Multifunctional bio-based modifier, method of making and use thereof

Abstract

This invention relates to a multifunctional bio-based modifier, its preparation method, and its uses, belonging to the field of PLA composite materials. By weight, it comprises 10 parts adenosine monophosphate, 5-8 parts β-cyclodextrin, and 3-4 parts creatine. The preparation method includes the following steps: (1) adding 10 parts adenosine monophosphate and 4-5 parts of a 37%-40% formaldehyde aqueous solution to 200 parts of water, heating to 75-85℃, and reacting for 1-2 hours; (2) after the reaction, adding 5-8 parts β-cyclodextrin, heating to 80-100℃, and reacting for 2-3 hours; (3) finally adding 3-4 parts creatine, cooling to 45-55℃, and reacting for 1.5-2.5 hours. After filtration, washing, and drying, the multifunctional bio-based modifier is obtained. The multifunctional bio-based modifier of this invention can impart flame retardant, toughening, UV aging resistance, and recyclability to PLA at low addition levels, thus showing good industrial application prospects.

Description

Technical Field

[0001] This invention relates to a multifunctional bio-based modifier, its preparation method, and its uses, belonging to the field of PLA composite materials. Background Technology

[0002] Polylactic acid (PLA) is an environmentally friendly polymer with good biocompatibility, high transparency, and biodegradability, making it widely used in medical, packaging, textile, building materials, and 3D printing fields. However, several inherent defects of PLA limit its further large-scale application. First, PLA is highly flammable, with a low limiting oxygen index (LOI) of approximately 19%, making it difficult to self-extinguish once ignited. Second, as a thermoplastic brittle material, PLA lacks toughness and is prone to brittle fracture. Third, PLA is sensitive to ultraviolet (UV) radiation (such as sunlight), and exposure to UV rays reduces its mechanical properties and lifespan, thus limiting its long-term outdoor use. Fourth, the degradation and recycling of PLA still require improvement. Although PLA is biodegradable, its degradation rate in the natural environment is slow. Furthermore, the unavoidable thermomechanical degradation effect during mechanical (physical) recycling reduces its molecular weight, thereby weakening the mechanical properties of recycled PLA. In contrast, a chemical recycling pathway that depolymerizes PLA back to monomers, purifies them, and then repolymerizes them is considered a more attractive alternative. Fifth, PLA's slow crystallization rate results in long injection molding cycles, which is detrimental to industrial production. Therefore, improving these properties is crucial for expanding the application boundaries of PLA.

[0003] Driven by the dual demands of performance improvement and green sustainability, researchers often use biomass-based materials to modify PLA. However, most bio-based additives struggle to simultaneously enhance multiple properties and exhibit low flame retardancy, requiring high addition amounts to achieve the UL94-V0 rating, which can easily lead to a decline in the material's mechanical properties.

[0004] To date, there is no additive that can be prepared by a simple method that can simultaneously achieve high flame retardancy, toughening, UV aging resistance, and improved recyclability of PLA. Summary of the Invention

[0005] To address the above issues, this study uses β-cyclodextrin (CD), adenosine monophosphate (AMP), and creatine as bio-based raw materials to synthesize a multifunctional bio-based modifier (CD-PN). Through rational design, a multifunctional reinforced polylactic acid is achieved.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0007] A multifunctional bio-based modifier, comprising, by weight, 10 parts adenosine monophosphate, 5-8 parts β-cyclodextrin, and 3-4 parts creatine.

[0008] The preparation method of the multifunctional bio-based modifier of the present invention includes the following steps: (1) Add 10 parts of adenosine monophosphate and 4-5 parts of 37-40 wt% formaldehyde aqueous solution to 200 parts of water, heat to 75-85℃, and react for 1-2 hours; (2) After the reaction is complete, add 5-8 parts of β-cyclodextrin, heat to 80-100℃, and react for 2-3 hours; (3) Finally, add 3-4 parts of creatine, cool to 45-55℃, react for 1.5-2.5h, filter, wash and dry to obtain a multifunctional bio-based modifier.

[0009] The application of the multifunctional bio-based modifier of the present invention in improving the performance of PLA.

[0010] Furthermore, preferably, the application in improving PLA performance specifically involves enhancing the thermal properties, flame retardancy, and fire safety of PLA.

[0011] Furthermore, preferably, the application in improving PLA performance specifically involves increasing the crystallinity and crystallization rate of PLA.

[0012] Furthermore, preferably, the application in improving PLA performance specifically involves increasing the tensile strength, Young's modulus, and elongation at break of PLA.

[0013] Furthermore, preferably, the application in improving PLA performance specifically refers to enhancing the ultraviolet shielding performance of PLA.

[0014] Furthermore, preferably, the application in improving PLA performance specifically involves accelerating the degradation of PLA composite materials.

[0015] Further, preferably, the amount of the multifunctional bio-based modifier added is 1-3 wt%.

[0016] The beneficial effects of this invention are: The multifunctional bio-based modifier of this invention uses β-cyclodextrin, adenosine monophosphate, and creatine as raw materials. Cyclodextrin, produced from starch, is inexpensive and readily available, and its molecules are rich in hydroxyl groups, making it a highly efficient and green carbon source. Furthermore, recent studies have shown that cyclodextrin can dissipate a significant amount of energy during stretching through a sacrificial conformation mechanism, thereby increasing material toughness. Creatine, a widely used sports supplement, is also inexpensive and readily available. As a bio-based nitrogen source, its nitrogen content can reach approximately 32 wt%, and its carboxyl groups can also serve as a gas source and improve interfacial compatibility with PLA.

[0017] The multifunctional bio-based modifier of this invention can comprehensively improve the performance of polylactic acid (PLA) with small amounts. Only 3 wt% of CD-PN is needed to achieve the UL-94 V-0 flame retardant standard for PLA, with a limiting oxygen index (LOI) as high as 36.8%. In cone calorimetry (CCT), the peak average heat release rate (pARHE), total heat release (THR), and total smoke release (TSR) are significantly reduced, with reductions of 23%, 25.7%, and 23.1%, respectively. Furthermore, while improving crystallinity, it also improves mechanical properties; based on a novel toughening mechanism—conformation dissipation—it can increase the elongation at break to 22.6% with an addition of 1 wt%. Furthermore, the composite material exhibits a high UV protection factor (UPF) of 203.5. Due to the excellent free radical scavenging ability of CD-PN, after 100 hours of accelerated UV aging testing, its tensile strength, Young's modulus, and elongation at break remained at 43%, 95%, and 53%, respectively, all significantly higher than pure PLA, indicating its superior UV protection and anti-aging properties. Moreover, CD-PN can significantly improve the degradation rate of the composite material, achieving complete degradation within 6 hours in an alkaline solution, which helps improve the recycling efficiency of PLA. This study ingeniously designed and prepared a multifunctional bio-based modifier that can impart flame retardant, toughening, UV aging resistance, and recyclability to PLA at low addition levels, thus demonstrating promising industrial application prospects. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 The figure shows the characterization results of the multifunctional bio-based modifier. Figure 2 Digital photographs of the combustion process of PLA and its composites in UL-94 testing; Figure 3 The graph shows the results of the determination of the limiting oxygen index of PLA and its composites. Figure 4 The figure shows the measurement results of PLA and PLA composite materials under simulated actual combustion environment. Figure 5 The graph shows the results of the crystallization properties determination of PLA and its composites. Figure 6 The graph shows the results of mechanical property testing of PLA and its composite materials. Figure 7 The graph shows the results of the UV shielding performance measurement of PLA and its composite materials. Figure 8 Figure 1 shows the results of photoaging tests on PLA and its composite materials. Figure 9 The graph shows the results of the degradation performance test of PLA composite materials. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are also described.

[0021] Example 1: Preparation of a multifunctional bio-based modifier A method for preparing a multifunctional bio-based modifier includes the following steps: (1) Add 10 parts of adenosine monophosphate and 5 parts of 40 wt% formaldehyde aqueous solution to 200 parts of water, heat to 80℃, and react for 2 hours; (2) After the reaction is complete, add 6 parts of β-cyclodextrin, heat to 90℃, and react for 3 hours; (3) Finally, add 4 parts of creatine, cool to 50°C, react for 2 hours, filter, wash and dry to obtain a multifunctional bio-based modifier.

[0022] Example 2: Preparation method of PLA / CD-PN composite material PLA was dried in an oven at 80°C for 12 hours. PLA and the CD-PN powder prepared in Example 1 were melt-blended at 170°C using a WLG10A micro twin-cone screw extruder at 85 rpm for 7 minutes. For mechanical testing samples, CD-PN and PLA flakes were vacuum degassed and mixed at 170°C. After cooling, the mixture was crushed to obtain a high-concentration masterbatch, which was used to replace the CD-PN powder in subsequent processing, while all other processing conditions remained unchanged. The addition amount of CD-PN in PLA was set at 1 wt%, 2 wt%, and 3 wt%, and the corresponding samples were named PLA / 1% CD-PN, PLA / 2% CD-PN, and PLA / 3% CD-PN, respectively. The blends were then transferred to a WZS10D micro injection molding machine preheated to 180°C. The mold temperature was set to 30°C, the injection pressure to 8 MPa, and the holding time to 20 seconds. After cooling, the molded samples were demolded.

[0023] Test methods Fourier transform infrared (FTIR) spectroscopy was performed using an ALPHA II spectrometer (Bruker GmbH, Germany) in attenuated total reflectance (ATR) mode.

[0024] X-ray photoelectron spectroscopy (XPS) was performed using a PHI VersaProbe III spectrometer (Physical Electronics, Inc., USA) with a monochromatic Al Kα source (hν = 1486.6 eV). The full-spectrum scan had a pass energy of 280 eV with a step size of 1.0 eV; the high-resolution spectrum had a pass energy of 112 eV with a step size of 0.10 eV. Charge neutralization was performed using an electron neutralization gun. Binding energies were referenced to the C–C peak (284.8 eV).

[0025] Morphological observation was performed using a Phenom Pure Plus scanning electron microscope (SEM, Thermo Fisher Scientific, USA), equipped with an energy-dispersive X-ray spectroscopy (EDS) detector and an accelerating voltage of 5 kV.

[0026] Thermogravimetric analysis (TGA) was performed using a STA PT 1600 instrument (Linseis, Germany) in an N2 gas flow (20 mL / min). -1 ) at 10 K min -1 The heating rate is from 70 °C to 800 °C.

[0027] The UL-94 test was conducted using a PX-03-001 instrument (Phinix Instruments, China), according to ASTM D3801 standard, with a sample size of 130 × 13 × 3 mm. 3 .

[0028] The limiting oxygen index (LOI) was measured using a 5801A automatic oxygen index analyzer (VOUCH Corporation, China) according to ISO 4589 standard. The sample size was 130 × 6.5 × 3 mm. 3 .

[0029] The cone calorimeter (CC) test was conducted using an iCone Classic instrument (FTT, UK), with an external heat flux density of 35 kW m³. -2 The sample size is 100 × 100 × 3 mm. 3 Specifically, smoke emission data were corrected for. The FRI (Fire Performance Index) is calculated using the following formula:

[0030] Raman spectroscopy analysis was performed using an XploRA Via-Reflex laser Raman spectrometer (HORIBA Corporation, Japan).

[0031] Differential scanning calorimetry (DSC) was performed using a DSC 200 F3 instrument (NETZSCH, Germany) under a nitrogen atmosphere. The sample was initially sampled at 10 K min. -1 Heat from 25 °C to 200 °C, then at 10 K min. -1 Cool to 20 °C, and finally again at 10 K min. -1 Heat to 200 °C. Crystallinity (Xc) is calculated using the following formula:

[0032] Where ΔHm is the enthalpy of melting of the PLA composite material, ΔH CC ΔH is the enthalpy of cold crystallization, wf is the mass fraction of PLA in the composite material, and ΔH is the enthalpy of cold crystallization. m 0 The enthalpy of fusion of 100% crystalline PLA is 93.6 J g. -1 ).

[0033] Tensile tests were conducted using a CMT4204 universal testing machine (SANS Corporation, China) according to GB / T 1040.2-2006 standard, with a tensile rate of 5 mm / min. -1 Each sample should be tested at least five times, and the average value should be reported.

[0034] Ultraviolet Protection Factor (UPF) and Ultraviolet (UV) Transmittance were measured using a UV-2600 spectrophotometer (Shimadzu Corporation, Japan). UPF values ​​were calculated according to AS / NZS 4399:1996 using the following formula:

[0035] Among them, E λ ε λ and T λ Solar spectral irradiance (W·m) -2 ·nm -1 The ratio of relative erythema effect to spectral transmittance is given by Δλ, where Δλ is the wavelength interval (nm). Note that the UPF calculation program used in this study was independently developed and is available on GitHub: https: / / github.com / Flykra-Talloran / UPF-Calculator.

[0036] The UV aging test was conducted in an HT-UV-225 UV aging test chamber (Jing Yu Machine Co., Ltd., China), with an aging temperature of 60 °C and a distance of 20 cm between the sample and the light source.

[0037] The free radical scavenging ability was evaluated using the DPPH free radical scavenging method. The absorbance of the control DPPH solution and the sample solution at 515 nm was measured using a UV-2600 spectrophotometer (Shimadzu Corporation, Japan). The DPPH free radical scavenging activity was calculated using the following formula:

[0038] Where Asample is the absorbance of the sample solution and Acontrol is the absorbance of the control DPPH solution.

[0039] The degradation behavior of the obtained material was tested in an alkaline solution. A 10 wt% NaOH solution was prepared before the test. The modified sample (10 × 10 × 2 mm³) was immersed in the NaOH solution at 60 °C, with a solution-to-sample mass ratio of 25:1. The sample was removed at fixed time intervals, the surface moisture was blotted dry with a paper towel, and then it was weighed.

[0040] TG-FTIR tests were performed using a STA 6000 thermogravimetric analyzer (PerkinElmer, USA) coupled with a Frontier Fourier transform infrared spectrometer (PerkinElmer, USA). The test was conducted in an N2 gas flow (50 mL / min). -1 ) at 10K min -1 The heating rate was from 40 °C to 800 °C. The heating transfer line and gas cell were maintained at 260 °C. The FTIR spectral recording range was 4000–450 cm⁻¹. -1 The resolution is 4 cm. -1 The scan count was 4. A time-to-temperature conversion program was independently developed to construct the temperature axis, which can be obtained on GitHub: https: / / github.com / Flykra-Talloran / Secs_to_Temp_for_TG-FTIR.

[0041] Performance testing: I. Structural Characterization of CD-PN CD-PN was characterized using FTIR, XPS, SEM, and TGA. Relevant information is as follows: Figure 1 As shown.

[0042] Figure 1(a) shows the FTIR spectra of CD-PN, creatine, and β-cyclodextrin; (b) shows the XPS full spectrum of CD-PN; (cf) shows the precision C1s, O1s, N1s, and P2p spectrograms of CD-PN; (g) shows the SEM image and EDS energy dispersive spectroscopy of CD-PN; and (h, i) show the TG and DTG curves of CD-PN, PLA, and their composite materials.

[0043] Figure 1 (a) shows the FTIR spectra of CD-PN and the raw material. The spectrum of CD shows CO (1020 cm⁻¹). -1 ), and -OH (3289 cm) -1 A strong absorption peak. Creatine exhibits fine infrared characteristics in the high wavenumber region: 2795 cm⁻¹. -1 The characteristic absorption of –COOH is 3259 cm⁻¹. -1 The ν(N–H···O) vibration is attributed to hydrogen bonding, while 3056 cm⁻¹ -1 This exhibits characteristic absorption bands associated with guanidine groups. Additionally, C=O (1684 cm⁻¹), C=N (1595 cm⁻¹), and –COO groups were also observed. - (1389 cm -1 ), CN (1301 cm⁻¹). After reaction with phosphorus oxychloride, CO (1035 cm⁻¹) was observed in the product CD-PN. -1 ), NH (3007 cm) -1 ), C=N(1623 cm⁻¹), C=N(1544 cm⁻¹), where 1343 cm⁻¹ -1 Primarily classified as C–N, possibly with COO. - Symmetric stretching contribution, and the newly observed P=O (1241 cm⁻¹), POC (1168, 1071 cm⁻¹) and O–P–O (681, 650 cm⁻¹) indicate that the three have been successfully combined.

[0044] XPS full spectrum analysis of CD-PN (Figure 1(b)) shows that CD-PN is mainly composed of C, O, N, and P elements. Further peak fitting of the fine spectra of these elements yielded more detailed chemical environment information (Figure 1(cf)). The C 1s spectrum shows four peaks corresponding to CC / CH (284.8 eV), CO / CN / COP (285.8 eV), OCO (287.1 eV), and OC=O (289.2 eV). The O 1s spectrum shows three peaks corresponding to O=C / O=P (531.3 eV), OC / PO (532.5 eV), and OH / O–C=O / surface adsorbed water (533.8 eV). The N 1s spectrum shows the presence of N=C (398.9 eV), NC / NH (400.6 eV), and NP / N+ (402 eV). The P 2p spectrum showed a spin-orbit doublet at 133.4 / 134.5 eV, indicating that phosphorus in the sample mainly exists as phosphate esters. Combined with other fine spectra, this signal can be attributed to structures such as phosphate esters and phosphoramides. These results collectively demonstrate the successful preparation of CD-PN and provide evidence for its structural characteristics.

[0045] The microstructure and elemental composition of CD-PN were characterized by SEM and EDS (Figure 1(g)). SEM images showed that CD-PN consisted of rough-surfaced microparticles. EDS surface scanning results indicated that the sample mainly contained C, O, N, and P elements, with mass contents of 31.1%, 26.6%, 29.6%, and 12.8%, respectively. The high N and P contents endowed CD-PN with excellent flame retardancy.

[0046] Table 1 shows that the thermal decomposition behavior of CD-PN can be divided into three stages. Specifically, the first stage, the onset decomposed (5 wt% mass loss), starts at 191 ˚C and ends at 224 ˚C, with a mass loss of approximately 10%. The second stage, from 224 ˚C to 392 ˚C, has a maximum decomposition temperature of 230 ˚C and a mass loss of 30%, representing a rapid decomposition stage. This is likely due to the decomposition of phosphate ester bonds in CD-PN. The third stage is a slow decomposition. The residual carbon content of CD-PN at high temperatures of 500 ˚C, 600 ˚C, and 700 ˚C is 53.4%, 48.5%, and 43.4%, respectively. This is attributed to the abundant polyhydroxy structure and high phosphorus content of cyclodextrin, which significantly increases the formation of residual carbon.

[0047] The tonset of pure PLA was 346 °C, and the Tmax was 230 °C. With increasing CD-PN content, the tonset of all samples decreased significantly, while the Tmax increased slightly. Adding 3% CD-PN resulted in a 13 °C decrease in tonset compared to pure PLA, while the Tmax increased by 4 °C. Furthermore, the maximum decomposition rate (Rmax) decreased from 4.9 wt% / °C to 2.6 wt% / °C. During thermal decomposition, the phosphoric acid produced by the premature decomposition of CD-PN promoted the dehydration and carbonization of CD and PLA. These substances further inhibited the decomposition of PLA, thus reducing Rmax. In addition, the higher residual weight also means less heat and volatile matter generated during combustion. This indicates that CD-PN can improve the thermal properties and fire safety of PLA.

[0048] Table 1. TGA data of CD-PN, PLA and their composites in N2 gas flow.

[0049] II. Combustion Behavior The flame retardant properties of PLA and its composites were evaluated using limiting oxygen index (LOI) testing and UL-94 vertical burning tests. The results are as follows: Figure 2 and Figure 3 As shown, pure PLA, a highly flammable polymer, has an LOI value of only 19.5%, burns violently in air, and produces a large number of flaming droplets, failing to meet UL-94 standards. However, surprisingly, adding only 1 wt% CD-PN significantly affected the combustion behavior of PLA: it did not ignite the absorbent cotton during the first ignition, and the self-extinguishing time was shortened to 0.7 s, while the LOI increased to 32.7%. This indicates a significant reduction in the flammability of PLA. Further, adding 2 wt% CD-PN increased the LOI to 35.2%, but still did not reach the V-0 flame retardant rating. Ultimately, PLA / 3% CD-PN achieved the UL-94 V-0 flame retardant rating, with the LOI increasing to 36.8%. Furthermore, during the first and second ignitions, the average total number of droplets significantly decreased from 15 drops in PLA / 1% CD-PN to 8 drops, mainly attributed to the good charring effect of CD-PN during combustion. Furthermore, the self-extinguishing time of the samples after removal from the flame was significantly shortened, by 0.2 s and 0.1 s, respectively. These results indicate that CD-PN has excellent flame-retardant properties and can significantly reduce the risk of fire.

[0050] The actual combustion environment was simulated using a cone calorimeter (CCT), and the results are shown in [Figure number missing]. Figure 4 And Table 2. Figure 4(a) is the heat release rate (HRR) curve; (b) is the total heat release (THR) curve; (c) is the average heat release rate (ARHE) curve; and (d) is the total smoke release (TSR) curve.

[0051] There was no significant difference in the Time to Ignition (TTI) values ​​between PLA and PLA / 3% CD-PN, indicating that the introduction of CD-PN did not significantly change the thermal decomposition behavior of PLA composites in the early stage of combustion.

[0052] The peak heat release rate (pHRR) of PLA is 349.5 kW / m³. 2 The pHRR of PLA / 3% CD-PN decreased to 317 kW / m 2 The decrease was 9.3%. Further characterization of the combustion trend using the average heat release rate (ARHE) and its peak pARHE showed that the decrease in pARHE was 23%, which means that CD-PN effectively suppressed the fire growth potential of PLA.

[0053] However, compared to pure PLA, the peak time of heat release rate (tpHRR) of PLA / 3% CD-PN was significantly earlier. This is likely due to the phosphoric acid compounds generated during the decomposition of CD-PN, which promote the early degradation and carbonization of the PLA composite material.

[0054] Further observation of the HRR curves revealed that the Flaming combustion time of PLA / 3% CD-PN was significantly shorter than that of pure PLA. It transitioned to Smoldering combustion at approximately 230 s, a slow, flameless combustion process that typically cannot be sustained after the removal of the external heat source. During the Smoldering combustion stage, the HRR decreased significantly, and its duration was not significantly longer than that of Flaming combustion in pure PLA. Although Smoldering combustion led to an increase in CO, rising from 0.006 kg / kg in pure PLA to 0.014 kg / kg, the overall absolute CO formation remained low, and Flaming combustion was suppressed, thus improving overall fire safety. Correspondingly, the Total Heat Release (THR) of PLA / 3% CD-PN decreased to 47.1 MJ·m⁻². -2Compared to pure PLA, the flame retardancy was reduced by 25.7%. As shown in Table 2, the flame retardant performance of PLA / 3% CD-PN was significantly improved using a dimensionless flame retardant index (FRI) proposed by Henri et al. Simultaneously, the total smoke emission (TSR) was also significantly reduced by 23.1%. Given that smoke is the most significant factor causing casualties in actual fires, this further demonstrates the excellent fire safety of the PLA / CD-PN composite material.

[0055] Table 2 Cone calorimeter data for PLA and PLA composite materials

[0056] III. Crystallization Properties The effect of CD-PN on the crystallization properties of PLA was studied by differential scanning calorimetry (DSC), and the results are as follows: Figure 5 As shown in Table 3. Figure 5 (a) DSC heating curve; (b) DSC cooling curve.

[0057] Due to the plasticizing effect of CD-PN, the Tg of the composite material gradually decreases and all exhibit a single Tg, indicating good thermodynamic compatibility between CD-PN and the matrix. Furthermore, the cold crystallization temperature (Tcc) of the composite material gradually decreases with increasing CD-PN content, and is consistently lower than that of pure PLA. The Tcc of PLA / 3% CD-PN decreases by 5.6°C, and the peak width narrows, reflecting an increased glassy crystallization rate and enhanced crystallization ability. Therefore, CD-PN can be considered a nucleating agent in the PLA matrix, providing heterogeneous nucleation sites and promoting the stacking of ordered crystal structures at low temperatures, thereby enhancing the crystallization ability of PLA. Compared to pure PLA, the melting point (Tm) of the composite material shifts towards lower temperatures. The Tm of PLA / 3% CD-PN is approximately 2.7°C lower than that of pure PLA. Previously, Painter et al. reported that hydrogen bonding interactions between components lead to a decrease in melting point. The structure of CD-PN contains both carboxyl and guanidine groups, which may form hydrogen bonds with carbonyl groups in the PLA chain, resulting in a decrease in melting point. Furthermore, the composite material exhibited two melting peaks, indicating that CD-PN, acting as a nucleating agent, promoted the transformation of the crystal structure. Therefore, with increasing CD-PN content, the crystallinity (Xc) of the composite material increased to 3.8%, 5.8%, and 6.5%, respectively. This further confirms that CD-PN, as a nucleating agent, can improve the crystallinity and crystallization rate of PLA.

[0058] Table 3 DSC characteristic parameters of PLA and its composites

[0059] IV. Mechanical Properties of PLA and its Composites As a brittle plastic, PLA inherently has poor toughness, which has limited its industrial applications to some extent. However, the introduction of modifiers typically further reduces the toughness of PLA. To evaluate the practical application value of PLA, we investigated its tensile properties, such as... Figure 6 As shown, Figure 6 In the figure, (a) is the stress-strain curve; (b) is the tensile strength, Young's modulus and elongation at break.

[0060] The tensile strength of pure PLA was 64.6 MPa, the Young's modulus was 1.3 GPa, and the elongation at break was 7.7%. The PLA / CD-PN composite exhibited higher Young's modulus and elongation at break than pure PLA. The PLA / 1% CD-PN sample showed the highest elongation at break at 9.44%, a 22.6% increase compared to pure PLA. With further increases in CD-PN content, both tensile strength and elongation at break decreased. At a CD-PN content of 3%, the tensile strength was 57.16 MPa, the Young's modulus was 1.5 GPa, and the elongation at break was 8.3%.

[0061] V. Ultraviolet Protection Performance Figure 7 The UV protection performance of PLA and its composites is shown in the following figures: (a) UV transmittance curve; (b) UV protection factor; (c) mass loss rate after 100 hours of UV aging; (df) mechanical properties after 100 hours of UV aging; (g) digital photograph before UV aging; (h, i) side digital photograph of the illuminated surface after 20 hours of UV aging; (j) digital photograph of the illuminated surface after 100 hours of UV aging; (k) SEM images of the illuminated surface before and after 100 hours of UV aging; and (l) DSC curves of the illuminated surface before and after 100 hours of UV aging.

[0062] Figure 7 (a) and (b) demonstrate the UV shielding performance of PLA and its composites. Pure PLA exhibits high transmittance in the UV band. After adding 3% CD-PN, the transmittance of the composite material in the UVC, UVB, and UVA bands decreased to 0.05%, 0.28%, and 0.73%, respectively. Compared with pure PLA, the transmittance in the UVC, UVB, and UVA bands decreased by 99.8%, 99.6%, and 99%, respectively. The UV protection factor (UPF) evaluates the UV shielding performance of a product. PLA's UPF value is only 1.41, meaning that pure PLA has no UV shielding capability. After adding CD-PN, the UPF value of the composite material rapidly increases, reaching 230.52 at 3%. Its UPF value is more than 163 times higher than that of control PLA, and according to standards, its protective performance reaches an excellent level.

[0063] To further evaluate the UV resistance of the composite material, accelerated UV aging experiments were conducted to study its impact on service life. Figure 7 (c) shows the mass retention rate of the PLA samples after UV aging treatment. It can be seen that adding 3% CD-PN can protect the PLA material from UV damage, retain more mass, and increase the mass retention rate from 94.2% for pure PLA to 98.4%. Figure 7 (d, e, and f) show the mechanical properties before and after 100 hours of UV irradiation. The tensile strength, Young's modulus, and elongation at break of pure PLA all decreased significantly, to only 5.2 MPa, 0.3 GPa, and 1.47%, respectively, with retention rates of 17%, 24%, and 19%. Manual inspection of the specimens also showed that the strength and toughness of the material decreased sharply, causing it to fail under slight external force, indicating that it had almost completely lost its mechanical properties.

[0064] The tensile strength, Young's modulus, and elongation at break of the PLA / 3%CD-PN composite material after UV aging were significantly retained, at 24.4 MPa, 1.42 GPa, and 4.42%, respectively, with retention rates of 43%, 95%, and 53%. Moreover, these parameters were significantly improved compared to pure PLA, with increases of 368%, 350%, and 201%, respectively.

[0065] Figure 7 (gi) shows the surface morphology of PLA composite material after being exposed to ultraviolet light for different periods of time. Figure 7 (h,i) indicates that after only 20 hours of irradiation, the pure PLA sample underwent significant bending deformation, its surface changed from transparent to white, and it became sticky. In contrast, the sample with 3% CD-PN largely maintained its original morphology, with no significant surface changes. Figure 7 (h,i) indicates that after 100 hours of irradiation, pure PLA turned significantly yellow, and the surface oil content increased further. The angular areas melted slightly and could not be maintained, while the addition of 3% CD-PN resulted in almost no sticky surface and maintained a good overall morphology.

[0066] To further investigate the changes in the surface of the composite material after UV aging, we performed scanning electron microscopy (SEM) characterization. Figure 7As shown in (k), the surface of the PLA composite material underwent significant changes before and after photoaging. After 100 hours of UV irradiation, the surface of pure PLA changed from a smooth structure to a gyri-like wrinkled structure with a width of approximately 2 μm, with almost no flat areas. This indicates that UV irradiation caused severe photoinduced chain breakage and photooxidation reactions on the PLA surface, forming a shrinking and brittle oxide layer. The strain mismatch between this layer and the matrix resulted in wrinkles and bulges. In contrast, the PLA / 3% CD-PN composite material under the same conditions only showed a small number of larger but continuous bulges. These bulges maintained good continuity and bonding between the surface layer and the matrix, with no obvious interface debonding or crack propagation, indicating that UV aging reduced the damage depth to the matrix interior. Furthermore, the surface protrusions may also be due to UV-induced or thermally driven migration and enrichment of CD-PN on the composite surface. This prevents UV radiation from damaging the deeper matrix layers, consistent with its better mechanical retention.

[0067] To further investigate the effects of UV aging on crystallization behavior and thermal properties, DSC was used for testing. The results are as follows: Figure 7 As shown in (i), due to UV degradation, the PLA molecular chains underwent severe breakage, generating a large number of short chain segments and oxidation products, increasing the difficulty of Tg identification. After UV aging, Tg decreased from 9.7°C to 36.2°C. No melting peak was observed after conventional heat history elimination treatment (cooling to 40 °C and holding for 2 min). To promote crystallization, the cooling program was modified (cooling to -10 °C and holding for 10 min), and only then was a weak melting peak observed. Xc decreased from 2.33% to 0.96% after UV aging. This indicates that UV aging significantly increased the disorder of molecular chain length, weakened the crystallization ability of PLA, and caused severe structural damage. In contrast, the two melting peaks of PLA / 3% CD-PN remained unchanged after UV aging. Xc decreased from 6.45% to 3.44%, Tg and Tm decreased by about 2°C, while Tcc increased by 1.5°C. This indicates that although the molecular chain crystallization ability of PLA composite material was slightly weakened, it could still maintain a regular arrangement.

[0068] These results indicate that adding only 3% CD-PN can effectively improve the UV shielding performance and UV aging resistance of PLA composites, thereby effectively extending the service life of PLA composites.

[0069] Figure 8Photoaging images of PLA and its composites are shown, where (af) are the ATR-FTIR spectra before photoaging and after 100 hours of photoaging; (h) are the transmission FTIR spectra of the thin film; (i) are the thermogravimetric curves of the mixed powder (PM) under air and nitrogen; and (g) are the UV absorption spectra and digital photographs of DPPH, mixtures of DPPH with AO1010 or CD-PN.

[0070] The decomposition of LA segments during photoaging conforms to the Norrish reaction mechanism. The enhancement of characteristic peaks for OH, anhydride, and olefins after 100 h of photoaging serves as evidence of this reaction. To accurately compare the relative changes in characteristic peak areas, the hydroxyl index (HI) and anhydride index (AI) were calculated, with the –OH group (3400 cm⁻¹) as the reference value. -1 ) and anhydride groups (1841cm) -1 The peak area of ​​) remains essentially unchanged before and after photoaging of –CH 2- (1453 cm) -1 The peak area ratio is used to represent the ratio of the peak areas. As shown in Figure 8(c–f), it can be clearly seen that after adding 3% CD-PN, the characteristic peaks representing PLA degradation and cleavage, including OH and acid anhydride groups, are significantly weakened, with the hydroxyl index decreasing by 62.7% compared to pure PLA. Before photoaging, no characteristic peaks of acid anhydride groups appeared in PLA; however, after photoaging, the peak area of ​​acid anhydride groups in pure PLA increased significantly. In comparison, the acid anhydride index in the composite material with added 3% CD-PN was 24.3% lower than that of pure PLA. Regarding the change in carbonyl groups, the carbonyl peak area of ​​both increased after photoaging, and the increase was similar. It is worth noting that from Figure 8 (e) It can be seen that the carbonyl absorption band of pure PLA red-shifts and broadens significantly after photoaging. UV-induced chain breakage and oxidation lead to a decrease in polymer molecular weight and the generation of a large number of small molecule carboxylic acids, thereby broadening the carbonyl absorption band; in addition, the –COOH / –OH generated by degradation can also form hydrogen bonds with the carbonyl group, causing the absorption peak to shift to lower wavenumbers.

[0071] In addition, a DPPH radical scavenging activity assay developed by Blois was performed to investigate the ability of CD-PN to capture free radicals. In this study, the commercial antioxidant AO1010 (pentaerythritol tetraalkyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate) and CD-PN were added to a DPPH solution to obtain UV absorption spectra. Figure 8As shown in (g), a strong absorption peak appears at 515 nm in the control DPPH curve, but the intensity of this absorption peak is significantly reduced after the addition of AO1010 or CD-PN. The free radical scavenging activity (RSA) values ​​of AO1010 and CD-PN are 95.9% and 94.3%, respectively. These results indicate that CD-PN has excellent free radical scavenging ability, thereby inhibiting the photo-oxidation reaction.

[0072] We investigated the phenomenon that adding polylactic acid to pale yellow CD-PN caused the composite material to turn black, and we believe that this color change is closely related to the improvement of its UV resistance. Figure 8 (h) shows the transmission FTIR spectra of the PLA film before and after the addition of CD-PN, in which no significant new olefin or other absorption peaks were observed. To further investigate, we mixed PLA powder and CD-PN powder and performed thermogravimetric analysis under nitrogen and air atmospheres, respectively. The results are as follows... Figure 8 As shown in (i), the sample mass losses were 0.95% and 4.86% within the processing temperature range of 100–200 °C, respectively. Black substances were observed at the interface between CD-PN and polylactic acid. Figure 8 (h) The infrared spectrum did not change significantly, and we speculate that the black substance may have originated from carbon produced by the trace decomposition of the modifier during the processing.

[0073] Based on the above analysis, the UV protection mechanism of CD-PN can be deduced. It has been reported that the terminal groups of PLA molecules react with oxygen under UV irradiation to generate peroxide free radicals, which then decompose into acid anhydrides, small molecule compounds, and other free radicals through β-cleavage. The phosphoramide, guanidine, and carboxyl groups in CD-PN, as well as the small amount of carbides formed during processing, can act as UV absorbers, effectively inhibiting UV penetration throughout the matrix through good absorption. Furthermore, the polar groups in CD-PN, including guanidine and carboxyl groups, can quench free radicals generated during photo-oxidation, blocking chain reactions and inhibiting chain breakage, effectively reducing UV damage to PLA, thus maintaining good mechanical properties and extending the service life of polylactic acid.

[0074] VI. Degradation performance of PLA composite materials To evaluate the degradation performance of the material, the sample was placed in a 10% NaOH solution at 60 °C, and digital photographs were taken at different time points, and the sample mass was measured. The results are as follows: Figure 9 As shown, Figure 9(a,c) are digital photographs of PLA degradation; (b,d) are digital photographs of PLA / 3% CD-PN degradation; (e) is the mass loss rate of the PLA sample; (f) are SEM images of PLA before degradation and 6 hours later; (g) are SEM images of PLA / 3% CD-PN before degradation and 6 hours later.

[0075] As shown in Figures 9 (a–e), there is a significant difference in the degradation rate between PLA and PLA / 3% CD-PN: pure PLA loses approximately 30% of its mass within 7 hours, with little change in appearance; in contrast, the PLA / 3% CD-PN sample degrades almost completely within 7 hours, and the solution gradually turns yellow. These results indicate that the introduction of CD-PN can significantly accelerate the alkaline degradation process of PLA composites.

[0076] To evaluate the degradation performance of the materials, they were placed in a 60°C 10wt% sodium hydroxide solution, and digital photographs were taken and sample mass was measured. As shown in Figure 10(a–e), the degradation rates of PLA and PLA / 3% CD-PN differed significantly. Pure PLA lost approximately 30% of its mass within 7 hours, while the PLA / 3% CD-PN sample was completely degraded within 7 hours, and the solution gradually turned yellow.

[0077] To investigate the accelerated degradation mechanism of CD-PN in PLA, we used scanning electron microscopy (SEM) to observe the morphology of the composite material during the degradation process. Figure 9 As shown in (f, g), the composite material generates numerous pores during degradation. Subsequently, the pores gradually increase in number and size, eventually connecting together, and the composite material decomposes into small fragments. These pores are caused by the leaching of additives. This is consistent with the observed yellowing of the solution. The leaching of the solution allows it to fully penetrate the interior of the composite material, resulting in a change in the degradation mode from surface erosion to uniform erosion. These results indicate that the addition of CD-PN can significantly accelerate the degradation process of PLA composite materials, which is beneficial for the recycling and utilization of PLA.

[0078] Example 3 Preparation of Multifunctional Bio-based Modifier A method for preparing a multifunctional bio-based modifier includes the following steps: (1) Add 10 parts of adenosine monophosphate and 4 parts of 40 wt% formaldehyde aqueous solution to 200 parts of water, heat to 85℃, and react for 1 h; (2) After the reaction is complete, add 5 parts of β-cyclodextrin, heat to 80℃, and react for 2 hours; (3) Finally, add 3 parts of creatine, cool to 45°C, react for 2.5 hours, filter, wash and dry to obtain a multifunctional bio-based modifier.

[0079] Example 4 Preparation of Multifunctional Bio-based Modifier A method for preparing a multifunctional bio-based modifier includes the following steps: (1) Add 10 parts of adenosine monophosphate and 5 parts of 37wt% formaldehyde aqueous solution to 200 parts of water, heat to 75℃, and react for 2 hours; (2) After the reaction is complete, add 8 parts of β-cyclodextrin, heat to 100℃, and react for 2 hours; (3) Finally, add 4 parts of creatine, cool to 55°C, react for 1.5 h, filter, wash and dry to obtain a multifunctional bio-based modifier.

[0080] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A multi-functional bio-based modifier, characterized in that: Based on weight, it includes 10 parts adenosine monophosphate, 5-8 parts β-cyclodextrin, and 3-4 parts creatine.

2. A method for preparing a multifunctional bio-based modifier as described in claim 1, characterized in that, Includes the following steps: (1) Add 10 parts of adenosine monophosphate and 4-5 parts of 37-40 wt% formaldehyde aqueous solution to 200 parts of water, heat to 75-85℃, and react for 1-2 hours; (2) After the reaction is complete, add 5-8 parts of β-cyclodextrin, heat to 80-100℃, and react for 2-3 hours; (3) Finally, add 3-4 parts of creatine, cool to 45-55℃, react for 1.5-2.5h, filter, wash and dry to obtain a multifunctional bio-based modifier.

3. The application of the multifunctional bio-based modifier prepared according to claim 2 in improving the performance of PLA.

4. The application according to claim 3, characterized in that: The specific applications in improving PLA performance include enhancing PLA's thermal properties, flame retardancy, and fire safety.

5. The application according to claim 3, characterized in that: The specific application in improving PLA performance is to increase the crystallinity and crystallization rate of PLA.

6. The application according to claim 3, characterized in that: Specifically, the application in improving PLA performance involves increasing the tensile strength, Young's modulus, and elongation at break of PLA.

7. The application according to claim 3, characterized in that: The specific application in improving PLA performance is to enhance the ultraviolet shielding performance of PLA.

8. The application according to claim 3, characterized in that: The specific application in improving PLA performance is accelerating the degradation of PLA composite materials.

9. The application according to any one of claims 3-8, characterized in that: The amount of the multifunctional bio-based modifier added is 1-3 wt%.

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