Adhesive for food contact material and product and preparation method of adhesive

Abstract

The invention discloses an adhesive for food contact materials and products and a preparation method of the adhesive, and the adhesive for the food contact materials and the products comprises the following components in parts by weight: 23-27 parts of deionized water, 29-31 parts of gelatin, 11-13 parts of magnesium sulfate heptahydrate, 17-19 parts of polylactic resin, 1-2 parts of carrageenan and 13-15 parts of lignin A. According to the method, the recycled disposable bamboo chopsticks are used as raw materials, the lignin A is prepared through the processes of one-step ethanol fractionation and the like after being sliced, the heterogeneity of the lignin extracted through the process is reduced, the antibacterial activity is obviously improved, wood waste and environmental pollution are reduced, and the method has important significance on sustainable development. The adhesive prepared from the lignin A is excellent in antibacterial property, the antibacterial ability is better than that of lignin sulfate existing in the market, the adhesive can be applied to adhesion of paper suction tubes, adhesion of beverage milk bags and PP covers and other food contact materials and paper products, and no harmful substance is separated out.

Description

Technical Field

[0001] The present invention relates to the technical field of adhesives, and in particular to an adhesive for food contact materials and products and a preparation method thereof. Background Art

[0002] As the world's most populous country, my country uses a huge amount of bamboo, but the utilization rate of discarded bamboo is at a medium-low level in the world. Among the more than 45 billion pairs of disposable bamboo chopsticks produced in my country each year, few are recycled after use, which has caused a huge waste of resources and is not in line with my country's current sustainable development concept. The recycling and reuse of bamboo chopsticks should be taken seriously. This practice not only wastes precious resources, but also pollutes the environment. Therefore, strengthening the utilization rate of discarded disposable bamboo chopsticks and broadening the utilization channels are of great significance to improving resource utilization and the sustainable development of forestry.

[0003] With the changes of the times and the improvement of consumption levels, people have increasingly stringent requirements for food contact materials such as food packaging and adhesives. Common food contact materials and adhesives used in products use preservatives to inhibit the growth of bacteria and other microorganisms. Since bacteria are easily bred in food, when the amount of preservatives used is lower than the national standard, it is difficult to inhibit bacteria below the food safety requirements; when the amount of preservatives is excessive, it will cause digestive tract flora imbalance, affect the normal absorption and digestive function of the gastrointestinal tract, and may also induce various gastrointestinal diseases.

[0004] Lignin is the second most abundant natural polymer in the plant kingdom and the only one containing aromatic rings. It is considered to be an excellent substitute for fossil energy due to its many different types of functional groups in its structure and its natural renewability, easy degradation, and non-toxicity. It is widely used in metallurgy, medicine, construction, home furnishing, etc. Common lignin is recovered and extracted from pulping waste liquid. Lignin is obtained by alkali recovery and membrane separation. However, due to the different sources and extraction methods of lignin, the antibacterial ability of the obtained lignin is significantly different. In addition, due to the heterogeneity of lignin, its complex structure and wide molecular weight distribution lead to unstable performance.

[0005] In view of the above problems, the present invention discloses a method for extracting antibacterial lignin from disposable bamboo chopsticks, and making the same into a lignin adhesive. On the one hand, by recycling disposable bamboo chopsticks, the pollution to the environment is reduced, wood resources are saved, and the felling of trees is reduced, which helps to reduce carbon emissions and combat climate change; on the other hand, the lignin A prepared by the present invention is used in the adhesive. Since lignin A has good antibacterial properties, it is added to the adhesive as a raw material, so that the adhesive has strong antibacterial ability without adding preservatives, and performs well in bonding different substrates, and can be widely used in food packaging, food contact surface material composites, medical food containers and other fields. Summary of the invention

[0006] The purpose of the present invention is to address the deficiencies of the prior art and provide an adhesive for food contact materials and products and a preparation method thereof.

[0007] The objective of the present invention is achieved through the following technical solutions:

[0008] In a first aspect, the present invention provides an adhesive for food contact materials and products, which comprises, by weight, 23 to 27 parts of deionized water, 29 to 31 parts of gelatin, 11 to 13 parts of magnesium sulfate heptahydrate, 17 to 19 parts of polylactic acid resin, 1 to 2 parts of carrageenan, and 13 to 15 parts of lignin A.

[0009] Furthermore, the lignin A is prepared by the following method, in parts by weight:

[0010] (1) using a wood chipper to chip the disposable bamboo chopstick powder into bamboo chips with a thickness of 5 to 20 mm, preferably 5 to 10 mm;

[0011] (2) Weigh 10 to 20 parts of water into a reactor, boil the bamboo chips at 150 to 170° C. for 0.5 to 1.5 h, filter, and dry at 50 to 60° C.;

[0012] (3) Weighing 22 to 24 parts of sodium sulfide solution into a new reactor, steaming the dried bamboo chips at 140 to 180° C. for 1 to 3 hours, and filtering to obtain black liquor;

[0013] (4) then adding 3 to 5 parts of hydrochloric acid to the black liquor while stirring, adjusting the pH to 1.5 to 2.0, and then filtering to obtain the precipitate;

[0014] (5) The precipitate was washed by centrifugation with distilled water. When the pH of the supernatant reached 7.0 to 8.0, the precipitate was collected and dried in an oven at 50 to 60° C. for 18 to 24 h to obtain sample a.

[0015] (6) Using magnetic stirring at room temperature, fully dissolve sample a in 21 to 23 parts of ethanol and stir for 0.5 to 1.5 hours;

[0016] (7) Then, the upper layer solution was filtered and ethanol was removed using an industrial rotary evaporator to obtain sample b;

[0017] (8) Dry sample b at 50-60°C to obtain lignin A.

[0018] In a second aspect, the present invention further provides a method for preparing an adhesive for food contact materials and products, which comprises the following steps, measured in parts by weight:

[0019] (a) weighing 23-27 parts of deionized water and 29-31 parts of gelatin into a reaction kettle, stirring and dissolving, heating to 65-75° C., and keeping the temperature for 1-2 hours;

[0020] (b) then adding 11 to 13 parts of magnesium sulfate heptahydrate and keeping the temperature for 0.5 to 1.5 hours;

[0021] (c) then adding 17 to 19 parts of polylactic acid resin and keeping the temperature for 0.5 to 1.5 hours;

[0022] (d) adding 1 to 2 portions of carrageenan and keeping warm for 0.5 to 1.5 hours;

[0023] (e) finally adding 13 to 15 parts of lignin A and keeping warm for 0.5 to 1.5 hours;

[0024] (f) stopping stirring and discharging the material to obtain the adhesive for food contact materials and products.

[0025] The beneficial effects of the present invention are:

[0026] 1) The present invention uses disposable chopsticks as the raw material for obtaining lignin, which can save wood resources, create new economic value and social impact, and realize the recycling of resources;

[0027] 2) The present invention purifies lignin by a one-step ethanol fractionation process to break chemical bonds such as ether bonds to increase the phenolic hydroxyl content and reduce the molecular weight, thereby increasing the activity of lignin and reducing its heterogeneity;

[0028] 3) The present invention applies lignin A to adhesives for food contact materials and products. Since the phenolic hydroxyl groups in lignin can reduce the pH value around bacterial cells, destroy the bacterial cell membrane, and denature the protein, lignin can effectively inhibit the respiration of microbial cells and the activity of the electron transfer enzyme system, thereby achieving an antibacterial effect, so that no additional preservatives need to be added to the formula. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical scheme and advantages of the present invention more clear, the present invention is further described in detail in combination with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0030] The invention provides an adhesive for food contact materials and products, which comprises, by weight, 23 to 27 parts of deionized water, 29 to 31 parts of gelatin, 11 to 13 parts of magnesium sulfate heptahydrate, 17 to 19 parts of polylactic acid resin, 1 to 2 parts of carrageenan, and 13 to 15 parts of lignin A.

[0031] The lignin A is prepared by the following method, in parts by weight:

[0032] (1) using a wood chipper to chip the disposable bamboo chopstick powder into bamboo chips with a thickness of 5 to 20 mm, preferably 5 to 10 mm;

[0033] (2) Weigh 10 to 20 parts of water into a reactor, boil the bamboo chips at 150 to 170° C. for 0.5 to 1.5 h, filter, and dry at 50 to 60° C.;

[0034] (3) Weighing 22 to 24 parts of sodium sulfide solution into a new reactor, steaming the dried bamboo chips at 140 to 180° C. for 1 to 3 hours, and filtering to obtain black liquor;

[0035] (4) then adding 3 to 5 parts of hydrochloric acid to the black liquor while stirring, adjusting the pH to 1.5 to 2.0, and then filtering to obtain the precipitate;

[0036] (5) The precipitate was washed by centrifugation with distilled water. When the pH of the supernatant reached 7.0 to 8.0, the precipitate was collected and dried in an oven at 50 to 60° C. for 18 to 24 h to obtain sample a.

[0037] (6) Using magnetic stirring at room temperature, fully dissolve sample a in 21 to 23 parts of ethanol and stir for 0.5 to 1.5 hours;

[0038] (7) Then, the upper layer solution was filtered and ethanol was removed using an industrial rotary evaporator to obtain sample b;

[0039] (8) Dry sample b at 50-60°C to obtain lignin A.

[0040] The present invention also provides a method for preparing an adhesive for food contact materials and products, which comprises the following steps, measured in parts by weight:

[0041] (a) weighing 23-27 parts of deionized water and 29-31 parts of gelatin into a reaction kettle, stirring and dissolving, heating to 65-75° C., and keeping the temperature for 1-2 hours;

[0042] (b) then adding 11 to 13 parts of magnesium sulfate heptahydrate and keeping the temperature for 0.5 to 1.5 hours;

[0043] (c) then adding 17 to 19 parts of polylactic acid resin and keeping the temperature for 0.5 to 1.5 hours;

[0044] (d) adding 1 to 2 portions of carrageenan and keeping warm for 0.5 to 1.5 hours;

[0045] (e) finally adding 13 to 15 parts of lignin A and keeping warm for 0.5 to 1.5 hours;

[0046] (f) stopping stirring and discharging the material to obtain the adhesive for food contact materials and products.

[0047] Example 1

[0048] An adhesive for food contact materials and products, the preparation process and formula of which are as follows, in parts by weight:

[0049] (1) Preparation of lignin A1:

[0050] (1.1) Use a wood chipper to chip disposable bamboo chopsticks into bamboo chips with a thickness of 5 to 20 mm;

[0051] (1.2) Weigh 15 parts of water into a reactor, boil the bamboo chips at 160°C for 1 hour, filter them, and dry them at 55°C;

[0052] (1.3) Weigh 23 parts of sodium sulfide solution into a new reactor, boil the dried bamboo chips at 140°C for 1 hour, and filter to obtain black liquor;

[0053] (1.4) Then, 4 parts of hydrochloric acid were added to the black liquor while stirring, and the pH was adjusted to 1.5, and then the precipitate was obtained by suction filtration;

[0054] (1.5) The precipitate was washed by centrifugation with distilled water. When the pH of the supernatant reached 8.0, the precipitate was collected and dried in an oven at 55°C for 20 h to obtain sample a.

[0055] (1.6) Dissolve sample a in 22 parts of ethanol using magnetic stirring at room temperature and stir for 1 h;

[0056] (1.7) Then filter the upper layer solution and remove ethanol using an industrial rotary evaporator to obtain sample b;

[0057] (1.8) Sample b was dried at 55°C to obtain lignin A1.

[0058] (2) Weigh 25 parts of deionized water and 30 parts of gelatin into a reactor and dissolve them. Heat the reactor to 70°C and keep the temperature for 1.5 hours.

[0059] (3) Slowly add 12 parts of magnesium sulfate heptahydrate and keep warm for 1 hour.

[0060] (4) Slowly add 18 parts of polylactic acid resin and keep warm for 1 hour.

[0061] (5) Add 1 portion of carrageenan and keep warm for 1 hour.

[0062] (6) Slowly add 14 parts of lignin A1 and keep warm for 0.5 h.

[0063] (7) Stop stirring and discharge the material to obtain the adhesive for food contact materials and products.

[0064] Example 2

[0065] An adhesive for food contact materials and products, the preparation process and formula of which are as follows, in parts by weight:

[0066] (1) Preparation of lignin A2:

[0067] (1.1) Use a wood chipper to chip disposable bamboo chopsticks into bamboo chips with a thickness of 5 to 20 mm;

[0068] (1.2) Weigh 15 parts of water into a reactor, boil the bamboo chips at 160°C for 1 hour, filter them, and dry them at 55°C;

[0069] (1.3) Weigh 23 parts of sodium sulfide solution into a new reactor, boil the dried bamboo chips at 160°C for 1 hour, and filter to obtain black liquor;

[0070] (1.4) Then, 4 parts of hydrochloric acid were added to the black liquor while stirring, and the pH was adjusted to 1.5, and then the precipitate was obtained by suction filtration;

[0071] (1.5) The precipitate was washed by centrifugation with distilled water. When the pH of the supernatant reached 8.0, the precipitate was collected and dried in an oven at 55°C for 20 h to obtain sample a.

[0072] (1.6) Dissolve sample a in 22 parts of ethanol using magnetic stirring at room temperature and stir for 1 h;

[0073] (1.7) Then filter the upper layer solution and remove ethanol using an industrial rotary evaporator to obtain sample b;

[0074] (1.8) Sample b was dried at 55°C to obtain lignin A2.

[0075] (2) Weigh 25 parts of deionized water and 30 parts of gelatin into a reactor and dissolve them. Heat the reactor to 70°C and keep the temperature for 1.5 hours.

[0076] (3) Slowly add 12 parts of magnesium sulfate heptahydrate and keep warm for 1 hour.

[0077] (4) Slowly add 18 parts of polylactic acid resin and keep warm for 1 hour.

[0078] (5) Add 1 portion of carrageenan and keep warm for 1 hour.

[0079] (6) Slowly add 14 parts of lignin A2 and keep warm for 0.5 h.

[0080] (7) Stop stirring and discharge the material to obtain the adhesive for food contact materials and products.

[0081] Example 3

[0082] An adhesive for food contact materials and products, the preparation process and formula of which are as follows, in parts by weight:

[0083] (1) Preparation of lignin A3:

[0084] (1.1) Use a wood chipper to chip disposable bamboo chopsticks into bamboo chips with a thickness of 5 to 20 mm;

[0085] (1.2) Weigh 15 parts of water into a reactor, boil the bamboo chips at 160°C for 1 hour, filter them, and dry them at 55°C;

[0086] (1.3) Weigh 23 parts of sodium sulfide solution into a new reactor, boil the dried bamboo chips at 180°C for 1 hour, and filter to obtain black liquor;

[0087] (1.4) Then, 4 parts of hydrochloric acid were added to the black liquor while stirring, and the pH was adjusted to 1.5, and then the precipitate was obtained by suction filtration;

[0088] (1.5) The precipitate was washed by centrifugation with distilled water. When the pH of the supernatant reached 8.0, the precipitate was collected and dried in an oven at 55°C for 20 h to obtain sample a.

[0089] (1.6) Dissolve sample a in 22 parts of ethanol using magnetic stirring at room temperature and stir for 1 h;

[0090] (1.7) Then filter the upper layer solution and remove ethanol using an industrial rotary evaporator to obtain sample b;

[0091] (1.8) Sample b was dried at 55°C to obtain lignin A3.

[0092] (2) Weigh 25 parts of deionized water and 30 parts of gelatin into a reactor and dissolve them. Heat the reactor to 70°C and keep the temperature for 1.5 hours.

[0093] (3) Slowly add 12 parts of magnesium sulfate heptahydrate and keep warm for 1 hour.

[0094] (4) Slowly add 18 parts of polylactic acid resin and keep warm for 1 hour.

[0095] (5) Add 1 portion of carrageenan and keep warm for 1 hour.

[0096] (6) Slowly add 14 parts of lignin A3 and keep warm for 0.5 h.

[0097] (7) Stop stirring and discharge the material to obtain the adhesive for food contact materials and products.

[0098] Example 4

[0099] An adhesive for food contact materials and products, the preparation process and formula of which are as follows, in parts by weight:

[0100] (1) Preparation of lignin A4:

[0101] (1.1) Use a wood chipper to chip disposable bamboo chopsticks into bamboo chips with a thickness of 5 to 20 mm;

[0102] (1.2) Weigh 15 parts of water into a reactor, boil the bamboo chips at 160°C for 1 hour, filter them, and dry them at 55°C;

[0103] (1.3) Weigh 23 parts of sodium sulfide solution into a new reactor, boil the dried bamboo chips at 140°C for 2 hours and filter to obtain black liquor;

[0104] (1.4) Then, 4 parts of hydrochloric acid were added to the black liquor while stirring, and the pH was adjusted to 1.5, and then the precipitate was obtained by suction filtration;

[0105] (1.5) The precipitate was washed by centrifugation with distilled water. When the pH of the supernatant reached 8.0, the precipitate was collected and dried in an oven at 55°C for 20 h to obtain sample a.

[0106] (1.6) Dissolve sample a in 22 parts of ethanol using magnetic stirring at room temperature and stir for 1 h;

[0107] (1.7) Then filter the upper layer solution and remove ethanol using an industrial rotary evaporator to obtain sample b;

[0108] (1.8) Sample b was dried at 55°C to obtain lignin A4.

[0109] (2) Weigh 25 parts of deionized water and 30 parts of gelatin into a reactor and dissolve them. Heat the reactor to 70°C and keep the temperature for 1.5 hours.

[0110] (3) Slowly add 12 parts of magnesium sulfate heptahydrate and keep warm for 1 hour.

[0111] (4) Slowly add 18 parts of polylactic acid resin and keep warm for 1 hour.

[0112] (5) Add 1 portion of carrageenan and keep warm for 1 hour.

[0113] (6) Slowly add 14 parts of lignin A4 and keep warm for 0.5 h.

[0114] (7) Stop stirring and discharge the material to obtain the adhesive for food contact materials and products.

[0115] Example 5

[0116] An adhesive for food contact materials and products, the preparation process and formula of which are as follows, in parts by weight:

[0117] (1) Preparation of lignin A5:

[0118] (1.1) Use a wood chipper to chip disposable bamboo chopsticks into bamboo chips with a thickness of 5 to 20 mm;

[0119] (1.2) Weigh 15 parts of water into a reactor, boil the bamboo chips at 160°C for 1 hour, filter them, and dry them at 55°C;

[0120] (1.3) Weigh 23 parts of sodium sulfide solution into a new reactor, boil the dried bamboo chips at 160°C for 2 h, and filter to obtain black liquor;

[0121] (1.4) Then, 4 parts of hydrochloric acid were added to the black liquor while stirring, and the pH was adjusted to 1.5, and then the precipitate was obtained by suction filtration;

[0122] (1.5) The precipitate was washed by centrifugation with distilled water. When the pH of the supernatant reached 8.0, the precipitate was collected and dried in an oven at 55°C for 20 h to obtain sample a.

[0123] (1.6) Dissolve sample a in 22 parts of ethanol using magnetic stirring at room temperature and stir for 1 h;

[0124] (1.7) Then filter the upper layer solution and use an industrial rotary evaporator to remove ethanol to obtain sample b;

[0125] (1.8) Sample b was dried at 55°C to obtain lignin A5.

[0126] (2) Weigh 25 parts of deionized water and 30 parts of gelatin into a reactor and dissolve them. Heat the reactor to 70°C and keep the temperature for 1.5 hours.

[0127] (3) Slowly add 12 parts of magnesium sulfate heptahydrate and keep warm for 1 hour.

[0128] (4) Slowly add 18 parts of polylactic acid resin and keep warm for 1 hour.

[0129] (5) Add 1 portion of carrageenan and keep warm for 1 hour.

[0130] (6) Slowly add 14 parts of lignin A5 and keep warm for 0.5 h.

[0131] (7) Stop stirring and discharge the material to obtain the adhesive for food contact materials and products.

[0132] Example 6

[0133] An adhesive for food contact materials and products, the preparation process and formula of which are as follows, in parts by weight:

[0134] (1) Preparation of lignin A6:

[0135] (1.1) Use a wood chipper to chip disposable bamboo chopsticks into bamboo chips with a thickness of 5 to 20 mm;

[0136] (1.2) Weigh 15 parts of water into a reactor, boil the bamboo chips at 160°C for 1 hour, filter them, and dry them at 55°C;

[0137] (1.3) Weigh 23 parts of sodium sulfide solution into a new reactor, boil the dried bamboo chips at 180°C for 2 h, and filter to obtain black liquor;

[0138] (1.4) Then, 4 parts of hydrochloric acid were added to the black liquor while stirring, and the pH was adjusted to 1.5, and then the precipitate was obtained by suction filtration;

[0139] (1.5) The precipitate was washed by centrifugation with distilled water. When the pH of the supernatant reached 8.0, the precipitate was collected and dried in an oven at 55°C for 20 h to obtain sample a.

[0140] (1.6) Dissolve sample a in 22 parts of ethanol using magnetic stirring at room temperature and stir for 1 h;

[0141] (1.7) Then filter the upper layer solution and use an industrial rotary evaporator to remove ethanol to obtain sample b;

[0142] (1.8) Sample b was dried at 55°C to obtain lignin A6.

[0143] (2) Weigh 25 parts of deionized water and 30 parts of gelatin into a reactor and dissolve them. Heat the reactor to 70°C and keep the temperature for 1.5 hours.

[0144] (3) Slowly add 12 parts of magnesium sulfate heptahydrate and keep warm for 1 hour.

[0145] (4) Slowly add 18 parts of polylactic acid resin and keep warm for 1 hour.

[0146] (5) Add 1 portion of carrageenan and keep warm for 1 hour.

[0147] (6) Slowly add 14 parts of lignin A6 and keep warm for 0.5 h.

[0148] (7) Stop stirring and discharge the material to obtain the adhesive for food contact materials and products.

[0149] Example 7

[0150] An adhesive for food contact materials and products, the preparation process and formula of which are as follows, in parts by weight:

[0151] (1) Preparation of lignin A7:

[0152] (1.1) Use a wood chipper to chip disposable bamboo chopsticks into bamboo chips with a thickness of 5 to 20 mm;

[0153] (1.2) Weigh 15 parts of water into a reactor, boil the bamboo chips at 160°C for 1 hour, filter them, and dry them at 55°C;

[0154] (1.3) Weigh 23 parts of sodium sulfide solution into a new reactor, boil the dried bamboo chips at 140°C for 3 hours and filter to obtain black liquor;

[0155] (1.4) Then, 4 parts of hydrochloric acid were added to the black liquor while stirring, and the pH was adjusted to 1.5, and then the precipitate was obtained by suction filtration;

[0156] (1.5) The precipitate was washed by centrifugation with distilled water. When the pH of the supernatant reached 8.0, the precipitate was collected and dried in an oven at 55°C for 20 h to obtain sample a.

[0157] (1.6) Dissolve sample a in 22 parts of ethanol using magnetic stirring at room temperature and stir for 1 h;

[0158] (1.7) Then filter the upper layer solution and remove ethanol using an industrial rotary evaporator to obtain sample b;

[0159] (1.8) Sample b was dried at 55°C to obtain lignin A7.

[0160] (2) Weigh 25 parts of deionized water and 30 parts of gelatin into a reactor and dissolve them. Heat the reactor to 70°C and keep the temperature for 1.5 hours.

[0161] (3) Slowly add 12 parts of magnesium sulfate heptahydrate and keep warm for 1 hour.

[0162] (4) Slowly add 18 parts of polylactic acid resin and keep warm for 1 hour.

[0163] (5) Add 1 portion of carrageenan and keep warm for 1 hour.

[0164] (6) Slowly add 14 parts of lignin A7 and keep warm for 0.5 h.

[0165] (7) Stop stirring and discharge the material to obtain the adhesive for food contact materials and products.

[0166] Example 8

[0167] An adhesive for food contact materials and products, the preparation process and formula of which are as follows, in parts by weight:

[0168] (1) Preparation of lignin A8:

[0169] (1.1) Use a wood chipper to chip disposable bamboo chopsticks into bamboo chips with a thickness of 5 to 20 mm;

[0170] (1.2) Weigh 15 parts of water into a reactor, boil the bamboo chips at 160°C for 1 hour, filter them, and dry them at 55°C;

[0171] (1.3) Weigh 23 parts of sodium sulfide solution into a new reactor, boil the dried bamboo chips at 160°C for 3 hours and filter to obtain black liquor;

[0172] (1.4) Then, 4 parts of hydrochloric acid were added to the black liquor while stirring, and the pH was adjusted to 1.5, and then the precipitate was obtained by suction filtration;

[0173] (1.5) The precipitate was washed by centrifugation with distilled water. When the pH of the supernatant reached 8.0, the precipitate was collected and dried in an oven at 55°C for 20 h to obtain sample a.

[0174] (1.6) Dissolve sample a in 22 parts of ethanol using magnetic stirring at room temperature and stir for 1 h;

[0175] (1.7) Dissolve sample a in 22 parts of ethanol using magnetic stirring at room temperature and stir for 1 h;

[0176] (1.8) Sample b was dried at 55°C to obtain lignin A8.

[0177] (2) Weigh 25 parts of deionized water and 30 parts of gelatin into a reactor and dissolve them. Heat the reactor to 70°C and keep the temperature for 1.5 hours.

[0178] (3) Slowly add 12 parts of magnesium sulfate heptahydrate and keep warm for 1 hour.

[0179] (4) Slowly add 18 parts of polylactic acid resin and keep warm for 1 hour.

[0180] (5) Add 1 portion of carrageenan and keep warm for 1 hour.

[0181] (6) Slowly add 14 parts of lignin A8 and keep warm for 0.5 h.

[0182] (7) Stop stirring and discharge the material to obtain the adhesive for food contact materials and products.

[0183] Example 9

[0184] An adhesive for food contact materials and products, the preparation process and formula of which are as follows, in parts by weight:

[0185] (1) Preparation of lignin A9:

[0186] (1.1) Use a wood chipper to chip disposable bamboo chopsticks into bamboo chips with a thickness of 5 to 20 mm;

[0187] (1.2) Weigh 15 parts of water into a reactor, boil the bamboo chips at 160°C for 1 hour, filter them, and dry them at 55°C;

[0188] (1.3) Weigh 23 parts of sodium sulfide solution into a new reactor, boil the dried bamboo chips at 180°C for 3 hours and filter to obtain black liquor;

[0189] (1.4) Then, 4 parts of hydrochloric acid were added to the black liquor while stirring, and the pH was adjusted to 1.5, and then the precipitate was obtained by suction filtration;

[0190] (1.5) The precipitate was washed by centrifugation with distilled water. When the pH of the supernatant reached 8.0, the precipitate was collected and dried in an oven at 55°C for 20 h to obtain sample a.

[0191] (1.6) Dissolve sample a in 22 parts of ethanol using magnetic stirring at room temperature and stir for 1 h;

[0192] (1.7) Then filter the upper layer solution and use an industrial rotary evaporator to remove ethanol to obtain sample b;

[0193] (1.8) Sample b was dried at 55°C to obtain lignin A9;

[0194] (2) Weigh 25 parts of deionized water and 30 parts of gelatin into a reactor and dissolve them. Heat the reactor to 70°C and keep the temperature for 1.5 hours.

[0195] (3) Slowly add 12 parts of magnesium sulfate heptahydrate and keep warm for 1 hour.

[0196] (4) Slowly add 18 parts of polylactic acid resin and keep warm for 1 hour.

[0197] (5) Add 1 portion of carrageenan and keep warm for 1 hour.

[0198] (6) Slowly add 14 parts of lignin A9 and keep warm for 0.5 h.

[0199] (7) Stop stirring and discharge the material to obtain the adhesive for food contact materials and products.

[0200] The minimum inhibitory concentration of the adhesives for food contact materials and products prepared in Examples 1 to 9 was tested using the agar dilution method. The test results are shown in Table 1.

[0201] Table 1: Minimum inhibitory concentration test results of adhesives for food contact materials and products prepared in Examples 1 to 9

[0202]

[0203] From the test results shown in Table 1, the antibacterial property of lignin is the best when the bamboo chips are cooked in sodium sulfate solution at 140°C for 3 h.

[0204] The adhesives for food contact materials and products prepared in Examples 1 to 9 were tested for heat resistance and bonding strength in the following manner. The test results are shown in Table 2.

[0205] Table 2: Test results of heat resistance and bonding strength of adhesives for food contact materials and products prepared in Examples 1 to 9

[0206]

[0207] From the test results shown in Table 2, the lignin A7 prepared by cooking bamboo strips in a sodium sulfate solution at 140°C for 3 hours has the best heat resistance temperature and bonding strength under different substrates. Commercially available lignin sulfate was used to replace it.

[0208] Comparative Example 1

[0209] An adhesive, the preparation process and formula of which are as follows, in parts by weight:

[0210] (1) Weigh 25 parts of deionized water and 30 parts of gelatin into a reactor and dissolve them. Heat the reactor to 70°C and keep the temperature for 1.5 hours.

[0211] (2) Slowly add 12 parts of magnesium sulfate heptahydrate and keep warm for 1 hour.

[0212] (3) Slowly add 18 parts of polylactic acid resin and keep warm for 1 hour.

[0213] (4) Add 1 portion of carrageenan and keep warm for 1 hour.

[0214] (5) Stop stirring and discharge the material to obtain the adhesive.

[0215] Comparative Example 2

[0216] An adhesive, the preparation process and formula of which are as follows, in parts by weight:

[0217] (1) Weigh 25 parts of deionized water and 30 parts of gelatin into a reactor and dissolve them. Heat the reactor to 70°C and keep the temperature for 1.5 hours.

[0218] (2) Slowly add 12 parts of magnesium sulfate heptahydrate and keep warm for 1 hour.

[0219] (3) Slowly add 18 parts of polylactic acid resin and keep warm for 1 hour.

[0220] (4) Add 1 portion of carrageenan and keep warm for 1 hour.

[0221] (5) Add 14 parts of lignin sulfate and keep warm for 0.5 h.

[0222] (6) Stop stirring and discharge the material to obtain the adhesive.

[0223] Comparative Example 3

[0224] An adhesive, the preparation process and formula of which are as follows, in parts by weight:

[0225] (1) Weigh 25 parts of deionized water and 30 parts of gelatin into a reactor and dissolve them. Heat the reactor to 70°C and keep the temperature for 1.5 hours.

[0226] (2) Slowly add 12 parts of magnesium sulfate heptahydrate and keep warm for 1 hour.

[0227] (3) Slowly add 18 parts of polylactic acid resin and keep warm for 1 hour.

[0228] (4) Add 1 portion of carrageenan and keep warm for 1 hour.

[0229] (5) Add 5 parts of lignin A7 prepared in Example 7 and 9 parts of lignin sulfate, and keep warm for 0.5 h.

[0230] (6) Stop stirring and discharge the material to obtain the adhesive.

[0231] Comparative Example 4

[0232] An adhesive, the preparation process and formula of which are as follows, in parts by weight:

[0233] (1) Weigh 25 parts of deionized water and 30 parts of gelatin into a reactor and dissolve them. Heat the reactor to 70°C and keep the temperature for 1.5 hours.

[0234] (2) Slowly add 12 parts of magnesium sulfate heptahydrate and keep warm for 1 hour.

[0235] (3) Slowly add 18 parts of polylactic acid resin and keep warm for 1 hour.

[0236] (4) Add 1 portion of carrageenan and keep warm for 1 hour.

[0237] (5) Add 10 parts of lignin A7 prepared in Example 7 and 4 parts of lignin sulfate, and keep warm for 0.5 h.

[0238] (6) Stop stirring and discharge the material to obtain the adhesive.

[0239] The minimum inhibitory concentration test was performed on the adhesives prepared in Comparative Examples 1 to 4, the competitive products and the adhesive for food contact materials and products prepared in Example 7 using the agar dilution method. The test results are shown in Table 3.

[0240] Table 3: Minimum inhibitory concentration test results of adhesives prepared in Comparative Examples 1 to 4, competitive products and adhesives for food contact materials and products prepared in Example 7

[0241]

[0242] From the test results shown in Table 3, the antibacterial performance of the adhesive increases with the increase in the amount of lignin A7, and the antibacterial effect is best when all the lignin is lignin A7. The antibacterial ability of the adhesive is stronger than that of competing products.

[0243] The adhesives prepared in Comparative Examples 1 to 4, the competitive products and the adhesive for food contact materials and products prepared in Example 7 were tested for heat resistance and bonding strength in the following manner. The test results are shown in Table 4.

[0244] Table 4: Test results of heat resistance and bonding strength of adhesives prepared in Comparative Examples 1 to 4, competitive products and adhesives for food contact materials and products prepared in Example 7

[0245]

[0246]

[0247] From the test results shown in Table 4, it can be seen that with the increase in the amount of lignin A7, the heat resistance and bonding strength of the adhesive in paper-paper, paper-PP, and PP-PP bonding are significantly improved. When the filler part is all made of lignin A7, the heat resistance and bonding strength are the best, and are significantly better than those of competing adhesives.

[0248] In summary, the lignin prepared by the present invention can significantly improve the antibacterial ability, heat resistance and bonding strength of the adhesive, and can be widely used in food packaging bonded with paper-paper, paper-PP, PP-PP, food contact surface material composites, medical food containers and other fields.

[0249] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. An adhesive for food contact materials and products, characterized in that: The invention comprises, by weight, 23 to 27 parts of deionized water, 29 to 31 parts of gelatin, 11 to 13 parts of magnesium sulfate heptahydrate, 17 to 19 parts of polylactic acid resin, 1 to 2 parts of carrageenan, and 13 to 15 parts of lignin A.

2. The adhesive for food contact materials and products according to claim 1, characterized in that: The lignin A is prepared by the following method, in parts by weight: (1) using a wood chipper to chip the disposable bamboo chopstick powder into bamboo chips with a thickness of 5 to 20 mm, preferably 5 to 10 mm; (2) Weigh 10 to 20 parts of water into a reactor, boil the bamboo chips at 150 to 170° C. for 0.5 to 1.5 h, filter, and dry at 50 to 60° C.; (3) Weighing 22 to 24 parts of sodium sulfide solution into a new reactor, steaming the dried bamboo chips at 140 to 180° C. for 1 to 3 hours, and filtering to obtain black liquor; (4) then adding 3 to 5 parts of hydrochloric acid to the black liquor while stirring, adjusting the pH to 1.5 to 2.0, and then filtering to obtain the precipitate; (5) The precipitate was washed by centrifugation with distilled water. When the pH of the supernatant reached 7.0 to 8.0, the precipitate was collected and dried in an oven at 50 to 60° C. for 18 to 24 h to obtain sample a. (6) Using magnetic stirring at room temperature, sample a was fully dissolved in 21 to 23 parts of ethanol and stirred for 0.5 to 1.5 hours; (7) Then, the upper layer solution was filtered and ethanol was removed using an industrial rotary evaporator to obtain sample b; (8) Dry sample b at 50-60°C to obtain lignin A.

3. The method for preparing the adhesive for food contact materials and products according to any one of claims 1 to 2, characterized in that: By weight, the method comprises the following steps: (a) weighing 23-27 parts of deionized water and 29-31 parts of gelatin into a reaction kettle, stirring and dissolving, heating to 65-75° C., and keeping the temperature for 1-2 hours; (b) then adding 11 to 13 parts of magnesium sulfate heptahydrate and keeping the temperature for 0.5 to 1.5 hours; (c) then adding 17 to 19 parts of polylactic acid resin and keeping the temperature for 0.5 to 1.5 hours; (d) adding 1 to 2 portions of carrageenan and keeping warm for 0.5 to 1.5 hours; (e) finally adding 13 to 15 parts of lignin A and keeping warm for 0.5 to 1.5 hours; (f) stopping stirring and discharging the material to obtain the adhesive for food contact materials and products.

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