl ketone oxime blocked polyurethane emulsion and acetone oxime blocked polyurethane emulsion.

[0033] The nitrogen-containing heterocyclic compound blocked waterborne polyurethane is selected from 3,5-dimethyl pyrazole blocked polyurethane emulsion and 1,2,4-triazole blocked polyurethane emulsion.

[0034] The alcohol blocked waterborne polyurethane is selected from ethanol blocked polyurethane emulsion.

[0035] The phenol blocked waterborne polyurethane is selected from phenol blocked polyurethane emulsion.

[0036] The ester blocked waterborne polyurethane is selected from malonic acid diethyl ester blocked waterborne polyurethane emulsion and acetoacetic acid ethyl ester blocked polyurethane emulsion.

[0037] Further preferably, the crosslinking agent is selected from ester blocked waterborne polyurethane.

[0038] It is found through experiments that in the system of the present application, the plant fiber foam material prepared by using ester blocked waterborne polyurethane as the crosslinking agent has higher 50% strain compression strength and smaller compression strength change under different humidity conditions.

[0039] Preferably:

[0040] The mass ratio of the plant fiber subjected to the defibration to the crosslinking agent is 100: (5-25) in terms of the solid content of the crosslinking agent.

[0041] It is found through experiments that when the weight ratio of the plant fiber subjected to the defibration to the crosslinking agent is small (such as 100:2), the compression strength change of the final plant fiber foam material under the humidity conditions of 85% RH and 50% RH is large, and when the weight ratio of the plant fiber subjected to the defibration to the crosslinking agent is large (such as 100:30), the foaming ratio of the foam material is small, and the density is large.

[0042] Further preferably, the mass ratio of the defibrated plant fiber to the crosslinking agent is 100:25.

[0043] The plant fiber foam material prepared with the further preferred ratio has a lower moisture absorption rate, a higher compression strength at 50% strain and a smaller change in compression strength under different humidity.

[0044] Preferably, the defibrated plant fiber is prepared by a method comprising the following steps:

[0045] The heating foaming can employ a heating device commonly used in the art, such as a microwave heater, a flat vulcanization instrument, a hot air dryer, etc.

[0046] Preferably, the heating foaming is performed at a temperature of 105-200℃.

[0047] The temperature for the heating foaming is 105-200℃.

[0048] Further preferably, the temperature for the heating foaming is 120-150℃.

[0049] Preferably, in step two, the defibrated plant fiber is mixed with the crosslinking agent at a mass ratio of 100:25.

[0050] The other additives include a binder, a plasticizer and a nucleating agent.

[0051] The binder is selected from one or more of the conventional types in the art, such as starch, sodium alginate, gelatin, guar gum, etc.

[0052] The plasticizer is selected from one or more of the conventional types in the art, such as glycerol, ethylene glycol, mannitol, sorbitol, etc.

[0053] The nucleating agent is selected from one or more of the conventional types in the art, such as talc powder, mica powder, silicon dioxide, calcium carbonate, sodium borate, calcium borate, boron oxide, etc.

[0054] Preferably, the defibrated plant fiber is mixed with the binder, the plasticizer and the nucleating agent at a mass ratio of 100:(20-50):(10-30):(1-10).

[0055] The product after the heating foaming and drying to constant weight is left to equilibrate for a period of time under normal temperature and humidity.

[0056] The product after the heating foaming and drying to constant weight is left to equilibrate for a period of time under normal temperature and humidity.

[0057] Preferably, in step three, the product after the heating foaming is coated with a sizing agent.

[0058] Preferably, the coating is performed 1-3 times.

[0059] The sizing amount after the coating is 0.02-0.5g / cm 2 .

[0060] It has been found through experiments that when the sizing amount is too low (e.g. 0.01g / cm 2The moisture absorption rate of plant fiber foam materials will not decrease, and the surface coverage will be uneven, affecting the appearance; when the sizing amount is too high (e.g., 1g / cm³), the moisture absorption rate will not decrease, and the surface coverage will be uneven, affecting the appearance. 2 If the number of coatings is too high (e.g., 4 times), the moisture absorption rate of the plant fiber foam material will not decrease further, and it will result in waste of emulsion and increase the number of processes.

[0061] Further optimization:

[0062] The amount of sizing applied after coating is 0.2~0.5 g / cm³. 2 .

[0063] Preferred:

[0064] The high-temperature drying temperature is 120~180℃, and the time is 5~30 minutes;

[0065] Experiments have shown that the high-temperature baking temperature is used to control the curing reaction of the crosslinking agent. If the temperature is too low (e.g., 110℃) or the baking time is too short (e.g., 3 min), there is no curing effect, and the compressive strength of the plant fiber foam material changes significantly under humidity conditions of 85%RH and 50%RH. If the temperature is too high (e.g., 190℃) or the baking time is too long (e.g., 40 min), it will affect the appearance of the plant fiber foam material.

[0066] Further optimization is achieved by using a high-temperature drying temperature of 130~160℃.

[0067] After baking, place the food at room temperature and humidity for a period of time to equilibrate.

[0068] This invention also discloses a plant fiber foam material with low moisture absorption rate prepared according to the above method, wherein the density of the foam material is ≤85kg / m³. 3 The saturated moisture absorption rate after 24 hours is ≤8%, and the saturated moisture absorption rate after 72 hours is ≤15%; the change in 50% strain compressive strength under humidity conditions of 85%RH and 50%RH is no more than 35%.

[0069] Compared with the prior art, the present invention has the following beneficial effects:

[0070] This invention discloses a method for preparing a low-hygroscopicity plant fiber foam material coated with a hydrophobic emulsion. First, plant fibers are used as raw materials, and after hydrophobic modification, a plant fiber emulsion is prepared. Then, this emulsion is used as a coating on the surface of a foamed plant fiber material. The plant fiber foam material prepared by this process exhibits excellent cushioning performance and extremely low moisture absorption, while also demonstrating stable compressive strength under different humidity conditions.

[0071] The density of the plant fiber foam material prepared by this invention is ≤85kg / m³. 3The saturated moisture absorption rate after 24 hours is less than or equal to 8%, and the saturated moisture absorption rate after 72 hours is less than or equal to 15%; the 50% strain compression strength change under the humidity conditions of 85% RH and 50% RH is less than or equal to 35%; and the plant fiber foamed material is expected to be widely applied in the field of packaging materials, especially high-end electronic device packaging. DETAILED DESCRIPTION

[0072] In order to make the purpose, technical scheme and advantages of the embodiments of the present application more clear, the technical scheme in the embodiments of the present application will be clearly and completely described below. If the specific conditions are not specified in the embodiments, the conventional conditions or the conditions recommended by the manufacturer are adopted. If the manufacturers of the reagents or instruments are not specified, the conventional products that can be purchased in the market are adopted.

[0073] The features and performances of the present application will be further described in detail below in combination with the embodiments.

[0074] In the present application, the static compression performance test of the plant fiber foamed material refers to the GB / T 8168-2008 standard. The plant fiber foamed material is pretreated for more than 72 hours under the conditions of 23℃, 50% RH and 55℃, 85% RH before the static compression performance test.

[0075] The moisture absorption rate test method of the plant fiber foamed material is as follows: first, the plant fiber foamed material is dried in a 105℃ oven until the mass no longer changes, and the mass is recorded as m1, then it is placed under the conditions of 55℃, 85% RH for a certain time (the treatment time in the present application is 24 hours or 72 hours), and the mass after moisture absorption is recorded as m2.

[0076] Moisture absorption rate (%) = (m2-m1) / m1*100%

[0077] Embodiment 1

[0078] Step one, the wood pulp fiber is dispersed in water after mechanical stirring, and the defibrated plant fiber is obtained after dewatering treatment, 100g of the defibrated plant fiber (dry weight) is added with 20g of liquid paraffin, 10g of LDPE wax, 5g of glycerol monostearate and 100g of water, and a plant fiber emulsion coated with a hydrophobic oil film is prepared by mechanical ball milling at a speed of 1400rpm.

[0079] Step two, 200g of adhesive composed of starch and gelatin (mass ratio 4:1), 120g of glycerol, 40g of talc and 110g of propandioic acid diethyl ester blocked waterborne polyurethane emulsion (Sivac Chemical, BPUD-1045, solid content 45%) are added to 1kg of the defibrated plant fiber, and the mixture is uniformly mixed to obtain a slurry, 150g of the slurry is injected into a mold with the size of 130*130*3cm, heated to 140℃ and foamed, and after the foaming is completed, the sample is taken out after drying at 105℃ until the weight is constant.

[0080] Step three, the plant fiber emulsion prepared in step one is coated on the surface of the sample prepared in step two with a sizing amount of 0.02 g / cm 2 and then baked at 160°C for 5 min. After baking, the sample is placed in a constant temperature and humidity environment for 24 h to obtain a hydrophobic emulsion coated low moisture absorption plant fiber foam material.

[0081] Example 2

[0082] The preparation process is basically the same as in Example 1, except that:

[0083] In step one, the mass of liquid paraffin is replaced with 50 g, the mass of LDPE wax is replaced with 40 g, the mass of glycerol monostearate is replaced with 20 g, and the mass of water is replaced with 150 g.

[0084] Example 3

[0085] The preparation process is basically the same as in Example 1, except that:

[0086] In step one, the mass of liquid paraffin is replaced with 100 g, the mass of LDPE wax is replaced with 50 g, the mass of glycerol monostearate is replaced with 30 g, and the mass of water is replaced with 200 g.

[0087] Example 4

[0088] The preparation process is basically the same as in Example 1, except that:

[0089] In step one, the hydrophobic modifier is replaced with 20 g of naphthenic oil and 10 g of nano calcium carbonate.

[0090] Example 5

[0091] The preparation process is basically the same as in Example 1, except that:

[0092] In step one, the hydrophobic modifier is replaced with 20 g of naphthenic oil, 5 g of LLDPE wax, and 5 g of nano calcium carbonate.

[0093] Example 6

[0094] The preparation process is basically the same as in Example 1, except that:

[0095] In step two, the mass of diethyl malonate blocked waterborne polyurethane emulsion as a crosslinking agent is replaced with 550 g.

[0096] Example 7

[0097] The preparation process is basically the same as in Example 1, except that:

[0098] In step two, the crosslinking agent was replaced by equal mass of 3,5-dimethylpyrazole-terminated polyurethane emulsion (Soviet Chemical, BPUD-1545, solid content 45%).

[0099] Example 8

[0100] The preparation process was basically the same as in Example 1, except that:

[0101] In step two, the crosslinking agent was replaced by equal mass of methyl ethyl ketoxime-terminated polyurethane emulsion (Soviet Chemical, BPUD-1245, solid content 45%).

[0102] Example 9

[0103] The preparation process was basically the same as in Example 6, except that:

[0104] In step two, the foaming temperature was replaced by 150°C.

[0105] Example 10

[0106] The preparation process was basically the same as in Example 1, except that:

[0107] In step two, 100g of slurry was injected into the mold.

[0108] Example 11

[0109] The preparation process was basically the same as in Example 1, except that:

[0110] In step three, the plant fiber emulsion prepared in step one was coated on the surface of the sample prepared in step two at a sizing amount of 0.4g / cm 2 .

[0111] Example 12

[0112] The preparation process was basically the same as in Example 1, except that:

[0113] In step three, the high-temperature baking temperature was replaced by 130°C, and the baking time was 30min.

[0114] Example 13

[0115] In step one, the bamboo pulp fiber was dispersed in water after mechanical stirring, and the defibrated plant fiber was obtained after dewatering treatment. The defibrated plant fiber (dry weight 100g) was added with liquid paraffin 50g, LDPE wax 20g, glycerol monostearate 15g and water 150g, and a hydrophobic oil film-coated plant fiber emulsion was prepared by mechanical ball milling at a speed of 1400rpm.

[0116] Step two, 1 kg of the defibrated plant fiber was mixed with 200 g of the adhesive composed of starch and gelatin (mass ratio 4:1), 120 g of glycerol, 40 g of talc, and 550 g of diethyl malonate blocked waterborne polyurethane emulsion to obtain a slurry. 150 g of the slurry was injected into a mold with the size of 130*130*3 cm, and then foaming was performed after heating to 150°C. After the foaming was completed, the sample was taken out after drying to constant weight.

[0117] Step three, the plant fiber emulsion prepared in step one was coated on the surface of the sample prepared in step two at a sizing amount of 0.4 g / cm 2 , and then baking was performed at 160°C for 5 min. After the baking was completed, the sample was placed at room temperature and humidity for 24 h.

[0118] Comparative example 1

[0119] 1 kg of the defibrated plant fiber was mixed with 200 g of the adhesive composed of starch and gelatin (mass ratio 4:1), 120 g of glycerol, and 40 g of talc to obtain a slurry. 150 g of the slurry was injected into a mold with the size of 130*130*3 cm, and then foaming was performed after heating to 140°C. After the foaming was completed, the sample was taken out after drying to constant weight.

[0120] Comparative example 2

[0121] 1 kg of the defibrated plant fiber was mixed with 20 g of liquid paraffin, 10 g of LDPE wax, 5 g of glycerol monostearate, 200 g of the adhesive composed of starch and gelatin (mass ratio 4:1), 120 g of glycerol, and 40 g of talc to obtain a slurry. 150 g of the slurry was injected into a mold with the size of 130*130*3 cm, and then foaming was performed after heating to 140°C. After the foaming was completed, the sample was taken out after drying to constant weight.

[0122] Comparative example 3

[0123] The preparation process was basically the same as that in example 1, and the difference was that:

[0124] In step one, the mass of the liquid paraffin was replaced with 5 g, the mass of the LDPE wax was replaced with 5 g, and the mass of the glycerol monostearate was replaced with 2 g.

[0125] Comparative example 4

[0126] The preparation process was basically the same as that in example 1, and the difference was only that:

[0127] In step two, the crosslinking agent diethyl malonate blocked waterborne polyurethane emulsion was not added.

[0128] Comparative example 5

[0129] The preparation process was basically the same as that in example 1, and the difference was only that:

[0130] In step two, the crosslinking agent was replaced from diethyl malonate blocked waterborne polyurethane emulsion to equal mass of conventional crosslinking agent - citric acid.

[0131] Comparative Example 6

[0132] The preparation process was basically the same as in Example 1, except that:

[0133] In step two, the crosslinking agent was replaced from diethyl malonate blocked waterborne polyurethane emulsion to equal mass of conventional crosslinking agent - potassium borate.

[0134] Comparative Example 7

[0135] The preparation process was basically the same as in Example 1, except that:

[0136] In step two, the mass of the crosslinking agent was replaced by 670 g.

[0137] The moisture absorption rate and compressive strength data of the plant fiber foam materials prepared in each example and comparative example are listed in Table 1 below.

[0138] Table 1

[0139]

[0140] a: poor foaming effect, not in line with test standards, unable to test.

[0141] The above discloses the preferred embodiments, but the protection scope of the present application is not limited thereto, and those skilled in the art can easily understand the spirit of the present application according to the above embodiments, and make different inferences and changes, as long as they do not deviate from the spirit of the present application, they are within the protection scope of the present application.

Claims

1. A process for the production of a hydrophobic emulsion-coated, low hygroexpansivity plant fiber foam material, characterized in that, The method comprises the following steps: Step one, mixing the defibrated plant fiber, hydrophobic modifier, emulsifier and water to obtain a plant fiber emulsion; Step two, mixing the defibrated plant fiber, crosslinking agent and other additives, and then heating and foaming to obtain an intermediate product; Step three, coating the plant fiber emulsion prepared in step one on the surface of the intermediate product prepared in step two, and then drying at high temperature to obtain the hydrophobic emulsion coated low moisture absorption plant fiber foam material.

2. The process for producing a hydrophobic emulsion-coated low hygroexpansivity plant fiber foam material according to claim 1, characterized by, In steps one and two: The plant fiber is independently selected from one or more of needle wood pulp fiber, broadleaf wood pulp fiber, bamboo pulp fiber, cane pulp fiber and straw pulp fiber.

3. The process for producing a hydrophobic emulsion-coated low hygroexpansivity plant fiber foam material according to claim 1, characterized by, In step one: The hydrophobic modifier is selected from one or more of liquid paraffin, naphthenic oil, PE wax, LDPE wax, HDPE wax, LLDPE wax, nano silicon dioxide, nano calcium carbonate and nano silicon powder; The emulsifier is selected from one or more of glycerol monooleate, glycerol monostearate, glycerol monolaurate, polyglyceryl-3 disiloxane dimethicone, PEG-10 dimethicone, PEG-9 dimethicone and C12-C20 fatty alcohol.

4. The process for producing a hydrophobic emulsion-coated low hygroexpansivity plant fiber foam material according to claim 1, characterized by, In step one: The mass ratio of the defibrated plant fiber, hydrophobic modifier, emulsifier and water is 100: (20-150): (5-30): (100-200) based on the dry weight of the defibrated plant fiber.

5. The process for producing a hydrophobic emulsion-coated low hygroexpansivity plant fiber foam material according to claim 1, characterized by, In step two: The crosslinking agent is selected from one or more of oxime blocked waterborne polyurethane, nitrogen-containing heterocyclic compound blocked waterborne polyurethane, alcohol blocked waterborne polyurethane, phenol blocked waterborne polyurethane and ester blocked waterborne polyurethane; The mass ratio of the defibrated plant fiber to the crosslinking agent is 100: (5-25) based on the solid content of the crosslinking agent; The heating and foaming temperature is 105-200℃.

6. The process for producing a hydrophobic emulsion-coated low hygroexpansivity plant fiber foam material according to claim 1, characterized by, In step two: The other additives include adhesive, plasticizer and nucleating agent; The mass ratio of the defibrated plant fiber to the adhesive, plasticizer and nucleating agent is 100: (20-50): (10-30): (1-10).

7. The method for preparing the hydrophobic emulsion coated low moisture absorption plant fiber foam material according to claim 6, characterized in that: The adhesive is selected from one or more of starch, sodium alginate, gelatin and guar gum; The plasticizer is selected from one or more of glycerol, ethylene glycol, mannitol and sorbitol; The nucleating agent is selected from one or more of talc powder, mica powder, silicon dioxide, calcium carbonate, sodium borate, calcium borate and boron oxide.

8. The process for producing a hydrophobic emulsion-coated low hygroexpansivity plant fiber foam material according to claim 1, characterized by, In step three: The sizing amount after coating is 0.02-0.5 g / cm 2 .

9. The process for producing a hydrophobic emulsion-coated low hygroexpansivity plant fiber foam material according to claim 1, characterized by, In step three: The drying temperature is 120-180℃, and the drying time is 5-30 min.

10. The hydrophobic emulsion coated low moisture absorption plant fiber foam material prepared by the method according to any one of claims 1-9.

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