A depolymerized shrimp and crab shell modified low free formaldehyde amino resin adhesive and preparation method thereof

Abstract

The present invention provides a low-free formaldehyde amino resin adhesive modified by depolymerization of shrimp and crab shells and a preparation method thereof. The shells of crustaceans are crushed into powder by mechanical force to reduce their particle size, form micrometer-scale shrimp and crab shell particles, and increase the specific surface area. Part of the calcium carbonate and protein in the shrimp and crab shell powder are dissolved in turn with acid and alkali, respectively, and a large amount of chitosan will be exposed on the surface of the shrimp and crab shell particles. The protein is dissolved with alkali solution, which will also cause the chitosan to deacetylate and produce functional groups such as ‑NH2. In this way, a large amount of amino-containing chitosan will be generated on the surface of the particles. The amino group reacts with the free formaldehyde / hydroxymethyl in the urea-formaldehyde resin, which not only strengthens the resin but also reduces the free formaldehyde content.

Description

Technical Field

[0001] The invention belongs to the field of adhesive preparation, and particularly relates to a low-free formaldehyde amino resin adhesive modified by depolymerizing shrimp and crab shells and a preparation method thereof. Background Art

[0002] The combination of adhesives and wood can realize the use of small wood materials in large quantities and inferior wood materials in high-quality ways. Its annual consumption in the wood processing industry accounts for more than 60% of the total output. Among them, amino resin adhesives represented by urea-formaldehyde resin (UF) account for more than 80% of the wood adhesive consumption due to its cost-effectiveness. The problem of free formaldehyde release caused by it has also long plagued the development of the wood processing industry. Adding formaldehyde scavengers to UF, partially replacing or completely replacing the formaldehyde in UF with non-formaldehyde materials, and changing the synthesis process of UF to reduce the F / U molar ratio to reduce the amount of formaldehyde are the three common ways to reduce the free formaldehyde content in UF. For example, Qiao Zhengyang et al. used glycoluril / phenol as formaldehyde scavenger. By changing the amount of glycoluril and phenol added, the free formaldehyde in UF was reduced to a minimum mass fraction of about 0.0426% (Qiao Zhengyang, Li Longjiang. Preparation and performance study of phenol / glycouril modified urea-formaldehyde resin adhesive [J]. Modern Chemical Industry, 2018, 38(05): 131-133+135.). Jiang Xin et al. synthesized melamine-urea-glyoxal resin and used it to modify poplar wood boards. When the molar ratio of melamine, urea and glyoxal was 0.08:0.4:1, the flexural strength and elastic modulus of the modified poplar wood increased the most, by 17.5% and 18.5% respectively (Jiang Xin, Li Qiheng, Zhang Jun et al. Curing performance and structural analysis of melamine-urea-glyoxal co-condensation resin [J]. Chemical Research and Application, 2023, 35(08):1897-1907.). Chen Lianqing successfully synthesized a modified UF with low free formaldehyde content by reducing the F / U ratio, adding polyvinyl alcohol and melamine for modification, and feeding urea three times (Chen Lianqing. Optimization of the synthesis process of environmentally friendly urea-formaldehyde resin adhesive [J]. Journal of South-Central University for Nationalities (Natural Science Edition), 2007(03):4-7.). However, the cross-linking degree of these modified adhesives after curing is low, resulting in a decrease in bonding strength. Summary of the invention

[0003] The object of the present invention is to provide a low-free formaldehyde amino resin adhesive modified by depolymerizing shrimp and crab shells and a preparation method thereof.

[0004] To achieve the above object, the present invention adopts the following technical solution:

[0005] A method for preparing a low-free formaldehyde amino resin adhesive modified by depolymerizing shrimp and crab shells, comprising the following steps:

[0006] Step 1, depolymerization of shrimp and crab shells:

[0007] (1) Crush the shrimp and crab shells into particles ≥2000 mesh and set aside;

[0008] (2) Mix the shrimp and crab shell particles with the quantitative acid solution, stir at 60 rpm for 10 min at room temperature, let stand for 20 min, and collect the bottom sediment;

[0009] (3) mixing 10-50 parts by weight of the precipitate from step (2) with 10-50 parts by weight of an alkaline solution, and keeping the mixture at 50-90° C. for 10-30 minutes to prepare depolymerized shrimp and crab shells for later use;

[0010] Step 2, preparation of low free formaldehyde amino resin adhesive:

[0011] 1) Add 300-600 parts by weight of formaldehyde solution to the reactor, raise the temperature to 50°C, and keep warm;

[0012] 2) Add 10-20 parts by weight of depolymerized shrimp and crab shells, add 100-200 parts by weight of amino compounds, raise the temperature to 85-95°C, and keep warm for 30-50 minutes;

[0013] 3) Cool down to 80-85℃, adjust pH to 4.8 with acid solution, and keep warm for 10-30min;

[0014] 4) Add 100-200 parts by weight of amino compound and keep warm at 85°C for 20-40 minutes;

[0015] 5) Add 50-100 parts by weight of modifier, stir at 85°C for 30 minutes;

[0016] 6) Cooling to 35° C. within 40 minutes and discharging the material to obtain the low free formaldehyde amino resin adhesive.

[0017] Furthermore, the modifier is crustacean shell particles, preferably the shells of one or more of hairy crabs, swimming crabs, king crabs, lobsters, and prawns are crushed into particles with a particle size of ≥2000 mesh.

[0018] Furthermore, the alkaline solution is a solution of one or more of sodium hydroxide, potassium hydroxide, calcium hydroxide, and ammonia water, with a concentration of 15wt%-25wt%.

[0019] Furthermore, the acid solution is a mixture of one or more of hydrochloric acid, sulfuric acid, formic acid, acetic acid, and oxalic acid, with a concentration of 1wt%-10wt%.

[0020] Furthermore, the amino compound is urea or melamine.

[0021] Furthermore, the concentration of the formaldehyde solution is 37 wt %.

[0022] Furthermore, the water is boiler steam condensate.

[0023] Principle: Use mechanical force to crush the shells of crustaceans into powder, reduce their particle size, form micrometer-sized shrimp and crab shell particles, and increase the specific surface area. Use acid and alkali to dissolve part of the calcium carbonate and protein in the shrimp and crab shell powder, respectively, and a large amount of chitosan will be exposed on the surface of the shrimp and crab shell particles. Using alkali to dissolve protein will also cause chitosan to deacetylate and produce -NH 2 In this way, a large amount of chitosan containing amino groups will be generated on the surface of the particles. The amino groups react with the free formaldehyde / hydroxymethyl in the urea-formaldehyde resin, which not only strengthens the resin but also reduces the free formaldehyde content.

[0024] The advantages of the present invention are:

[0025] The low free formaldehyde amino resin adhesive cleverly depolymerizes the shrimp and crab shells into particles with amino structures on the surface, and further utilizes the amino structures on the surface of the shrimp and crab shell particles to react with formaldehyde in the preparation process of the amino resin, which not only absorbs free formaldehyde but also participates in the polycondensation reaction of the resin, thereby reducing the free formaldehyde content of the amino resin. The shrimp and crab shell particles can enhance the strength of the resin after curing. The cross-linked and cured adhesive layer is an organic / inorganic hybrid three-dimensional network structure containing shrimp and crab shell particles, which has excellent heat resistance, mechanical strength and water resistance. The present invention not only makes full use of waste from fishery production, but also improves the water-resistant bonding performance of the adhesive after curing; compared with ordinary amino resin adhesives, the adhesive exhibits the advantages of good heat resistance, low free formaldehyde content and high strength. DETAILED DESCRIPTION

[0026] In order to make the above features and advantages of the present invention more clearly understood, the following embodiments are given for detailed description. The methods of the present invention are all conventional methods in the art unless otherwise specified.

[0027] Example 1

[0028] A method for preparing a low-free formaldehyde amino resin adhesive modified by depolymerizing shrimp and crab shells, comprising the following steps:

[0029] Step 1, lobster shell depolymerization:

[0030] (1) Crush the lobster shells into particles ≥2000 mesh and set aside;

[0031] (2) Mix the lobster shell particles with 10 wt% hydrochloric acid solution at a solid-liquid ratio of 3:1 g / ml, stir at 60 rpm for 10 min at room temperature, let stand for 20 min, and collect the bottom sediment;

[0032] (3) 10 parts by weight of the precipitate from step (2) and 10 parts by weight of a 15 wt% sodium hydroxide solution are mixed and kept at 50° C. for 10 minutes to prepare depolymerized lobster shells for later use;

[0033] Step 2, preparation of low free formaldehyde amino resin adhesive:

[0034] 1) Add 300 parts by weight of 37wt% formaldehyde solution to the reactor, raise the temperature to 50°C, and keep warm;

[0035] 2) Add 10 parts by weight of depolymerized lobster shells and 100 parts by weight of urea, raise the temperature to 85°C, and keep warm for 30 minutes;

[0036] 3) Cool down to 80℃, adjust pH to 4.8 with hydrochloric acid, and keep warm for 10 minutes;

[0037] 4) Add 100 parts by weight of urea and keep warm at 85°C for 20 minutes;

[0038] 5) Add 50 parts by weight of lobster shell particles as a modifier, heat at 85°C, and stir for 30 minutes;

[0039] 6) Cooling to 35° C. within 40 minutes and discharging the material to obtain the low free formaldehyde amino resin adhesive.

[0040] The ordinary adhesive in the control group is obtained by replacing the 10wt% hydrochloric acid solution and the 15wt% sodium hydroxide solution in the above step 1 with boiler steam condensate, respectively, and leaving other ingredients unchanged.

[0041] Example 2

[0042] A method for preparing a low-free formaldehyde amino resin adhesive modified by depolymerizing shrimp and crab shells, comprising the following steps:

[0043] Step 1, depolymerization of hairy crab shells:

[0044] (1) Crush the hairy crab shells into particles ≥2000 mesh and set aside;

[0045] (2) Mix the hairy crab shell particles with 5 wt% sulfuric acid solution at a solid-liquid ratio of 1:2 g / ml, stir at 60 rpm for 10 min at room temperature, let stand for 20 min, and collect the bottom sediment;

[0046] (3) 30 parts by weight of the precipitate from step (2) was mixed with 30 parts by weight of a 20 wt% potassium hydroxide solution, and the mixture was kept at 70° C. for 20 min to prepare depolymerized hairy crab shells for later use;

[0047] Step 2, preparation of low free formaldehyde amino resin adhesive:

[0048] 1) Add 450 parts by weight of 37wt% formaldehyde solution to the reactor, raise the temperature to 50°C, and keep warm;

[0049] 2) Add 15 parts by weight of depolymerized hairy crab shells and 150 parts by weight of melamine, raise the temperature to 90° C., and keep warm for 40 minutes;

[0050] 3) Cool down to 82°C, adjust pH to 4.8 with sulfuric acid solution, and keep warm for 20 minutes;

[0051] 4) Add 150 parts by weight of melamine and keep warm at 85°C for 30 minutes;

[0052] 5) Add 70 parts by weight of hairy crab shell particles as a modifier, heat at 85°C, and stir for 30 minutes;

[0053] 6) Cooling to 35° C. within 40 minutes and discharging the material to obtain the low free formaldehyde amino resin adhesive.

[0054] The ordinary adhesive in the control group is obtained by replacing the 5wt% sulfuric acid solution and the 20wt% potassium hydroxide solution in step 1 with boiler steam condensate, respectively, with no other changes.

[0055] Example 3

[0056] A method for preparing a low-free formaldehyde amino resin adhesive modified by depolymerizing shrimp and crab shells, comprising the following steps:

[0057] Step 1, depolymerization of swimming crab shells:

[0058] (1) Crush the swimming crab shells into particles ≥2000 mesh and set aside;

[0059] (2) Mix the swimming crab shell particles with 2 wt% formic acid solution at a solid-liquid ratio of 1:5 g / ml, stir at 60 rpm for 10 min at room temperature, let stand for 20 min, and collect the bottom sediment;

[0060] (3) 50 parts by weight of the precipitate obtained in step (2) was mixed with 50 parts by weight of a 25 wt% ammonia solution, and the mixture was kept at 90° C. for 30 min to prepare depolymerized swimming crab shells for later use;

[0061] Step 2, preparation of low free formaldehyde amino resin adhesive:

[0062] 1) Add 600 parts by weight of 37wt% formaldehyde solution to the reactor, raise the temperature to 50°C, and keep warm;

[0063] 2) adding 20 parts by weight of depolymerized swimming crab shells and 200 parts by weight of urea, raising the temperature to 95°C and keeping the temperature for 50 minutes;

[0064] 3) Cool down to 85°C, adjust pH to 4.8 with formic acid solution, and keep warm for 30 minutes;

[0065] 4) Add 200 parts by weight of urea and keep warm at 85°C for 40 minutes;

[0066] 5) Add 100 parts by weight of the modifying agent, swimming crab shell particles, and stir at 85°C for 30 minutes;

[0067] 6) Cooling to 35° C. within 40 minutes and discharging the material to obtain the low free formaldehyde amino resin adhesive.

[0068] The ordinary adhesive in the control group is obtained by replacing the 2wt% formic acid solution and the 25wt% ammonia solution in step 1 with boiler steam condensate, respectively, with no other changes.

[0069] Performance: This adhesive can be used to produce particleboard, fiberboard, plywood and other artificial boards. For example, when used to make plywood, the double-sided glue application amount is 240-300g / m 2 , which can be achieved by manual gluing or roller gluing; at room temperature, with a surface pressure of 5-10MPa, pre-pressing for 0.5-1 hour, and then hot pressing at 1.0MPa, 110-130℃, 1-2 min / mm, the bonding strength can meet the requirements of Class II plywood in GB / T 9846-2015, and the free formaldehyde content of the prepared artificial board can reach E0 level, which can be widely used in furniture or decoration industry, and has broad application prospects.

[0070]

[0071] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made according to the scope of the patent application of the present invention should fall within the scope of the present invention.

Claims

1. A method for preparing a low-free formaldehyde amino resin adhesive modified by depolymerizing shrimp and crab shells, characterized in that: The following steps are involved: Step 1, depolymerization of shrimp and crab shells: (1) Crush the shrimp and crab shells into particles ≥2000 mesh and set aside; (2) Mix the shrimp and crab shell particles with the quantitative acid solution, stir at 60 rpm for 10 min at room temperature, let stand for 20 min, and collect the bottom sediment; (3) mixing 10-50 parts by weight of the precipitate from step (2) with 10-50 parts by weight of an alkaline solution, and keeping the mixture at 50-90° C. for 10-30 minutes to prepare depolymerized shrimp and crab shells for later use; Step 2, preparation of low free formaldehyde amino resin adhesive: 1) Add 300-600 parts by weight of formaldehyde solution to the reactor, raise the temperature to 50°C, and keep warm; 2) Add 10-20 parts by weight of depolymerized shrimp and crab shells, add 100-200 parts by weight of amino compounds, raise the temperature to 85-95°C, and keep warm for 30-50 minutes; 3) Cool down to 80-85℃, adjust pH to 4.8 with acid solution, and keep warm for 10-30min; 4) Add 100-200 parts by weight of amino compound and keep warm at 85°C for 20-40 minutes; 5) Add 50-100 parts by weight of modifier, stir at 85°C for 30 minutes; 6) Cooling to 35° C. within 40 minutes and discharging the material to prepare the low free formaldehyde amino resin adhesive; The modifier is a crustacean shell particle; The alkaline solution is a solution of one or more of sodium hydroxide, potassium hydroxide, calcium hydroxide, and ammonia water, with a concentration of 15wt%-25wt%; The acid solution is one or a mixture of hydrochloric acid, sulfuric acid, formic acid, acetic acid, and oxalic acid, with a concentration of 1wt%-10wt%; Amino compounds are urea and melamine; The concentration of the formaldehyde solution is 37wt%.

2. The low free formaldehyde amino resin adhesive obtained according to the preparation method according to claim 1.

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