A low-density plant fiber material for molded packaging articles using coconut coir as raw material, and a method for preparing and using the same

Abstract

The embodiment of the application relates to a low-density molded packaging product plant fiber material taking coconut fiber as raw material and a preparation method and application thereof, and belongs to the technical field of fiber packaging materials. The preparation method of the low-density molded packaging product plant fiber material taking coconut fiber as raw material comprises the following steps: step one, pretreatment; step two, chemical immersion; step three, grinding separation; step four, high-concentration immersion waste liquid extraction and impurity removal; and step five, fine grinding treatment. The fiber material provided by the embodiment of the application can improve the performance of molded products, further expand the application range of molded products, expand the industrial utilization range of characteristic plant fiber raw materials, improve the industrial utilization added value, reduce the dependence of the molded industry on paper pulp raw materials for papermaking, and relieve the pressure of insufficient paper pulp supply.

Description

TECHNICAL FIELD

[0001] The embodiment of the present application relates to the technical field of fiber packaging materials, in particular to a low-density molded packaging product plant fiber material using coconut fiber as raw material and a preparation method and application thereof. BACKGROUND

[0002] Although coconut fiber products have a wide range of uses, the product has low added value, the processing mode is extensive, the product type is single and most of them are primary products, and some are processed into fiber thin pads, sofa pads, sports pads, high-end memory foam mattress and high-grade automobile cushion and other soft decorative products.

[0003] From the function and characteristics of the product, it can be found that people have noticed that coconut fiber has high strength, high toughness, moisture resistance, corrosion resistance, insect resistance, good air permeability and other physical properties, but the research and development technology of high-value utilization products based on the characteristics of coconut fiber is far from enough.

[0004] The existing paper pulp molding industry basically uses various types of paper pulp for papermaking, such as waste paper pulp, domestic commodity pulp board and even imported commodity pulp board as raw materials, and through wet or dry forming, dehydration through heat conduction oil drying, hot air drying and other drying methods, and then through heat setting to prepare various types of cushion packaging, thermal packaging products.

[0005] Because the paper pulp fiber used as raw material is based on the principle of hydrogen bond combination, the fiber itself lacks the necessary rigidity, and at the same time, it fails to fully utilize the new fiber combination principle generated by high temperature and high pressure during heat setting of the molded product, such as lignin thermal recombination, lignin polycondensation and phenolic condensation in addition to hydrogen bond combination, resulting in a high density of the existing molded packaging product, generally 0.35g / cm 3 The above limits the improvement of the cushioning and thermal insulation performance of the molded packaging product by means of low density, making the molded packaging product lack competitiveness with packaging products such as foamed plastic in the fields of heavy load cushioning packaging and high-efficiency thermal insulation packaging, and limiting the play of the green degradable advantage of the molded packaging product.

[0006] With the increase of the production of molded packaging products, the demand for paper pulp in the traditional molded industry based on paper pulp raw materials has further increased, which undoubtedly brings greater raw material supply pressure to the papermaking industry which is already short of paper pulp supply.

[0007] Therefore, it is urgent to develop special molded fiber materials more suitable for the function of molded packaging products based on the special plant fiber chemical properties of coconut fiber and other characteristic plant fiber raw materials in China. SUMMARY

[0008] Therefore, the application provides a low-density plant fiber material for molded packaging products using coconut fiber as raw material, a preparation method and application thereof, which can improve the performance of molded products, expand the application range of molded products, expand the industrial utilization range of characteristic plant fiber raw materials, improve the added value of industrial utilization, reduce the dependence of the molded industry on paper pulp raw materials for papermaking, and relieve the pressure of insufficient supply of paper pulp for papermaking.

[0009] The first aspect of the application provides a preparation method of a low-density plant fiber material for molded packaging products using coconut fiber as raw material, which comprises the following steps:

[0010] Step one, pretreatment: cut the coconut fiber raw material to 10-30 mm, and screen out impurities to obtain qualified fiber;

[0011] Step two, chemical immersion: immerse the fiber obtained in step one in an alkaline immersion chemical to dissolve trace components and modify lignin in the fiber, maintain the total content of modified lignin and lignin above 30%, soften the fiber, and obtain semi-fiber;

[0012] Step three, grinding and separation: keep the fiber concentration of the semi-fiber obtained in step two at 10-35%, and grind and separate the semi-fiber into a reticular structure to obtain fine fiber;

[0013] Step four, high-concentration immersion waste liquid extraction and impurity removal: extract high-concentration immersion waste liquid by countercurrent washing method, and simultaneously elute impurities, so that the impurity content in the fine fiber obtained in step three is less than 25%, and obtain refined fiber;

[0014] Step five, fine grinding treatment: keep the fiber concentration of the refined fiber in step four at 3-10%, and perform fiber surface splitting and beating of the refined fiber to obtain finished fiber.

[0015] It should be noted that the alkali solution reacts with lignin, such as: generating alkali lignin or activating sulfonated lignin.

[0016] In some embodiments that can include the above embodiments, in step one, the cutting is completed by at least one of a knife disc grass cutter, a knife roller grass cutter, a grass rubbing machine, and a flying knife crusher; or

[0017] The screening is completed by at least one of a cyclone dust collector, a sheep horn screen, a cylindrical screen, and a conical screen; or

[0018] The impurities include coconut bran.

[0019] In some embodiments which can comprise the above-mentioned embodiments, in step two, the specific conditions of the impregnation are as follows: the solid-liquid ratio is 1:(3.5-10.0), the amount of alkali used is 2.0-12.0%, the impregnation temperature is 100-170°C, and the impregnation time is 10-90 min.

[0020] It should be noted that the amount of alkali used is calculated in terms of the amount of NaOH equivalent to the same molar weight.

[0021] In some embodiments which can comprise the above-mentioned embodiments, in step two, the alkali impregnation chemical is selected from one or more of NaOH, KOH, a mixture of NaOH and Na2SO3, and a mixture of KOH and Na2SO3.

[0022] The impregnation is completed using at least one of a vertical cooking pot, a steaming ball, a horizontal tube continuous digester, and a inclined tube continuous digester.

[0023] In some embodiments which can comprise the above-mentioned embodiments, in step three, the specific conditions of the refining separation are as follows: the refining zone refining gap is 0.3 mm, and the bundle fiber content is 10-50% under the condition of maintaining a 0.3 mm screen gap.

[0024] In some embodiments which can comprise the above-mentioned embodiments, in step three, the refining separation is completed using at least one of a high-pressure high-concentration disc refiner, an atmospheric high-concentration disc refiner, and a double-roll refiner.

[0025] In some embodiments which can comprise the above-mentioned embodiments, in step four, the extraction is completed using at least one of a single-screw extruder, a double-screw extruder, or a high-concentration inclined screen.

[0026] In some embodiments which can comprise the above-mentioned embodiments, in step five, the refining treatment is completed using at least one of a low-concentration disc refiner, a medium-concentration disc refiner, a conical refiner, and a beater.

[0027] The specific conditions of the beating are as follows: under the condition of a screen gap of 0.3 mm and a bundle fiber content of 5-50%, the material knuckle degree is 20-45 o SR.

[0028] The second aspect of the embodiments of the present application further provides a plant fiber material for low-density molded packaging products, which is prepared from coconut fiber and is prepared by the method described above.

[0029] The third aspect of the embodiments of the present application further provides the use of the plant fiber material for low-density molded packaging products prepared from coconut fiber by the method described above or the plant fiber material for low-density molded packaging products prepared from coconut fiber described above in the preparation of low-density molded packaging products.

[0030] Compared with the prior art, the embodiment of the present application has the following beneficial effects:

[0031] The present application uses coconut fiber as raw material, adheres to the fiber separation principle of high lignin retention and limited fiber separation, and prepares a special plant fiber material for low-density molded packaging products, which has the characteristics of high stiffness, low impurity content, and high content of net-shaped fiber bundles, etc. The lignin content is more than 30%, the bundle-shaped fiber content is 5-50% under the condition of 0.3mm screen gap, the impurity content is less than 25%, the prepared material is 20-45 o SR, which meets the requirements of high fiber bonding strength and low density, improves the industrialized utilization of coconut fiber and the added value of coconut fiber, improves the performance of low-density molded packaging products, and alleviates the pressure of insufficient supply of paper pulp raw materials in China. BRIEF DESCRIPTION OF DRAWINGS

[0032] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiment or prior art description will be briefly introduced below. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0033] Figure 1 It is an optical microscope photo of the transverse section of coconut fiber;

[0034] Figure 2 It is a scanning electron microscope photo of the transverse section of coconut fiber after liquid nitrogen freezing and fracturing;

[0035] Figure 3 It is an optical microscope photo of the plant fiber material for low-density molded packaging products in the embodiment of the present application, which uses coconut fiber as raw material. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical solutions and advantages of the embodiments of the present application more clear, the technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are some embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0037] In the following examples and comparative examples, all raw materials can be obtained by commercial purchase or conventional methods, unless otherwise specified.

[0038] Example 1

[0039] Step 1, coconut fiber preparation treatment: using a knife roll grass cutter, the coconut fiber raw material is cut into 15-25mm, and long filaments and coconut husks are removed through a series of goat horn screen and double cylinder screen, and the long filaments are sent back to the front of the grass cutter for re-cutting.

[0040] Step 2, chemical impregnation of the material: chemical impregnation is carried out using a vertical cooking pot, the impregnation chemical is selected from NaOH, the solid-liquid ratio is 1:4.5, the alkali dosage is 6.0%, the highest temperature environment is 155°C, indirect heating is adopted, the temperature is raised for 45min, the highest temperature is maintained for 30min, the chemical impregnation yield is 81±2%, and the total lignin content of the semi-material is 36±3%.

[0041] Step 3, semi-material grinding and separation: under the condition of maintaining a high concentration of 15% fiber concentration, limited grinding and separation is realized by high-concentration disc mill grinding (i.e. to obtain a network structure), the grinding gap of the refining area is 0.3mm, and the content of bundle-shaped fibers is maintained at 30±2% under the condition of maintaining a 0.3mm screen gap.

[0042] Step 4, high-concentration impregnation waste liquid extraction and impurity removal: three double-screw extruders are used in series, and the high-concentration impregnation waste liquid is extracted by using a countercurrent washing method, and impurities are washed out at the same time, wherein the screen plate hole diameters of the extruders are 6mm, 4mm and 3mm in sequence, the feeding fiber concentration is 10%, the discharging fiber concentration is 30%, and the content of fine material impurities is maintained at 20±3%.

[0043] Step 5, refining: two low-concentration disc mills are used in series, and the fiber surface is separated and feathered under the condition of maintaining a low concentration of 4% fiber concentration, the content of bundle-shaped fibers is 10±3% under the condition of maintaining a 0.3mm screen gap, and the beating degree of the finished material is controlled to be 35±2 o SR, and the finished material is obtained.

[0044] Example 2

[0045] Step 1, coconut fiber preparation treatment: using a knife roll grass cutter, the coconut fiber raw material is cut into 15-25mm, and long filaments and coconut husks are removed through a series of goat horn screen and double cylinder screen, and the long filaments are sent back to the front of the grass cutter for re-cutting.

[0046] Step 2, chemical impregnation of the material: chemical impregnation is carried out using a vertical cooking pot, the impregnation chemical is selected from NaOH, the solid-liquid ratio is 1:4.5, the alkali dosage is 6.0%, the highest temperature environment is 155°C, indirect heating is adopted, the temperature is raised for 45min, the highest temperature is maintained for 30min, the chemical impregnation yield is 81±2%, and the total lignin content of the semi-material is 36±3%.

[0047] Step 3, half stock refining separation: under the condition of keeping the fiber concentration of each section inlet at 15%, the three-section primary refining is carried out by a double-screw roll refiner, and the screen plate aperture of the three sections is 2.0, 0.8, and 0.5 mm respectively; then the fiber concentration is 20% and the refining gap is 0.3 mm under the condition of high-concentration disc refiner, so as to realize the bundle fiber content of 20±2% under the condition of 0.3 mm screen gap.

[0048] Step 4, high-concentration impregnation waste liquid extraction and impurity removal: two single-screw extruders are used in series to extract the high-concentration impregnation waste liquid and wash off the impurities at the same time. The screen plate aperture of the extruders is 5 mm and 3 mm in sequence, the feeding fiber concentration is 12%, and the discharging fiber concentration is 32%, so as to keep the fine impurity content at 15±3%.

[0049] Step 5, refining: two low-concentration conical refiners are used in series to carry out the fiber surface splitting and fanning under the condition of low fiber concentration of 5.0%, so as to realize the bundle fiber content of 8±3% under the condition of 0.3 mm screen gap, and control the beating degree of the finished material at 30±2 o SR, and obtain the finished material.

[0050] Example 3

[0051] The difference between this embodiment and Example 1 or Example 2 is that the cutting in Step 1 uses a grass rubbing machine or a flying knife crusher. The other steps and parameters are the same as those in Example 1 or Example 2.

[0052] Example 4

[0053] The difference between this embodiment and Example 1 or Example 2 is that the alkaline impregnation chemical in Step 2 is a mixed solution of NaOH and Na2SO3. The other steps and parameters are the same as those in Example 1 or Example 2.

[0054] Example 5

[0055] The difference between this embodiment and Example 1 or Example 2 is that the alkaline impregnation chemical in Step 2 is a mixed solution of KOH and Na2SO3. The other steps and parameters are the same as those in Example 1 or Example 2.

[0056] Example 6

[0057] The difference between this embodiment and Example 1 or Example 2 is that the impregnation in Step 2 uses a steaming ball or a continuous digester. The other steps and parameters are the same as those in Example 1 or Example 2.

[0058] Example 7

[0059] The difference between this embodiment and Example 1 or Example 2 is that the grinding separation in Step 3 uses a high-pressure high-concentration disc grinder or a double-roll refiner. The other steps and parameters are the same as in Example 1 or Example 2.

[0060] Example 8

[0061] The difference between this embodiment and Example 1 or Example 2 is that the extraction in Step 4 uses a high-concentration inclined screen. The other steps and parameters are the same as in Example 1 or Example 2.

[0062] Example 9

[0063] The difference between this embodiment and Example 1 or Example 2 is that the refining treatment in Step 5 uses a medium-concentration disc grinder or a beater. The other steps and parameters are the same as in Example 1 or Example 2.

[0064] Application Example

[0065] Low-density molded packaging products are mainly used for heavy-load cushion packaging against large impact or thermal insulation packaging with large air filling. Regardless of which type of packaging, the products are required to have large void fraction, and at the same time, the bonding strength between the junctions of the fibers in the product structure is required to be large to ensure the basic mechanical properties of the product.

[0066] To achieve this goal, the fiber material used to prepare the product is required to have high rigidity itself, which means that the fiber material cannot be excessively separated to maintain the basic size of the individual fibers, so the fiber separation needs to achieve "limited separation" different from the papermaking requirements; at the same time, the individual fibers cannot undergo excessive chemical reactions leading to excessive removal of lignin and degradation of cellulose leading to a decrease in crystallinity. According to this analysis, it means that the material cannot use chemical fiber separation methods mainly for the purpose of delignification, but only mechanical fiber separation methods.

[0067] At the same time, if mechanical fiber separation is used, according to the traditional pulping and papermaking theory, if the formation of the bonding strength between the fibers only relies on "hydrogen bonding", due to the presence of a large amount of residual lignin, the bonding strength between the fibers will not be satisfactory. However, a large number of previous studies have shown that, in terms of the molding process, in the basic process of "molding - dewatering - heat setting", the last "heat setting" link is under high temperature and high pressure conditions above 170°C, and under these conditions, in addition to the formation of hydrogen bonding between the fibers due to dewatering, there are also new fiber bonding effects such as lignin thermal reorganization, lignin polycondensation, and phenolic condensation. This means that a large amount of residual lignin fiber material will not cause a decrease in fiber bonding strength when used for papermaking, but on the contrary, it will be improved, which provides a basic theoretical basis for the design of the material of the present application.

[0068] 1. Biological form

[0069] From Figure 1 It can be seen that the coconut fiber is evenly distributed in the coconut husk under the filling of coconut shell, and the coconut fiber is gathered in a bundle in the form of coconut fiber, and there is no close connection between the coconut fibers.

[0070] From Figure 2 It can be seen that the coconut fiber is gathered in a bundle in the form of "cluster", the outer layer of the cluster has a shell tissue, the fibers in the cluster are arranged in parallel, and the position indicated by the arrow in the figure means that the fibers are separated due to the separation process, which means that the fibers are not firmly connected.

[0071] From the above observation, it can be obtained that: (1) the uniform and concentrated state of coconut fiber has the basic condition for realizing limited separation; (2) the relatively weak state of fiber combination in the cluster means that the coconut fiber has the condition of being separated into a net-like "fiber bundle" through processes such as swelling and rubbing.

[0072] From Figure 3 It can be seen that the fiber separation effect prediction based on the understanding of the raw material is confirmed, the bundle-shaped fibers in the fiber material exist in a net-like form, which not only maintains the basic rigidity of the material, but also moderately expands the specific surface area of the material, which helps to improve the fiber combination strength of the product.

[0073] 2, Chemical composition of coconut fiber

[0074] Table 1 is the chemical composition of various plant fiber raw materials including coconut fiber.

[0075] From Table 1, compared with other wood raw materials, coconut fiber has the characteristic of super-high extract content, which means that through simple chemical immersion, it is easier to realize the dissolution of trace components, improve the porosity of coconut fiber, and improve the uniformity of immersion liquid penetration, overcome the problem of penetration affected by the shell outer layer of coconut fiber.

[0076] From Table 1, it can also be seen that the lignin content of coconut fiber is much higher than that of general wood, which is not defined as "high-quality raw material" in the traditional pulping and papermaking sense, but has special positive significance in the sense of maintaining high lignin residue of the fiber material required by the present application.

[0077] Table 1 Chemical composition of commonly used plant fiber raw materials

[0078]

[0079] In summary, according to the characteristics of the fiber material required by the present application, the coconut fiber gathered in a cluster and the relatively weak fiber combination state of the fiber in the coconut shell mean that the coconut fiber has the natural condition of realizing limited separation of fibers and forming a net-like fiber bundle structure.

[0080] In addition, the higher extractive content of coconut coir means that the porous structure is easier to form during the impregnation process, which is conducive to the improvement of impregnation uniformity and is suitable for mechanical separation by chemical impregnation and mechanical separation.

[0081] Finally, the ultra-high lignin content of coconut coir lays the foundation for the high rigidity of the separated fiber material and the formation of fiber bonding strength during the molding and heat setting process.

[0082] 3. Performance test

[0083] Imported bleached conifer pulp, domestic waste paper pulp and coconut coir low-density molding plant fiber material were selected respectively, and refined to 35 o SR, vacuum suction forming at a fiber concentration of 2.5%, vacuum drying at 105°C to a moisture content of 30%, and hot pressing at 190°C to prepare different raw material and different density 200mm diameter molding sample boards. The basic performance test results are shown in Table 2.

[0084] Table 2 Comparison table of test results of molding sample boards made of various molding fiber materials

[0085]

[0086] Among them, the coconut coir fiber material is prepared by the process technology of Example 1.

[0087] As can be seen from Table 2, the low-density molding sample board prepared from coconut coir fiber material under classical molding process conditions has much higher mechanical strength than XPS (extruded polystyrene board) and thermal insulation performance not weaker than XPS, which has the potential to replace and further expand its application range in cushioning packaging and thermal insulation packaging fields.

[0088] Compared with the commercial pulp and waste paper pulp currently commonly used in the molding packaging industry, the material prepared in the present application has the advantages of lower density under the same molding process conditions, better thermal insulation performance and more excellent mechanical properties, which further illustrates the urgency of the present application to meet market demand.

[0089] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present application, but not to limit them; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that they can still modify the technical solutions described in the foregoing examples, or make equivalent substitutions for part or all of the technical features; and these modifications or substitutions do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for preparing a low-density molded packaging material using coconut fiber as raw material, characterized in that, Includes the following steps: Step 1: Pre-treatment: Cut the coconut shreds to 10-30mm, sieve out impurities, and obtain qualified shreds; Step 2, Chemical Impregnation: The filaments obtained in Step 1 are impregnated with alkaline impregnation chemicals to dissolve trace components and modify the lignin in the filaments, maintaining the total content of modified lignin and lignin at more than 30%, softening the filaments to obtain semi-finished material; Step 3, Grinding and Separation: While maintaining the fiber concentration in the semi-finished material obtained in Step 2 at 10-35%, the semi-finished material is ground and separated to form a network structure, resulting in fine material; Step 4: Extraction and removal of high-concentration impurity from impurity soaking liquid: The high-concentration impurity soaking liquid is extracted using a countercurrent washing method, while impurities are washed away, so that the impurity content in the fine material obtained in Step 3 is less than 25%, thus obtaining refined material; Step 5, Fine grinding treatment: While maintaining the fiber concentration in the refined material from Step 4 at 3-10%, the refined material is subjected to fiber surface fibrillation pulping to obtain the finished product; In step two, the specific conditions for impregnation are as follows: solid-liquid ratio of 1:(3.5-10.0), alkali dosage of 2.0-12.0%, impregnation temperature of 100-170℃, and impregnation time of 10-90 min; In step three, the specific conditions for the grinding and separation are as follows: the grinding gap in the fine grinding zone is 0.3 mm, and the bundled fiber content is 10-50% while maintaining a 0.3 mm sieve opening. The specific conditions for pulping are as follows: with a screen opening of 0.3 mm and a bundle fiber content of 5-50%, the freeness of the finished product is 20-45. o SR; Adhering to the fiber separation principle of high lignin retention and limited fiber separation, a low-density plant fiber material for molding packaging products with high stiffness, low impurity content, and high content of network fiber bundles was prepared. In the basic molding process of "molding-dehydration-heat setting", the final "heat setting" stage is carried out in a high temperature and high pressure environment above 170°C. Under these conditions, in addition to the hydrogen bonding formed between fibers due to dehydration, there are also new fiber bonding effects such as lignin thermal recombination, lignin condensation, and phenolic condensation.

2. The preparation method according to claim 1, characterized in that, In step one, the cutting is accomplished using at least one of a disc cutter, a roller cutter, a grass shredder, and a fly knife shredder; or The screening is performed using at least one of a cyclone dust collector, a horn screen, a cylindrical screen, and a conical screen; or The impurities include coconut coir.

3. The preparation method according to claim 1, characterized in that, In step two, the alkaline impregnation chemical is selected from one or more of NaOH, KOH, a mixture of NaOH and Na2SO3, and a mixture of KOH and Na2SO3; or The impregnation is performed using at least one of a vertical cooking pot, a steam ball, a horizontal tube continuous cooking device, and an inclined tube continuous cooking device.

4. The preparation method according to claim 1, characterized in that, In step three, the grinding and separation is carried out using at least one of a high-pressure high-consistency disc mill, an atmospheric-pressure high-consistency disc mill, and a twin-roll mill.

5. The preparation method according to claim 1, characterized in that, In step four, the extraction is performed using at least one of a single-screw extruder, a twin-screw extruder, or a high-concentration inclined screen.

6. The preparation method according to claim 1, characterized in that, In step five, the fine grinding process is carried out using at least one of a low-consistency disc mill, a medium-consistency disc mill, a conical refiner, and a pulping machine.

7. A plant fiber material for low-density molded packaging products made from coconut fiber, characterized in that, Prepared using the method described in any one of claims 1-6.

8. The application of the plant fiber material for low-density molded packaging products made from coconut fiber as described in claim 7 in the preparation of low-density molded packaging products.

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