PREPARATION METHOD OF BIODEGRADABLE AND ANTIBACTERIAL BAMBOO FIBER-BASED PAPER STRAW

CROSS-REFERENCE TO RELATED APPLICATION

[0001]This application claims priority to Chinese Patent Application No. 202510009391.1, filed on Jan. 3, 2025, which is herein incorporated by reference in its entirety.

TECHNICAL FIELD

[0002]The disclosure relates to a preparation method of a paper straw.

BACKGROUND

[0003]Plastic products have been widely used in daily life due to their advantages such as light weight, low cost, durability, and convenient production. However, microplastics generated during the degradation and weathering of plastic products can spread into the food chain and are difficult to degrade, posing negative impacts on the environment and human health. In particular, polypropylene (PP) plastic straws, as disposable products, are difficult to recycle due to their light weight and small size. Replacing plastic straws with biomass-based alternatives has become an inevitable trend in industry development.

[0004]Cellulose, as the most abundant green resource on the earth, is renewable, biodegradable, and low-cost, and thus is a potential raw material for straw production. Bamboo, one of the most important non-wood forest resources, is widely distributed and diverse in species. The bamboo pulping and papermaking processes are well-established. For instance, a Chinese patent with application No.: CN202221658830.X discloses a naturally degradable paper straw. The interior of the straw body is provided with a detachable structure and a durable structure, the durable structure includes kraft paper, the kraft paper is arranged inside the straw body, one side of the kraft paper is provided with bamboo fiber, the other side of the kraft paper is provided with a polylactic acid film, and the paper straw has a complicated structure and high preparation costs.

SUMMARY

[0005]The disclosure aims to solve the technical problems of complex structure and high production costs associated with existing bamboo fiber paper straws, and provides a preparation method for a biodegradable and antibacterial bamboo fiber-based paper straw. This paper straw exhibits excellent hydrophobic and antibacterial properties.

[0013]In an embodiment, an average weight of the rectangular paper sheet in step 2 is in a range of 0.2-0.3 grams (g).

[0014]In an embodiment, dimensions of the rectangular paper sheet in step 2 are in a range of (3-4) centimeters (cm)×(10-12) cm.

[0015]The disclosure uses bleached bamboo fibers as raw materials to prepare paper via a papermaking process. The paper is then pretreated with solutions of CA and CQAS to enhance crosslinking interactions between the fibers. Subsequently, the paper is rolled into a paper straw, and the paper straw is immersed in a mixed solution of SA and PA to impart excellent hydrophobicity and antibacterial properties. The biodegradable and antibacterial bamboo fiber-based paper straw of the disclosure maintains a contact angle in a range of 90°-120° even after 30 min of water contact. The hydrophobic performance is verified through measurements of water absorption rate and contact angle. Additionally, the paper straw achieves a 100% inhibition rate against Escherichia coli and a 99.63% inhibition rate against Staphylococcus aureus, demonstrating good antibacterial efficacy. Under 40-day soil burial conditions, the paper straw achieves 100% complete degradation. The paper straw is also suitable for various beverages such as tea, coffee, milk, and cola, exhibiting broad applicability, and shows good stability in room-temperature and 0° C. aqueous solutions. Furthermore, the preparation method is a low-carbon, green, and pollution-free process throughout, yielding a safe and environmentally friendly antibacterial straw. The paper straw of the disclosure is a bamboo fiber-based paper straw with good water stability, biodegradability, and antibacterial properties, which can be used in the food field.

BRIEF DESCRIPTION OF DRAWINGS

[0016]FIG. 1 illustrates a comparison diagram of maximum water contact angles for BBF, a CA/CQAS/BBF straw, and a SA/PA/BBF straw in an embodiment 1.

[0017]FIG. 2 illustrates a scanning electron microscope (SEM) image of surfaces and cross-sections of the BBF, the CA/CQAS/BBF straw, and the SA/PA/BBF straw in the embodiment 1.

[0018]FIG. 3 illustrates an elemental distribution map of the SA/PA/BBF straw prepared in the embodiment 1.

[0019]FIG. 4 illustrates a Fourier transform infrared (FTIR) spectrogram of the BBF, the CA/CQAS/BBF straw, and the SA/PA/BBF straw prepared in the embodiment 1, a CA/CQAS/SA/BBF straw prepared in a comparative embodiment 1, and SA.

[0020]FIG. 5 illustrates an X-ray diffraction (XRD) spectrogram of the BBF, the CA/CQAS/BBF straw, and the SA/PA/BBF straw prepared in the embodiment 1, the CA/CQAS/SA/BBF straw prepared in the comparative embodiment 1, and the SA.

[0021]FIGS. 6A and 6B respectively illustrate a thermogravimetric analysis (TGA) curve graph and a derivative thermogravimetry (DTG) curve graph of the BBF, the CA/CQAS/BBF straw, and the SA/PA/BBF straw prepared in the embodiment 1, the CA/CQAS/SA/BBF straw prepared in the comparative embodiment 1, and the SA.

[0022]FIG. 7 illustrates an antibacterial evaluation diagram of the BBF, the CA/CQAS/BBF straw, and the SA/PA/BBF straw prepared in the embodiment 1 against Escherichia co/i and Staphylococcus aureus.

[0023]FIG. 8 illustrates a comparison diagram of dry bending strengths of the BBF, the CA/CQAS/BBF straw, and the SA/PA/BBF straw prepared in the embodiment 1.

[0024]FIG. 9 illustrates a wet bending strength of the SA/PA/BBF straw prepared in the embodiment 1.

[0025]FIG. 10 illustrates a degradation test diagram of the SA/PA/BBF straw prepared in the embodiment 1, a PP straw, a polylactic acid (PLA) straw, and a commercial paper straw.

[0026]FIG. 11 illustrates a water stability diagram of the BBF, the CA/CQAS/BBF straw, and the SA/PA/BBF straw prepared in the embodiment 1 at 25° C.

[0027]FIGS. 12A-12D illustrate comparative diagrams showing applicability of the BBF, the CA/CQAS/BBF straw, and the SA/PA/BBF straw prepared in the embodiment 1 in four beverages.

[0028]FIG. 13 illustrates a comparative diagram showing applicability of the BBF, the CA/CQAS/BBF straw, and the SA/PA/BBF straw prepared in the embodiment 1.

[0029]FIG. 14 illustrates a water stability comparison diagram of the BBF, the CA/CQAS/BBF straw, and the SA/PA/BBF straw prepared in the embodiment 1 at 0° C.

[0030]FIG. 15 illustrates a performance radar diagram of the SA/PA/BBF straw prepared in the embodiment 1, the commercial paper straw, and the PLA straw.

[0031]FIG. 16 illustrates a contact angle photograph of biodegradable and antibacterial bamboo fiber-based paper straws prepared in embodiments 2-5.

DETAILED DESCRIPTION OF EMBODIMENTS

[0032]The beneficial effects of the disclosure are verified using the following embodiments.

Embodiment 1

[0033]A preparation method of a biodegradable and antibacterial bamboo fiber-based paper straw includes the following steps 1-3.

[0037]Step 2, the bamboo fiber-based paper is cut into rectangular paper sheets each with dimensions of 3 cm×10 cm and an average weight being m=0.25 g; the rectangular paper sheet is wetted with a CA solution at a weight percentage concentration of 10% followed by a CQAS solution at a concentration of 10 g/L to obtain a wet rectangular paper sheet; the wet rectangular paper sheet is rolled onto a PTFE rod with edges pressed together, dried at room temperature, and then separated from the PTFE rod to obtain a CA/CQAS/BBF straw.

[0038]Step 3, a SA at a weight percentage concentration of 13% and a PA at a weight percentage concentration of 14% is added to a solvent being absolute ethanol and mixed uniformly to obtain a mixture, and the mixture is heated to 70° C. under stirring until a clear mixed solution is obtained; and the CA/CQAS/BBF straw obtained in step 2 is immersed into the clear mixed solution for 14 min, and then taken out and naturally dried at room temperature to obtain the biodegradable and antibacterial bamboo fiber-based paper straw, denoted as a SA/PA/BBF straw.

Comparative Embodiment 1

[0039]This comparative embodiment differs from the embodiment 1 in step 3 is replaced with the following operation.

[0040]Step 3, an SA solution is prepared with a weight percentage concentration of 20%; and the CA/CQAS/BBF straw obtained in step 2 is immersed into the SA solution for 14 min, and then taken out and naturally dried at room temperature to obtain a bamboo fiber-based paper straw, denoted as a CA/CQAS/SA/BBF straw. All other steps and parameters remain the same as in the embodiment 1.

[0041]Contact angle tests are performed on the BBF obtained in step 1, the CA/CQAS/BBF straw obtained in step 2, and the SA/PA/BBF straw obtained in step 3 of the embodiment 1. The obtained contact angles are shown in FIG. 1. As can be seen from FIG. 1, the maximum water contact angles of the BBF and the CA/CQAS/BBF straw are 260 and 37°, respectively, while the SA/PA/BBF straw obtained in step 3 exhibits a maximum initial contact angle of 134.4°, and the contact angle of the SA/PA/BBF straw remains at 1190 after 30 min. Compared to the CA/CQAS/SA/BBF straw, the treatment with the PA significantly enhances the hydrophobic stability of the paper straw. This confirms that the combined treatment with the PA and the SA, through ionic crosslinking with the cations in CQAS, improves the hydrophobic properties. Simultaneously, the SA increases the surface roughness of the straw, and its crystalline state enhances the repulsive force against water molecules, playing a crucial role in the hydrophobic effect.

[0042]FIG. 2 illustrates an SEM image of surfaces and cross-sections of the BBF obtained in step 1, the CA/CQAS/BBF straw obtained in step 2, and the SA/PA/BBF straw obtained in step 3 in the embodiment 1; where (a) and (d) represent SEM images of surfaces of the BBF, (b) and (e) represent SEM images of surfaces of the CA/CQAS/BBF straw, (c) and (f) represent SEM images of surfaces of the SA/PA/BBF straw, (g) represents an SEM image of a cross-section of the BBF, (h) represents an SEM image of a cross-section of the CA/CQAS/BBF straw, and (i) represents an SEM image of a cross-section of the SA/PA/BBF straw. From (a), (d), and (g), it can be observed that the bleached bamboo fibers are interconnected with numerous pores between the fibers, allowing water molecules to easily penetrate the internal structure, resulting in super-hydrophilic properties of the paper straw at this stage. From images (b), (e), and (h), it can be observed that after treatment with the CA and the CQAS on the fibers, the anions in CA and cations in CQAS interact through ionic interactions, leading to tighter cross-linking between the fibers and a reduction in pore size. From (c), (f), and (i), it can be clearly seen that in BBF modified with the SA and PA mixture, the fiber surfaces and cross-sections exhibit a dense structural state. The anions in the SA and the PA enhance the fiber surface density by combining with cations in the CQAS, while SA crystals attach to the fiber surfaces, thereby increasing surface roughness of the fibers. This provides the potential for the SA/PA/BBF straw to achieve high water resistance and hydrophobicity.

[0043]FIG. 3 illustrates an elemental distribution map of the SA/PA/BBF straw prepared in the embodiment 1. As can be seen from FIG. 3, elements carbon (C), nitrogen (N), oxygen (O), and phosphorus (P) are uniformly distributed throughout the SA/PA/BBF straw, with contents of 36%, 6%, 10%, and 7%, respectively. This confirms that PA has been successfully introduced onto the surface of the SA/PA/BBF paper straw.

[0044]FIG. 4 illustrates an FTIR spectrogram of the BBF, the CA/CQAS/BBF straw and the SA/PA/BBF straw prepared in the embodiment 1, the CA/CQAS/SA/BBF straw prepared in the comparative embodiment 1, and the SA. As shown in FIG. 4, for the BBF straw, the peaks at 3321 cm⁻¹ and 2901 cm⁻¹ correspond to O—H and C—H vibrations, respectively. The peaks at 1326 cm⁻¹ and 1023 cm⁻¹ are attributed to 0-H bending vibration and C—O stretching vibration. After CA/CQAS treatment, some changes are observed: a new peak appears at 1724 cm⁻¹, corresponding to C═O stretching vibration, indicating that multiple CA and CQAS molecules formed a dense cross-linked network structure on the straw surface. Further changes are observed after SA and PA treatment: new peaks appeared at 1702 cm⁻¹, 1471 cm⁻¹, and in the 1380-1150 cm⁻¹ range, corresponding to C═O stretching vibration and bending vibrations of methyl and methylene groups in the SA. These results demonstrate the successful binding of the SA and the PA with bamboo fibers. Additionally, the strong band at 945 cm⁻¹ indicates the C-type polymorphic form of the SA, consistent with the wide-angle X-ray diffraction (WAXD) results.

[0045]FIG. 5 illustrates an XRD spectrogram of the BBF, the CA/CQAS/BBF straw, and the SA/PA/BBF straw prepared in the embodiment 1, the CA/CQAS/SA/BBF straw prepared in the comparative embodiment 1, and the SA. As shown in FIG. 5, different crystal peaks corresponding to different d-spacings can be observed in the SA crystals. The “long spacing” of SA appears at three diffraction angles: 13.3 Ångstrom (Å) (7.2°), 8.0 Å (11.7°), and 5.7 Å (15.5°), indicating the thickness and ordered arrangement of SA molecules. Simultaneously, the “short spacing” appears at diffraction angles of 4.1 Å (21.6°) and 3.7 Å (23.9°), demonstrating the transverse stacking order of the hydrocarbon chains. The BBF straw, the CA/CQAS/BBF straw, and the CA/CQAS/SA/BBF straw exhibit characteristic peaks of cellulose I at 16.5° and 22.6°. For the CA/CQAS/SA/BBF straw, the peaks at 7.2°, 11.7°, 21.6°, and 23.9° represent the crystal spacings of the SA, indicating that the SA exists in a crystalline state on the surface. These values correspond well with the monoclinic C-form SA.

[0046]FIGS. 6A and 6B respectively illustrate a TGA curve graph and a DTG curve graph of the BBF, the CA/CQAS/BBF straw, and the SA/PA/BBF straw prepared in the embodiment 1, the CA/CQAS/SA/BBF straw prepared in the comparative embodiment 1, and the SA. FIG. 6A illustrates the TGA curve graph, and FIG. 6B illustrates the DTG curve graph. The thermal stability of straws is crucial for their normal production and use. As shown in FIGS. 6A and 6B, before the temperature rises to 160° C., the CA/CQAS/BBF straw, the CA/CQAS/SA/BBF straw, and the SA/PA/BBF straw exhibit slow weight loss. For the BBF straw, slow weight loss occurs before the temperature reaches 280° C., which can be attributed to the evaporation of moisture from the straw paper surface. As the temperature continues to increase, the weight loss rate of the samples gradually accelerates. The SA begins to decompose at approximately 207° C., the CA decomposes at around 176° C., the CQAS decomposes at around 331° C., and the PA decomposes at around 260° C. The fibers of the uncoated paper decompose at approximately 348° C. When the temperature reaches 379° C., the weight of the samples gradually stabilizes. Compared with the uncoated paper, the residual weight of the modified paper increases, and the thermal weight loss rate of the modified paper decreases, which may be related to changes in fiber size and crystal structure during the modification process. All straws show good thermal stability at temperatures below 100° C., indicating that these straws can be applied to daily life use.

[0047]The comparative antibacterial property diagram of the BBF straw and the SA/PA/BBF straw prepared in the embodiment 1, and the CA/CQAS/SA/BBF straw in the comparative embodiment 1 is shown in FIG. 7. As can be seen from FIG. 7, the CA/CQAS/SA/BBF straw exhibits poor antibacterial activity against Escherichia coli and Staphylococcus aureus, with inhibition rates of 21.94% and 67.65%, respectively. In contrast, the SA/PA/BBF straw treated with the PA achieves a 100% inhibition rate against the Escherichia co/i and a 99.63% inhibition rate against the Staphylococcus aureus. This is attributed to the PA contains six active phosphate groups, which chelate divalent cations in lipopolysaccharides, lower the environmental pH, and damage the cell wall. The integrity of the bacterial cell wall and cell membrane is compromised, increasing permeability and causing leakage of cytoplasmic contents, which leads to elevated alkaline phosphatase levels and higher conductivity. Moreover, the PA not only roughens the bacterial surface but also induces rupture, collapse, and pore formation on the cell surface, thereby resulting in the leakage of cellular protoplasm.

[0048]FIG. 8 illustrates a comparison diagram of dry bending strengths of the BBF straw, the CA/CQAS/BBF straw, and the SA/PA/BBF straw prepared in the embodiment 1. As can be seen from FIG. 8, under air conditions, the three straws underwent complete bending at applied loads of 110 g, 130 g, and 180 g, respectively. This indicates that treatment with CA and CQAS, and treatment with SA and PA significantly enhance the bending resistance of the straws.

[0049]As shown in FIG. 9, a comparison of the load-bearing capacity in water for the SA/PA/BBF straw prepared in the embodiment 1 reveals that the BBF straw and CA/CQAS/BBF straw exhibit poor load-bearing capacity in water, immediately softening upon immersion and unable to support any weight. In contrast, the SA/PA/BBF straw can support a load of 50 g for 2 min while fully submerged in water. This enhanced performance is attributed to the interaction between anions in the SA and the PA with cations in CQAS, which increases fiber compactness, and the presence of the SA on the fiber surface, thereby improving water stability. Additionally, as shown in Table 1, the mechanical strength (tensile strength (TS) and elongation at break (EB)) of the SA/PA/BBF straw still needs improvement.

[0050]The PP straw, the PLA straw, the commercial paper straw, and the SA/PA/BBF straw prepared in the embodiment 1 are subjected to degradation testing. The PP straw, the PLA straw, the commercial paper straw, and the SA/PA/BBF straw prepared in the embodiment 1 were buried in the same soil environment, and the morphological changes of different straws within 40 days were observed, as shown in FIG. 10. From FIG. 10, it can be seen that the SA/PA/BBF straw achieves complete degradation within 40 days, and has a degradation rate better than that of the commercial paper straw. In contrast, the PP and PLA straws show no significant degradation during the same period, highlighting their poor biodegradability. Due to the excellent biodegradability, the SA/PA/BBF straw is promising to partially replace plastic straws and help solve the white pollution problem.

[0051]The hydrophilic and hydrophobic property comparison diagram for the BBF straw, the CA/CQAS/BBF straw, and the SA/PA/BBF straw prepared in the embodiment 1 at room temperature is shown in FIG. 11. To facilitate observation of capillary action, each straw is immersed in a bright blue solution. The results show that the BBF straw and the CA/CQAS/BBF straw exhibit superhydrophilicity: the bright blue solution reaches top ends of the straws within 2 min and 3 min, respectively, causing phenomena such as swelling, softening, and fiber detachment in the straws. However, the SA/PA/BBF straw remains morphologically stable within 4 h, showing no signs of delamination or edge cracking. After being removed from the solution, the SA/PA/BBF straw could still maintain a straight shape.

[0052]The BBF straw, the CA/CQAS/BBF straw, and the SA/PA/BBF straw prepared in the embodiment 1 each is immersed in tea, coffee, cola, and milk to simulate usage scenarios, as shown in FIGS. 12A-12D. The BBF straw maintained its integrity for only 2 min in tea, 4 min in coffee, 1 min in cola, and 3 min in milk. The CA/CQAS/BBF straw showed slightly improved durability, lasting 3 min in tea, 5 min in coffee, 3 min in cola, and 7 min in milk. While there was a trend towards increased stability, it still fell short of practical requirements. In contrast, the SA/PA/BBF straw remained stable after being immersed in all beverages for 2 hours, showing no signs of swelling or bending, as illustrated in FIG. 13. This demonstrates the superior stability and durability of the SA/PA/BBF straw.

[0053]The water stability of the BBF straw, the CA/CQAS/BBF straw, and the SA/PA/BBF straw prepared in the embodiment 1 is evaluated at 0° C. by immersing each straw in water at 0° C. to assess their applicability, as shown in FIG. 14. As can be seen from FIG. 14, the BBF straw and the CA/CQAS/BBF straw are fully saturated due to capillary action within 2 min and 3 min, respectively, with water progressively wicking upward toward the top of the straws, leading to softening and collapse. In contrast, the SA/PA/BBF straw retains its original shape even after 2 h, showing no signs of delamination or cracking.

[0054]The performance radar diagram of the SA/PA/BBF straw prepared in the embodiment 1, the commercial paper straw, and the PLA straw is shown in FIG. 15. As illustrated in FIG. 15, a comprehensive comparison between the SA/PA/BBF straw and two commonly used biodegradable straws (the PLA straw and the commercial paper straw) is conducted across various manufacturing and performance parameters including cost, biodegradability, wax coverage, taste, hydrophobicity, and mass production efficiency. The cost of the SA/PA/BBF straw is approximately five times less than that of the PLA straw and ten times less than that of the commercial paper straw. Additionally, the PLA straw requires specific conditions to achieve complete degradation. The commercial paper straw addresses water stability issues by applying multiple layers of waterproof wax, which not only increases costs but also limits the speed of large-scale production. In contrast, the SA/PA/BBF straw effectively addresses the primary drawbacks of both the PLA straw and the commercial paper straw while exhibiting excellent antibacterial properties against the Escherichia coli and the Staphylococcus aureus, making the SA/PA/BBF straw a promising superior alternative to plastic straws.

Embodiment 2

[0055]This embodiment differs from the embodiment 1 in that the concentration of the SA solution in step 3 is 10%. All other steps and parameters are the same as in the embodiment 1. The biodegradable, antibacterial bamboo fiber-based paper straw obtained in this embodiment is designated as a SA10/PA13/BBF straw.

Embodiment 3

[0056]This embodiment differs from the embodiment 1 in that the concentration of the SA solution in step 3 is 18%. All other steps and parameters are the same as in the embodiment 1. The biodegradable, antibacterial bamboo fiber-based paper straw obtained in this embodiment is designated as a SA18/PA13/BBF straw.

Embodiment 4

[0057]This embodiment differs from the embodiment 1 in that the concentration of the PA solution in step 3 is 10%. All other steps and parameters are the same as in the embodiment 1. The biodegradable, antibacterial bamboo fiber-based paper straw obtained in this embodiment is designated as a SA14/PA10/BBF straw.

Embodiment 5

[0058]This embodiment differs from the embodiment 1 in that the concentration of the PA solution in step 3 is 20%. All other steps and parameters are the same as in the embodiment 1. The biodegradable, antibacterial bamboo fiber-based paper straw obtained in this embodiment is designated as a SA14/PA20/BBF straw.

[0059]The contact angle photograph of the biodegradable and antibacterial bamboo fiber-based paper straws prepared in the embodiment 2-5 are shown in FIG. 16, with specific data provided in Table 2. From FIG. 16 and Table 2, it can be seen that the addition of PA overall improves the hydrophobic stability of the straws. Even after 30 min, the contact angle of the paper straw remains above 90°, demonstrating good stability.

[0060]The disclosure utilizes bleached bamboo pulp to make paper and pre-treats the straw paper through the ionic bond interaction between the CA and the CQAS. The SA, a saturated fatty acid extracted from animals and plants, can be found in almost all oils and fats, and is a widely-sourced fatty acid. The unique eighteen-carbon structure endows the SA with hydrophobic potential, and the disclosure achieves hydrophobic modification of the straw by adding the SA. The PA is a non-toxic, renewable, and low-cost natural compound extracted from plants such as soybeans and corns. Due to its special structure with six phosphate groups, the PA has excellent antibacterial properties. The disclosure gives the straw good antibacterial performance by adding the PA. This straw also exhibits excellent biodegradability and wide applicability.