Polyvinyl Alcohol-based Degradable Plastic, Preparation Method Therefor and Application Thereof, and Recycling Method Therefor

Abstract

Disclosed in the present invention are a polyvinyl alcohol (PVA)-based degradable plastic, a preparation method therefor and application thereof, and a recycling method therefor. The preparation method comprises the following steps: a PVA solution is subjected to a chemical grafting reaction under an acidic condition under the action of a modifier; there are a phenyl group, an aldehyde group, and at least one group capable of forming a hydrogen bond with PVA in a structural formula of the modifier. The polyvinyl alcohol-based degradable plastic provided in the present invention has the advantages of being high in transparency, high in mechanical strength, not affected by environmental humidity, easy to degrade, good in thermal stability and good in biocompatibility, and has the advantages of recyclability, low costs, easy large-scale preparation and the like.

Claims

1. A preparation method for polyvinyl alcohol-based degradable plastic, wherein the preparation method comprises the following steps: the PVA solution is subjected to a chemical grafting reaction under an acidic condition and under the action of a modifier; there are a phenyl group, an aldehyde group, and at least one group capable of forming a hydrogen bond with PVA in a structural formula of the modifier; the aldehyde group and the group capable of forming a hydrogen bond with PVA respectively substitute the hydrogen on the different carbon atoms on the phenyl group; the group capable of forming a hydrogen bond with PVA is one or more selected from the group consisting of hydroxyl, methoxy, ethoxy, fluoro, carboxy, methoxycarbonyl and methyl; the mole percentage of the modifier with respect to a repeating structural unit of the PVA is 15% to 60%.

2. The preparation method according to claim 1, wherein, the molecular weight of the modifier is 106-300; or, the aldehyde group and the group capable of forming a hydrogen bond with PVA substitute the hydrogen on different carbon atoms on the phenyl group by using meta or para substitution.

3. The preparation method according to claim 1, wherein the molar percentage of the modifier with respect to a repeating structural unit of the PVA is 20%-40%.

4. The preparation method according to claim 1, wherein the PVA solution is a solution obtained by dissolving PVA in a soluble solvent.

5. The preparation method according to claim 1, wherein the acidic condition is a strongly acidic condition, an acidic condition with pH of 3 or less; or, the acidic condition is achieved by using a pH regulator.

6. The preparation method according to claim 1, wherein after the chemical grafting reaction, a post-treatment is further performed; the post-treatment comprises carrying out drying in form of coating film or melt-blowing film forming for the reaction solution.

7. A polyvinyl alcohol-based degradable plastic prepared by the preparation method according to claim 1.

8. An application of the polyvinyl alcohol-based degradable plastic according to claim 7.

9. A recycling method for the polyvinyl alcohol-based degradable plastic according to claim 7, wherein it comprises the following steps: completely dissolving the polyvinyl alcohol-based degradable plastics in a soluble solvent.

10. The recycling method according to claim 9, wherein the soluble solvent is dimethyl sulfoxide, or a mixed solvent formed by dimethyl sulfoxide and water; or, the dissolving is performed at room temperature; or, after the completely dissolving, a post-treatment is further performed; the post-treatment comprises carrying out drying in form of coating film or melt-blowing film forming for the reaction solution.

11. The preparation method according to claim 1, wherein, the modifier is one or more selected from the group consisting of p-hydroxybenzaldehyde, 3,4-dihydroxybenzaldehyde, vanillin, ethyl vanillin, 4-fluorobenzaldehyde, p-aldehyde benzoic acid, m-aldehyde benzoic acid, 4-dimethylaminobenzaldehyde, methyl p-formyl benzoate and p-tolualdehyde.

12. The preparation method according to claim 11, wherein, the modifier is p-formyl benzoic acid, or methyl p-formyl benzoate, or m-formyl benzoic acid, or a combination of p-methylbenzaldehyde and ethyl vanillin.

13. The preparation method according to claim 12, wherein, when the modifier is a combination of p-tolualdehyde and ethyl vanillin, the molar ratio of p-tolualdehyde and ethyl vanillin is 1:1-1:3.

14. The preparation method according to claim 4, wherein, the mass percentage of PVA in the PVA solution is 6%-11%.

15. The preparation method according to claim 4, wherein, the molecular weight of PVA is 40,000 to 140,000.

16. The preparation method according to claim 4, wherein, the soluble solvent is dimethyl sulfoxide, or a mixed solvent formed by dimethyl sulfoxide and water.

17. The preparation method according to claim 4, wherein, the dissolving is carried out at 70-90° C.

18. The preparation method according to claim 5, wherein, the acidic condition is an acidic condition with pH of 1; or, the acidic condition is achieved by using a pH regulator, and the pH regulator is preferably hydrochloric acid.

19. The preparation method according to claim 5, wherein, the temperature of the chemical grafting reaction is 70-90° C.; or, the time of the chemical grafting reaction is 1-3 h.

20. The preparation method according to claim 6, wherein, the temperature of drying in form of coating film is 60-120° C., and the time is 10 min-30 min; or, the temperature of the melt-blowing film forming is 160-190° C.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0038] FIG. 1(a) shows the infrared spectrum of the polyvinyl alcohol-based degradable plastic of Example 1.

[0039] FIG. 1 (b) shows the test result of the transmittance in visible light region of the polyvinyl alcohol-based degradable plastic of Example 1.

[0040] FIG. 2 shows the test result of the mechanical properties of the polyvinyl alcohol-based degradable plastic of Example 1.

[0041] FIG. 3 shows the test result of mechanical properties of the polyvinyl alcohol-based degradable plastic of Example 1 after being saturated with water.

[0042] FIG. 4 shows the comparison result of the thermal stability of the polyvinyl alcohol-based degradable plastic of Example 1 and the PVA thin film.

[0043] FIG. 5 shows the test result of biocompatibility of the polyvinyl alcohol-based degradable plastic of Example 1.

[0044] FIG. 6 shows the test result of the mechanical performance of the polyvinyl alcohol-based degradable plastic of Example 2 after being saturated with water (grafting rate 15%).

[0045] FIG. 7 shows the test result of the mechanical performance of the polyvinyl alcohol-based degradable plastic of Example 3 after being saturated with water (grafting rate 30%).

[0046] FIG. 8 shows the test result of the mechanical performance of the polyvinyl alcohol-based degradable plastic of Example 4 after being saturated with water (grafting rate 40%).

[0047] FIG. 9 shows the test result of the mechanical performance of the polyvinyl alcohol-based degradable plastic of Example 5 after being saturated with water (grafting rate 50%).

[0048] FIG. 10 shows the test result of the mechanical performance of the polyvinyl alcohol-based degradable plastic of Example 6 after being saturated with water (grafting rate 60%).

[0049] FIG. 11 shows the test result of the mechanical performance of the polyvinyl alcohol-based degradable plastic of Example 1 after being saturated with water (grafting rate 10%).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0050] The following examples further illustrate the present disclosure, but the present disclosure is not limited thereto to the scope of the described examples. In the following examples, the experimental methods without specific conditions are selected according to conventional methods and conditions, or according to the product specification.

[0051] The raw materials in the following examples, PVA powder was purchased from Aladdin Company, with a molecular weight of 70,000.

Example 1

[0052] In Example 1, the preparation method of polyvinyl alcohol-based degradable plastic is: PVA was dissolved in organic solvent DMSO at 90° C. with a mass percentage of 6%, then the solution was heated to 70° C., and the pH of the solution was adjusted to 1 by using hydrochloric acid, then the modifier para-aldehyde benzoic acid was added to the solution, with a grafting mole percentage of 20%, and the reaction was carried out for two hours to obtain the solution of PVA modified with supramolecular force groups; then the solution was dried in form of coating film (drying conditions: 80° C., 20 min) to obtain a polyvinyl alcohol-based degradable plastic (hereafter also referred to as “PVA-based supramolecular plastic”) thin film with a thickness of 30 microns.

Effect Example 1

[0053] This effect example is mainly for testing performance of the polyvinyl alcohol-based degradable plastic thin film prepared in Example 1, comprising the following:

Infrared Detection

[0054] Infrared detection was performed on the degradable plastic with a thickness of 30 microns obtained in Example 1. As shown in FIG. 1(a), the result showed that the new infrared peak of the PVA-based degradable plastic at the wavelength of 1017cm.sup.−1 is the infrared characteristic peak of acetal (which is the product obtained by the condensation of one molecule of aldehyde and two molecules of alcohol), which proves the success of the acetal reaction and thus reflects the success of the grafting reaction.

[0055] In FIG. 1(a), the sample of “supramolecular force group” represents the modifier para-aldehyde benzoic acid used in Example 1, and the sample of “PVA” represents a PVA thin film with a thickness of 30 microns, which is made by dissolving commercially available PVA powder and then drying it to form a form, wherein the film-forming process by drying is the same as the film-forming process by drying in Example 1.

Light Transmittance Detection

[0056] The degradable plastic obtained in Example 1 was also tested for light transmittance, as shown in FIG. 1(b). The results show that the transmittance of more than 98% can be maintained in the visible light region.

Mechanical Performance Test

[0057] The mechanical performance of the degradable plastic with a thickness of 30 microns obtained in Example 1 was also tested, meanwhile, a daily-used polyethylene plastic bag with a thickness of 30 microns and a polyethylene sealed bag with a thickness of 30 microns were tested for comparison, as shown in FIG. 2, the results show that the tensile strength of the degradable PVA-based supramolecular plastic is about 47 MPa, and the modulus is as high as 400 MPa (calculated based on the slope of the curve in the figure). Compared with the daily-used polyethylene plastic bags (tensile strength is about 21 MPa) and sealed bags (tensile strength is about 23 MPa), the degradable plastic has a huge improvement in strength.

Load Detection

[0058] The degradable plastic with a thickness of 30 microns obtained in Example 1 was tested for its load-bearing performance, and the specific method was as follows: using plastic to lift a weight of 2 kg from the bottom, and the result showed that the degradable plastic was intact.

Mechanical Performance Test after being Saturated with Water

[0059] FIG. 3 shows that the degradable PVA-based supramolecular plastic obtained in Example 1 has excellent stability in fresh water, after being saturated with water, the water content is only 9 wt % and the tensile strength is about 26 MPa, which is still higher than the tensile strength (about 21 MPa) of the daily-used polyethylene plastic bags, and commercial PVA thin films will dissolve in water when it meets with water. It shows that the degradable PVA-based supramolecular plastic of the present invention still has better performance than the commercialized PVA thin film after being saturated with water.

Degradation Performance Test

[0060] The degradation performance test of the polyvinyl alcohol-based degradable plastic obtained in Example 1 shows that:

[0061] Polyvinyl alcohol-based degradable plastic with a thickness of 30 microns was completely dissolved in an alkaline aqueous solution (sodium hydroxide solution with pH of 12) in 1 minute at room temperature.

[0062] PVA-based degradable plastic with a thickness of 30 microns was cut into small pieces of uniform size, about 2 cm*3 cm*30 microns, which were weighed separately and then buried in the soil. After two days, the quality was reduced by 12%, after one week, the quality was reduced by 29%, after two weeks, the quality was reduced by 76%, and after 20 days, it was completely degraded in the soil.

[0063] PVA-based degradable plastic with a thickness of 30 microns became a sol state in seawater in three days and was completely degraded in ten days.

[0064] It shows that the degradable PVA-based supramolecular plastic can be completely degraded in an alkaline aqueous solution at room temperature, and even the supramolecular plastic can be completely degraded in soil and seawater.

Thermal Stability Test

[0065] FIG. 4 shows a comparison result of the thermal stability of the polyvinyl alcohol-based degradable plastic of Example 1 and the PVA thin film. Wherein, the

[0066] PVA thin film was made by dissolving commercially available PVA powder and then drying it to form a film, and the film-forming process by drying was the same as that of Example 1, and the thickness of the two thin film samples used for testing were both 30 microns.

[0067] According to FIG. 4, PVA begins to decompose at 226° C., and supramolecular plastic begins to decompose around 265° C., the decomposition temperature increases by 39° C.; supramolecular plastic is particularly stable below 100° C. FIG. 4 shows that degradable PVA-based supramolecular plastic have better thermal stability than PVA thin film.

Biocompatibility Test

[0068] The supramolecular plastic with a thickness of 30 microns obtained in Example 1 were cut into small pieces of a certain quality, and soaked in a certain volume of cell culture medium for 5 days to obtain cell culture medium with different concentrations (specific concentrations were set according to the standard as shown in FIG. 5, a control group with the concentration of 0 mg/mL, and experimental groups with the concentrations of 0.5, 1, 2 mg/mL respectively were set), and then the culture medium was used to culture human normal liver cells (LO2 cell), mouse fibroblasts (L929 cells). After 72 hours of culturing, the activity of the cells was observed and counted to reflect the cytotoxicity of supramolecular plastic.

[0069] The results are shown in FIG. 5, the results show that normal human hepatocytes and mouse fibroblasts maintain a high survival rate in the culture medium without supramolecular plastic (corresponding to a control group with a concentration of 0 mg/mL) and in the culture medium with supramolecular plastic (corresponding to the experimental groups with concentrations of 0.5, 1, 2mg/mL), above 95%, proving that supramolecular plastics are basically non-cytotoxic.

Recyclability Test

[0070] The specific steps are as follows: the polyvinyl alcohol-based degradable plastic with a thickness of 30 microns obtained in Example 1 was further cut into fragments, dissolved in DMSO at room temperature, and then the film-forming process by drying in Example 1 was re-operated to obtain recycled product. After testing, the performance of the recycled product was exactly the same as that of the raw material before recycling (the polyvinyl alcohol-based degradable plastic obtained in Example 1).

[0071] It shows that, compared with the degradable material based on covalent bonds, the degradable supramolecular material prepared by the present invention based on supramolecular force has a faster degradation rate and milder degradation conditions, and also has fast and efficient fracture-recombination performance, because the internal force is a weak interaction force, so it is recyclable.

Examples 2-6

[0072] On the basis that the raw materials for preparation, the process steps and the conditions were the same as those in Example 1, the test results of experiments with the grafting rate (15%, 30%, 40%, 50%, 60%, respectively) as the only variable were investigated. The water absorption saturation rate and the strength data after being saturated with water of the PVA-based supramolecular plastic prepared in each example are shown in Table 1 below and shown in FIGS. 6-10.

TABLE-US-00001 TABLE 1 Performance comparison between Examples 1-6 and Comparative Example 1 Water absorption Strength after being saturation rate saturated with Samples Grafting rate (%) (wt %) water (MPa) Examples 1 20 9 26 Examples 2 15 60 15.5 Examples 3 30 6 32.5 Examples 4 40 3 37.5 Examples 5 50 2 42 Examples 6 60 0.5 63 Comparative 10 75 2.7 Example 1

[0073] It is noted that although the tensile strength corresponding to the grafting rate of 15% in Example 2 cannot reach the tensile strength of the daily used polyethylene plastic bags (about 21 MPa), the tensile strength can also meet the basic use requirements, and perfectly overcome the defect that polyethylene plastic bags cannot be degraded.

[0074] When the grafting rate is 50%, the water content of the PVA-based supramolecular plastic obtained after being saturated with water is only 2%, as shown by the tensile data, the tensile strength of the material after being saturated with water is 42 MPa (the result is shown in FIG. 9). It can be seen that although increasing the grafting rate can further improve the stability of the material in water, increasing the grafting rate means that more raw materials are consumed, and the PVA-based supramolecular plastic with a grafting rate of 50% shows a certain yellow color.

[0075] When the grafting rate is 60%, although the strength of the material after being saturated with water is further improved (the result is shown in FIG. 10), the diseconomy caused by raw material consumption and yellowness are more serious than the case where the grafting rate is 50%.

[0076] In contrast, the supramolecular plastic with a grafting rate of 20-40% not only has high mechanical strength and water resistance, but also has high transparency and relatively low production costs.

[0077] In addition, the degradable plastic with a thickness of 30 microns obtained in Examples 2-6 was respectively subjected to infrared detection, light transmittance detection, load detection, degradation performance test, and thermal stability test, biocompatibility test and recyclability test as shown in Effect Example 1, the results show that the effects can reach the level equivalent to the effects of Example 1.

Comparative Example 1

[0078] On the basis that the raw materials for preparation, the process steps and the conditions were the same as in those Example 1, the comparison results of the experiments with the grafting rate as the only variable were investigated.

[0079] When the grafting rate is 10%, the water content of the PVA-based supramolecular plastic after being saturated with water is as high as 75%, as shown by the tensile data, the tensile strength of the material after being saturated with water is low, only 2.7 MPa (the result is shown in the FIG. 11 and Table 1), that is to say, the PVA-based supramolecular plastic with a grafting rate of 10% becomes very soft after absorbing water and cannot fully meet the needs for daily use.

Example 7

[0080] On the basis that the raw materials for preparation, the process steps and the conditions are the same as those in Example 1, the test results of the experiment with modifier type (the modifier specifically used in this example is m-aldehyde benzoic acid) as the only variable were investigated.

[0081] The degradable plastic with a thickness of 30 microns obtained in this example was respectively subjected to infrared detection, light transmittance detection, load detection, mechanical performance detection after being saturated with water, degradation performance test, thermal stability test, biocompatibility testing and recyclability testing as shown in Effect Example 1, and the results show that the effects can reach the level equivalent to the effects of Example 1.

Example 8

[0082] On the basis of that the raw materials for preparation, the process steps and conditions are the same as those in Example 1, the test results of the experiment with the modifier type (the modifier specifically used in this example is a mixture of methyl benzaldehyde and ethyl vanillin, wherein the molar ratio of p-methyl benzaldehyde and ethyl vanillin is 1:1) as the only variable were investigated.

[0083] The degradable plastic with a thickness of 30 microns obtained in this embodiment was respectively subjected to infrared detection, light transmittance detection, load detection, mechanical performance detection after being saturated with water, degradation performance test, thermal stability test, biocompatibility testing and recyclability testing as shown in Effect Example 1, and the results show that the effects can reach the level equivalent to the effects of Example 1.

Example 9

[0084] On the basis that the raw materials for preparation, process steps and conditions are the same as those in Example 1, the test results of the experiment with the modifier type (the modifier specifically used in this example is methyl p-formyl benzoate) as the only variable were investigated.

[0085] The degradable plastic with a thickness of 30 microns obtained in this embodiment was respectively subjected to infrared detection, light transmittance detection, load detection, mechanical performance detection after being saturated with water, degradation performance test, thermal stability test, biocompatibility testing and recyclability testing as shown in Effect Example 1, and the results show that the effects can reach the level equivalent to the effects of Example 1.