CN110368717B - Polylactic acid non-woven filter cloth material for oil/water separation and preparation method thereof - Google Patents
Polylactic acid non-woven filter cloth material for oil/water separation and preparation method thereof Download PDFInfo
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Abstract
The invention belongs to the technical field of functional polymer environment-friendly materials, and particularly discloses a polylactic acid non-woven filter cloth material for oil/water separation and a preparation method thereof. The preparation method mainly comprises the following steps: (1) dissolving polylactic acid in a good solvent to prepare a polylactic acid solution; (2) adding a non-solvent into the polylactic acid solution, and stirring until no floccule appears to obtain a polylactic acid coating solution; (3) and (3) coating the polylactic acid coating solution prepared in the step (2) on a polylactic acid non-woven fabric, and drying to obtain the polylactic acid non-woven filter cloth material for oil/water separation. The polylactic acid non-woven filter cloth material for oil/water separation prepared by the invention has super-hydrophobic and super-oleophylic properties, can quickly realize the separation of oil-water mixture by a filtering mode, has short separation time, high separation efficiency, good separation effect and good biodegradability, and is simple in preparation method and environment-friendly.
Description
Technical Field
The invention belongs to the field of functional polymer environment-friendly materials, and particularly relates to a polylactic acid non-woven filter cloth material for oil/water separation and a preparation method thereof.
Background
The rapid increase of fossil fuel consumption and frequent oil leakage accidents generate a large amount of oily wastewater, seriously threaten the sustainable development of human beings and force the oil pollution to become a problem to be solved urgently. The traditional oil pollution treatment strategies mainly comprise degradation of a chemical dispersant, use of an oil skimmer, combustion, sponge absorption and the like. Although the conventional method can effectively alleviate the oil stain problem to a certain extent, the conventional method still has some insurmountable disadvantages, such as high cost, high equipment requirement, low recovery efficiency and the like. In order to solve the problems, the materials with special wetting surfaces have important application values for the treatment of oily wastewater and the purification of water, the extensive research on the materials is stimulated, but most of the used materials are difficult to biodegrade, so that the treatment of the materials at the later stage causes serious secondary pollution to the ecological environment; and the preparation method is complex and causes pollution to the environment. Therefore, the development of a full-bio-based biodegradable high-efficiency oil/water separation material and a preparation method thereof have been the focus of attention.
The wettability of the material surface is mainly determined by the chemical properties and the surface topography of the material. Based on this, a large number of super-wetting materials have been successfully developed and applied in the field of oil/water separation, such as super-hydrophobic/super-oleophilic materials and super-oleophobic/super-hydrophilic materials. The preparation method of the super-hydrophobic/super-oleophylic material is more, such as a biological template method, a photoetching method, a chemical deposition method and the like, and the super-hydrophobic material with higher surface energy is easier to show the super-oleophylic property because the surface tension of water is greater than that of oil. The separation efficiency of the super oleophobic/super hydrophilic material is often dependent on the viscosity of the organic solvent or oil, and has larger application limitation. For this reason, the preparation of superhydrophobic/superoleophilic materials that readily and selectively separate oil/water mixtures has become the focus of research.
Super-hydrophobic/super-oleophilic materials for oil/water separation are mainly classified into two major categories: the first is an absorbent material mainly comprising sponge, aerogel and porous polymer; the other is a filtering material mainly comprising a separation membrane and a metal net. For The absorbent material, 2016, Cao et al designed a Nanodiamond (ND) hydroxylated with Polydopamine (PDA) to react with 1H, 1H, 2H, 2H-Perfluorodecanethiol (PFDT) on The Chemical Engineering Journal,2016,307:319-,finally, a series of super-hydrophobic/super-oleophylic polyurethane sponges are prepared, and reported application results are good, for example, the oil absorption capacity of the prepared polyurethane sponges to oil or organic solvents can reach 15-60 times of the self weight, and the number of times of recycling can reach more than 10 times. However, the preparation process is complex, the fluorine-containing material which is expensive and difficult to biodegrade is also needed, and the sponge prepared has low absorption efficiency on normal hexane, which is only 3.75 times of the self weight, and is difficult to meet the actual requirement of treating the oil leakage problem. To solve the inefficiency problem of such absorbent materials, a large number of separation materials were developed one after another, for example, 2017 Gu et al published in ACS appl.mater.interfaces,2017,9(7),5968 on a super-hydrophobic/super-oleophilic silica/polystyrene/polylactic acid (SiO) design assisted by dopamine2/PS/PLA), the results show: the separation material has good wettability and stable separation efficiency even under stretching or extreme conditions. However, the material contains PS and other component materials which are difficult to biodegrade, and the problem of ecological environment pollution is caused in the post-treatment process of the material.
In summary, most of the currently designed oil/water separation materials are not biodegradable, and cannot be used in oil-water separation engineering which requires difficult recovery and causes secondary pollution to the environment (for example, in the treatment of marine oil leakage, the separation material is preferably fully biodegradable so as to protect the ecological environment); and the existing preparation process of the oil-water separation material is relatively complex, and the intermediate product may bring harm to the environment. Therefore, it is necessary to develop an oil-water separation technology which is green and environment-friendly in the whole processes of material selection, preparation and product treatment.
The applicant discloses in chinese patents CN105085953A (2015.11.25), CN 107090087A (2017.08.25) and Soft Matter,2016,12,2766 respectively, that a fully biodegradable polylactic acid (PLA) with a micron/nanometer second-order hierarchical structure has a high adhesion and an adhesion-controllable superhydrophobic surface prepared by a non-solvent alcohol or ester assisted method, and no inorganic nanoparticles or fluorine-containing substance with low surface energy need to be added in the process of preparing the superhydrophobic film. However, the used non-solvents are various, contain toxic and harmful substances and have secondary pollution to the environment, and most of the documents are materials with super-hydrophobic property, so the problem of preparing the oil/water separation filter cloth material of the whole PLA by using the methods is not solved.
Disclosure of Invention
Aiming at the problems and the defects in the prior art, the invention aims to provide a polylactic acid non-woven filter cloth material for oil/water separation and a preparation method thereof.
In order to realize the purpose of the invention, the technical scheme adopted by the invention is as follows:
a preparation method of a polylactic acid non-woven filter cloth material for oil/water separation comprises the following steps:
(1) dissolving polylactic acid in a good solvent to prepare a polylactic acid solution;
(2) adding a non-solvent into the polylactic acid solution, and stirring until no floccule appears to obtain a polylactic acid coating solution;
(3) and (3) coating the polylactic acid coating solution prepared in the step (2) on a polylactic acid non-woven fabric, and drying to obtain the polylactic acid non-woven filter cloth material for oil/water separation.
According to the preparation method, in the step (2), the non-solvent is absolute ethyl alcohol, and the volume ratio of the polylactic acid solution to the absolute ethyl alcohol is 1: (1.2-1.6), and more preferably, the volume ratio of the polylactic acid solution to the absolute ethyl alcohol is 1: 1.4.
According to the above production method, preferably, the good solvent in the step (1) is chloroform.
According to the above production method, preferably, the concentration of the polylactic acid solution of the step (1) is 50 mg/ml.
According to the above production method, preferably, the polylactic acid nonwoven fabric in the step (3) has a size of 30g/m2～80g/m2。
According to the above preparation method, preferably, the coating manner in the step (3) is dipping.
According to the above production method, preferably, the temperature of the drying in the step (3) is 30 to 50 ℃.
The polylactic acid non-woven filter cloth material for oil/water separation prepared by the preparation method.
The polylactic acid non-woven filter cloth material for oil/water separation can be used for separating oil/water mixture.
The specific mechanism that the polylactic acid non-woven filter cloth prepared by the invention can be used for oil/water separation is as follows: the polylactic acid non-woven fabric (substrate) is a three-dimensional porous network structure formed by crossing and overlapping fibers with micron-sized diameters, the three-dimensional porous network structure provides possibility for quickly realizing the separation of an oil/water mixture, and after the polylactic acid coating solution is coated on the polylactic acid non-woven fabric substrate, a phase separation is carried out while a solvent is volatilized, namely, the polylactic acid solution in the coating solution is subjected to non-solvent auxiliary phase separation to enable the whole system to form two phases: a PLA-poor phase containing only good solvent and non-solvent and a PLA-rich phase consisting of good solvent and polylactic acid. In the PLA poor phase, because the poor solvent is volatilized slower than the good solvent, with the reduction of the good solvent, the PLA is separated out and adsorbed on the polylactic acid non-woven fabric substrate to form polylactic acid particles with nano-scale dimensions; in the PLA rich phase, with the reduction of the good solvent, the PLA is subjected to coagulation and adsorption on the polylactic acid non-woven fabric substrate to form polylactic acid particles with micron-sized dimensions. Therefore, the polylactic acid solution is subjected to phase separation under the assistance of a non-solvent, so that polylactic acid particles with different micron and nanometer sizes are tightly attached to the micron fibers of the polylactic acid non-woven fabric substrate to form a micro/nano structure with certain roughness, and the PLA non-woven fabric has excellent super-hydrophobic performance; and the surface tension of oil and organic solvent is low, so that the PLA non-woven filter cloth can be completely wetted, and the PLA non-woven filter cloth has excellent super-oleophylic property. The PLA non-woven filter cloth material prepared by the invention has different selective absorptions for water and oil, so that the PLA non-woven filter cloth material can be applied to separation of oil/water mixture.
Compared with the prior art, the invention has the following positive beneficial effects:
(1) the polylactic acid non-woven fabric (substrate) is a three-dimensional porous network structure formed by intersecting and overlapping micron-sized fibers, has poor self hydrophobic property and cannot be used for separating oil/water mixtures.
(2) The polylactic acid non-woven filter cloth for oil/water separation prepared by the invention has a three-dimensional porous reticular structure, has super-hydrophobic and super-oleophylic characteristics, oily components can specifically permeate through micropores on the polylactic acid non-woven filter cloth, and water components cannot permeate through micropores on the polylactic acid non-woven filter cloth, so that the separation of an oil-water mixture can be rapidly realized in a filtering mode, the separation time is short, the separation efficiency is high, and the separation effect is good.
(3) Compared with other non-solvents, the anhydrous ethanol is non-toxic and volatile, is convenient for drying treatment of the polylactic acid non-woven filter cloth in the later period, has no residue, is low in price, and is green and environment-friendly.
(4) The volume ratio of the polylactic acid solution to the absolute ethyl alcohol in the polylactic acid coating liquid prepared by the invention is 1: (1.2-1.6) because, after the non-solvent assisted phase separation has occurred, the entire system is separated into two phases: a PLA-poor phase containing only good solvent and non-solvent and a PLA-rich phase consisting of good solvent and polylactic acid; when the volume ratio of the PLA solution to the absolute ethyl alcohol is less than 1:1.2, the volume of the ethyl alcohol is low, and the volume of the chloroform in the PLA poor phase is large, so that the phase separation degree of the PLA is reduced, the chloroform continues to dissolve the PLA non-woven fabric, and finally the needed PLA non-woven filter cloth cannot be formed; when the volume ratio of the polylactic acid solution to the non-solvent is increased from 1:1.2 to 1:1.4, the contact angle of the surface of the polylactic acid non-woven filter cloth material for oil/water separation is increased from 140 degrees to 151 degrees, and the polylactic acid non-woven filter cloth material has good super-hydrophobic performance; when the volume ratio of the polylactic acid solution to the non-solvent is increased from 1:1.4 to 1:1.6, the solubility parameter of the sample solution is too high, the compatibility of the polylactic acid with the mixed solvent (i.e. the mixed solvent formed by anhydrous ethanol and chloroform) is poor, the polylactic acid is completely precipitated, and the contact angle is reduced, so that the contact angle of the surface of the polylactic acid non-woven filter cloth material for oil/water separation is reduced from 151 degrees to 146 degrees. Therefore, the optimal concentration is obtained when the volume ratio of the polylactic acid solution to the non-solvent is 1:1.4, and the prepared polylactic acid non-woven filter cloth material for oil/water separation has good super-hydrophobic performance.
(5) The preparation method is simple, the PLA solution is prepared firstly, then the non-solvent absolute ethyl alcohol is added into the PLA solution to cause phase separation, and finally the PLA non-woven filter cloth is soaked into the PLA coating solution and is evaporated and dried to obtain the PLA non-woven filter cloth for oil/water separation; the preparation period is short, only more than 30 hours are needed, compared with the reaction time which is as long as one week in the prior art, the method has the advantages of short reaction period, high time efficiency, no need of adding non-degradable raw materials and expensive equipment, and the problem of pollutant discharge can be solved by evaporating chloroform and absolute ethyl alcohol through a simple collection device.
(6) The polylactic acid non-woven filter cloth material prepared by the invention realizes the rapid separation of oil/water mixture in a filtering mode, has short separation time and high separation efficiency, can be recycled after being used through simple drying treatment, has low recycling treatment cost and good recycling performance, and has biodegradability and can avoid the problem of secondary pollution to the environment caused by the material.
Drawings
FIG. 1 is a surface topography (SEM) picture of the polylactic acid non-woven filter cloth material prepared in example 7.
FIG. 2 is a graph showing the effect of surface selective adsorption of the polylactic acid non-woven filter cloth material prepared in example 7.
FIG. 3 is a view of an oil-water separator.
FIG. 4 is a graph showing the oil/water separation efficiency of the polylactic acid non-woven filter cloth material prepared in example 7.
FIG. 5 is a chart showing the cycle of oil/water separation efficiency of the polylactic acid non-woven filter cloth material prepared in example 7.
FIG. 6 shows the surface contact angles of the polylactic acid non-woven filter cloth material prepared in example 7 at different pH values.
Detailed Description
The present invention will be described in further detail with reference to specific examples, but the scope of the present invention is not limited thereto.
(first) non-solvent species screening experiment
In order to investigate the influence of the kind of non-solvent on the water contact angle of the surface of the prepared polylactic acid non-woven filter cloth material, the inventors conducted the following experiments, i.e., examples 1 to 4, and the specific results are shown in table 1.
Example 1:
a preparation method of a polylactic acid non-woven filter cloth material for oil/water separation comprises the following steps:
(1) adding a polyacid into chloroform by taking the chloroform as a good solvent, and stirring for 4 hours at room temperature (25 +/-2 ℃) to prepare a polylactic acid solution with the polylactic acid concentration of 50 mg/ml;
(2) taking 5ml of the polylactic acid solution prepared in the step (1), gradually adding a non-solvent into the polylactic acid solution according to the volume ratio of the polylactic acid solution to the non-solvent of 1:1.2, and stirring until the mixture is uniform and has no obvious floccules to obtain a polylactic acid coating solution; wherein the non-solvent is absolute ethyl alcohol;
(3) soaking a polylactic acid non-woven fabric with the diameter of 10cm into the polylactic acid coating solution prepared in the step (2), standing at room temperature, putting the polylactic acid coating solution into a drying oven at 40 ℃ for drying after the polylactic acid coating solution is evaporated into gel, so that a good solvent and a non-solvent are completely volatilized, and obtaining the polylactic acid non-woven fabric material for oil/water separation, wherein the specification of the polylactic acid non-woven fabric is 30g/m2～80g/m2。
Example 2:
the content of example 2 is substantially the same as that of example 1, except that: the non-solvent is n-butanol.
Example 3:
the content of example 3 is substantially the same as that of example 1, except that: the non-solvent is ethyl acetate.
Example 4:
example 4 is substantially the same as example 1 except that: the non-solvent is a mixed non-solvent which is prepared by mixing absolute ethyl alcohol, n-butyl alcohol and ethyl acetate according to the volume ratio of 1:1: 1.
TABLE 1 selection of non-solvent species
As can be seen from Table 1, when the non-solvent is absolute ethyl alcohol or a mixed non-solvent, the contact angle of the surface of the prepared polylactic acid non-woven filter cloth material is large, which indicates that the prepared polylactic acid non-woven filter cloth material has strong hydrophobicity; when the non-solvent is selected from n-butyl alcohol and ethyl acetate, the water contact angle of the surface of the prepared polylactic acid non-woven filter cloth material is smaller; and the water contact angle of the surface of the polylactic acid non-woven filter cloth material prepared by using absolute ethyl alcohol as a non-solvent is basically the same as that of the mixed non-solvent. The anhydrous ethanol is volatile and nontoxic, so that the drying treatment of the polylactic acid non-woven filter cloth in the later period is facilitated, no residue is left, the price is low, and the environment is protected; the mixed non-solvent is not easy to volatilize, the solvent is remained in the later period, the cost is high, the environment is not protected, and the preparation process is complicated. Therefore, anhydrous ethanol is selected as a non-solvent for economic and environmental protection.
Effect of (II) amount of non-solvent on surface Water contact Angle
In order to investigate the influence of the amount of non-solvent on the water contact angle of the surface of the prepared polylactic acid non-woven filter cloth material, the inventors performed the following experiments, i.e., example 5 to example 9.
Example 5:
a preparation method of a polylactic acid non-woven filter cloth material for oil/water separation comprises the following steps:
(1) adding a polyacid into chloroform by taking the chloroform as a good solvent, and stirring for 4 hours at room temperature (25 +/-2 ℃) to prepare a polylactic acid solution with the polylactic acid concentration of 50 mg/ml;
(2) taking 5ml of the polylactic acid solution prepared in the step (1), gradually adding absolute ethyl alcohol into the polylactic acid solution according to the volume ratio of the polylactic acid solution to the absolute ethyl alcohol of 1:1.2, and stirring until the polylactic acid solution is uniform and has no obvious floccules to obtain a polylactic acid coating solution;
(3) soaking a polylactic acid non-woven fabric with the diameter of 10cm into the polylactic acid coating solution prepared in the step (2), standing at room temperature, putting the polylactic acid coating solution into a drying oven at 40 ℃ for drying after the polylactic acid coating solution is evaporated into gel, so that a good solvent and a non-solvent are completely volatilized, and obtaining the polylactic acid non-woven fabric material for oil/water separation, wherein the specification of the polylactic acid non-woven fabric is 30g/m2～80g/m2。
Example 6:
the contents of example 6 are substantially the same as those of example 5, except that: the volume ratio of the polylactic acid solution to the absolute ethyl alcohol in the step (2) is 1: 1.3.
Example 7:
example 7 is substantially the same as example 5 except that: the volume ratio of the polylactic acid solution to the absolute ethyl alcohol in the step (2) is 1: 1.4.
Example 8:
example 8 is substantially the same as example 5 except that: the volume ratio of the polylactic acid solution to the absolute ethyl alcohol in the step (2) is 1: 1.5.
Example 9:
example 9 is substantially the same as example 5 except that: the volume ratio of the polylactic acid solution to the absolute ethyl alcohol in the step (2) is 1: 1.6.
The polylactic acid non-woven filter cloth materials for oil/water separation prepared in examples 5 to 9 were subjected to a test of water contact angle of the surface, and the effect of the volume of the non-solvent on the water contact angle of the surface of the prepared polylactic acid non-woven filter cloth materials for oil/water separation was analyzed, and the results are shown in table 2.
TABLE 2 Effect of non-solvent volume on surface Water contact Angle
| Examples | Volume ratio of polylactic acid solution to absolute ethyl alcohol | Surface water contact angle of prepared sample |
| Example 5 | 1:1.2 | 140±2° |
| Example 6 | 1:1.3 | 146±3° |
| Example 7 | 1:1.4 | 151±1° |
| Example 8 | 1:1.5 | 148±2° |
| Example 9 | 1:1.6 | 146±1° |
From the thermodynamics of polymer dissolution, the free energy change of polymer dissolution is: Δ GM＝ΔHM-TΔSM. Wherein, Δ GM、ΔHM、ΔSMThe Gibbs mixing free energy, mixing heat and mixing entropy of the mixture of the polymer and the solvent molecule are respectively, and T is the dissolving temperature. For PLA, the dissolution process is endothermic, i.e., Δ HMIs greater than 0. The heat change upon mixing of the polymer with the solvent follows the Hildebrand formula:
in the formula (I), the compound is shown in the specification,
is the volume fraction of solvent and polymer, VMFor the total volume after mixing, δ1,δ2Is a solubility parameter for solvents and polymers. Based on the above discussion, the closer the solubility parameter of the polylactic acid and the mixed solution is, the stronger the solubility is, otherwise, the microphase separation phenomenon occurs due to the weakened solubility, thereby precipitating polylactic acid particles with micro-nano size. By utilizing the principle, after the polylactic acid coating solution is coated on the non-woven fabric, a super-hydrophobic structure with certain roughness can be formed on the surface of the non-woven fabric, and the polylactic acid coating solution is further used for oil-water separation.
As can be seen from Table 1, when the volume ratio of the polylactic acid solution to the non-solvent was increased from 1:1.2 to 1:1.4, the contact angle of the surface of the polylactic acid non-woven filter cloth material for oil/water separation was increased from 140 to 151, indicating that the solubility parameter (solubility parameter. delta.) of the mixed solvent of the non-solvent and the good solvent (i.e., the mixed solvent of anhydrous ethanol and chloroform) was increased as the volume of the non-solvent was increasedGeneral assemblyHas the advantages of linear addition property and linear addition property,
with the increase of the above-mentioned rate, the phase separation effect is more obvious until reaching the critical state (polymer-solvent interaction parameter chi)11/2) to create a perfect surface structure with a consequent increase in contact angle. However, when the volume ratio of the polylactic acid solution to the non-solvent was increased from 1:1.4 to 1:1.6, the contact angle of the surface of the polylactic acid non-woven filter cloth material for oil/water separation was decreased from 151 ° to 146 °. This indicates that the addition of the non-solvent is continued, so that the solubility parameter of the sample solution is too high, and the compatibility of the polylactic acid with the mixed solvent (i.e., the mixed solvent formed by anhydrous ethanol and chloroform) is poor, so that the polylactic acid is completely precipitated, and the contact angle tends to be lowered. Therefore, the optimal concentration is achieved when the volume ratio of the polylactic acid solution to the non-solvent is 1:1.4, the surface water contact angle of the polylactic acid non-woven filter cloth material for oil/water separation reaches the maximum value of 151 +/-1 degrees, and therefore, the prepared polylactic acid non-woven filter cloth material for oil/water separation has super-hydrophobic performance.
Scanning electron microscopy is adopted to detect the surface topography of the polylactic acid non-woven fabric (substrate) and the polylactic acid non-woven filter cloth material for oil/water separation prepared in example 7, and the detection result is shown in fig. 1, wherein a is the surface topography of the polylactic acid non-woven fabric (substrate), b is a partial enlarged view of a, c is the surface topography of the polylactic acid non-woven filter cloth material for oil/water separation prepared in example 7, d is a partial enlarged view of c, e is the surface topography of the polylactic acid non-woven filter cloth material for oil/water separation prepared in example 7 after oil absorption, and f is a partial enlarged view of e.
As can be seen from a in FIG. 1, the polylactic acid non-woven fabric (substrate) is internally composed of a plurality of crossed and overlapped three-dimensional porous reticular structures of microfibers with the diameter of about 14.75um, the partially enlarged view b of a shows that the fiber surface of the interior is quite smooth, and the pore diameter of the three-dimensional porous reticular structures is about 10-100 mu m, so that a good foundation is laid for realizing oil-water separation; from c, it can be seen that the PLA particles inside the polylactic acid non-woven filter cloth material for oil/water separation adhere tightly to the surfaces of the microfibers by van der waals force, making the originally smooth fiber surfaces very rough, resulting in increased fiber diameter and decreased pore size. From the enlarged view d of the part c, it can be further seen that a part of the PLA particles is directly attached to the surface of the fiber, and another part is attached to the surface of the fiber in an agglomerated form, so that the micro-sized fiber and the nano-sized PLA particles together form the micro/nano-scale structure necessary for superhydrophobicity. It can be seen from e that the surface appearance of the polylactic acid non-woven filter cloth material for oil/water separation is almost unchanged after oil absorption. Therefore, the existence of the micro-sized fiber and nano-sized PLA particle structure and the rough surface provide possibility for realizing the super-hydrophobic and super-lipophilic performance of the PLA filter non-woven fabric.
(III) performance analysis experiment:
the polylactic acid nonwoven filter cloth material for oil/water separation prepared in example 7 was subjected to a surface selective absorption property analysis experiment, an organic solvent absorption property experiment, an oil/water separation efficiency analysis experiment, an oil/water separation efficiency cyclicity analysis experiment, and a surface contact angle analysis experiment under different pH conditions. The specific experimental procedures and results thereof were analyzed as follows.
1. Surface selective absorption Performance analysis experiment
The specific experimental operation is as follows: 4 to 5. mu.l of water or oil droplets were dropped on the surface of the polylactic acid nonwoven filter cloth material for oil/water separation prepared in example 7, and the shapes of the water or oil droplets at different times were recorded.
The effect of the selective absorption performance on the surface of the polylactic acid non-woven filter cloth material is shown in figure 2. Wherein a is a wetting effect diagram of water drops on the polylactic acid non-woven filter cloth material, and as can be seen from the diagram, when the water drops just contact with the surface of the polylactic acid non-woven filter cloth material, the water drops are spherically stabilized on the surface of the material; after 20s, water drops can keep uniform spherical shapes on the surface of the material without permeation, and the contact angle of the water drops is not changed obviously, which shows that the prepared polylactic acid non-woven filter cloth material has excellent super-hydrophobic performance. b is a wetting effect diagram of oil drops on the polylactic acid non-woven filter cloth material, and as can be seen from the diagram, once the oil drops contact the surface of the non-woven filter cloth, the oil drops immediately permeate into the material to wet the surface of the material; the polylactic acid non-woven filter cloth material is completely absorbed by the non-woven filter cloth within short 3s, and the contact angle of oil drops after 3s is 0 degrees, which shows that the polylactic acid non-woven filter cloth material has excellent oleophylic property. Therefore, as can be seen from the change of the wettability of the water drops and the oil drops in fig. 2, the surface of the prepared polylactic acid non-woven filter cloth material has excellent selective absorption performance for different liquids.
2. Analysis experiment of oil/water separation efficiency
The specific experimental operation is as follows: the organic solvent and water are respectively dyed by Sudan III and anhydrous copper sulfate, and then 20ml of dyed organic solvent is poured into 20ml of dyed water to form an oil-water mixed solution. The oil-water mixture was poured into an oil-water separator (see fig. 3, a in fig. 3, water dyed with anhydrous copper sulfate, b is an organic solvent dyed with sudan iii, and c is an oil-water separator) to separate, and the oil-water separator used the polylactic acid nonwoven filter cloth material prepared in example 7 as a separation membrane, and the volume of the organic solvent before and after separation was measured. The formula for calculating the separation efficiency η is: eta ═ v2-v1)/v1Wherein v is1、v2The volumes of organic solvent before and after separation, respectively.
FIG. 4 is a graph showing the results of the separation efficiency of the polylactic acid nonwoven filter cloth material for different oil/water and solvent/water. As can be seen from the figure, the separation efficiency of the polylactic acid non-woven filter cloth material can reach 99.5%, 98%, 97.5%, 96% and 95% for soybean oil, normal hexane, styrene, diesel oil, normal heptane and silicone oil. It is noted that the polylactic acid non-woven filter cloth material has a low separation efficiency of the silicone oil compared to other solvents or oils, which may be due to a relatively high density of the silicone oil, resulting in clogging of some pores and a large amount of silicone oil remaining in the polylactic acid non-woven filter cloth material during the separation process. In conclusion, the prepared polylactic acid non-woven filter cloth material has higher separation efficiency on most of oil and organic solvent.
3. Cyclic analysis experiment of oil/water separation efficiency
The specific experimental operation is as follows: dyeing an organic solvent (n-hexane) and water by using Sudan III and anhydrous copper sulfate respectively, then pouring 20ml of dyed organic solvent into 20ml of dyed water to form an oil-water mixed solution, pouring the oil-water mixed solution into a separator for separation, and testing the volume of the organic solvent before and after the separation. And (3) drying the polylactic acid non-woven filter cloth material subjected to the primary separation in a vacuum oven at 40 ℃ for 30min, and then performing the next separation for use. The formula for calculating the separation efficiency η for each separation is: eta ═ v2-v1)/v1Wherein v is1、v2The volumes of organic solvent before and after separation, respectively.
FIG. 5 is a graph showing the separation efficiency cycle results of the polylactic acid non-woven filter cloth material. From the figure, it can be seen that the separation efficiency of the polylactic acid non-woven filter cloth material is not reduced along with the increase of the using times of the non-woven fabrics in the 20 times of the oil/water separation cycle experiment, and the separation efficiency of the prepared polylactic acid non-woven filter cloth material to the n-hexane/water mixture is still kept above 97% after the 20 th cycle, thereby showing that the polylactic acid non-woven filter cloth material prepared by the invention has excellent recycling performance.
4. Surface contact angle analysis experiments under different pH conditions
The specific experimental operation is as follows: three kinds of aqueous solutions with different pH (pH 1, pH 7, and pH 13) were obtained by adjusting the pH of water with hydrochloric acid and NaOH, and 4 μ l to 5 μ l of each aqueous solution was dropped on the surface of the polylactic acid nonwoven filter cloth material, and the surface contact angles under different pH conditions were measured with a contact angle measuring instrument.
FIG. 6 is a surface contact angle diagram of the polylactic acid non-woven filter cloth material under different pH conditions. As can be seen from the figure, the water contact angles of the surfaces of the polylactic acid non-woven filter cloth materials are all larger than 144 ° under the conditions of pH 1, pH 7 and pH 13, which shows that the prepared PLA non-woven filter cloth has extraordinary chemical resistance and wide practical application range to aqueous solutions of strong acid, strong alkali and the like.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the present invention, but rather as the following description is intended to cover all modifications, equivalents and improvements falling within the spirit and scope of the present invention.
Claims (7)
1. A preparation method of a polylactic acid non-woven filter cloth material for oil/water separation is characterized by comprising the following steps:
(1) dissolving polylactic acid in a good solvent to prepare a polylactic acid solution, wherein the good solvent is chloroform;
(2) adding a non-solvent into the polylactic acid solution, and stirring until no floccule appears to obtain the polylactic acid coating solution, wherein the non-solvent is absolute ethyl alcohol, and the volume ratio of the polylactic acid solution to the absolute ethyl alcohol is 1: (1.2-1.6);
(3) and (3) coating the polylactic acid coating solution prepared in the step (2) on a polylactic acid non-woven fabric, and drying to obtain the polylactic acid non-woven filter cloth material for oil/water separation.
2. The method according to claim 1, wherein the concentration of the polylactic acid solution in the step (1) is 50 mg/ml.
3. The method according to claim 1Characterized in that the specification of the polylactic acid non-woven fabric in the step (3) is 30g/m2～80g/m2。
4. The method according to claim 3, wherein the coating in step (3) is dipping.
5. The method according to claim 4, wherein the temperature of the drying in the step (3) is 30 to 50 ℃.
6. The polylactic acid non-woven filter cloth material for oil/water separation prepared by the preparation method of any one of claims 1 to 5.
7. Use of the polylactic acid non-woven filter cloth material for oil/water separation according to claim 6 for separating oil/water mixture.
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| CN111304922B (en) * | 2020-04-07 | 2022-10-04 | 浙江理工大学 | Preparation method and product of super-hydrophobic polylactic acid non-woven material |
| CN112301541B (en) * | 2020-10-20 | 2023-02-28 | 西安工程大学 | Easily-degradable reusable efficient non-woven oil absorption material and preparation method thereof |
| CN113737525B (en) * | 2021-09-24 | 2023-07-28 | 中国计量大学 | Preparation method of novel combined capillary force oil-water separation non-woven fabric |
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