A fully biodegradable starch foaming formulation and preparation method

Abstract

The application discloses a kind of full biodegradable starch foaming formula and preparation method, it is related to foaming material technical field, by composite modification starch, enzymatic fiber, nano reinforcing agent and composite foaming agent synergistic design, in combination with microwave auxiliary gradient hot-pressing forming process, realize the complete biodegradability of material in normal temperature natural environment and function integration.Product has high mechanical strength, antibacterial, high transparency and low water absorption cushioning performance, compared with traditional PLA material cost is greatly reduced, and no industrial compost facilities, from raw material to process whole process breaks through "performance-degradation-cost" restriction, realizes green material industrialization replacement.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of foaming materials, in particular to a full-biodegradable starch foaming formula and a preparation method. BACKGROUND

[0002] Traditional petroleum-based foam materials (such as EPS foam) have long dominated the fields of packaging, cushioning and thermal insulation due to their lightweight, low cost and mature technology, but their non-degradability leads to more than ten million tons of microplastics penetrating into the ecological chain every year, seriously threatening soil, water and biological health. In recent years, although biodegradable materials represented by PLA (polylactic acid) have achieved partial substitution, they are limited by the following bottlenecks:

[0003] Insufficient mechanical properties: the compressive strength of PLA foaming material is only 0.35 MPa, and the risk of brittle fracture is high, which is difficult to meet the high load requirement scenarios of electronic products, medical devices and the like;

[0004] Single function: existing biodegradable materials lack composite functions such as antibacterial, barrier, transparent, etc., and need to rely on additional coating or composite process, resulting in a sharp increase in cost (500%-800% higher than EPS);

[0005] Poor environmental adaptability: PLA degradation depends on industrial composting conditions (high temperature of 55-60℃), but only 3% of biodegradable plastics in the world enter the industrial composting system, and more than 90% still flow into landfills or natural environments, resulting in a sharp decrease in degradation efficiency.

[0006] Although starch-based biodegradable materials are considered as a replacement, natural starch has technical defects such as strong water absorption, poor mechanical properties, and narrow processing window, which leads to a market share of less than 3%. Existing technologies mostly improve performance through physical blending (such as starch-PLA composite) or chemical modification (such as grafting and crosslinking), but have high modification costs (more than 40% of the cost of raw materials), complex processes (special equipment is required), and unstable degradation period. SUMMARY

[0007] In view of the deficiencies of the prior art, the present application provides a full-biodegradable starch foaming formula and a preparation method, which solves the problems raised in the background art.

[0008] To achieve the above purpose, the present application realizes the following technical scheme: a full-biodegradable starch foaming formula, comprising, by weight percentage:

[0009] 50-80% of starch, 10-30% of modified starch, 5-15% of enzymatically treated plant fibers, 8-18% of nano-enhancing agent, 1-5% of release agent, 1-5% of composite foaming agent, and 0.5-3% of sodium alginate, wherein the enzymatic treatment is a composite treatment of cellulase and xylanase at a ratio of 1:0.5-1:2.

[0010] Further, the starch is any one of corn starch, potato starch, and cassava starch.

[0011] Further, the modified starch is a composite modified starch compounded from acetylated starch and oxidized starch at a ratio of 2:1 to 4:1.

[0012] Further, the enzymatic plant fiber is any one of enzymatic broadleaf pulp fiber, enzymatic needle leaf pulp fiber, and enzymatic wheat straw fiber.

[0013] Further, the nano-enhancing agent is a mixture of nano calcium carbonate and nano silicon dioxide, preferably, the mass ratio of nano calcium carbonate to nano silicon dioxide is 3:1 to 5:1.

[0014] Further, the composite foaming agent is a reaction-type foaming agent composed of sodium bicarbonate and citric acid at a ratio of 1:0.3 to 1:0.6, and a physical foaming agent puffed carbon-hydrogen compound accounting for 10% to 20% of the total amount.

[0015] Further, the formula further comprises 0.1% to 0.5% of nano-silver antibacterial agent, and the nano-silver particle size is 20nm to 50nm.

[0016] A preparation method of a fully biodegradable starch foaming formula, comprising the following steps:

[0017] (1) The plant fiber is pre-treated at 45°C to 55°C for 30 minutes to 60 minutes after being crushed by using a composite biological enzyme;

[0018] (2) The pre-treated fiber is mixed with other raw materials, and water is added to 40% to 50% of the total weight;

[0019] (3) Gradient stirring: stirring at 100rpm for 3 minutes to 5 minutes, stirring at 200rpm for 2 minutes to 3 minutes, and stirring at 300rpm for 3 minutes to 5 minutes;

[0020] (4) Microwave-assisted hot pressing: preheating for 20 seconds to 30 seconds at 2GHz to 5GHz, and then pressing at 170°C to 200°C and 0.3MPa to 0.5MPa for 40 seconds to 70 seconds.

[0021] Further, the microwave-assisted hot pressing adopts three-stage temperature control:

[0022] The first stage is maintained at 160°C to 170°C for 10 seconds to 15 seconds;

[0023] The second stage is heated to 180°C to 190°C and maintained for 20 seconds to 30 seconds;

[0024] The third stage is cooled to 170°C to 175°C and maintained for 10 seconds to 15 seconds.

[0025] Further, a vacuum defoaming treatment is added after the stirring process, the vacuum degree is -0.08 to -0.1 MPa, and the treatment time is 2 to 3 min.

[0026] The application provides a fully biodegradable starch foaming formula and a preparation method.

[0027] Through multi-component synergistic effect and process innovation, the starch-based material has high mechanical support (the load-bearing performance reaches the medical grade standard), complete biodegradability (non-toxic degradation products are compatible with soil / water), and multi-functional integration such as antibacterial, barrier and transparency under normal temperature and natural environment, breaks through the traditional biological material "performance-cost-environmental adaptability" triangular dilemma, and can provide a green solution that can replace petroleum-based plastics on a large scale. DETAILED DESCRIPTION

[0028] In the following, the technical solutions of the application will be described in detail through specific embodiments, but it should be clear that these embodiments are used for illustration, but not to be interpreted as limiting the scope of the application. Example 1

[0029] A fully biodegradable starch foaming formula is as follows:

[0030]

[0031] A preparation method is as follows:

[0032] 1. Fiber pretreatment: broadleaf pulp fiber is crushed to 100 mesh, composite enzymes (cellulase 2000 U / g, xylanase 1000 U / g) are added, and enzyme hydrolysis is stirred at 50°C for 45 min, then filtered and dried.

[0033] 2. Mixing and stirring:

[0034] The pretreated fiber is mixed with the remaining dry materials, and water is added in three times (total water amount 50%), and the stirring program is as follows:

[0035] 100 rpm stirring for 4 min (uniform mixing)

[0036] 200 rpm stirring for 2.5 min (initial dispersion)

[0037] 300 rpm stirring for 4 min (forming a thick slurry)

[0038] Vacuum defoaming (-0.09 MPa, 2.5 min) to remove bubbles.

[0039] 3. Microwave-assisted hot pressing:

[0040] Microwave preheating: 2.45 GHz microwave preheating for 25 s (target temperature 165°C)

[0041] Three-stage heat pressing:

[0042] First stage: 165°C / 0.3 MPa / 12 s (surface solidification)

[0043] Second stage: 185°C / 0.4 MPa / 25 s (foam expansion)

[0044] Third stage: 172°C / 0.35 MPa / 13 s (shape setting and cooling)

[0045] 4. Demolding and post-processing: naturally cooled to room temperature, and cut into 200x200x10 mm standard samples. Example 2

[0046] A fully biodegradable starch foaming formula is as follows:

[0047]

[0048] The preparation method is as follows:

[0049] 1. Fiber pretreatment: conifer pulp fibers are crushed to 120 mesh, and complex enzymes (cellulase 2500 U / g, xylanase 2000 U / g) are enzymolyzed at 50°C for 30 min, and then washed with ethanol and dried.

[0050] 2. Mixing and stirring:

[0051] Water is added in two times (total water amount 45%), and the gradient stirring program is adjusted as follows:

[0052] 100 rpm stirring for 5 min (high viscosity formula prolongs mixing time)

[0053] 200 rpm stirring for 3 min

[0054] 300 rpm stirring for 5 min

[0055] Vacuum degassing (-0.1 MPa, 3 min).

[0056] 3. Microwave-assisted heat pressing:

[0057] Microwave preheating: 5 GHz microwave preheating for 30 s (target temperature 170°C)

[0058] Three-stage heat pressing:

[0059] First stage: 160°C / 0.4 MPa / 15 s

[0060] Second stage: 180°C / 0.5 MPa / 30 s

[0061] Third stage: 170°C / 0.4 MPa / 15 s

[0062] 4. Post-treatment: Drying at 60°C for 2h to remove surface moisture. Example 3

[0063] A fully biodegradable starch foaming formulation as follows:

[0064]

[0065] Preparation method as follows:

[0066] 1. Fiber pretreatment: Wheat straw fiber was ground to 80 mesh, and then enzymatic hydrolysis was performed at 55°C for 60 min using a complex enzyme (cellulase 1500 U / g, xylanase 2250 U / g). After acid-base neutralization, freeze-drying was performed.

[0067] 2. Mixing and stirring:

[0068] Moisture gradient control: First add 30% water and stir at 100 rpm for 3 min, then add the remaining water and stir at 200 rpm for 2 min, and finally stir at 300 rpm for 3 min.

[0069] Vacuum degassing (-0.08 MPa, 2 min).

[0070] 3. Microwave-assisted hot-pressing molding:

[0071] Microwave preheating: 2 GHz microwave preheating for 20 s (target temperature 168°C)

[0072] Three-stage hot pressing:

[0073] First stage: 168°C / 0.35 MPa / 10 s

[0074] Second stage: 190°C / 0.45 MPa / 20 s

[0075] Third stage: 175°C / 0.3 MPa / 10 s

[0076] Surface treatment: Immediately after hot pressing, spray 0.5% chitosan solution (2 wt%) to enhance barrier properties.

[0077] Performance comparison test

[0078] 1. Test object

[0079] Existing product A: Traditional EPS foam (density 0.03-0.05 g / cm³, non-degradable, low cost, weak mechanical properties);

[0080] Existing product B: Commercially available PLA foaming material (density 0.12-0.18 g / cm³, compostable, high cost, high brittleness);

[0081] Example 1 (Corn starch-based high-strength antibacterial foaming material, density 0.28 g / cm³, focusing on mechanics and antibacterial properties);

[0082] Example 2 (Potato starch-based low-water absorption cushioning material, density 0.18 g / cm³, focusing on water absorption control and cushioning);

[0083] Example 3 (Cassava starch-based high-transparency barrier material, density 0.22 g / cm³, focusing on optical and barrier properties).

[0084] 2. Experimental data and comparative analysis

[0085] I. Comparison of mechanical properties

[0086]

[0087] Conclusion:

[0088] A. Example 1 achieves a 500% increase in compressive strength compared to PLA through high-content nano-enhancing agents (nano-calcium carbonate: nano-silicon dioxide = 4:1) and a three-stage heat pressing process, meeting the requirements of medical-grade load-bearing;

[0089] B. Example 2 uses a low-density formula (starch accounts for 60%) and nano-calcium carbonate as the main reinforcing agent (5:1), with a 28% increase in resilience compared to PLA, making it suitable for precision instrument shock absorption;

[0090] C. Example 3 balances mechanical stability and optical transparency through low-viscosity sodium alginate (100-200 mPa·s) and a bimodal pore size design.

[0091] II. Comparison of degradation performance

[0092]

[0093] Conclusion:

[0094] A. Example 2 improves microbial adhesion area through high-proportion nano-calcium carbonate (5:1) and enzymatic wheat straw fibers, with a 16% increase in degradation rate compared to PLA, and non-toxic degradation products that can improve soil;

[0095] B. Example 3 still maintains degradation performance after introducing nano-silver antibacterial agents, proving that antibacterial function and degradation are not in conflict.

[0096] III. Comparison of functional properties

[0097]

[0098] Conclusion:

[0099] A, Example 1 by nano silver antibacterial agent (20-30nm) with sodium alginate synergistic, antibacterial rate than PLA coating process to improve 99%, and no additional process;

[0100] B, Example 2 using high proportion of nano silica (3:1) and low water absorption starch (potato starch), water absorption rate than PLA reduced by 47%, suitable for high humidity environment;

[0101] C, Example 3 by low viscosity sodium alginate and nano calcium carbonate synergistic nucleation, light transmittance of 78%, compared with PLA transparent foam material to improve 65%.

Claims

1. A method of preparing a fully biodegradable starch foamed formulation, characterized by, Comprise, by weight percentage: Starch 50-80%, modified starch 10-30%, enzymatic treatment of plant fiber 5-15%, nano-enhancing agent 8-18%, release agent 1-5%, composite foaming agent 1-5%, sodium alginate 0.5-3%, the enzymatic treatment is composite treatment of cellulase and xylanase in a ratio of 1:0.5-1:2; The modified starch is a composite modified starch compounded by acetylated starch and oxidized starch in a ratio of 2:1-4:1; The enzymatic treatment of plant fiber uses any one of enzymatic treatment of broadleaf pulp fiber, enzymatic treatment of conifer pulp fiber, and enzymatic treatment of wheat straw fiber; The composite foaming agent is a reaction type foaming agent composed of sodium bicarbonate and citric acid in a ratio of 1:0.3-1:0.6, and a physical foaming agent puffed carbon-hydrogen compound accounting for 10-20% of the total amount; The preparation method comprises the following steps: (1) After the plant fiber is crushed, it is pretreated at 45-55℃ for 30-60min using composite biological enzymes; (2) Mix the pretreated fiber with other raw materials, and add water to 40-50% of the total weight; (3) Gradient stirring: 100rpm stirring for 3-5min, 200rpm stirring for 2-3min, and 300rpm stirring for 3-5min; (4) Microwave-assisted hot pressing: first preheat for 20-30s at 2-5GHz, and then press at 170-200℃ and 0.3-0.5MPa for 40-70s; The microwave-assisted hot pressing adopts three-stage temperature control: The first stage is maintained at 160-170℃ for 10-15s; The second stage is heated to 180-190℃ and maintained for 20-30s; The third stage is cooled to 170-175℃ and maintained for 10-15s; The nano-enhancing agent is a mixture of nano calcium carbonate and nano silicon dioxide, and the mass ratio of nano calcium carbonate to nano silicon dioxide is 3:1-5:

1.

2. The process for preparing a fully biodegradable starch foamed formulation according to claim 1, characterized in that, The starch uses any one of corn starch, potato starch, and cassava starch.

3. The method of making a fully biodegradable starch foam formulation according to claim 1, wherein, It also contains 0.1-0.5% of nano-silver antibacterial agent, and the particle size of the nano-silver is 20-50nm.

4. The method of making a fully biodegradable starch foam formulation according to claim 1, wherein, A vacuum degassing treatment is added after the stirring process, the vacuum degree is-0.08--0.1MPa, and the treatment time is 2-3min.

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