Preparation method, product and application of a novel polylactic acid composite fiber filament

Abstract

The present invention discloses a preparation method, product and application of a novel polylactic acid composite fiber filament, including: thermal blending and masterbatch preparation: fully mixing PLA, PEO and curcumin, feeding them into an extruder to prepare strip samples, and making them into masterbatch, wherein the mass ratio of PLA, PEO and curcumin is 80-95:3-15:0.2-5; after melt spinning the masterbatch, stretching is carried out to obtain the polylactic acid composite fiber filament. The present invention prepares biodegradable PLA / PEO / curcumin fibers by melt spinning method, and characterizes their mechanical properties, thermal properties, microstructural properties, anti-free radical and biodegradable properties. The results show that the prepared composite material has very excellent properties.

Description

Technical Field

[0001] The present invention belongs to the technical field of fiber preparation, and particularly relates to a preparation method, products and applications of a novel polylactic acid composite fiber filament. Background Art

[0002] In recent decades, low carbon dioxide emissions and sustainable development have attracted increasing attention. Personal protective equipment (PPE) such as masks, respirators, and protective clothing for virus protection or environmental pollution, which have been mass-produced in the past few years using fossil resources as the main raw materials, are becoming new sources of pollution.

[0003] As an eco-friendly resource, biomass is rich in sources, renewable, and has great potential to partially replace traditional fossil resources in many applications. Compared with fibers obtained from fossil resources, biomass fibers have better biodegradability, but poor mechanical properties, poor thermal properties, and high costs.

[0004] Polylactic acid (PLA) fiber is a material that is expected to be biodegradable. It is synthesized from lactic acid obtained by bacterial fermentation of renewable biomass resources such as corn and straw. In the past few decades, extensive research has been conducted on the morphology, thermodynamic properties, and degradation kinetics of polylactic acid fibers. In the melt spinning of PLA, due to mechanical shear causing macromolecular chain breakage, thermal degradation occurs at high temperatures above the melting point, or hydrolysis occurs in water vapor near the spinneret holes in air, and the fibers usually suffer significant strength loss. Many researchers have pointed out that high temperatures above 200 °C will have an obvious negative impact on the spinning efficiency and quality of PLA fibers, including an increase in bubbles in the spinning solution leading to an increase in broken ends, a sharp drop in molecular weight and mechanical strength, etc.

[0005] Due to differences in chemical composition and microstructure, PLA fibers have obvious defects such as brittleness, lower glass transition temperature and strength, and slower crystallization rate compared with polyester. These have greatly hindered the potential application of polylactic acid fibers in certain fields. Techniques such as copolymerization, blending, and grafting can offset these disadvantages. During the polymerization process, acrylic monomers and lactic acid are mixed at the molecular level, which can also improve the strength of the composite material. Summary of the Invention

[0006] The purpose of this part is to outline some aspects of the embodiments of the present invention and briefly introduce some preferred embodiments.

[0007] As one aspect of the present invention, the present invention provides a preparation method of a novel polylactic acid composite fiber filament, which includes,

[0008] Hot melt blending and masterbatch preparation: PLA, PEO, and curcumin are fully mixed and fed into an extruder to prepare strip samples and then made into masterbatch. Among them, the mass ratio of PLA, PEO, and curcumin is 80-95:3-15:0.2-5;

[0009] After melt spinning the masterbatch, stretching is carried out to obtain polylactic acid composite fiber filaments.

[0010] As a preferred scheme of the preparation method of the novel polylactic acid composite fiber filaments of the present invention: the mass ratio of PLA, PEO, and curcumin is 87-87.5:10-12:0.5-1.0.

[0011] As a preferred scheme of the preparation method of the novel polylactic acid composite fiber filaments of the present invention: the feeding into the extruder to prepare strip samples includes using a single-screw extruder and extruding at 190-195°C to obtain the strip samples.

[0012] As a preferred scheme of the preparation method of the novel polylactic acid composite fiber filaments of the present invention: the making into masterbatch includes using a rotary cold cutter to make the strip samples into masterbatch, and the particle size of the masterbatch is 2-3 mm.

[0013] As a preferred scheme of the preparation method of the novel polylactic acid composite fiber filaments of the present invention: the melt spinning includes using a single-screw spinning extruder for melt spinning, and the spinning temperature is 195°C.

[0014] As a preferred scheme of the preparation method of the novel polylactic acid composite fiber filaments of the present invention: the diameter of the composite fiber single filament is 25-60 μm.

[0015] Advantages of the present invention: The present invention selects medium molecular weight PEO, that is, polyethylene oxide (PEO, MW = 100,000), to endow the entanglement between PEO and PLA in the polymer matrix, and achieve a balance among the plasticizing ability of PEO, degradability, and the mechanical properties of the final fiber. Due to the chain slippage caused by the introduction of small molecule polyethylene glycol, inevitable fiber strength loss occurs. Polylactic acid is a hydrophobic and biocompatible aliphatic polymer, which degrades slowly through hydrolysis or enzymatic reactions. The hydrophilic PEO in the composite fiber can accelerate these processes. The present invention prepares biodegradable PLA / PEO / curcumin fibers by melt spinning method, and characterizes their mechanical properties, thermal properties, microstructure properties, anti-free radical, and biodegradable properties. The results show that the prepared composite materials have very excellent properties. Description of the Drawings

[0016] To more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the accompanying drawings required for the description of the embodiments. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings. Among them:

[0017] Figure 1 is the strength-strain curve of the fiber.

[0018] Figure 2 is the XRD pattern of the PLA / PEO / curcumin filaments.

[0019] Figure 3 are the optical microscope and scanning electron microscope images.

[0020] Figure 4 is the scavenging efficiency of the PLA / PEO / curcumin fiber on DPPH radicals. Specific Embodiments

[0021] To make the above objects, features, and advantages of the present invention more obvious and understandable, the following will describe the specific embodiments of the present invention in detail with reference to specific examples.

[0022] Example 1:

[0023] Raw Materials:

[0024] PLA pellets (Ingeo 6400D), PEO (M.W. = 100,000, industrial grade, T g = -67 °C, T m = 65 °C, Jiangsu Haian Petrochemical Factory, Jiangsu, China), curcumin ((1E,6E)-1,7-bis(4-hydroxy-3-methoxyphenyl)-1,6-heptadiene-3,5-dione, M.W. = 363.38, T m = 183 °C, Sinopharm Chemical Reagent Co., Ltd., China), without further purification. All materials were dried in a vacuum oven at 40 °C for 48 hours to fully remove moisture.

[0025] 1,1-Diphenyl-2-picrylhydrazyl (DPPH, M.W. = 394, λ max = 517 nm, biochemical reagent, Hefei BASF Biotechnology Co., Ltd., Anhui, China) and absolute ethanol (M.W. = 46, analytical grade, Sinopharm Chemical Reagent Co., Ltd., China) were used.

[0026] Thermal Blending and Masterbatch Preparation:

[0027] To obtain uniform filaments, PLA, PEO, and curcumin were thoroughly mixed and then fed into a single-screw extruder of model S35 (Jiangsu Oury Machinery Co., Ltd., China) with a diameter of S35, operating at 190 °C to prepare round bar-shaped samples. The rotational speed was 10 revolutions per minute. The samples of PLA:PEO:curcumin with 6 different weight ratios are marked as shown in the following table:

[0028] Composition of PLA / PEO / Curcumin Samples

[0029] Sample PLA / w.t. % PEO / w.t. % Curcumin / w.t. % <![CDATA[S0]]> 100.0 / / <![CDATA[S1]]> 91.5 8.0 0.5 <![CDATA[S2]]> 91.0 8.0 1.O <![CDATA[S3]]> 87.5 12.0 0.5 <![CDATA[S4]]> 87.0 12.0 1.0 <![CDATA[S5]]> 95.5 4.0 0.5

[0030] The strips S1 - S5 were naturally cooled at room temperature and then granulated into masterbatch with a diameter of about 2.5 mm using a rotary cold cutting machine. For S0, no strip and masterbatch were needed, and the PLA particles could be directly used in the spinning process. Before further melt spinning, all masterbatches were dried under the same conditions as the PLA particles.

[0031] Melt Spinning and Drawing:

[0032] The masterbatch was melt spun using a single-screw spinning extruder, extruded at 195 °C, with 6 spinnerets, each with a diameter of 1.0 mm. The rotational speed was set at 10 revolutions per minute. Subsequently, during the fiber cooling process, it was drawn using a drawing machine. The temperature of the first roll was 40 °C, and the temperatures of the second and third rolls were both 55 °C. The draw ratios were 2.0× and 1.5× respectively, so the total draw ratio was 3.0×. The single-filament diameter of the finally obtained polylactic acid composite fiber filaments was: 25 μm.

[0033] Characteristics:

[0034] Tensile properties. The tensile characteristics of the fibers were recorded at 22 °C on a CMT-4304 stress-strain instrument (MTS Systems (China) Co., Ltd.), with a gauge length of 20 mm, a pre-tightening force of 0.2 cN, and a tensile speed of 100 mm / min -1 . Twenty single filaments of each sample were tested. The breaking strength, elongation at break, and initial modulus (modulus value at an elongation of 2.0%) were analyzed based on the curves. The data were expressed as the mean and error calculated by the t-distribution at a 95% confidence level in the form of.

[0035] Microscopic morphology. The fibers were observed by scanning electron microscopy (SEM) using a FEI Nova Nano SEM 450 (Thermo Fisher Scientific, USA). Cross-sectional and longitudinal photos were taken to observe the fiber surface structure.

[0036] Crystallinity. Using CuKα radiation (λ = 0.1542 nm, 40 KV, 40 mA), on X′Pert 3The powdered samples cut from the fibers were analyzed on a powder X-ray diffractometer (Malvern Panalytical Ltd, UK). The range of angle 2θ was from 10° to 50°. The crystal size was calculated according to the Scherrer equation, and the crystallinity was calculated according to the ratio of the crystalline peak area to the total area of the crystalline and amorphous regions.

[0037] DPPH· free radical scavenging test. The free radical scavenging activity of curcumin was determined by the DPPH method. 0.1 mmol L -1 DPPH ethanol solution, aliquots of 0.5 mL were taken and diluted with ethanol, and the regression equation of absorbance and DPPH concentration was obtained according to the Lambert-Beer law.

[0038] To extract curcumin from the fibers, 1.00 g of the fibers was soaked in 4.00 ml of ethanol at room temperature for 6 hours. 1.00 ml was taken and mixed with 4.00 ml of 0.1 mmol L -1 of DPPH ethanol solution and stored in the dark for 30 minutes. Finally, the absorbance of the mixture at λ max = 517 nm was recorded on a TU-1900 UV-visible spectrophotometer (Beijing General Analytical Instrument Co., Ltd). The free radical scavenging efficiency calculation formula is:

[0039]

[0040] where A c is the absorbance of the control sample (without fibers and / or curcumin), and A s is the absorbance of the sample containing fibers (S0 - S4).

[0041] Each sample was tested three times. The data was presented in the form of mean value and error and the error (Δ) was obtained according to the T distribution at a 95% confidence level.

[0042] The stress-strain curves of the prepared fibers are as Figure 1 shown, and the corresponding characteristic values are listed in Table 1. It can be clearly found that S0 shows a rigid tensile mode without any obvious yield point. This is mainly because the previous draw ratio of 3× at around 55 °C greatly eliminated the defects of the fibers and improved the strength of the fibers. As is well known, drawing can significantly improve the orientation of polymer chains along the fiber axis and induce crystallinity. However, under the test conditions, when stretched at a higher speed (100 mm min -1 ), the PLA macromolecules cannot rearrange or flow rapidly. The results show that S0 has the lowest elongation at break, the highest strength and initial modulus. (Table 1).

[0043] Figure 1It is the strength-strain curve of PLA / PEO / curcumin fiber, and each curve is the average value of multiple tensile data curves of the sample.

[0044] Table 1 Tensile property values of PLA / PEO / curcumin fiber

[0045] Elongation at break (%) <![CDATA[Breaking strength (cN / dtex -1 )]]> <![CDATA[Initial modulus (cN / dtex -1 )]]> <![CDATA[S0]]> 3.92±0.36 2.32±0.22 0.74±0.08 <![CDATA[S1]]> 52.56±6.53 2.04±0.14 0.21±0.03 <![CDATA[S2]]> 46.84±5.45 2.17±0.13 0.25±0.02 <![CDATA[S3]]> 75.12±9.70 1.71±0.16 0.18±0.03 <![CDATA[S4]]> 68.87±11.79 2.01±0.02 0.19±0.02

[0046] Note: We selected medium molecular weight PEO and found that it can significantly improve the strength of PLA. Previous studies found that when preparing samples with low molecular weight PEO (M.W = 2,000), the measured elongation at break was 16.24%, and the breaking strength was 1.12 cN dtex -1 , and the initial modulus was 0.16 cN dtex -1 , and the mechanical properties of the fiber were poor. While for the samples prepared with high molecular weight PEO (M.W = 1 million), the measured elongation at break was 82.63%, and the breaking strength was 2.76 cN dtex -1 , and the initial modulus was 1.35 cN dtex -1 , although the mechanical properties of the fiber were improved, the degradation performance of high molecular weight PEO was significantly worse than that of medium molecular weight PEO. Therefore, medium molecular weight PEO was finally preferred.

[0047] Crystallinity:

[0048] Figure 2 Describes the XRD patterns of the prepared fibers. In S0, the diffraction angles 2θ of about 16.44°, 19.0° and 14.8° correspond to the (200), (203) and (104) reflections of semi-crystalline polylactic acid (ICDD#00-064-1624). The broad peak at about 16.4° at 2θ indicates a low crystallinity of S0, while the sharp peaks of other samples indicate a high crystallinity. Due to the low content of PEO (ICDD#00-055-1815), its diffraction pattern could not be clearly identified in S1-S4. Table 2 lists the crystallinity and grain size calculated from the curves.

[0049] Table 2 Crystallinity and grain size of PLA / PEO / curcumin fiber

[0050] Crystallinity / % Microcrystalline size / nm <![CDATA[S0]]> 17.3 2.0 <![CDATA[S1]]> 26.6 2.8 <![CDATA[S2]]> 28.2 4.2 <![CDATA[S3]]> 22.0 6.5 <![CDATA[S4]]> 26.6 7.8

[0051] Microscopic morphology:

[0052] Optical microscope and scanning electron microscope images are as Figure 3 shown to analyze the morphology of the fibers after preparation.

[0053] After the spinning and stretching processes, all the fibers had a smooth appearance, and no obvious pits and pores were observed ( Figure 3, a to e, g to j). Pale yellow curcumin is evenly distributed on the fiber surface without agglomeration ( Figure 3 . b to e, h and i). Due to the relatively high spinning temperature, PEO and curcumin had melted before leaving the orifice, indicating that mechanical shear in the spinning melt could blend PEO and curcumin more evenly with PLA. As a result, fibers with uniform texture and smooth surface were obtained.

[0054] Figure 3 are the optical and scanning electron microscope photos of PLA / PEO / curcumin fibers. Samples a to e were cut into short fibers and photographed under an optical microscope. S0; b, S1; c, S2; d, S3; e, S4; f and g. The segment head morphology of b to e indicates that the presence of PEO makes the fibers ductile.

[0055] However, after extraction in absolute ethanol, the PEO on the fiber surface layer was removed, leaving flaky and rough insoluble PLA ( Figure 3 , j, k).

[0056] To investigate the scavenging ability of DPPH· free radicals in the fibers, we conducted DPPH assays and obtained a linear regression (R 2 = 0.9942):

[0057] Absorbance = 10.4586[DPPH·] + 0.0705

[0058] where the concentration unit of [DPPH·] is mmolL -1 .

[0059] The free radical scavenging effects of each sample were determined according to the formula, and the results are as Figure 4 shown.

[0060] Figure 4 is the scavenging efficiency of PLA / PEO / curcumin fibers against DPPH free radicals. The inset is the residual solution after the DPPH test. Most of it is still purple in S0, indicating extremely low anti-free radical efficiency.

[0061] The scavenging ability of the fibers added with curcumin (S1-S4) against DPPH· radicals increased from 2.9% without curcumin addition to 83% after addition. As the curcumin content in the fibers increased from 0.5 w.t.% to 1.0 w.t.%, the radical scavenging effect increased from 83.3% to 94.1% (S1 and S2, PEO 8.0 w.t.% group) and from 88.8% to 96.2% (S3 and S4, PEO 12.0 w.t.% group), respectively. This may be because a higher PEO content introduces more amorphous regions in the composite fibers, as shown in the crystallinity measurement mentioned above, thus improving the radical scavenging effect of curcumin. The results show that more curcumin can be extracted by ethanol in the DPPH· test, enhancing the radical scavenging effect. When the PEO content is lower (S5), the radical scavenging effect of the fibers further decreases to 72.6%, mainly due to the decrease in the concentration of curcumin that can be dissolved during the test caused by the decrease in the PEO content.

[0062] After the DPPH solution in ethanol was mixed with the curcumin extracted from the composite fibers, the color changed from purple to yellow, indicating that an oxidation-reduction reaction occurred. After experiencing the harsh conditions of high-temperature melt spinning, the curcumin in the fibers still maintained a high radical scavenging activity. It should be noted that curcumin is insoluble in water but soluble in ethanol. In any case, treating the fibers with ethanol is a severe condition in the daily end-use of the fabric. Therefore, the PLA / PEO / curcumin fibers also have the ability to scavenge similar free radicals such as O· (oxygen free radical) and NO· (nitric oxide free radical) that appear in the living environment, which can reduce their potential harm to human skin.

[0063] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of the present invention, and they should all be covered within the scope of the claims of the present invention.

Claims

1. Application of a novel polylactic acid composite fiber filament in multifunctional fibers with free radical resistance, biodegradability and high strength, characterized in that: The preparation method of the novel polylactic acid composite fiber includes: Thermal blending and masterbatch preparation: PLA, PEO, and curcumin are fully mixed and sent into an extruder to prepare a strip sample, and then made into a masterbatch. Among them, the mass ratio of PLA, PEO, and curcumin is 87-87.5:10-12:0.5-1.0; the molecular weight of the PEO is 100,000; After melt-spinning the masterbatch, stretching is carried out to obtain polylactic acid composite fiber filaments; The step of sending into the extruder to prepare a strip sample is to use a single-screw extruder to extrude at 190 °C to obtain the strip sample; The melt-spinning includes using a single-screw spinning extruder for melt-spinning, and the spinning temperature is 195 °C.

2. The application according to claim 1, wherein: The step of making the masterbatch includes using a rotary cold cutter to make the strip sample into a masterbatch, and the particle size of the masterbatch is 2-3 mm.

3. The application according to claim 2, wherein: The single-filament diameter of the composite fiber filaments is 25-60 μm.

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