Composite film with high transmittance and high haze in near-infrared region as well as preparation method and application of composite film

Abstract

The invention relates to the technical field of preparation of optical thin film materials, in particular to a composite thin film with high transmittance and high haze in a near-infrared region as well as a preparation method and application of the composite thin film. The preparation method of the composite film comprises the following steps: (1) carrying out oxidation treatment on degreased coffee grounds by adopting a TEMPO oxidation system to obtain oxidized cellulose containing lignin; mixing the lignin-containing oxidized cellulose with water, and performing high-pressure homogenization treatment to obtain a coffee residue-based lignocellulose-containing nanofiber suspension; (2) adding a plasticizer and a sodium carboxymethyl cellulose solution into the suspension containing the lignocellulose nanofibers prepared in the step (1), and uniformly mixing to obtain a blended solution; and pouring the blended solution, and drying to obtain the composite film. The composite film is widely applied to the aspects of medical near-infrared biological imaging homogenization, intelligent coverage of agricultural greenhouses, energy-saving windows of intelligent buildings, information security and privacy protection.

Description

Technical Field

[0001] The present invention relates to the technical field of optical film material preparation, and in particular to a composite film with high transmittance and high haze in the near-infrared region, and a preparation method and application thereof. Background Art

[0002] Light management films are functional thin film materials that achieve precise control of light transmission, scattering, and absorption properties through nanostructure design or chemical modification. Their core goal is to selectively manage light within specific wavelengths through interactions between the material and light (e.g., size-matched scattering and interfacial optical effects). In modern technology, light management films are widely used in display technology, solar cells, optical sensors, and information storage, improving light utilization efficiency, enhancing display quality, protecting privacy, and achieving specific optical functions. For example, in solar cells, light management films can effectively enhance the solar cell's light capture capacity, thereby increasing energy conversion efficiency; in display technology, they can improve screen contrast and viewing angles. However, existing technologies suffer from multiple drawbacks: inorganic substrates (glass, metal oxides) are brittle, difficult to process, and have a narrow light control range; organic materials (plastics, dyes) have poor weather resistance, contain toxic solvents, and are prone to aging; and precision optical coating processes (e.g., electron beam evaporation and ion sputtering) are energy-intensive, costly, and difficult to achieve uniform coating over large areas. Therefore, developing simple, environmentally friendly, and high-performance light management films is a current research hotspot and a challenge.

[0003] In recent years, the use of biomass resources to prepare functional films has become a research hotspot. Lignocellulose nanofibers have shown great potential in the preparation of film materials due to their high specific surface area, controllable optical properties and biodegradability. At present, the research on lignin-containing cellulose nanofibers in the visible light to ultraviolet region (200-780nm) has been relatively extensive. For example, by regulating its crystal structure and surface properties, composite films with high transmittance and ultraviolet shielding properties can be prepared. Related results have been applied in optical devices, packaging materials and other fields. In the near-infrared region (NIR, 780-1400nm), existing research focuses on high transmittance-low haze systems, which can achieve near-infrared transmittance >90%, but the haze is close to 0%. This type of material shows unique application potential in data security, environmental monitoring and other fields.

[0004] However, in application scenarios that require both high haze (>80%) and high near-infrared transmittance (>85%) in the near-infrared region, such as in medical near-infrared bioimaging (diffuse optical tomography requires a uniform light field to eliminate artifacts) and near-infrared laser therapy (to avoid local overheating), agricultural greenhouses (to ensure uniform transmission of near-infrared light to promote photosynthesis), and military security (scattered near-infrared light interferes with thermal imaging detection), there are significant gaps in existing technologies. SUMMARY

[0005] In view of the problems and deficiencies in the prior art, the present application aims to provide a composite film with high transmittance and high haze in the near-infrared region and a preparation method and application thereof.

[0006] To achieve the object of the present application, the technical scheme adopted by the present application is as follows:

[0007] The present application provides a preparation method of a composite film with high transmittance and high haze in the near-infrared region, which specifically comprises the following steps:

[0008] (1) The defatted coffee grounds are subjected to oxidation treatment using a TEMPO oxidation system to obtain oxidized cellulose containing lignin; the oxidized cellulose containing lignin is mixed with water and subjected to high-pressure homogenization treatment to obtain a coffee-ground-based lignin-containing cellulose nanofiber suspension;

[0009] (2) A plasticizing agent, a sodium carboxymethyl cellulose solution are added to the lignin-containing cellulose nanofiber suspension prepared in step (1) and mixed to obtain a blended liquid; the blended liquid is cast and dried to obtain a composite film.

[0010] Preferably, in step (2), the content of the lignin-containing cellulose nanofiber in the blended liquid is 70% to 100% by mass percentage, the content of the plasticizing agent is 0 to 10%, and the content of the sodium carboxymethyl cellulose is 0 to 20%.

[0011] Preferably, in step (2), the solid content in the lignin-containing cellulose nanofiber suspension is 0.8 to 2%, and the concentration of the sodium carboxymethyl cellulose solution is 0.5 to 2 wt%. More preferably, the solid content in the lignin-containing cellulose nanofiber suspension is 1.2%, and the concentration of the sodium carboxymethyl cellulose solution is 2 wt%.

[0012] Preferably, in step (2), the plasticizing agent is glycerol.

[0013] Preferably, in step (1), the specific steps of the oxidation treatment of the defatted coffee grounds using the TEMPO oxidation system are as follows: the defatted coffee grounds are dispersed in ultrapure water to obtain a dispersion liquid; TEMPO and sodium bromide are added to the dispersion liquid and mixed to obtain a mixed liquid; sodium hypochlorite solution is added dropwise to the mixed liquid under stirring at 35 to 45℃, and the pH of the mixed liquid is controlled to 10 to 11 by an alkaline solution during the dropwise addition of the sodium hypochlorite solution; the reaction liquid after the reaction is centrifuged to collect the precipitate, and the precipitate is washed until the pH of the washing liquid is neutral to obtain coffee-ground-based oxidized cellulose containing lignin.

[0014] Preferably, the mass ratio of coffee grounds, TEMPO, sodium bromide and sodium hypochlorite solution in the reaction solution is 24:0.15-0.45:0.4-0.8:120-180. More preferably, the mass ratio of coffee grounds, TEMPO, sodium bromide and sodium hypochlorite solution in the reaction solution is 24:0.32:0.8:150.

[0015] Preferably, the concentration of the sodium hypochlorite solution is 10wt%.

[0016] Preferably, the stirring reaction time is 6-8 hours. More preferably, the stirring reaction time is 7 hours.

[0017] The second aspect of the present application provides a composite film prepared by the method.

[0018] The third aspect of the present application provides the use of the composite film in biomedical imaging, temperature control windows, agricultural greenhouses and privacy protection.

[0019] Compared with the prior art, the present application has the following positive and beneficial effects:

[0020] (1) The present application adjusts the mass ratio of coffee grounds-based lignin-containing cellulose nanofiber suspension, plasticizing agent and carboxymethyl cellulose solution to control the transmittance and haze of the composite film. The composite structure of coffee grounds-derived lignin-containing cellulose nanofiber and sodium carboxymethyl cellulose effectively preserves the transmission channel of near-infrared light, making the transmittance of the prepared composite film at near-infrared light 1400nm reach 90.36%, and the haze reach 80.50%. The unique performance combination meets the stringent requirements of biomedical near-infrared imaging homogenization, agricultural greenhouse intelligent covering, intelligent building energy-saving windows and other applications that require selective regulation of near-infrared light, showing great application potential and market value.

[0021] (2) The composite film has super strong ultraviolet shielding (material protection) ability and excellent visible light shielding (privacy protection) ability, making it have a wide application prospect in scenes that require visual information isolation such as information security and privacy protection.

[0022] (3) The present application uses coffee grounds, a biomass waste, as raw material, realizes the high-value utilization of coffee grounds, reduces waste discharge, and meets the concepts of green environmental protection and sustainable development. In addition, the preparation process mainly includes coffee grounds pretreatment, TEMPO oxidation, centrifugal treatment, high-pressure homogenization, blending and film formation, etc. The operation is simple, easy to realize industrialized production, and the preparation cost is relatively low. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1A composite film based on coffee grounds having high transmittance and high haze in the near-infrared region obtained in Example 3;

[0024] Figure 2 A transmittance graph of the samples of Examples 1 to 4 and Comparative Examples 1 and 2;

[0025] Figure 3 A haze graph of the samples of Examples 1 to 4 and Comparative Examples 1 and 2;

[0026] Figure 4 An infrared thermal imaging demonstration graph when a 980 nm laser passes through the composite film prepared in Example 3;

[0027] Figure 5 An infrared thermal imaging demonstration graph when a 980 nm laser passes through the sample of Comparative Example 1;

[0028] Figure 6 An infrared thermal imaging demonstration graph when a 980 nm laser passes through the sample of Comparative Example 2. DETAILED DESCRIPTION

[0029] The present application is further described in detail by specific examples, but the scope of the present application is not limited thereto.

[0030] Example 1:

[0031] A method for preparing a composite film having high transmittance and high haze in the near-infrared region, the specific steps are as follows:

[0032] (1) Add n-hexane to the cleaned coffee grounds and stir for 48 h for degreasing treatment, and dry the degreased coffee grounds at 105℃ to constant weight to obtain degreased coffee grounds;

[0033] (2) Take 24 g of the degreased coffee grounds in step (1) and disperse them in 500 ml of ultrapure water, then add 0.32 g of TEMPO and 0.8 g of sodium bromide to the dispersed solution, titrate 150 g of 10 wt% sodium hypochlorite solution at 40℃, and terminate the reaction after 7 hours of stirring. During the titration of the sodium hypochlorite solution, titrate 0.2 M NaOH solution to adjust the pH value to 10.5, then transfer the reaction solution to a centrifuge tube (rotating speed 8500 r / min, 25 min) for 5 times of centrifugation, collect the precipitate, and wash the precipitate until the washing liquid is neutral, to obtain lignin-containing oxidized cellulose. Mix the lignin-containing oxidized cellulose with water and perform high-pressure (25000 PSI) homogenization treatment for 8 times to obtain a lignin-containing cellulose nanofiber suspension based on coffee grounds, and the solid content of the lignin-containing cellulose nanofiber suspension is 1.2%;

[0034] (3) Take 26.62 g of the lignin-containing cellulose nanofiber suspension prepared in step (2), dilute 1-fold with ultrapure water, and blend and stir at 45°C and a rotation speed of 500 rpm for 30 min to obtain a blended liquid. After stopping the stirring, the blended liquid is vacuumed to remove bubbles for 10 min. Finally, the blended liquid after removing the bubbles is poured into a polystyrene culture dish with a diameter of 10 cm, and dried at 30°C for 72 h to obtain a thin film with a thickness of about 40 μm;

[0035] (4) The transmittance and haze of the thin film in the near-infrared light to ultraviolet light region (1400-200 nm) are detected.

[0036] Example 2:

[0037] Example 2 is basically the same as Example 1, except that in step (3), the blended liquid is composed of the lignin-containing cellulose nanofiber suspension and glycerol, and after blending, ultrapure water is added to dilute 2-fold. According to the mass percentage content, the solid content of the lignin-containing cellulose nanofiber suspension in the blended liquid accounts for 90%, and the content of glycerol accounts for 10%.

[0038] Example 3:

[0039] Example 3 is basically the same as Example 1, except that in step (3), the blended liquid is composed of the lignin-containing cellulose nanofiber suspension, glycerol, and a 2wt% carboxymethyl cellulose sodium solution, and after blending, ultrapure water is added to dilute 2-fold. According to the mass percentage content, the solid content of the lignin-containing cellulose nanofiber suspension in the blended liquid accounts for 80%, the content of glycerol accounts for 10%, and the content of carboxymethyl cellulose sodium accounts for 10%. The prepared sample is shown in Figure 1 .

[0040] Example 4:

[0041] Example 4 is basically the same as Example 1, except that in step (3), the blended liquid is composed of the lignin-containing cellulose nanofiber suspension, glycerol, and a 2wt% carboxymethyl cellulose sodium solution, and after blending, ultrapure water is added to dilute 2-fold. According to the mass percentage content, the solid content of the lignin-containing cellulose nanofiber suspension in the blended liquid accounts for 70%, the content of glycerol accounts for 10%, and the content of carboxymethyl cellulose sodium accounts for 20%.

[0042] Comparative Example 1:

[0043] (1) 2wt% sodium carboxymethyl cellulose solution 15.71g was diluted 2 times with ultrapure water, and stirred at 45°C and 500rpm for 30min to obtain a blending solution. After stopping the stirring, the blending solution was vacuumed for 10min to remove bubbles. Finally, the blending solution after removing bubbles was poured into a polystyrene culture dish with a diameter of 10cm, and dried at 30°C for 72h to obtain a film with a thickness of about 40μm;

[0044] (2) The transmittance and haze of the film were detected in the near-infrared light to ultraviolet light region (1400-200nm).

[0045] Comparative Example 2:

[0046] The transmittance and haze of a commercial polystyrene optical diffusion plate (thickness about 1.1mm) were detected in the near-infrared light region to the ultraviolet light region (1400-200nm).

[0047] Performance test and application of sample

[0048] (1) Transmittance and haze test of sample

[0049] The transmittance and haze of the composite film prepared in Examples 1-4 and the samples of Comparative Examples 1-2 were detected in the near-infrared light region to the ultraviolet light region (1400-200nm), and the test results are shown in Figure 2 and Figure 3 ; wherein the transmittance and haze values at near-infrared light 1400nm and visible light 550nm are shown in Table 1.

[0050] Table 1 Test results of transmittance and haze at near-infrared light 1400nm and visible light 550nm

[0051]

[0052] In combination with Table 1, Figure 2 and Figure 3It can be seen that the transmittance of the composite film prepared in Examples 1-4 is more than 89% at 1400 nm in the near-infrared region, among which the transmittance of the composite film prepared in Example 3 can reach 90.36%, close to the transmittance of Comparative Example 1 (91.16%), and significantly better than the transmittance of the commercial material of Comparative Example 2 (70.05%), which indicates that the composite structure of the coffee grounds-derived lignin-containing cellulose nanofiber and sodium carboxymethyl cellulose effectively retains the transmission channel of near-infrared light; the haze value of the composite film prepared in Examples 1-4 is 73.63%-80.50% at 1400 nm, which is much higher than that of Comparative Example 1 (0.21%), and slightly lower than that of the commercial material of Comparative Example 2 (96.66%), but still maintains a high haze value; in combination with the transmittance, the composite film prepared in Examples 1-4 maintains high near-infrared transmittance while still having high haze, which can realize the scattering effect of near-infrared light, thereby realizing selective light regulation in the near-infrared region.

[0053] As shown in Table 1, at 550 nm in the visible light region, the transmittance of the composite film prepared in Examples 1-4 is 30.21%-47.87%, which is much lower than that of the sample of Comparative Example 1 (91.16) and the commercial material of Comparative Example 2 (57.97%), which indicates that the composite film can effectively block visible light, meeting the needs of privacy protection and information shielding. The haze value of the composite film prepared in Examples 1-4 is all higher than 82.39%, close to that of Comparative Example 2 (99.31%), indicating that the visible light is strongly scattered, further verifying the visual shielding effect of the composite film. Figure 2 As can be seen, in the ultraviolet region, the transmittance of the composite film is very low (average <0.2%), especially in the short-wave ultraviolet region (200-280 nm), the transmittance is about equal to 0, indicating that the natural ultraviolet absorption capacity of lignin and the scattering effect of the porous structure synergistically work together to almost completely block ultraviolet light. The transmittance of the sample of Comparative Example 1 in the ultraviolet (UVA, UVB) region is as high as 80-90%, without ultraviolet shielding capacity, which is easy to cause light degradation of the material; the transmittance of the commercial board of Comparative Example 2 in the ultraviolet (UVA, UVB) region is lower than that of Comparative Example 1 (30-45%), but is still significantly higher than that of the composite film prepared in Examples 1-4, indicating that the ultraviolet absorption capacity is limited.

[0054] (2) Application of the composite film

[0055] The infrared thermal imaging demonstration diagram of the sample of Example 3, Comparative Example 1 and Comparative Example 2 passing through the 980 nm laser is shown in Figure 4 , Figure 5 and Figure 6 . From Figure 4 , Figure 5 and Figure 6It can be seen that when the composite film prepared in Example 3 and the sodium carboxymethyl cellulose film of Comparative Example 1 are placed in front of a 980 nm near-infrared laser light source, both of them exhibit near-infrared light penetration, however, the composite film prepared in Example 3 exhibits a significant light scattering effect, the transmitted near-infrared light forms a diffuse hot spot on the receiving surface, the heat is uniformly distributed and the coverage area is significantly expanded; while the comparative example 1 presents a focused hot spot, the heat is concentrated in the central area, compared with the comparative example 2, although it has a higher haze, the near-infrared light transmittance is very poor, so the heat radiation obtained by the receiving surface is suddenly reduced, which causes it to not form an effective hot spot, so it does not have the effect of near-infrared band effective penetration and light scattering. The above results show that the composite film prepared in Example 3 simultaneously realizes high near-infrared light penetration and high scattering, which gives it unique application value in the following fields: 1. Biomedical imaging field (such as diffuse optical tomography): the high haze property of the film enables it to uniformly scatter near-infrared light and form a diffuse light spot (such as Figure 4 infrared thermal imaging demonstration), effectively eliminating imaging "hot spots" and improving imaging uniformity, which provides a new way to replace expensive traditional diffractive optical elements and realize low-cost laser homogenization devices; 2. Agricultural greenhouse covering film: the high haze (shielding vision) and low transmittance (protecting privacy) of the film in the visible light region can block the plant protection operations and other activities inside the greenhouse, at the same time, its high transmittance and high haze (uniform transmission) in the near-infrared region ensure that the near-infrared light required for promoting photosynthesis can effectively and uniformly enter the greenhouse; 3. Intelligent building and energy saving (such as near-infrared temperature control window): the film allows a high proportion of uniform near-infrared light to penetrate into the room (utilizing solar heat in winter), while blocking ultraviolet light (protecting indoor items) and providing certain privacy protection through high haze in the visible light region, which is helpful for building energy saving and intelligent control; 4. Information security and privacy protection: effective shielding of visible light (low transmittance and high haze) makes it suitable for scenarios that require visual information isolation.

[0056] In summary, the present application uses waste coffee grounds as raw material, through a simple, environmentally friendly and low-cost TEMPO oxidation combined with sodium carboxymethyl cellulose / glycerol modification and blending film preparation process, successfully obtains a composite film with breakthrough "high transmittance-high haze" synergistic performance in the near-infrared region, at the same time, the composite film has super strong ultraviolet shielding (material protection) ability and excellent visible light shielding (privacy protection). Its unique performance combination makes it have great application potential and market value in the following application scenarios: 1. Biomedical near-infrared imaging homogenization: the high haze property of the film enables it to uniformly scatter near-infrared light and form a diffuse light spot (such as

[0057] The above examples are specific embodiments of the present application, but the embodiments of the present application are not limited by the above examples, and any other combinations, changes, modifications, substitutions, simplifications that do not exceed the design ideas of the present application fall within the protection scope of the present application.

Claims

1. A method for preparing a composite film having high transmittance and high haze in the near-infrared region, characterized in that: The specific steps include: (1) Defatted coffee grounds are oxidized using a TEMPO oxidation system to obtain lignin-containing oxidized cellulose; the lignin-containing oxidized cellulose is mixed with water and subjected to high-pressure homogenization to obtain a lignin-containing cellulose nanofiber suspension based on coffee grounds; (2) adding a plasticizer and a sodium carboxymethyl cellulose solution to the lignin-containing cellulose nanofiber suspension prepared in step (1), and mixing to obtain a blend; The blended liquid is cast and dried to obtain a composite film.

2. The method for preparing a composite film having high transmittance and high haze in the near-infrared region according to claim 1, characterized in that: In step (2), the blended liquid contains 70-100% lignin cellulose nanofibers, 0-10% plasticizer, and 0-20% sodium carboxymethyl cellulose, calculated by weight percentage.

3. The method for preparing a composite film having high transmittance and high haze in the near-infrared region according to claim 2, characterized in that: In step (2), the solid content of the lignin-containing cellulose nanofiber suspension is 0.8-2%, and the concentration of the sodium carboxymethyl cellulose solution is 0.5-2 wt%.

4. The method for preparing a composite film having high transmittance and high haze in the near infrared region according to any one of claims 1 to 3, characterized in that: In step (2), the plasticizer is glycerol.

5. The method for preparing a composite film having high transmittance and high haze in the near-infrared region according to claim 1, characterized in that: In step (1), the specific steps of oxidizing the defatted coffee grounds using the TEMPO oxidation system are as follows: dispersing the defatted coffee grounds in water to obtain a dispersion; adding TEMPO and sodium bromide to the dispersion, mixing, and obtaining a mixed solution; dropping sodium hypochlorite solution into the mixed solution at 35 to 45° C. and stirring to react, and during the addition of the sodium hypochlorite solution, controlling the pH of the mixed solution to 10 to 11 by using an alkaline solution, centrifuging the reaction solution after the reaction, collecting the precipitate, and washing the precipitate until the pH of the washing solution is neutral, thereby obtaining oxidized cellulose containing lignin.

6. The method for preparing a composite film having high transmittance and high haze in the near-infrared region according to claim 5, characterized in that: The mass ratio of coffee grounds, TEMPO, sodium bromide and sodium hypochlorite solution in the reaction solution is 24:0.15-0.45:0.4-0.8:120-180.

7. The method for preparing a composite film having high transmittance and high haze in the near-infrared region according to claim 6, characterized in that: The concentration of the sodium hypochlorite solution is 10 wt %.

8. The method for preparing a composite film having high transmittance and high haze in the near infrared region according to any one of claims 5 to 7, characterized in that: The stirring reaction time is 6 to 8 hours.

9. A composite film prepared by the method according to any one of claims 1 to 8.

10. Use of the composite film according to claim 9 in near-infrared biological imaging, military security, temperature-controlled windows, agricultural greenhouses, and privacy protection.

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