A photosensitive resin and its closed-loop recycling and recycling method for 3D printing

Abstract

This invention discloses a photosensitive resin comprising a precursor containing active functional groups, a precursor containing thiol groups, and a photoactivated catalyst. The active functional groups are selected from aldehyde groups, carbonyl groups, or hindered unsaturated double bonds. This invention also discloses a method for closed-loop recycling and cyclic 3D printing of the photosensitive resin, comprising: irradiating the photosensitive resin with a light source in a photopolymerization 3D printing device to obtain a 3D printed product; dissolving the 3D printed product to be recycled, and depolymerizing it to generate oligomers or monomers with thiol end groups and active functional groups, followed by adding a neutralizing agent as a recycling system; and re-adding the photoactivated catalyst to the recycling system to prepare a new photosensitive resin for cyclic 3D printing. This photosensitive resin can achieve closed-loop recycling and multiple cycles of photopolymerization 3D printing, and features mild recycling conditions and complete resource recovery of waste.

Description

Technical fields:

[0001] This invention relates to the field of photocurable 3D photosensitive resins, and more particularly to a photosensitive resin and a method for closed-loop recycling and cyclic 3D printing thereof. Background Technology

[0002] 3D printing technology, as an additive manufacturing method, has gained increasing attention and application in global manufacturing due to its unique flexibility, customization, and multi-degree-of-freedom characteristics. Among these, photosensitive resins are an important type of 3D printing raw material, widely applicable to various 3D printing technologies, such as stereolithography (SLA), digital light processing (DLP), and selective area photopolymerization (LCD). These resins typically consist of monomers containing photosensitive groups (such as acrylate groups and epoxy groups) and photoinitiators. When irradiated by a light source (usually ultraviolet or visible light), the photoinitiator is activated, initiating free radical or cationic polymerization of the monomers to form a cross-linked network. Besides 3D printing, these resins can also be used in photolithography, coatings, adhesives, and other fields. However, after polymerization, photosensitive resins usually form a network backbone composed of carbon-carbon or carbon-oxygen single bonds. This chemical structure is very stable, and the resulting network exhibits a three-dimensional cross-linked state, lacking the ability to depolymerize, thus making it impossible to recycle it to a precursor liquid state suitable for repolymerization. With the increasing popularity of 3D printing technology as the next generation of manufacturing tools, designing resin materials that can be recycled and printed in a closed loop has become a key focus and challenge in current sustainable development research.

[0003] By introducing dynamic covalent bonds into traditional acrylic resin systems, 3D printing networks can be depolymerized, achieving a degree of material chemical recycling. To achieve recyclable printing, current methods involve redistributing recycled material as filler in new photosensitive resins, or recovering some material through the depolymerization of dynamic ester / hindered urea bonds and regrafting acrylate groups for reprinting (e.g., the paper "Repeatedly recyclable 3D printing catalyst-free dynamic thermosetting photopolymers, Recyclable photoresins for light-mediated additive manufacturing towards loop 3D printing"). However, these systems require the introduction of a large amount of new photosensitive monomers for recyclable printing, resulting in low recycling rates (recycled raw materials account for less than 25% of new printing material) and changes in the properties of the pre-printing fluid (increased viscosity). Summary of the Invention

[0004] The purpose of this invention is to provide a photosensitive resin and a method for its closed-loop recycling and cyclic 3D printing, wherein the photosensitive resin can achieve closed-loop recycling and multiple cycles of photocuring 3D printing.

[0005] This invention provides the following technical solutions:

[0006] A photosensitive resin, comprising a precursor containing an active functional group, a precursor containing a thiol group, and a photoactivated catalyst, wherein the active functional group is selected from aldehyde, carbonyl, or hindered unsaturated double bond; wherein the precursor containing the active functional group is a monomer or oligomer, and the precursor containing the thiol group is a monomer or oligomer.

[0007] The precursor in the photosensitive resin provided by this invention comprises monomers and / or oligomers having thiol and aldehyde groups, carbonyl groups, or hindered unsaturated double bonds; by adjusting the structure and composition of the oligomers, the mechanical properties of the material can be effectively controlled to meet the needs of different application scenarios.

[0008] The photosensitive resin provided by this invention can generate a highly efficient catalyst after being irradiated by the light source of a photocurable 3D printing device, thereby achieving rapid polymerization of the resin and obtaining 3D printed products.

[0009] Preferably, the aldehyde-containing precursor includes, but is not limited to, one or more of vanillin, p-hydroxybenzaldehyde, p-anisaldehyde, p-tert-butylbenzaldehyde, p-cyanobenzaldehyde, m-hydroxybenzaldehyde, benzaldehyde, two-arm or multi-arm aldehydes derived from vanillin, furfural, 5-methylfurfural, 2-thiophenecarboxaldehyde, 5-methyl-2-thiophenecarboxaldehyde, and aldehyde-containing oligomers, some of which have the following structural formulas:

[0010]

[0011] Preferably, the carbonyl-containing precursor includes, but is not limited to, one or more of the following: 2,5-octanedione, spiro[5.5]undecane-3,9-dione, 2,7-dimethyl-3,6-octanedione, 2,15-hexadecanedione, 4,5-octanedione, 3-ethyl-2,4-pentanedione, 1,3-diphenylpropanetrione, 1,3,5-tribromo-1,3,5-thiazinane-2,4,6-trione, 1,3-dibenzoylacetone, 2,3,5-hexanetrione, heptane-2,3,5-trione, or ketone-containing oligomers, with some structural formulas as follows:

[0012]

[0013] Preferably, the precursor containing hindered unsaturated double bonds includes, but is not limited to, one or more of the following: diisopropylacetone, 5-methylhexa-1,4-dien-3-one, eugenone, 2,6-dimethyl-2,5,7-octtrien-4-one, 2,6-dimethyl-2,5-octadien-4-one, bimethylstyrene ketone, or oligomers containing hindered unsaturated double bonds, with some structural formulas as follows:

[0014]

[0015] Preferably, the thiol-containing precursor includes, but is not limited to, one or more of the following: 2,2-(1,2-ethylenedioxy)diethylthiol, stilbene-4,4-dithiol, 1,11-undecanedithiol, dithiothreitol, 1,16-hexadecanedithiol, hexa(ethylene glycol)disulfide, 1,6-hexyldithiol, 2,3-pentanedithiol, 3,7-dithia-1,9-nonanedithiol, bis(3-mercaptopropionic acid)ethylene glycol, 2-ethyl-2-(mercaptomethyl)-1,3-propanedithiol, pentaerythritol tetra(3-mercaptoacetic acid), pentaerythritol tetra(3-mercaptopropionic acid), pentaerythritol tetra(3-mercaptobutyric acid), or oligomers with thiol end groups.

[0016] Preferably, the photoactivated catalyst is selected from photo-acid production or photo-alkali production, and its photoexcitation wavelength is 200nm to 800nm.

[0017] Further preferably, the photo-acid-producing compounds include, but are not limited to, one or more of aromatic diazonium salts, diaryliodomonium salts, triarylthionium salts, dialkylformylmethylthionium salts, or ferrocene salts.

[0018] Further preferably, the photo-generated alkali includes, but is not limited to, one or more of the following: cobalt-ammonia complex, benzoyl photo-generated alkali, benzoylamine photo-generated alkali, quaternary ammonium salts containing aromatic ketone structures, or triaryl methanols.

[0019] Preferably, the photosensitive resin includes a light absorber. The light absorber is eosin Y, methyl red, Sudan red, Sudan black B, phthalocyanine red, phthalocyanine blue, or gold red, etc.

[0020] This invention also provides a method for closed-loop recycling and cyclic 3D printing of photosensitive resin, the method comprising:

[0021] (1) The above photosensitive resin is irradiated by the light source of the photocuring 3D printing equipment to obtain 3D printed products;

[0022] (2) Dissolve the 3D printed product to be recycled, and after dissolution, depolymerize to generate oligomers or / and monomers with end groups of thiol and active functional groups. Then add a neutralizing agent as a recycling system.

[0023] (3) The photoactivated catalyst was added back into the recycling system to prepare a new photosensitive resin for cyclic 3D printing.

[0024] Unlike traditional photopolymer 3D printing, which is based on chain polymerization mechanisms such as free radical or cationic polymerization, this invention uses photoactivated catalyst-catalyzed stepwise polymerization as the printing mechanism, with dynamic thioether bonds as the basic building blocks. Under mild conditions, dynamic thioether bonds can depolymerize into monomers and / or oligomers containing active groups. Thus, this invention achieves minimal or no resin consumption during the cyclic printing process, thereby realizing the complete resource utilization of waste. This not only has sustainability in terms of environmental protection, but also significantly reduces the cost of 3D photosensitive resin through recycling.

[0025] Preferably, the photopolymer 3D printing includes, but is not limited to, stereolithography (SLA), digital light processing (DLP), and selective area photopolymerization (LCD).

[0026] In step (2), the neutralizing reagent includes acidic and basic reagents. The acidic reagents include, but are not limited to, hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, acetic acid, carbonic acid, hydrogen cyanide, boric acid, citric acid, aluminum trichloride, ferric chloride, zinc chloride, hexafluoroantimonylic acid, boron trifluoride, boron chloride, phosphorus pentachloride, antimony pentafluoride, triarylphosphine salts, or diaryliodomonium salts. The basic reagents include, but are not limited to, sodium bicarbonate, sodium carbonate, potassium carbonate, sodium acetate, sodium hydroxide, potassium hydroxide, methylamine, ethylamine, dimethylamine, trimethylamine, triethylamine, aniline, pyridine, pyrrole, imidazole, morpholine, piperidine, guanidines, 1,5,7-triazabicyclo[4.4.0]dec-5-ene, 1,8-diazabicyclo[5.4.0]undec-7-ene, or 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene.

[0027] In step (2), the 3D printed product to be recycled is depolymerized under the action of a depolymerization catalyst; wherein, the residual photoactivated catalyst in the 3D printed product to be recycled is directly used as a depolymerization catalyst, or an acidic or alkaline reagent is added to act as a depolymerization catalyst simultaneously for depolymerization, wherein the acidic reagent is selected from one or more of the following: hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, acetic acid, carbonic acid, hydrogen cyanide, boric acid, citric acid, aluminum trichloride, ferric chloride, zinc chloride, hexafluoroantimonyic acid, boron trifluoride, boron chloride, phosphorus pentachloride, antimony pentafluoride, triarylphosphine salt, or diaryliodomonium salt. The alkaline reagent is selected from one or more of sodium bicarbonate, sodium carbonate, potassium carbonate, sodium acetate, sodium hydroxide, potassium hydroxide, methylamine, ethylamine, dimethylamine, trimethylamine, triethylamine, aniline, pyridine, pyrrole, imidazole, morpholine, piperidine, guanidines, 1,5,7-triazabicyclo[4.4.0]dec-5-ene, 1,8-diazabicyclo[5.4.0]undec-7-ene, or 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene; the amount of the depolymerization catalyst is 0.01 to 50 wt% of the mass of the photosensitive resin.

[0028] In step (2), a solvent is added to the 3D printed product to be recycled to dissolve it; the solvent includes, but is not limited to, one or more of water, formamide, dimethylformamide, dimethylacetamide, dimethyl sulfoxide, acetonitrile, hexamethylphosphoramide, alcohol, pyridine, furan, tetrahydrofuran, methyltetrahydrofuran, chloroform or toluene; the amount of solvent used in the depolymerization process is 0.1 to 100 times the mass of the photosensitive resin.

[0029] Further preferably, the solvent can be separated by methods such as vacuum distillation, absorption, condensation, adsorption, and membrane separation to achieve solvent recycling.

[0030] The depolymerization reaction temperature is 25–200°C; the reaction time is 1 min–50 h.

[0031] It should be noted that the inherent moisture or added moisture in the material can react with the dynamic thioether bonds in the polymer to generate oligomers and monomers containing active functional groups. The depolymerization catalyst can effectively promote this reaction process.

[0032] This method is simple to operate, has a short reaction time, and the solvent is easy to recover. All recovered products can be recycled, resulting in good economic benefits and social value.

[0033] Further optimization, taking polythioacetal as an example, shows that the thioacetal bond can be depolymerized under acid catalysis, and after the reaction, aldehyde and mercapto groups are generated (as shown in reaction formula I).

[0034]

[0035] Preferably, the recovered oligomers and monomers contain active functional groups at their end groups, including aldehyde groups, carbonyl groups, or hindered unsaturated double bonds and thiol groups. The topological structure of the oligomers can be linear, branched, or hyperbranched macromolecules.

[0036] Further preferably, the recovered oligomers and monomers account for 90% to 100% of the new photosensitive resin.

[0037] The photosensitive resin provided by this invention can be repeatedly recycled and 3D printed using the above method. Preferably, the number of times the closed-loop recycling and 3D printing is repeated is 1-10 times.

[0038] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0039] (1) The photosensitive resin recovered by the present invention can be directly used for printing without adding additional monomers, realizing multiple cycles of photocuring 3D printing. It has the advantages of mild recycling conditions, simple recycling path, and complete resource utilization of waste materials. It can solve the problem that the photosensitive resin obtained by the prior art cannot achieve complete closed-loop recycling and complete cycle printing.

[0040] (2) Unlike existing free radical or cationic chain polymerization, the photosensitive resin provided by the present invention adopts photocatalytic stepwise polymerization as its photocuring mechanism, which effectively solves the problem that traditional 3D printing materials are difficult to achieve closed-loop recycling. Attached Figure Description

[0041] Figure 1 This is a schematic diagram of the recycling process in Example 1.

[0042] Figure 2 The product obtained by 3D printing in Example 1. Detailed Implementation

[0043] The present invention will be further described in detail below with reference to embodiments. It should be noted that the embodiments described below are intended to facilitate the understanding of the present invention and are not intended to limit it in any way.

[0044] Example 1 (Rigid polydithioacetal polymer)

[0045] raw material:

[0046] Vanillin, McLean Pharmaceuticals; 2,2-(1,2-ethylenedioxy)diethylthiol, pentaerythritol tetrakis(3-mercaptopropionic acid) ester, TCI Pharmaceuticals; bis[(4-diphenylthionyl)benzene]sulfide-bis-hexafluoroantimony phosphate (PAG6976), Alibaba Group; sodium bicarbonate, tetrahydrofuran, Sinopharm Group; deionized water, Wahaha Group.

[0047] 3D printing:

[0048] A colorless and transparent resin is obtained by uniformly mixing vanillin, 2,2-(1,2-ethylenedioxydioxo)diethylthiol, and pentaerythritol tetrakis(3-mercaptopropionic acid) ester in a molar ratio of 1.4:0.6:0.4, and then adding 3 wt% PAG6976. The resin is then poured into an SLA 3D printer with a laser intensity of 300 mW / cm². 2 The printing speed is 500 mm / s, and the thickness of each layer is 200 μm. After printing, it is placed in a 70-degree vacuum oven for 24 hours for heat treatment, resulting in a yellow and transparent 3D printed product (such as...). Figure 2 (As shown). Mechanical properties were tested in a universal testing machine; the material's modulus was 141 MPa, and its elongation at break was 682%.

[0049] Recycling and cyclic printing:

[0050] like Figure 1 As shown, the 3D printed product, water, and tetrahydrofuran were added to a flask in a mass ratio of 1:0.02:4. The mixture was heated to 80°C and maintained for 120 minutes until the polymer was completely dissolved, yielding a transparent orange solution. The residual photo-generated acid in this solution served as the depolymerization catalyst. The solution was then treated with excess sodium bicarbonate as a neutralizing agent and stirred at room temperature for 5 minutes to neutralize the residual acid. Excess sodium bicarbonate was removed by filtration, and tetrahydrofuran was removed by rotary evaporation, ultimately yielding a liquid resin. Subsequently, 3 wt% PAG6976 and 10 wt% 2-butoxyethanol were added to the recovered resin to obtain a reprintable resin. The 3D printing and post-processing procedures were consistent with the above method. The mechanical properties of the obtained product were tested in a universal testing machine; the material modulus was 143 MPa, and the elongation at break was 539%.

[0051] Example 2 (Crystallic polydithioacetal polymer)

[0052] raw material:

[0053] Vanillin, McLean Inc.; 2,2-(1,2-ethylenedioxy)diethylthiol, pentaerythritol tetrakis(3-mercaptopropionic acid) and dibutyltin dilaurate, TCI Corporation; bis[(4-diphenylthionyl)benzene]sulfide-bis-hexafluoroantimony phosphate (PAG6976), Alibaba Group; sodium bicarbonate, toluene, methanol, 2-methyltetrahydrofuran, Sinopharm Corporation; deionized water, Wahaha Group; ε-caprolactone, ethylene glycol, triethylamine, ethyl acrylate 2-isocyanate, Aladdin Corporation.

[0054] Synthesis of mercapto-terminated polycaprolactone oligomers:

[0055] First, polycaprolactone was synthesized: ε-caprolactone (50 g), ethylene glycol (0.48 g), and dibutyltin dilaurate (0.1 g, catalyst) were mixed and stirred at 120 °C for 8 hours under a nitrogen atmosphere. The product was then dissolved in toluene (100 mL) and subsequently precipitated in methanol. This dissolution-precipitation process was repeated three times for purification. The final product was vacuum dried at room temperature for 24 hours.

[0056] Further synthesis of polycaprolactone diacrylate: Polycaprolactone (30 g), ethyl 2-isocyanate (1 g), and dibutyltin dilaurate (0.1 g, catalyst) were dissolved in toluene (15 mL), and then stirred at 80 °C for 4 hours under a nitrogen atmosphere. The solution precipitated in methanol, and the product was obtained after dissolution-precipitation purification. The final product was dried under vacuum at room temperature for 24 hours.

[0057] The final synthesis of thiol-terminated polycaprolactone oligomers was achieved by adding polycaprolactone diacrylate (10 g), 2,2-(1,2-ethylenedioxy)diethylthiol (0.62 g), toluene (10 g), and triethylamine (0.2 g) to a round-bottom flask and mixing thoroughly at room temperature until completely dissolved. The mixture was heated at 80 °C for 6 hours, and then filtered through methanol precipitation to obtain the product.

[0058] 3D printing:

[0059] Vanillin (0.24g), PTMP (0.19g), mercapto-terminated polycaprolactone oligomer (5.4g), acetonitrile (2.7g), and 1wt% PAG were mixed evenly until completely dissolved. A colorless, transparent resin was obtained. The resin was poured into an SLA 3D printer with a laser intensity of 300mW / cm². 2 The printing speed was 500 mm / s, and the thickness of each layer was 200 μm. After printing, the material was heat-treated in a 70-degree vacuum oven for 24 hours to obtain a white crystalline 3D printed product. Mechanical properties were tested in a universal testing machine; the material's modulus was 41.1 MPa, and its elongation at break was 1250%.

[0060] Recycling and cyclic printing:

[0061] The 3D-printed product, 2 wt% water, and 2-methyltetrahydrofuran were added to a flask in a 1:0.02:4 (mass ratio). The mixture was heated to 80°C and maintained for 120 minutes until the polymer was completely dissolved, yielding a transparent orange solution. The solution was then treated with excess sodium bicarbonate and stirred at room temperature for 5 minutes to neutralize any residual acid. Excess sodium bicarbonate was removed by filtration, and 2-methyltetrahydrofuran was removed by rotary evaporation, ultimately yielding a liquid resin. Subsequently, 3 wt% PAG6976 was added to the recovered resin to obtain a reprintable resin. The 3D printing and post-processing procedures were consistent with the methods described above. The mechanical properties of the obtained product were tested in a universal testing machine; the material modulus was 39.7 MPa, and the elongation at break was 1207%.

[0062] Example 3 (Polydithioacetal polymer, DLP printing)

[0063] raw material:

[0064] Furanaldehyde, Aladdin Corporation; 2,2-(1,2-ethylenedioxy)diethylthiol and pentaerythritol tetrakis(3-mercaptopropionic acid) ester, TCI Corporation; H6-isopropylbenzeneferrocene hexafluorophosphate (PAG261), Alibaba Group; Sodium bicarbonate and tetrahydrofuran, Sinopharm Group; Deionized water, Wahaha Group. 3D printing:

[0065] A colorless and transparent resin is obtained by uniformly mixing furanaldehyde, 2,2-(1,2-ethylenedioxydioxo)diethylthiol, and pentaerythritol tetrakis(3-mercaptopropionic acid) ester in a molar ratio of 1.4:0.6:0.4, and then adding 3 wt% PAG261. The resin is then poured into a DLP 3D printer with a light source intensity of 30 mW / cm². 2 A transparent 3D printed product can be obtained at a printing speed of 50mm / s.

[0066] Recycling and cyclic printing:

[0067] The 3D printed product, water, and tetrahydrofuran were added to a flask in a 1:0.02:4 (mass ratio). The mixture was heated to 80°C and maintained for 120 minutes until the polymer was completely dissolved, yielding a transparent orange solution. The solution was then treated with excess sodium bicarbonate and stirred at room temperature for 5 minutes to neutralize any residual acid. Excess sodium bicarbonate was removed by filtration, and tetrahydrofuran was removed by rotary evaporation, ultimately yielding a liquid resin. Subsequently, 3 wt% PAG261 was added to the recovered resin to obtain a photocurable resin. The printing process was repeated to obtain the 3D printed product.

[0068] Example 4 (Polydithioketal polymer, no organic solvent recovery)

[0069] raw material:

[0070] 2,15-Hexadecanedione, Aladdin Corporation; 2,2-(1,2-ethylenedioxy)bis(ethanethiol) and pentaerythritol tetrakis(3-mercaptopropionic acid) ester, TCI Corporation; bis[(4-diphenylthionyl)phenyl]sulfide-bis-hexafluoroantimony phosphate (PAG6976), Alibaba Group; sodium bicarbonate, Sinopharm Group; deionized water, Wahaha Group.

[0071] 3D printing:

[0072] A transparent resin is obtained by mixing 2,15-hexadecanedione, 2,2-(1,2-ethylenedioxy)diethylthiol, and pentaerythritol tetrakis(3-mercaptopropionic acid) in a molar ratio of 0.7:0.6:0.4 and then adding 3 wt% PAG6976. The resin is then poured into an SLA 3D printer with a laser intensity of 300 mW / cm². 2 A 3D printed product can be obtained at a printing speed of 500 mm / s.

[0073] Recycling and cyclic printing:

[0074] The 3D printed product and water were added to a flask at a ratio of 1:0.05. The mixture was heated to 80°C and maintained for 120 minutes until the polymer was completely dissolved, yielding a transparent orange solution. The solution was then treated with excess sodium bicarbonate and stirred at room temperature for 5 minutes to neutralize any residual acid. Excess sodium bicarbonate was removed by filtration, resulting in a liquid resin. Subsequently, 3 wt% PAG6976 was added to the recovered resin to obtain a reprintable resin. The printing process was repeated to obtain the 3D printed product.

[0075] Example 5 (Polydithioketal polymer, LCD printing)

[0076] raw material:

[0077] 2,5-Octanedione, Aladdin Corporation; 2,2-(1,2-ethylenedioxy)diethylthiol, pentaerythritol tetrakis(3-mercaptopropionic acid) ester, TCI Corporation; H6-cumeneferrocene hexafluorophosphate (PAG 261), Alibaba Group; Sodium bicarbonate, tetrahydrofuran, Sinopharm Group; Water, Wahaha Group; 3D printing:

[0078] A transparent resin is obtained by mixing 2,5-octanedione, 2,2-(1,2-ethylenedioxy)diethylthiol, and pentaerythritol tetrakis(3-mercaptopropionic acid) at a molar ratio of 0.7:0.6:0.4 and then adding 3 wt% PAG261. The resin is then poured into an LCD 3D printing instrument with a light source intensity of 30 mW / cm². 2 A transparent 3D printed product can be obtained at a printing speed of 50mm / s.

[0079] Recycling and cyclic printing:

[0080] A photocurable polymer, water, and tetrahydrofuran were added to a flask in a 1:0.02:4 (mass ratio). The mixture was heated to 80°C and maintained for 120 minutes until the polymer was completely dissolved, yielding a transparent orange solution. The solution was then treated with excess sodium bicarbonate and stirred at room temperature for 5 minutes to neutralize any residual acid. Excess sodium bicarbonate was removed by filtration, and tetrahydrofuran was removed by rotary evaporation, ultimately yielding a liquid resin. Subsequently, 3 wt% PAG261 was added to the recovered resin to obtain a recurable resin. The printing process was repeated to obtain 3D printed products.

[0081] Example 6 (Polythiodiene polymer)

[0082] raw material:

[0083] Diisopropylacetone, Sudan Red, Aladdin; 2,2-(1,2-ethylenedioxy)diethylthiol, pentaerythritol tetrakis(3-mercaptopropionic acid) ester, ketoibuprofen, 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD), TCI; toluene, acetic acid, Sinopharm.

[0084] Preparation of photoalkali:

[0085] 1,5,7-Triazabicyclo[4.4.0]dec-5-ene was complexed with ketoibuprofen to obtain photo-induced alkali production. The detailed steps are as follows: 0.200 g of TBD, 0.384 g of ketoibuprofen, and 2.366 g of toluene were weighed and added to a brown glass bottle wrapped in aluminum foil (protection from light is a crucial step). The mixture was stirred at room temperature for 2 hours until the reaction was almost complete. The resulting solution was stored in the dark.

[0086] 3D printing:

[0087] A transparent red resin is obtained by uniformly mixing diisopropylidene acetone, 2,2-(1,2-ethylenedioxy)diethylthiol, and pentaerythritol tetrakis(3-mercaptopropionic acid) ester in a molar ratio of 1.4:0.6:0.4, and then adding 3 wt% photo-based alkali and 0.1 wt% Sudan Red. The resin is then poured into an SLA 3D printing instrument with a laser intensity of 300 mW / cm². 2 A 3D printed product can be obtained at a printing speed of 500 mm / s.

[0088] Recycling and cyclic printing:

[0089] The 3D-printed product was heated to 80°C and held for 120 minutes until the polymer became liquid. Acetic acid was then added to neutralize it. Further, 3 wt% photo-alkali was added to the recycled resin to obtain a reprintable resin. The printing process was repeated to obtain the 3D-printed product.

[0090] Example 7 (Multiple-cycle printing of rigid polydithioacetal polymer)

[0091] raw material:

[0092] Vanillin, McLean Inc.; 2,2-(1,2-ethylenedioxy)diethylthiol, pentaerythritol tetrakis(3-mercaptoacetic acid) ester, TCI Corporation; bis[(4-diphenylthionyl)benzene]sulfide-bis-hexafluoroantimony phosphate (PAG6976), Alibaba Group; sodium bicarbonate, tetrahydrofuran, Sinopharm Group; deionized water, Wahaha Group.

[0093] 3D printing:

[0094] A colorless and transparent resin is obtained by mixing vanillin, 2,2-(1,2-ethylenedioxydioxo)diethylthiol, and pentaerythritol tetrakis(3-mercaptoacetic acid) in a molar ratio of 1.4:0.6:0.4 and then adding 3 wt% PAG6976. The resin is then poured into an SLA 3D printer with a laser intensity of 300 mW / cm². 2 The printing speed is 500 mm / s, and the thickness of each layer is 200 μm. After printing, it is placed in a 70-degree vacuum oven for 24 hours for heat treatment, resulting in a yellow and transparent 3D printed product (such as...). Figure 2 The mechanical properties of the material were tested in a universal testing machine. The modulus of the material was 141 MPa, and the elongation at break was 682%.

[0095] First loop printing:

[0096] The 3D-printed product, water, and tetrahydrofuran were added to a flask in a 1:0.02:4 (mass ratio). The mixture was heated to 80°C and maintained for 120 minutes until the polymer was completely dissolved, yielding a transparent orange solution. The solution was then treated with excess sodium bicarbonate and stirred at room temperature for 5 minutes to neutralize any residual acid. Excess sodium bicarbonate was removed by filtration, and tetrahydrofuran was removed by rotary evaporation, ultimately yielding a liquid resin. Subsequently, 3 wt% PAG6976 and 10 wt% 2-butoxyethanol were added to the recovered resin to obtain a reprintable resin. The 3D printing and post-processing procedures were consistent with the methods described above. The mechanical properties of the obtained product were tested in a universal testing machine; the material modulus was 143 MPa, and the elongation at break was 539%.

[0097] Second loop printing:

[0098] The 3D printed product, water, and tetrahydrofuran were added to a flask in a 1:0.02:4 (mass ratio). The mixture was heated to 80°C and maintained for 120 minutes until the polymer was completely dissolved, yielding a transparent orange solution. The solution was then treated with excess sodium bicarbonate and stirred at room temperature for 5 minutes to neutralize any residual acid. Excess sodium bicarbonate was removed by filtration, and tetrahydrofuran was removed by rotary evaporation, ultimately yielding a liquid resin. Subsequently, 3 wt% PAG6976 and 10 wt% 2-butoxyethanol were added to the recovered resin to obtain a reprintable resin. The 3D printing and post-processing procedures were consistent with the above method. The mechanical properties of the obtained product were tested in a universal testing machine; the material modulus was 143 MPa, and the elongation at break was 757%.

[0099] Third loop printing:

[0100] The 3D-printed product, water, and tetrahydrofuran were added to a flask in a 1:0.02:4 (mass ratio). The mixture was heated to 80°C and maintained for 120 minutes until the polymer was completely dissolved, yielding a transparent orange solution. The solution was then treated with excess sodium bicarbonate and stirred at room temperature for 5 minutes to neutralize any residual acid. Excess sodium bicarbonate was removed by filtration, and tetrahydrofuran was removed by rotary evaporation, ultimately yielding a liquid resin. Subsequently, 3 wt% PAG6976 and 10 wt% 2-butoxyethanol were added to the recovered resin to obtain a reprintable resin. The 3D printing and post-processing procedures were consistent with the methods described above. The mechanical properties of the obtained product were tested in a universal testing machine; the material modulus was 153 MPa, and the elongation at break was 530%.

Claims

1. A method for closed-loop recycling and recyclable 3D printing of photosensitive resin, characterized in that, The photosensitive resin comprises a precursor containing an active functional group, a precursor containing a thiol group, and a photoactivated catalyst. The active functional group is selected from aldehyde, carbonyl, or hindered unsaturated double bonds. The precursor containing the active functional group is a monomer or oligomer, and the precursor containing the thiol group is a monomer or oligomer. The photoactivated catalyst is selected from photoacid-producing or photoalkali-producing agents. The photoacid-producing agent is selected from one or more of aromatic diazonium salts, diaryliodothionium salts, triarylthionium salts, dialkylformylmethylthionium salts, or ferrocene salts. The photoalkali-producing agent is selected from one or more of cobalt-ammonia complexes, benzoyl photoalkali-producing agents, benzoylamine photoalkali-producing agents, quaternary ammonium salts containing aromatic ketone structures, or triaryl methanols. The method includes: (1) After the photosensitive resin is irradiated by the light source of the photocuring 3D printing equipment, a 3D printed product is obtained; (2) Dissolve the 3D printed products to be recycled, and after dissolution, depolymerize to generate oligomers or / and monomers with thiol end groups and active functional groups. Then add a neutralizing agent as a recycling system. (3) Add the photoactivated catalyst back into the recycling system to prepare a new photosensitive resin for cyclic 3D printing.

2. The method for closed-loop recycling and cyclic 3D printing of photosensitive resin according to claim 1, characterized in that, When the precursor containing the active functional group is an aldehyde-containing precursor, the aldehyde-containing precursor is selected from one or more of vanillin, p-hydroxybenzaldehyde, p-anisaldehyde, p-tert-butylbenzaldehyde, p-cyanobenzaldehyde, m-hydroxybenzaldehyde, benzaldehyde, vanillin-derived two-arm or multi-arm aldehydes, furfural, 5-methylfurfural, 2-thiophenecaraldehyde, 5-methyl-2-thiophenecaraldehyde, or aldehyde-containing oligomers; When the precursor containing the active functional group is a carbonyl-containing precursor, the carbonyl-containing precursor is selected from one or more of 2,5-octanedione, spiro[5.5]undecane-3,9-dione, 2,7-dimethyl-3,6-octanedione, 2,15-hexadecanedione, 4,5-octanedione, 3-ethyl-2,4-pentanedione, 1,3-diphenylpropanetrione, 1,3,5-tribromo-1,3,5-thiazinane-2,4,6-trione, 1,3-dibenzoylacetone, 2,3,5-hexanetrione, heptane-2,3,5-trione, or oligomers containing ketone groups; When the precursor containing the active functional group is a precursor containing a hindered unsaturated double bond, the precursor containing the hindered unsaturated double bond is selected from one or more of diisopropylacetone, 5-methylhexa-1,4-dien-3-one, eugenone, 2,6-dimethyl-2,5,7-octtrien-4-one, 2,6-dimethyl-2,5-octadien-4-one, bimethylstyrene ketone, or oligomers containing hindered unsaturated double bonds; The thiol-containing precursor is selected from one or more of the following: 2,2-(1,2-ethylenedioxy)bis(ethanethiol), stilbene-4,4-dithiol, 1,11-undecanedithiol, dithiothreitol, 1,16-hexadecanedithiol, hexa(ethylene glycol)disulfide, 1,6-hexyldithiol, 2,3-pentanedithiol, 3,7-dithia-1,9-nonanedithiol, bis(3-mercaptopropionic acid)ethylene glycol, 2-ethyl-2-(mercaptomethyl)-1,3-propanedithiol, pentaerythritol tetra(3-mercaptoacetic acid), pentaerythritol tetra(3-mercaptopropionic acid), pentaerythritol tetra(3-mercaptobutyric acid), or oligomers with thiol end groups.

3. The method for closed-loop recycling and cyclic 3D printing of photosensitive resin according to claim 1, characterized in that, The wavelength of photoexcitation of the photoactivated catalyst is 200 nm to 800 nm.

4. The method for closed-loop recycling and cyclic 3D printing of photosensitive resin according to claim 1, characterized in that, The photosensitive resin includes a light absorber.

5. The method for closed-loop recycling and cyclic 3D printing of photosensitive resin according to claim 1, characterized in that, In step (2), the neutralizing agent is selected from acidic or basic reagents. The acidic reagent is selected from one or more of hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, acetic acid, carbonic acid, hydrogen cyanide, boric acid, citric acid, aluminum trichloride, ferric chloride, zinc chloride, hexafluoroantimonyic acid, boron trifluoride, boron chloride, phosphorus pentachloride, antimony pentafluoride, triarylphosphine salt, or diaryliodomonium salt. The basic reagent is selected from sodium bicarbonate, sodium carbonate, potassium carbonate, sodium acetate, sodium hydroxide, potassium hydroxide, methylamine, ethylamine, dimethylamine, trimethylamine, triethylamine, aniline, pyridine, pyrrole, imidazole, morpholine, piperidine, guanidines, 1,5,7-triazabicyclo[4.4.0]dec-5-ene, 1,8-diazabicyclo[5.4.0]undec-7-ene, or 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene.

6. The method for closed-loop recycling and cyclic 3D printing of photosensitive resin according to claim 1, characterized in that, In step (2), the 3D printed product to be recycled is depolymerized under the action of a depolymerization catalyst; wherein, the residual photoactivated catalyst in the 3D printed product to be recycled is directly used as a depolymerization catalyst, or an acidic or alkaline reagent is added to act as a depolymerization catalyst simultaneously for depolymerization, wherein the acidic reagent is selected from one of hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, acetic acid, carbonic acid, hydrogen cyanide, boric acid, citric acid, aluminum trichloride, ferric chloride, zinc chloride, hexafluoroantimonyic acid, boron trifluoride, boron chloride, phosphorus pentachloride, antimony pentafluoride, triarylphosphine salt, or diaryliodomonium salt. Or a variety of alkaline reagents, wherein the alkaline reagent is selected from one or more of sodium bicarbonate, sodium carbonate, potassium carbonate, sodium acetate, sodium hydroxide, potassium hydroxide, methylamine, ethylamine, dimethylamine, trimethylamine, triethylamine, aniline, pyridine, pyrrole, imidazole, morpholine, piperidine, guanidines, 1,5,7-triazabicyclo[4.4.0]dec-5-ene, 1,8-diazabicyclo[5.4.0]undec-7-ene or 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene; the amount of the depolymerization catalyst is 0.01~50 wt% of the mass of the photosensitive resin.

7. The method for closed-loop recycling and cyclic 3D printing of photosensitive resin according to claim 1, characterized in that, In step (2), a solvent is added to the 3D printed product to be recycled to dissolve it; the solvent is selected from one or more of water, formamide, dimethylformamide, dimethylacetamide, dimethyl sulfoxide, acetonitrile, hexamethylphosphoramide, alcohol, pyridine, furan, tetrahydrofuran, methyltetrahydrofuran, chloroform or toluene; the amount of solvent used is 0.1 to 100 times the mass of the photosensitive resin.

8. The method for closed-loop recycling and cyclic 3D printing of photosensitive resin according to claim 1, characterized in that, In step (3), the recovered oligomers and / or monomers account for 90% to 100% of the new photosensitive resin.

9. The method for closed-loop recycling and cyclic 3D printing of photosensitive resin according to claim 1, characterized in that, The closed-loop recycling and cyclic 3D printing are performed 1-10 times.

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