Method for preparing a nanocellulose and metal-oxide mixture for use in an SPF booster composition

Abstract

The present invention discloses a method for preparing a nanocellulose and metal-oxide mixture for use in an SPF booster composition. The method comprises the steps of reducing a cellulose fiber size to obtain nanocellulose, and mixing a metal-oxide with the nanocellulose obtained from the size reduction step to obtain the nanocellulose and metal-oxide mixture. The step of mixing metal-oxide with the size-reduced nanocellulose is performed by homogenizing the nanocellulose and metal-oxide mixture at least twice under a pressure ranging from 2,000-30,000 pounds per square inch.

Description

[0001] METHOD FOR PREPARING A NANOCELLULOSE AND METAL-OXIDE MIXTURE FOR USE IN AN SPF BOOSTER COMPOSITION

[0002] TECHNICAL FIELD

[0003] Chemical technology related to a method for preparing a nanocellulose and metal-oxide mixture for use in an SPF booster composition

[0004] BACKGROUND OF THE INVENTION

[0005] Physical sunscreen products are sunscreen products that can protect the skin from ultraviolet or UV rays from sunlight by creating a barrier on the skin to reflect sunlight and UV rays away so that they do not reach the skin. As a result, they have a lower likelihood of causing allergies compared to chemical sunscreen products, which absorb sunlight and UV rays into their molecules to prevent the rays from directly penetrating the skin. Additionally, in terms of usage, physical sunscreen products offer advantages over chemical sunscreens. That is, the sunscreen agents in physical sunscreen products, which are generally mineral substances such as titanium dioxide or zinc oxide, can provide immediate protection upon application to the skin. Meanwhile, chemical sunscreens require at least 15-20 minutes after application to become effective.

[0006] Despite the advantages of physical sunscreen products mentioned above, in order to achieve sufficient effectiveness in protecting the skin from sunlight and UV rays, it is necessary to use a high amount of mineral-based sunscreen agents to obtain the required Sunburn Protection Factor (SPF) and UVA Protection Factor (UVAPF). This causes a white cast on the skin after application, which is undesirable for consumers. Furthermore, the use of a high amount of mineral-based sunscreen agents affects the texture of the product, making it highly viscous and difficult to spread evenly on the skin. As a result, it cannot thoroughly protect the skin against sunlight and UV rays.

[0007] Due to the problems mentioned above, there is an effort to invent and develop additives, including auxiliary compositions, that can improve the texture and enhance the effectiveness of sunlight and UV protection in physical sunscreen products, as well as reducing the amount of sunscreen agents used in the product. Examples of the published patent documents are as follows.

[0008] WO 2008126971 Al discloses polymer nanoparticles and UV-blocking agents comprising said polymer particles. The polymer nanoparticles are prepared by mixing the UV-blocking agents, such as zinc oxide (ZnO), titanium dioxide (TiOi), benzophenone-4, octyl salicylate, with a polymer solution, such as chitosan, gelatin, collagen, etc. Then, a crosslinker, such as sodium triphosphate, sodium citrate, or sodium oxalate, is added to obtain the polymer nanoparticles which offer protection against UV rays and are non-toxic to the human body.

[0009] CA 3011513 Al discloses a surface improvement of cellulose nanocrystals by coating melamine formaldehyde on the surface of said cellulose nanocrystals through a polycondensation process. Then, a hybridization is performed with nanoparticles of zinc oxide derivative, such as zinc acetate dihydrate, at a ratio of Zn2+to OH’ of 1:3.

[0010] SUMMARY OF THE INVENTION

[0011] It is an object of the present invention to provide a method for preparing an additive or auxiliary composition for use in or as an SPF booster composition which is a mixture of cellulose fibers and metal-oxide that enhances the effectiveness of sunlight and UV protection. It is also suitable for use in cosmetic products and personal care products, particularly physical sunscreen products.

[0012] In one aspect, the present invention relates to a method for preparing a nanocellulose and metal-oxide mixture for use in an SPF booster composition, the method comprising the steps of:

[0013] (i) reducing a cellulose fiber size to obtain nanocellulose, and

[0014] (ii) mixing a metal-oxide with the nanocellulose obtained from step (i) to obtain a nanocellulose and metal-oxide mixture, wherein step (ii) is performed by homogenizing the nanocellulose and metal-oxide mixture obtained from step (i) at least twice under a pressure ranging from 2,000-30,000 pounds per square inch (psi).

[0015] Preferably, step (ii) is performed using a homogenizer in conjunction with a microfluidizer.

[0016] In another aspect, the present invention relates to a nanocellulose and metal-oxide mixture for use in an SPF booster composition obtained from the method according to the present invention. Said mixture comprises nanocellulose with specific size, i.e., an average width ranging from 10-50 nm, an average length ranging from 700-1,200 nm, and a crystallinity index ranging from 60-75%; and the metal-oxide being dispersed within a network structure and / or on a surface of the nanocellulose.

[0017] The method for preparing the nanocellulose and metal-oxide mixture and the mixture obtained from the method according to the present invention can significantly enhance the effectiveness of sunlight and UV protection of the composition or sunscreen products. The mixture and the composition comprising the prepared mixture have increased light absorbance, SPF, and UVAPF.

[0018] BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Fig. 1 is a graph showing light absorbance of the nanocellulose and metal-oxide mixture sample prepared according to the method of the present invention (Sample 1) and comparative samples, which is a mixture prepared according to a conventional method ( Comparative Samples 1-5).

[0020] Fig. 2 is a graph showing light absorbance of the composition sample with the addition of the nanocellulose and metal-oxide mixture prepared according to the method of the present invention in a base lotion (Sample 2), a comparative sample which is a base lotion without the addition of sunscreen agents (Comparative Sample 8), a comparative sample which is a base lotion with the addition of mineral-based sunscreen agents (Comparative Sample 6), and a comparative sample which is a base lotion with the addition of a mixture of mineral-based sunscreen agents and nanocellulose which was not prepared by the method according to the present invention (Comparative Sample 7).

[0021] DETAILED DESCRIPTION

[0022] Any aspects shown herein shall encompass the application to other aspects of the present invention as well, unless specified otherwise.

[0023] Any tools, equipment, methods, materials, or chemicals mentioned herein, unless specified otherwise, shall mean the tools, equipment, methods, materials, or chemicals generally used or practiced by a person skilled in the art, unless expressly specified to be tools, equipment, methods, materials, or chemicals specific to the present invention.

[0024] The terms “comprise(s),” “consist(s) of,” “has / have,” and “include(s)” are open-ended verbs. For example, any methods which “consist of,” “comprise,” “have,” or “include” one or more components or one or more steps are not limited only to the one or more components or one or more steps, but also cover the components or steps that are not mentioned.

[0025] All components and / or methods disclosed and claimed in the present invention are intended to cover the aspects of the invention obtained from any actions, practices, modifications or changes of factors without conducting significantly different experiment from the present invention, and to obtain an object with properties, utilities and effects that are similar to the aspects of the present invention according to the opinions of a person of ordinary skill in the art, although not specifically stated in the claims. Therefore, substitutions or analogues of the aspects of the present invention, including any slight modification or change apparent to a person of ordinary skill in the art, should also be considered to be within the spirit, scope and concept of the present invention.

[0026] Technical and scientific terms used herein have the definitions as understood by a person of ordinary skill in the art, unless defined otherwise.

[0027] The term “homogenization / homogenizing” as used herein refer to any processes that enables a mixture or a composition to mix together and / or reduces the particle size of any component contained in said mixture or composition by applying pressure and / or shear force. Specifically, homogenization may be performed using a homogenizer, a microfluidizer, or a combination thereof.

[0028] The term “homogenizer” as used herein refers to a tool or device capable of performing homogenization or high-pressure homogenization. Generally, a homogenizer comprises a container in which pressure is applied, a valve or a membrane with a narrow slit. Additionally, a homogenizer may further comprise blades or a device that causes the substance or mixture in the container to collide at high speed to allow the substance or mixture to become homogeneous.

[0029] The term “ microfluidizer” as used herein refers to a tool or device capable of performing homogenization and / or reducing the material size to microscale and nanoscale. Generally, a microfluidizer comprises a pump that generates high pressure, causing any components (such as fibers) of the mixture to be disintegrated by shear force. The substance or mixture is fed into an inlet and moves through a Y-type or Z-type chamber under a high pressure. This results in the acceleration of the substance or mixture, creating a high shear rate and causing any components (such as fibers) of the mixture to be disintegrated and eventually reduced in size. The microfluidizer is the most commonly used high-pressure homogenizer.

[0030] Various aspects of the present invention will be described hereinafter in more detail.

[0031] According to the first aspect, a method for preparing a nanocellulose and metal-oxide mixture for use in an SPF booster composition according to the present invention comprises the steps of:

[0032] (i) reducing a cellulose fiber size to obtain nanocellulose, and

[0033] (ii) mixing a metal-oxide with the nanocellulose obtained from step (i) to obtain a mixture of nanocellulose and metal-oxide, wherein, step (ii) is performed by homogenizing the nanocellulose and metal-oxide mixture obtained from step (i) at least twice under a pressure ranging from 2,000-30,000 pounds per square inch (psi). According to a specific embodiment, the nanocellulose obtained from step (i) has an average width ranging from 10-50 nm, preferably 20-50 nm, more preferably 20-30 nm, and an average length ranging from 700-1,200 nm, preferably 200-500 nm.

[0034] Preferably, the nanocellulose obtained from step (i) has a crystallinity index ranging from 60-75%, preferably 65-75%, more preferably 70-75%.

[0035] According to a preferred aspect of the present invention, the nanocellulose obtained from step (i) is in a form of colloidal gel or gel suspension, preferably colloidal gel with a consistency ranging from 2-5%.

[0036] The nanocellulose obtained from step (i) is native nanocellulose, i.e., unmodified nanocellulose prepared by a mechanical method.

[0037] According to a specific embodiment of the invention, step (i) is performed using the cellulose fiber in a form of suspension. Preferably, a suspension of cellulose fiber which are to be reduced in size is controlled to achieve a consistency ranging from 1-20%, preferably 1-12%.

[0038] Step (i) is performed using cellulose fiber with an average particle size ranging from 10-20 pm.

[0039] Preferably, step (i) is performed using a microfluidizer.

[0040] The reduction of cellulose fiber size using the microfluidizer may require a chamber with various internal inlet and outlet diameters. As a preferred example, a chamber with different internal inlet and outlet diameters ranging from 50-500 pm may be used. For example, a chamber with an internal diameter of the inlet of 400 pm and an internal diameter of the outlet of 200 pm (abbreviated as “400 / 200 pm chamber”) or a chamber with an internal diameter of the inlet of 200 pm and an internal diameter of the outlet of 70 pm (abbreviated as “200 / 70 pm chamber”) may be used. Additionally, one or more chambers may be used for cellulose fiber size reduction, and the process may be carried out in one or more cycles.

[0041] In an exemplary preferred embodiment of the invention, step (ii) is performed using a homogenizer in conjunction with a microfluidizer. Preferably, step (ii) is performed using the homogenizer, followed by the microfluidizer.

[0042] As an example, the homogenizer in step (ii) is operated at a speed ranging from 5,000-12,000 rpm for 5-30 min. Preferably, the speed ranges from 9,000-12,000 rpm for 5-10 min.

[0043] The microfluidizer in step (ii) may use a chamber having an internal inlet diameter ranging from 300-500 pm and an internal outlet diameter ranging from 100-300 pm. For example, a 400 / 200 pm chamber, which has an internal inlet diameter of 400 pm and an internal outlet diameter of 200 pm, may be used. According to the present invention, step (ii) is performed using the metal-oxide with a particle size ranging from 40-800 nm and a weight ratio of the metal-oxide to nanocellulose ranging from 5:95 to 15:85, more preferably from 8:92 to 12:88.

[0044] Preferred examples of the metal-oxide for use in step (ii) are those selected from a group consisting of titanium dioxide, zinc oxide, and a combination thereof.

[0045] In another embodiment, the method for preparing the nanocellulose and metal-oxide mixture for use in the SPF booster composition according to the present invention may further comprise a step of preparing the cellulose fibers before performing step (i). As an example, the preparation of cellulose fiber is performed by subjecting dissolving pulp to an acid hydrolysis reaction. The acid used may be selected from, for example, hydrochloric acid, sulfuric acid, or a combination thereof.

[0046] Preferably, the acid hydrolysis reaction is performed at a temperature ranging from 60-75°C for 60-90 min.

[0047] The SPF booster composition according to the present invention comprises the nanocellulose and metal-oxide within a network structure of the nanocellulose and / or on a surface of the nanocellulose. The network structure of the nanocellulose serves to retain sunscreen particles within its structure and / or on its surface, preventing them from aggregating or agglomerating together and allowing them to disperse uniformly when applying and spreading the product on the skin. Furthermore, the metal-oxide dispersed within the structure and / or on the surface of the nanocellulose can also function as a sunscreen agent.

[0048] The mixture for use in the SPF booster composition prepared according to the specific method of the present invention can significantly enhance the effectiveness of sunlight and UV protection of the SPF booster composition, particularly when compared to the mixtures prepared by conventional methods, which are outside the scope of the present invention, as explained below in the experimental results.

[0049] Example

[0050] The present invention will now be described in more detail with reference to the examples of the invention and the experimental results to be mentioned hereinafter with reference to the accompanying drawings. The examples of the invention shown herein are not intended to limit the scope of the invention in any way.

[0051] 1. Experiment to evaluate the initial light absorption capability of the nanocellulose and metal-oxide mixture The nanocellulose and metal-oxide mixture sample according to the present invention and a comparative sample were prepared. The light absorbance in the UVA and UVB ranges was measured. The details are as follows.

[0052] 1.1) Sample preparation

[0053] Sample of the nanocellulose and metal-oxide mixture according to the present invention

[0054] The mixture sample for use as or in the SPF booster composition according to the present invention was prepared by the method with the following steps:

[0055] Step (1): Preparation of cellulose fiber

[0056] A cellulose fiber suspension was prepared by subjecting dissolving pulp derived from eucalyptus to the acid hydrolysis reaction using hydrochloric acid with a concentration of 3 molar at a temperature of 75°C for 90 min. Then, the cellulose fiber suspension was neutralized by washing it with water to obtain a highly pure cellulose fiber suspension with an average fiber width ranging from 14-17 pm.

[0057] Step (2): Cellulose fiber size reduction

[0058] The size of the cellulose fiber obtained from step (1) was reduced using the microfluidizer to obtain nanocellulose with an average fiber width ranging from 20-50 nm and an average fiber length ranging from 700-1,200 pm. The process is conducted sequentially by using the chamber having internal inlet and outlet diameters, the consistency of the cellulose fiber suspension, and the number of processing cycles. First, use a 400 / 200 pm chamber at a cellulose fiber suspension consistency of 10-12% for one cycle. Then, use a 200 / 70 pm chamber at a cellulose fiber suspension consistency of 5-7% for two cycles. Finally, use a 200 / 70 pm chamber at a cellulose fiber suspension consistency of 2-5% for one cycle.

[0059] The prepared nanocellulose is in the form of colloidal gel with a consistency ranging from 2-5% . The results of the characteristic analysis of the prepared nanocellulose using the Dynamic Light Scattering (DLS) technique are shown in Table 1, compared with commercially available nanocellulose.

[0060] Table 1

[0061] Step (3): Mixing metal-oxide with nanocellulose

[0062] The nanocellulose prepared in step (2) (NC-A) was mixed with metal-oxide (here, zinc oxide ( ZnO) ) with a weight ratio of the nanocellulose to zinc oxide of 90: 10 using the homogenizer (referred to as HM) at a speed of 10,000 rpm for approximately 5 min. After the specified time, the resulting mixture was introduced into the microfluidizer (referred to as MFD) using a 400 / 200 pm chamber for one cycle to obtain the nanocellulose and zinc oxide mixture (Sample 1 in Table 2 below).

[0063] Comparative sample

[0064] Mixtures which are comparative samples were prepared by using the nanocellulose sample prepared according to the method of the present invention (NC-A), zinc oxide (ZnO), and distilled water added in different amounts using the homogenizer (referred to as HM) and the microfluidizer (referred to as MFD) to obtain Comparative samples 1-5 in Table 2.

[0065] The nanocellulose sample prepared according to the method of the present invention (NC-A) was prepared by subjecting dissolving pulp derived from eucalyptus to the acid hydrolysis reaction to obtain cellulose fibers. Then, the cellulose fibers were subjected to size reduction using the microfluidizer to obtain nanocellulose with an average fiber width ranging from 10-50 nm and an average fiber length ranging from 700-1,200 pm.

[0066] Table 2

[0067] Notes:

[0068] * HM refers to mixing using the homogenizer at a speed of 10,000 rpm for 5 min.

[0069] MFD refers to mixing using the microfluidizer with a 400 / 200 pm chamber for one cycle. ** NC-A refers to the nanocellulose prepared according to the method of the present invention which is in the form of colloidal gel with a consistency ranging from 2-5%.

[0070] The sample of the nanocellulose and metal-oxide mixture according to the present invention (Sample 1) and Comparative samples 1-5 prepared above were measured for light absorbance in the UVA and UVB ranges at wavelengths of 280-400 nm using a Jasco V 650 UV spectrophotometer using a 10 mm cell length, photometer mode: absorbance, and light source D2W. Distilled water was used as a blank. A test sample was prepared by diluting the sample to be tested with distilled water in a volume ratio of the sample to be tested to distilled water of 1:49. The experimental results are shown in Fig. 1.

[0071] From the experimental results in Fig. 1, it can be seen that the nanocellulose and metal-oxide mixture prepared according to the method of the present invention (Sample 1) exhibits higher light absorbance in both the UVA and UVB ranges compared to Comparative samples 1-5 prepared by methods outside the scope of the present invention. For example, in the case of Sample 1 and Comparative sample 1, although both are mixtures containing equal amounts of nanocellulose and metal-oxide as components, Sample 1 was prepared by two mixing steps using the homogenizer in conjunction with the microfluidizer, while Comparative sample 1 was prepared by a single mixing step using only the homogenizer. From the experimental results in Fig. 1, it can be seen that Sample 1 exhibits significantly higher light absorbance in both the UVA and UVB ranges compared to Comparative sample 1.

[0072] In addition, Sample 1 also demonstrates superior light absorption performance in the UVA and UVB ranges compared to the mixture samples containing either nanocellulose or zinc oxide as a component (Comparative samples 3, 4, and 5).

[0073] Therefore, based on the above experimental results, it can be concluded that different preparation methods for the nanocellulose and metal-oxide mixture significantly affect the light absorption capability.

[0074] 2. Experiment to evaluate the light absorption capability of the nanocellulose and metal-oxide mixture in the base lotion

[0075] Composition samples for testing the light absorption efficiency in the UVA and UVB ranges were prepared, i.e., a composition comprising the nanocellulose and metal-oxide mixture prepared according to the method of the present invention (Sample 2 in Table 3) and comparative samples (Comparative samples 6-8 in Table 3) in the form of lotion. The amount of each component used is shown in Table 3. The total amount of zinc oxide (ZnO) in each sample was controlled to be in a range of 5-5.5% by weight, based on the total weight of the composition sample. Table 3

[0076] Notes:

[0077] * Base lotion is lotion which does not contain sunscreen agents.

[0078] ** Nanocellulose and metal-oxide mixture prepared according to the method of the present invention contains zinc oxide (ZnO) in an amount of 0.5 wt%, based on the total weight of the composition sample.

[0079] Then, the composition samples were measured for light absorbance in the UVA and UVB ranges at wavelengths of 280-400 nm using a Jasco V 650 UV spectrophotometer using a 10 mm cell length, photometer mode: light absorbance, and light source D2W. Distilled water was used as a blank. A test sample was prepared by diluting the sample to be tested with distilled water in a volume ratio of the sample to be tested to distilled water of 1:49. The experimental results are shown in Fig. 2.

[0080] From the experimental results in Fig. 2, it can be seen that the composition sample, which is a base lotion containing the nanocellulose and metal-oxide mixture prepared according to the method of the present invention (Sample 2), exhibits higher light absorbance in both the UVA and UVB ranges compared to Comparative sample 8, which is a base lotion without any added sunscreen agents, Comparative sample 6, which is a base lotion containing only a mineral-based sunscreen agent (ZnO), and Comparative sample 7, which is a base lotion with separately added mineral-based sunscreen agent (ZnO) and nanocellulose.

[0081] 3. Experiment to evaluate the light absorption capability of the nanocellulose and metal-oxide mixture in a standard sunscreen composition

[0082] The composition samples for testing the light absorption efficiency in the UVA and UVB ranges were prepared, i.e., a standard sunscreen composition sample with the addition of the nanocellulose-metal-oxide mixture prepared according to the method of the present invention (Sample 3 in Tables 4 and 5) and a comparative composition sample (Comparative samples 9-11 in Tables 4 and 5). The amount of each component used is shown in Table 4. The types and amounts of nanocellulose, mineral-based sunscreen, and metal-oxide comprised in the composition are shown in Table 5.

[0083] Table 4

[0084] Notes:

[0085] * Standard sunscreen is sunscreen which does not contain nanocellulose. The standard sunscreen according to the present invention contains mineral-based sunscreen agents, i.e., TiOi in an amount of 4 wt% and ZnO in an amount of 5.76 wt% , based on the total weight of the sunscreen composition.

[0086] ** The nanocellulose and metal-oxide mixture prepared according to the method of the present invention contains zinc oxide (ZnO) in an amount of 0.25 wt% , based on the total weight of the sunscreen composition.

[0087] Table 5 Then, the prepared composition samples were tested for the UV protection efficiency and the % improvement of each sample was compared, as shown in Table 6.

[0088] Table 6

[0089] From the experimental results in Fig. 3 and Table 6, it can be seen that using the nanocellulose and metal-oxide mixture prepared according to the method of the present invention (Sample 3) in the standard sunscreen composition containing TiCh in an amount of 4 wt% and ZnO in an amount of 5.76 wt% can increase the SPF from 17.77 to 41.32. This is higher than the addition of commercially available nanocellulose (NC-B), which increases the SPF from 17.77 to 31.39 (Comparative sample 10), and higher than using nanocellulose which was not mixed with metal-oxide using the method according to the present invention, which increases the SPF from 17.77 to 39.22 (Comparative sample 11). That is, the nanocellulose and metal-oxide mixture prepared according to the method of the present invention (Sample 3) can enhance the SPF in the standard sunscreen composition by up to 132.5%, which is higher than the SPF enhancement efficiency of Comparative samples 10 and 11, which increase the SPF by 76.6% and 120.7%, respectively.

[0090] In addition, the experimental results also show that using the nanocellulose and metal-oxide mixture prepared according to the method of the present invention (Sample 3) in the standard sunscreen composition containing TiCh in an amount of 4 wt% and ZnO in an amount of 5.76 wt% can increase the UVAPF from 6.08 to 9.02, which is higher than using commercially available nanocellulose (Comparative sample 10), which increases the UVAPF from 6.08 to 7.86, and higher than using nanocellulose that was not mixed with metal-oxide using the method according to the present invention (Comparative sample 11), which increases the UVAPF from 6.08 to 8.58. That is, the nanocellulose and metal-oxide mixture prepared according to the method of the present invention has an efficiency in increasing the UVAPF in the standard sunscreen composition of up to 48.4%, which is higher than the efficiency in increasing the UVAPF of Comparative samples 10 and 11, which increase the UVAPF by 29.3% and 41.1%, respectively. BEST MODE OF THE INVENTION

[0091] Best mode of the invention is as described in the detailed description of the invention.

Claims

WHAT IS CLAIMED IS:

1. A method for preparing a nanocellulose and metal-oxide mixture for use in an SPF booster composition, the method comprising the steps of:(i) reducing a cellulose fiber size to obtain nanocellulose, and(ii) mixing a metal-oxide with the nanocellulose obtained from step (i) to obtain a nanocellulose and metal-oxide mixture, wherein step (ii) is performed by homogenizing the nanocellulose and metal-oxide mixture obtained from step (i) at least twice under a pressure ranging from 2,000-30,000 pounds per square inch (psi).

2. The method according to claim 1, wherein the nanocellulose obtained from step (i) has an average width ranging from 10-50 nm and an average length ranging from 700-1,200 nm.

3. The method according to claim 1 or 2, wherein the nanocellulose obtained from step (i) has a crystallinity index ranging from 60-75%.

4. The method according to any one of claims 1-3, wherein the nanocellulose obtained from step (i) is in a form of colloidal gel or gel suspension with a consistency ranging from 2-5%.

5. The method according to claim 1, wherein step (i) is performed using the cellulose fiber in a form of suspension.

6. The method according to claim 1 or 5, wherein step (i) is performed using the cellulose fiber with an average particle size ranging from 10-20 pm.

7. The method according to any one of claims 1-6, wherein step (i) is performed using a microfluidizer.

8. The method according to claim 1, wherein step (ii) is performed using a homogenizer in conjunction with a microfluidizer.

9. The method according to claim 1 or 8, wherein step (ii) is performed using the homogenizer, followed by the microfluidizer.

10. The method according to claim 8 or 9, wherein the homogenizer in step (ii) is operated at a speed ranging from 5,000-12,000 rpm for 5-30 min.

11. The method according to claim 8 or 9, wherein the microfluidizer in step (ii) uses a chamber having an internal inlet diameter ranging from 300-500 pm and an internal outlet diameter ranging from 100-300 pm.

12. The method according to any one of claims 1, 8-11, wherein step ( ii) is performed using the metal-oxide with a particle size ranging from 40-800 nm.

13. The method according to any one of claims 1, 8-12, wherein step ( ii) is performed using a weight ratio of the metal-oxide to nanocellulose in a range of 5:95 to 15:85.

14. The method according to any one of claims 1, 8-13, wherein step (ii) is performed using the metal-oxide selected from a group consisting of titanium dioxide, zinc oxide, and a combination thereof.

15. The method according to claim 1 further comprising a step of preparing the cellulose fiber before performing step (i).

16. The method according to claim 15, wherein the preparation of cellulose fiber is performed by subjecting dissolving pulp to an acid hydrolysis reaction.

17. The method according to claim 16, wherein the acid hydrolysis reaction is performed using an acid selected from hydrochloric acid, sulfuric acid, or a combination thereof.

18. The method according to claim 16 or 17, wherein the acid hydrolysis reaction is performed at a temperature ranging from 60-75 °C for 60-90 min.

19. The method according to any one of claims 1-18, wherein the SPF booster composition comprises the nanocellulose and metal-oxide within a network structure of the nanocellulose and / or on a surface of the nanocellulose.

20. A nanocellulose and metal-oxide mixture for use in an SPF booster composition, prepared by the method according to any one of claims 1-19.

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