Degradable 3D printing material and preparation method thereof

Abstract

The invention discloses a degradable 3D printing material and a preparation method thereof, the material takes modified coffee grounds as a core and cooperates with PLA, PBAT, nano montmorillonite, alkali lignin and chitosan, through rigid-flexible blending, nano reinforcement, interfacial compatibility and antibacterial synergy, the performance breakthrough that the tensile strength is greater than or equal to 45 MPa, the elongation at break is greater than or equal to 30%, the degradation rate after composting for 90 days is greater than or equal to 93%, and the antibacterial rate is greater than or equal to 95% is realized. The problems of pollution and single function of a traditional material are solved, and the material has remarkable environment-friendly and practical values.

Description

Technical Field

[0001] The present invention relates to the technical field of 3D printing materials, and in particular to a degradable 3D printing material and a preparation method thereof, which has the functions of high strength, high toughness and fast degradation. Background Art

[0002] Material pollution problem: Traditional 3D printing materials mostly use polyethylene (PE), which takes hundreds of years to degrade after being discarded, causing white pollution. Although pure polylactic acid (PLA)-based materials are degradable, they are brittle (elongation at break <15%) and have poor low-temperature resistance (embrittlement below -10°C).

[0003] Bottleneck of coffee grounds application: Coffee grounds contain 30%-50% cellulose and can be used as a natural reinforcing filler, but their polar surface has poor compatibility with the non-polar matrix of PLA. Direct addition can easily lead to interfacial debonding and a 10%-20% decrease in tensile strength. Summary of the invention

[0004] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a degradable 3D printing material and a preparation method thereof, which realizes the performance coupling of "high strength (≥40MPa) - high toughness (elongation at break ≥30%) - fast degradation (composting 90-day degradation rate ≥90%) - antibacterial property (inhibition rate ≥95%)" through multi-component synergistic modification, and realizes structural customization through 3D printing technology.

[0005] The present invention provides a degradable 3D printing material, which comprises the following raw materials in parts by weight: 20-35 parts of modified coffee grounds; 20-35 parts of PLA; 5-15 parts of polybutylene adipate / terephthalate (PBAT); 2-5 parts of nano-montmorillonite (MMT); 3-8 parts of alkali lignin (AL); 2-5 parts of chitosan (CS); 5-10 parts of plasticizer (glycerol); and 3-8 parts of compatibilizer (PLA-g-MA).

[0006] Furthermore, the preparation process of the modified coffee grounds is as follows: alkali treatment: the coffee grounds are soaked in a 5% by mass NaOH solution at 60° C. for 2 hours to remove grease and impurities, washed with water until neutral, dried at 60° C. for 48 hours, and crushed through an 80-mesh sieve; surface grafting: the alkali-treated coffee grounds are reacted with 3% by mass volume percentage (w / v) of methacrylic anhydride in a DMF solvent at 60° C. for 3 hours, and a carboxyl group (-COOH) is introduced through an esterification reaction, with a grafting rate of 12%-15%.

[0007] As a further solution of the present invention, the raw material composition includes the following parts by weight: 25 parts of modified coffee grounds, 30 parts of PLA, 10 parts of PBAT, 3 parts of MMT, 5 parts of AL, 3 parts of CS, 8 parts of glycerol, and 6 parts of PLA-g-MA.

[0008] As a further solution of the present invention, the raw material composition includes the following parts by weight: 20 parts of modified coffee grounds, 25 parts of PLA, 15 parts of PBAT, 4 parts of MMT, 8 parts of AL, 2 parts of CS, 10 parts of glycerol, and 8 parts of PLA-g-MA.

[0009] As a further solution of the present invention, PLA is used to provide a rigid skeleton, PBAT forms a flexible ligament, and the modified coffee grounds are interspersed at the interface between the two phases to form an interlocking structure through the π-π action of alkali lignin.

[0010] A method for preparing a degradable 3D printing material comprises the following steps: The modified coffee grounds, PLA, PBAT, MMT, AL, CS, glycerol, and PLA-g-MA are added to a high-speed mixer, melt-blended by a twin-screw extruder, and granulated to obtain φ1.75 mm wires. The high-speed mixer is mixed at 1500 rpm for 10 minutes; the extrusion conditions of the twin-screw extruder are 170-190° C. and the screw speed is 200 rpm. It is further preferred that color pastes of different colors are added as needed during the mixing process of the high-speed mixer.

[0011] The invention has the following beneficial effects: the modified coffee grounds of the invention have a natural fiber skeleton and antibacterial components, provide a cellulose-reinforced network and polyphenol antibacterial substances; PLA, a rigid matrix, forms a rigid-flexible blended phase with PBAT; PBAT, flexible toughening and compatibility promotion, improves PLA brittleness and enhances interface bonding; nano-montmorillonite (MMT), nano-enhancement, improved heat resistance, and a sheet structure forming a nano-scale reinforced network; alkali lignin (AL), interface compatibility, degradation catalysis, homologous lignin enhancement, and promotion of enzymatic hydrolysis; chitosan (CS), antibacterial synergy, improved flexibility, amino groups and coffee grounds hydroxyl groups form hydrogen bonds, and enhance antibacterial properties; glycerol, improves melt fluidity; PLA-g-MA, a compatibilizer, promotes PLA / PBAT / coffee grounds interface bonding.

[0012] In order to explain the present invention more clearly, the present invention is described in detail below in conjunction with specific embodiments. DETAILED DESCRIPTION

[0013] The present invention will be further explained below in combination with relevant knowledge, and described clearly and completely. Obviously, the described application is only a part of the embodiments of the present invention, rather than all the embodiments.

[0014] The test method is as follows: Tensile strength and elongation at break: According to GB / T1040.3 "Determination of tensile properties of plastics Part 3: Test conditions for films and sheets", the 3D printed material was made into dumbbell-shaped splines with a total length of 150mm, a gauge length of 50mm, and a thickness of 2mm. The test was carried out using a universal material testing machine, and the tensile speed was set to 50mm / min. During the experiment, the equipment automatically recorded the maximum tensile load and the elongation of the gauge section at break, and the tensile strength and elongation at break were calculated based on this. The tensile strength formula is σ=F / (b×h), where F is the maximum tensile load, b is the spline width, and h is the spline thickness; the elongation at break formula is δ=(ΔL / L0)×100%, ΔL is the elongation of the gauge section at break, and L0 is the initial length of the gauge. Composting degradation rate: Referring to ASTMD5988 "Standard Test Method for Disintegration of Plastic Materials under Composting Conditions" or ISO14855 "Determination of the Ultimate Aerobic Biodegradability of Materials under Controlled Composting Conditions", the 3D printed materials were made into standard sheets of 50mm×50mm×2mm. In the simulated composting environment, the temperature was controlled to be 58±2℃, the humidity was 50%-60%, and the oxygen content was ≥10%. The samples were buried in the composting medium, taken out on the 7th, 14th, 28th, 56th, and 90th days, washed with deionized water, freeze-dried, and weighed. The degradation rate was calculated according to the formula "degradation rate (%) = (m0-m) / m0×100%", where m0 is the initial mass of the sample and m is the mass after t days of degradation. At the same time, the amount of CO2 released during the composting process was measured with the help of an infrared gas analyzer (IRGA), and the biodegradation rate was calculated to verify whether the material was completely degraded into CO2 and water.

[0015] Impact strength: According to GB / T1843 "Determination of cantilever beam impact strength of plastics", a simply supported beam impact testing machine is used to carry out impact tests on notched specimens to evaluate the impact resistance of the material and assist in verifying the synergistic toughening effect. Interlayer bonding strength: By preparing specific 3D printed multi-layer specimens, a tensile testing machine is used to perform interlayer peeling tests on them. The maximum tensile force during the peeling process is recorded and converted into interlayer bonding strength (unit: N / cm), thereby evaluating the bonding effect between layers during the 3D printing process. Low temperature impact resistance: Place the sample in a -20°C environment for a certain period of time to allow it to reach temperature equilibrium, then perform an impact test on it to observe whether the sample breaks, so as to evaluate the impact performance of the material in a low temperature environment. Antibacterial rate: Using the plate count method, test bacteria such as Escherichia coli and Staphylococcus aureus were inoculated into the culture medium containing the sample extract. After culturing at an appropriate temperature and time, the inhibition rate was calculated by comparing the number of colonies in the experimental group and the control group to evaluate the antibacterial properties of the material.

[0016] Example 1, a degradable 3D printing material, material formula (weight parts): modified coffee grounds 25, PLA 30, PBAT 10, MMT 3, AL 5, CS 3, glycerol 8, PLA-g-MA 6. Preparation process: printing temperature 195 ° C, layer thickness 0.15 mm, filling rate 45%, printing time 90 min.

[0017] Comparative Example 1, a degradable 3D printing material, material formula (weight parts): modified coffee grounds 30, PLA35, MMT3, AL5, CS3, glycerol 8, PLA-g-MA6. Preparation process: printing temperature 195°C, layer thickness 0.15mm, filling rate 45%, printing time 90min.

[0018] Example 2, a degradable 3D printing material, material formula (by weight): 20 parts of modified coffee grounds, 25 parts of PLA, 15 parts of PBAT, 4 parts of MMT, 8 parts of AL, 2 parts of CS, 10 parts of glycerol, and 8 parts of PLA-g-MA.

[0019] Preparation process: printing temperature 195℃, layer thickness 0.15mm, filling rate 45%, printing time 90min.

[0020] In the present invention, coffee grounds are modified by the following steps to enhance the interfacial activity: Alkali treatment: coffee grounds were soaked in 5% by mass NaOH solution at 60°C for 2 hours to remove oil and impurities, washed with water until neutral, dried at 60°C for 48 hours, and crushed through an 80-mesh sieve; Surface grafting: Alkali-treated coffee grounds were reacted with 3% weight volume percentage (w / v) methacrylic anhydride in DMF solvent at 60°C for 3 hours. Carboxyl groups (-COOH) were introduced through esterification reaction, and the grafting rate reached 12%-15% (determined by infrared spectroscopy).

[0021] In the present invention, a method for preparing a degradable 3D printing material is provided, wherein modified coffee grounds, PLA, PBAT, MMT, AL, CS, glycerol, and PLA-g-MA are added into a high-speed mixer (1500 rpm, 10 min), melt-blended by a twin-screw extruder (170-190° C., screw speed 200 rpm), and granulated to obtain a φ1.75 mm wire.

[0022] In the present invention, a rigid-flexible balance is achieved (PLA+PBAT+coffee grounds): PLA provides a rigid skeleton, PBAT forms flexible ligaments, and modified coffee grounds (fiber length 0.5-2mm) are interspersed at the interface between the two phases. Through the π-π action of alkaline lignin, an interlocking structure of "rigid fiber-flexible resin" is formed, so that the tensile strength of the composite material reaches 45.6MPa, and the elongation at break is increased to 32.1% (530% higher than pure PLA), solving the contradiction between "strong and brittle".

[0023] Nano-molecular interface compatibility (MMT+AL+PLA-g-MA): Nano-montmorillonite (sheet thickness 1-2nm) is evenly dispersed at the PLA / PBAT interface to form "nano rivets"; alkaline lignin molecular chains entangle coffee grounds fibers and insert into the montmorillonite layers, reacting with the anhydride groups of PLA-g-MA to increase the interfacial adhesion from 8.5N / mm to 15.2N / mm (pulling test), and SEM shows no obvious phase separation at the fracture.

[0024] Synergy of the entire degradation pathway (PBAT+coffee grounds+AL): The aliphatic ester bond (-COO-) of PBAT is easily decomposed by lipase, and the generated succinic acid promotes the breakage of the ester bond of PLA; coffee grounds lignin and alkali lignin provide microbial attachment sites, making the 60-day composting degradation rate reach 91% (pure PLA is 75%), and the 90-day degradation rate is ≥93%, far exceeding the GB / T19277.1-2011 standard.

[0025] Natural antibacterial synergy (CS + coffee ground polyphenols): The amino group (-NH2) of chitosan (CS) forms an antibacterial complex with chlorogenic acid from coffee grounds. The inhibition rate against Escherichia coli and Staphylococcus aureus is >95%, which is 10% higher than that of single CS, and avoids the toxicity risk of chemical antibacterial agents.

[0026] Performance Testing: Test items Example 1 Example 2 Comparative Example 1 Commercially available PLA products Tensile strength (MPa) 45.6 48.3 38.2 28.5 Elongation at break (%) 32.1 35.8 20.5 15.2 Composting degradation rate (90 days) 93% 94.5% 85% 75% Impact strength (kJ / m²) 25.2 28.7 15.3 / Interlayer bonding strength (N / cm) 25.3 28.5 18.1 / Low temperature shock resistance (-20℃) No break No break Brittle fracture fracture Antibacterial rate (%) 96.8 97.2 92.3 / The material of the present invention forms a high-strength degradable composite system through the rigid-flexible blending of PBAT and PLA, the flake reinforcement of nano-montmorillonite, the interface compatibility of alkali lignin and the antibacterial synergy of chitosan.

[0027] The present invention discloses a degradable 3D printing material and a preparation method thereof. The material is based on modified coffee grounds, and is coordinated with PLA, PBAT, nano-montmorillonite, alkali lignin, and chitosan. Through rigid-flexible blending, nano-enhancement, interface compatibility, and antibacterial synergy, the material achieves performance breakthroughs of tensile strength ≥45MPa, elongation at break ≥30%, composting 90-day degradation rate ≥93%, and antibacterial rate ≥95%. It solves the pollution and single function problems of traditional materials and has significant environmental protection and practical value.

[0028] The present invention constructs a six-component synergistic system of "modified coffee grounds-PLA-PBAT-nano-montmorillonite-alkali lignin-chitosan", breaks through the performance bottleneck of a single material, and achieves a perfect balance of high strength, high toughness, and fast degradation; the raw materials contain more than 30% coffee grounds waste, the degradation products are carbon dioxide and water, the antibacterial ingredients are all natural extracts, and there is no risk of chemical residues.

[0029] In the present invention, it should be particularly noted that coffee grounds polyphenols + chitosan + alkali lignin have synergistic antibacterial effects: coffee grounds contain polyphenols such as chlorogenic acid and caffeine (accounting for 5%-8%), which destroy the phospholipid bilayer of the bacterial cell membrane and have an initial antibacterial rate of 85% against Escherichia coli; the amino group (-NH2) of chitosan (CS) combines with the phosphate group in the bacterial DNA to inhibit its replication, and its single antibacterial rate is 92%; the catechol structure of alkali lignin (AL) chelates the metal ions (such as Fe²+) necessary for bacteria and blocks the metabolic pathway. The three form an antibacterial network through hydrogen bonds (-OH / -NH2), which increases the antibacterial rate of the composite system to 96.8% (for Escherichia coli and Staphylococcus aureus), and the 30-day continuous antibacterial rate is >95% (the existing technology is only 70%-80%). Through 3D printing and integrated molding, chitosan forms antibacterial micro-areas with a thickness of 0.1-0.3mm on the surface of the material. The antibacterial rate reaches more than 90% within 2 hours after contact with feces, avoiding the shedding problem of traditional coating processes (such as the effect of spraying the antibacterial agent is attenuated by 50% after 2 times).

[0030] Moreover, PLA and nano-montmorillonite form a rigid skeleton, and the annular reinforcement design makes the side wall compressive strength of the molded structure (such as the storage structure of the pet poop bag) reach 50N / cm². PBAT (350% elongation at break) and glycerol plasticizer form flexible ligaments, and there is no breakage in the low-temperature (-20℃) impact test. The low-temperature resistance is 2 times higher than that of pure PLA (traditional PLA becomes brittle below -10℃), and it can adapt to the environment from the polar cold to the tropical high temperature (60℃). Rapid degradation and no residue, the aliphatic ester bond of PBAT (accounting for 15%-20%) decomposes before PLA, and the generated succinic acid acts as a catalyst to increase the PLA ester bond breakage rate by 25%. The 60-day degradation rate of composting reaches 91% (traditional PLA is only 75%), and the 90-day degradation rate is ≥93%, and the residual fragment size is <1mm (traditional materials are >2mm). The formula contains coffee grounds (agricultural waste) and alkaline lignin (recycled black liquor from papermaking), and the raw material cost is 25% lower than that of pure PLA. The degradation products are tested by GC-MS and contain only carbon dioxide, water and a small amount of short-chain fatty acids (concentration <0.1ppm), without harmful intermediates. The porous structure of coffee grounds (specific surface area 60m² / g) and the interlayer gaps of nano-montmorillonite form a "multi-level adsorption network", with an adsorption capacity of 15mg / g and 10mg / g for ammonia and hydrogen sulfide respectively. Compared with traditional PLA pet poop bags, the odor diffusion time is extended by 3 times (from 2 hours to 6 hours), improving the comfort of the use environment, and is particularly suitable for the storage structure of pet poop bags.

[0031] The technical principle of the present invention is described above in combination with the specific embodiments, which are only preferred implementations of the present invention. The protection scope of the present invention is not limited to the above embodiments, and all technical solutions under the idea of ​​the present invention belong to the protection scope of the present invention. Those skilled in the art can think of other specific implementations of the present invention without creative work, and these methods will fall within the protection scope of the present invention.

Claims

1. A degradable 3D printing material, characterized in that: The invention comprises the following raw materials in parts by weight: 20-35 parts of modified coffee grounds; 20-35 parts of PLA; 5-15 parts of polybutylene adipate / terephthalate; 2-5 parts of nano-montmorillonite; 3-8 parts of alkali lignin; 2-5 parts of chitosan; 5-10 parts of plasticizer; and 3-8 parts of compatibilizer. The preparation process of the modified coffee grounds is as follows: alkali treatment: the coffee grounds are soaked in a 5wt% NaOH solution at 60°C for 2h to remove grease and impurities, washed with water to neutrality, dried at 60°C for 48h, and crushed to pass through an 80-mesh sieve; surface grafting: the alkali-treated coffee grounds are reacted with 3% w / v methacrylic anhydride in a DMF solvent at 60°C for 3h to introduce carboxyl groups through an esterification reaction.

2. A degradable 3D printing material according to claim 1, characterized in that: The plasticizer is glycerol, and the compatibilizer is PLA-g-MA.

3. A degradable 3D printing material according to claim 2, characterized in that: The invention comprises the following raw materials in parts by weight: 25 parts of modified coffee grounds, 30 parts of PLA, 10 parts of polybutylene adipate / terephthalate, 3 parts of nano-montmorillonite, 5 parts of alkali lignin, 3 parts of chitosan, 8 parts of glycerol and 6 parts of PLA-g-MA.

4. A degradable 3D printing material according to claim 2, characterized in that: The invention comprises the following raw materials in parts by weight: 20 parts of modified coffee grounds, 25 parts of PLA, 15 parts of polybutylene adipate / terephthalate, 4 parts of nano-montmorillonite, 8 parts of alkali lignin, 2 parts of chitosan, 10 parts of glycerol and 8 parts of PLA-g-MA.

5. A degradable 3D printing material as claimed in claim 4, characterized in that: PLA is used to provide a rigid skeleton, poly(butylene adipate) / terephthalate forms a flexible ligament, and modified coffee grounds are interspersed at the interface between the two phases to form an interlocking structure through the π-π interaction of alkali lignin.

6. A method for preparing a 3D printing material as claimed in claim 5, characterized in that: The following steps are involved: Modified coffee grounds, PLA, polybutylene adipate / terephthalate, nano-montmorillonite, alkali lignin, chitosan, glycerol, and PLA-g-MA were added into a high-speed mixer, melt-blended in a twin-screw extruder, and granulated to obtain φ1.75 mm wires.

7. The method according to claim 6, characterized in that The high-speed mixer was mixed at 1500 rpm for 10 min; the extrusion conditions of the twin-screw extruder were 170-190° C. and the screw speed was 200 rpm.

8. The method according to claim 6, characterized in that During the mixing process of the high-speed mixer, different colors of color paste can be added as needed.