Degradable composition and flame-retardant degradable plastic

Abstract

The invention relates to a degradable composition and flame-retardant degradable plastic. The degradable composition comprises PLA particles, modified lignin and a bio-based flame retardant, wherein the modified lignin is obtained by grafting polycaprolactone on lignin and then forming a core-shell structure on the surface of silane coupling modified calcium carbonate; the preparation method of the bio-based flame retardant comprises the following steps: heating and dissolving chitosan in an acetic acid solution, introducing nitrogen, adding an initiator, then adding a DOPO derivative with double bonds at the tail end, MDO and AA, and carrying out a polymerization reaction to prepare the flame retardant. According to the scheme, the lignin-PCL / calcium carbonate core-shell toughening agent and the P-N synergistic chitosan flame retardant are prepared and are jointly added into the PLA, the compatibility with the PLA is good, the problem of high brittleness of the PLA can be effectively solved, the elongation at break is improved, meanwhile, the material is endowed with flame retardance, and the biodegradability of the PLA material can be well kept.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of degradable plastics, in particular to a degradable composition and a flame-retardant degradable plastic. BACKGROUND

[0002] Plastics exist in all aspects of our daily life, bringing various conveniences. However, with the rapid development of society, the use of plastics has been excessive, and non-degradable plastic cups buried in the land have caused great pollution to the environment. With the continuous improvement of people's living standards, the demand for green and sustainable development is also increasing. As a typical biobased degradable plastic, polylactic acid (PLA) is widely used in packaging, textiles, medical treatment and other fields due to its renewable raw materials, harmless degradation products and other advantages.

[0003] However, PLA itself does not have flame-retardant properties, and in some specific situations, plastics are required to have certain flame-retardant properties, which requires the use of flame retardants. However, most of the commonly used flame retardants are not renewable and non-degradable, and although they can impart flame-retardant properties to PLA, they have an adverse effect on its degradability. SUMMARY

[0004] In view of the deficiencies in the prior art, the present application prepares modified lignin and a biobased flame retardant, which can effectively improve the mechanical properties of PLA when added to PLA, impart flame retardancy, and at the same time maintain its excellent degradation performance.

[0005] To achieve the above-mentioned purpose, the present application provides the following technical scheme: A degradable composition, comprising the following components by weight: 100 parts of PLA particles, 20-40 parts of modified lignin and 5-15 parts of a biobased flame retardant; The modified lignin is a calcium carbonate surface core-shell structure obtained by grafting polycaprolactone on lignin and then coupling modification; The preparation process of the biobased flame retardant is as follows: S1, preparation of a DOPO derivative with a terminal double bond S1-1, 1 equivalent of DOPO is dissolved in xylene, 1 equivalent of polyformaldehyde is slowly added under nitrogen, the temperature is raised to 140℃ for reflux reaction, hot water and ethanol are washed and filtered, and vacuum drying is performed to obtain DOPO-OH; S1-2, 1 equivalent of glycidyl methacrylate is dissolved in DMSO, the temperature is raised to 50-70℃, 1 equivalent of the DOPO-OH is added, a catalytic amount of tetraethylammonium bromide is added, and stirring is performed at 70℃ for 6-8h, the solid is precipitated by pouring into ice water, filtered, washed with ice water, filtered and dried to obtain DOPO-GMA; S1-3, dissolving DOPO-GMA in methanol, adding sodium hydroxide to adjust pH to 8-9; adding 2-chloro-4, 6-dimethoxy-1, 3, 5-triazine and methanol in a reaction bottle, stirring until completely dissolved, slowly adding the methanol solution of DOPO-GMA into the reaction bottle, stirring at room temperature for 4-6h, after the reaction is completed, filtering, washing, and drying to obtain ; S2, dissolving chitosan in acetic acid solution by heating, keeping the temperature at 60-70℃, blowing nitrogen for 30min, adding an initiator, then adding a terminal double bond DOPO derivative, 2-methylene-1, 3-dioxane and acrylic acid, and reacting for a certain time; S3, after the reaction is completed, reducing to room temperature, adjusting the pH of the system to neutral, pouring the reaction solution into ice methanol, precipitating the solid, filtering, washing with water and drying to obtain.

[0006] Further, the preparation process of the modified lignin is as follows: 1) drying calcium carbonate in an oven, after drying, adding anhydrous ethanol in a reaction bottle, heating to 70 o C, stirring for 5min, adding KH550, stirring and refluxing overnight, filtering and drying to obtain silane coupling calcium carbonate; 2) dissolving lignin in toluene solution, adding stannous octoate, heating to 110℃, slowly adding ε-caprolactone, stirring and reacting, after cooling, precipitating in cold methanol, filtering and drying to obtain lignin-based poly-caprolactone; 3) dispersing silane coupling calcium carbonate in toluene, adding triethylamine, heating and stirring for 30min, then adding lignin-based poly-caprolactone, adding DCC dropwise, stirring and reacting at 80℃ overnight, cooling, centrifugal filtering, washing and drying to obtain.

[0007] Further, the mass ratio of the lignin-based poly-caprolactone and the silane coupling calcium carbonate is 3-5:1.

[0008] Further, the deacetylation degree of the chitosan is 90±5%, the mass concentration of the acetic acid solution is 2-5%, and the mass / volume ratio of the chitosan and the acetic acid solution is 20-30 g / L.

[0009] Further, the initiator is ammonium persulfate or a mixture of potassium persulfate and sodium sulfite.

[0010] Further, the molar ratio of the terminal double bond DOPO derivative, 2-methylene-1, 3-dioxane and acrylic acid is 2-5:4-7:1; and the mass ratio of the chitosan, the mixed monomer and the initiator is 1:3-5:0.05-0.1.

[0011] The second object of the application provides a degradable plastic prepared by the following steps: The degradable composition is placed in a high-speed mixer to stir the mixture evenly; the mixture is put into a twin-screw extruder to melt blend, extrude, and then cut into particles by a pelletizer to obtain degradable plastic particles.

[0012] Compared with the prior art, the lignin-PCL / calcium carbonate core-shell toughening agent and P-N synergistic chitosan flame retardant prepared in the application have good compatibility with PLA when added together into PLA, can effectively solve the problem of large brittleness of PLA, improve the elongation at break, simultaneously impart flame retardancy to the material, and can well maintain the biodegradability of the PLA material. DETAILED DESCRIPTION

[0013] The technical solutions of the application will be described below in connection with the embodiments, obviously, the described embodiments are part of the embodiments of the application, rather than all the embodiments. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the application.

[0014] In addition, the technical features involved in different embodiments of the application described below can be combined with each other as long as there is no conflict.

[0015] Embodiment: A degradable plastic is prepared by the following steps: The degradable composition: 100 parts of PLA particles, 20-40 parts of modified lignin, and 5-15 parts of a bio-based flame retardant is placed in a high-speed mixer to stir the mixture evenly; the mixture is put into a twin-screw extruder to melt blend, extrude, and then cut into particles by a pelletizer to obtain degradable plastic particles.

[0016] The preparation process of the bio-based flame retardant is as follows: S1, preparation of a DOPO derivative with a terminal double bond S1-1, 1 equivalent of DOPO is dissolved in xylene, 1 equivalent of polyformaldehyde is slowly added under nitrogen, the temperature is raised to 140℃ for reflux reaction, hot water and ethanol are washed and filtered, and vacuum drying is performed to obtain DOPO-OH; S1-2, 1 equivalent of glycidyl methacrylate is dissolved in DMSO, the temperature is raised to 50-70℃, 1 equivalent of the DOPO-OH is added, a catalytic amount of tetraethylammonium bromide is added, stirring and mixing are performed at 70℃ for 6-8h, the solid is precipitated by pouring into ice water, filtered, washed with ice water, filtered and dried to obtain DOPO-GMA; S1-3, dissolve DOPO-GMA in methanol, add sodium hydroxide to adjust pH to 8-9; add 2-chloro-4, 6-dimethoxy-1, 3, 5-triazine and methanol in a reaction bottle, stir until completely dissolved, slowly drop the methanol solution of DOPO-GMA into the reaction bottle, stir at room temperature for 4-6h, after the reaction is completed, filter, wash, dry, and obtain ; S2, dissolve 10g chitosan in 500ml acetic acid solution by heating, keep the temperature at 60-70℃, blow nitrogen for 30min, add 0.8g initiator mixture of ammonium persulfate and sodium sulfite, then add 16g DOPO derivative with terminal double bond, 12.8g MDO and 1.2g AA (molar ratio of monomers is about 2:7:1), react for a certain time; S3, after the reaction is completed, reduce to room temperature, adjust the pH of the system to neutral, pour the reaction solution into ice methanol, precipitate the solid, filter, wash with water and dry.

[0017] DOPO is a new type of halogen-free flame retardant intermediate, which has better flame retardant performance than traditional organic phosphate. Through the dual mechanisms of free radical quenching in gas phase and carbonation in condensed phase, high-efficiency flame retardation is achieved. Chitosan is a natural macromolecule, which contains rich amino groups in its molecular structure; CDMT is a compound containing triazine structure, which contains rich nitrogen elements; all of them can absorb heat energy and decompose into non-combustible gas, dilute combustible gas, and achieve gas phase flame retardation.

[0018] MDO is a compound that can be ring-opening polymerized to form PCL-like segments, and its polymer chain is easily hydrolyzed by microorganisms, enzymes or acid and alkali, etc. The reaction of MDO with DOPO derivative with terminal double bond provides degradation sites for polymer, so that the macromolecule is degraded into small molecules. Chitosan itself has biodegradability, and forms a double degradation channel with PCL. Acrylic acid provides free radical active sites to promote the occurrence of polymerization reaction, and at the same time, the polyester segment is similar to PLA, which reduces the interface defects and avoids the local non-degradable area caused by phase separation.

[0019] When it is added to PLA, it can endow the degradable plastic with certain flame retardant performance, and at the same time, it has good compatibility with plastic particles, so as not to affect the degradation rate.

[0020] The preparation process of the modified lignin is as follows: 1) dry 10g calcium carbonate in an oven, after drying, add it to a reaction bottle, heat the anhydrous ethanol to 70 o C, stir for 5 min, add 20g KH550, stir and reflux overnight, filter, dry to obtain silane-coupled calcium carbonate; 2) 10 g of lignin was dissolved in toluene solution, stannous octoate was added, the temperature was raised to 110°C, ε-caprolactone was slowly added dropwise, stirred and reacted, precipitated in cold methanol after cooling, filtered and dried to obtain lignin-based poly (ε-caprolactone) ; 3) 2 g of silane-coupled calcium carbonate was dispersed in toluene, triethylamine was added, stirred and heated for 30 min, then 10 g of lignin-based poly (ε-caprolactone) was added, DCC was added dropwise, stirred and reacted at 80°C overnight, cooled, centrifuged and filtered, washed and dried.

[0021] The addition of bio-based lignin to PLA can promote crystallization and improve the toughness of PLA, but the problem of incompatibility may occur, which does not have a positive effect on the mechanical properties. Calcium carbonate as a filler can also enhance the mechanical properties of PLA, and the problem of compatibility also needs to be considered. In the above technical solution, the calcium carbonate is first treated with a silane coupling agent to bridge between inorganic particles and organic compounds; the lignin is grafted with PCL polymer chains on its surface, which is similar to the bio-based flame retardant and is compatible; the polyester structure is added to PLA with good interfacial compatibility; the modified lignin and the modified calcium carbonate are combined through chemical bonds, which improves the interfacial bonding force of the composite in PLA and synergistically improves the toughness of PLA.

[0022] Example 1: 100 parts of PLA particles, 20 parts of modified lignin and 5 parts of bio-based flame retardant were placed in a high-speed mixer and stirred uniformly to obtain a mixture; the mixture was fed into a twin-screw extruder for melt blending, extruded, then cut into particles by a granulator, and then cast, stretched, treated by corona discharge, pulled and wound.

[0023] Example 2: 100 parts of PLA particles, 25 parts of modified lignin and 10 parts of bio-based flame retardant were placed in a high-speed mixer and stirred uniformly to obtain a mixture; the mixture was fed into a twin-screw extruder for melt blending, extruded, then cut into particles by a granulator, and then cast, stretched, treated by corona discharge, pulled and wound.

[0024] Example 3: 100 parts of PLA particles, 30 parts of modified lignin and 15 parts of bio-based flame retardant were placed in a high-speed mixer and stirred uniformly to obtain a mixture; the mixture was fed into a twin-screw extruder for melt blending, extruded, then cut into particles by a granulator, and then cast, stretched, treated by corona discharge, pulled and wound.

[0025] Comparative Example 1: The same as Example 2, except that the bio-based flame retardant was replaced by ammonium polyphosphate.

[0026] Comparative Example 2: The same as Example 2, except that the modified lignin was replaced by an equal amount of a physical mixture of lignin and calcium carbonate.

[0027] The flame retardancy and mechanical properties of the PLA composite were investigated, and the results are recorded in Table 1.

[0028] Table 1 As can be seen from the data in Table 1, the plastic prepared by the composition provided in the application has certain flame retardancy, effectively improving the toughness of pure PLA. Due to the addition of more additives, the degradation performance of the final material is lower than that of pure PLA material, but it can still maintain a degradation rate of 85% in 180 days. Directly adding the existing polymer flame retardant with phosphorus and nitrogen elements, ammonium polyphosphate, has good flame retardant performance, but due to the problem of interface compatibility, the toughness decreases more compared to Example 2, and the degradation performance also has a more obvious decrease.

[0029] Although the embodiments of the present application have been disclosed as above, it is not limited to the application listed in the specification and the embodiments, and can be fully applied to various fields suitable for the present application. For those skilled in the art, other modifications can be easily realized, and therefore the present application is not limited to specific details, without departing from the general concept defined by the claims and the equivalent scope.

Claims

1. A degradable composition, characterized in that The composition comprises the following components in parts by weight: 100 parts PLA pellets, 20-40 parts modified lignin, and 5-15 parts bio-based flame retardant; The modified lignin is obtained by grafting polycaprolactone onto lignin and then coupling with a silane-modified calcium carbonate surface to form a core-shell structure; The preparation process of the bio-based flame retardant is as follows: S1. Preparation of DOPO derivatives with terminal double bonds S1-1, 1 equivalent of DOPO was dissolved in xylene. Under nitrogen, 1 equivalent of paraformaldehyde was slowly added dropwise. The temperature was raised to 140°C for reflux reaction. The mixture was washed with hot water and ethanol, filtered, and dried in vacuum to obtain DOPO-OH. S1-2. Dissolve 1 equivalent of glycidyl methacrylate in DMSO, heat to 50-70°C, add 1 equivalent of the DOPO-OH, add a catalytic amount of tetrakis ammonium bromide, stir at 70°C for 6-8 hours, pour into ice water to precipitate solid, filter, wash with ice water, filter and dry to obtain DOPO-GMA; S1-3, dissolve DOPO-GMA in methanol, add sodium hydroxide to adjust the pH to 8-9; add 2-chloro-4,6-dimethoxy-1,3,5-triazine and methanol to the reaction flask, stir until completely dissolved, slowly add the methanol solution of DOPO-GMA dropwise to the reaction flask, stir and react at room temperature for 4-6 hours, after the reaction is complete, filter, wash, and dry to obtain ; S2. Dissolve chitosan in acetic acid solution by heating, maintain the temperature at 60-70°C, introduce nitrogen gas for 30 minutes, add initiator, and then add DOPO derivative with terminal double bond, 2-methylene-1,3-dioxepane and acrylic acid, and react for a certain time; S3. After the reaction is completed, the temperature is cooled to room temperature, the pH of the system is adjusted to neutral, the reaction solution is poured into ice methanol, the solid is precipitated, filtered, washed with water, and dried.

2. The degradable composition according to claim 1, wherein The preparation process of the modified lignin is as follows: 1) Dry calcium carbonate in an oven, add anhydrous ethanol to the reaction flask and heat to 70 o C and stirred for 5 min, KH550 was added, stirred and refluxed overnight, filtered, and dried to obtain silane-coupled calcium carbonate; 2) Dissolve lignin in toluene solution, add stannous octoate, heat to 110°C, slowly add ε-caprolactone dropwise, stir to react, cool, precipitate in cold methanol, filter, and dry to obtain lignin-based polycaprolactone; 3) Disperse silane-coupled calcium carbonate in toluene, add triethylamine, heat and stir for 30 minutes, then add lignin-based polycaprolactone, add DCC dropwise, stir and react at 80°C overnight, cool, centrifuge, filter, wash and dry to obtain the product.

3. The degradable composition according to claim 2, wherein The mass ratio of the lignin-based polycaprolactone to the silane-coupled calcium carbonate is 3-5:

1.

4. The degradable composition according to claim 1, wherein The deacetylation degree of the chitosan is 90±5%, the mass concentration of the acetic acid solution is 2-5%, and the mass volume ratio of the chitosan to the acetic acid solution is 20-30 g / L.

5. The degradable composition according to claim 1, wherein The initiator is a mixture of ammonium persulfate or potassium persulfate and sodium sulfite.

6. The degradable composition according to claim 1, wherein The molar ratio of the DOPO derivative with a terminal double bond, 2-methylene-1,3-dioxepane and acrylic acid is 2-5:4-7:1; the mass ratio of chitosan, mixed monomer and initiator is 1:3-5:0.05-0.

1.

7. A degradable plastic, characterized in that: The method comprises the following steps: The degradable composition according to any one of claims 1 to 6 is placed in a high-speed mixer and stirred uniformly to obtain a mixture; the mixture is put into a twin-screw extruder for melt blending, extrusion, and then pelletized by a pelletizer to obtain degradable plastic particles.

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