A unidirectional moisture-wicking and heat-insulating polylactic acid flocculant, its preparation method and application

Abstract

This invention provides a unidirectional moisture-wicking and heat-insulating polylactic acid (PLA) wadding, its preparation method, and its applications, belonging to the field of functional materials technology. The unidirectional moisture-wicking and heat-insulating PLA wadding provided by this invention is obtained by needle punching a fiber web, the raw material for which the fiber web is prepared includes hollow PLA fibers; the pore size increases progressively from the upper surface to the lower surface of the unidirectional moisture-wicking and heat-insulating PLA wadding. The PLA wadding provided by this invention exhibits good unidirectional moisture wicking and heat retention properties.

Description

Technical Field

[0001] This invention relates to the field of functional materials technology, and in particular to a unidirectional moisture-wicking and heat-insulating polylactic acid flocculant, its preparation method, and its application. Background Technology

[0002] Fluffing refers to sheet-like, cotton-like materials (fiber webs) made from plant, animal, or chemical fibers for warmth or insulation, and it plays an important role in textiles. Moisture wicking is a crucial factor affecting the comfort of clothing and other textiles. If the human body secretes excessive sweat, and the textile cannot quickly wick the sweat to its outer surface for evaporation, it will not only cause discomfort but also foster bacterial growth and unpleasant odors, threatening human health. One-way moisture-wicking fabrics are high-value functional textiles with significantly different moisture-wicking properties on their front and back sides. This allows sweat to be quickly conducted from the inner layer to the outer layer, evaporating as fast as possible, and preventing sweat from flowing back into the inner layer.

[0003] In existing technologies, unidirectional moisture-wicking fabrics typically employ a composite layer structure. For example, Chinese patent CN110846809A discloses a unidirectional moisture-wicking needle-punched composite multilayer wadding, comprising a hydrophilic nonwoven wadding layer, a hydrowicking nonwoven wadding layer, and a hydrophobic nonwoven wadding layer sequentially stacked and needle-punched together by a needle-punching mechanism. That is, each individual wadding layer is first prepared, and then the individual wadding layers are composited. This patent does not explicitly describe the warmth retention effect of the composite multilayer wadding prepared by its method. However, it is generally difficult to simultaneously achieve both unidirectional moisture wicking and warmth retention. How to prepare a wadding that simultaneously possesses good unidirectional moisture wicking and warmth retention is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0004] The purpose of this invention is to provide a unidirectional moisture-wicking and heat-insulating polylactic acid flocculant, its preparation method, and its application. The polylactic acid flocculant provided by this invention has good unidirectional moisture wicking and heat retention properties.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0006] This invention provides a unidirectional moisture-wicking and heat-insulating polylactic acid (PLA) wadding, which is obtained by needle punching a fiber web. The raw material for preparing the fiber web includes hollow PLA fibers. The pore size increases from the upper surface to the lower surface of the unidirectional moisture-wicking and heat-insulating PLA wadding.

[0007] Preferably, the raw materials for preparation further include non-hollow polylactic acid fibers, and the content of non-hollow polylactic acid fibers in the raw materials for preparation is ≤90wt%.

[0008] Preferably, the hollow polylactic acid fiber has the following specifications: a fineness of 2.5-7D, a length of 38-105mm, and a hollowness of 15-25%; the non-hollow polylactic acid fiber has the following specifications: a fineness of 0.8-7D and a length of 38-105mm.

[0009] Preferably, the needle-punching process further includes a hydrophilic treatment, which is applied to the lower surface of the unidirectional moisture-wicking and heat-insulating polylactic acid flocculant.

[0010] Preferably, the areal density of the unidirectional moisture-wicking and heat-insulating polylactic acid wadding sheet is 30–350 g / m³. 2 The thickness is 3-25mm;

[0011] The moisture conductivity change rate of the unidirectional moisture-wicking and heat-insulating polylactic acid (PLA) wadding is 3-30%, and the moisture conductivity change rate of the unidirectional moisture-wicking and heat-insulating PLA wadding is calculated according to the formula shown in Equation I:

[0012] A=(A1-A2) / A1×100% Formula I;

[0013] In Formula I, A is the rate of change of moisture conduction of the unidirectional moisture-conducting and heat-insulating polylactic acid flocculant, A1 is the moisture conduction from the lower surface to the upper surface, and A2 is the moisture conduction from the upper surface to the lower surface.

[0014] This invention provides a method for preparing the unidirectional moisture-wicking and heat-insulating polylactic acid flocculant described in the above technical solution, comprising the following steps:

[0015] A fiber web is provided, wherein the raw material for preparing the fiber web includes hollow polylactic acid fibers;

[0016] The fiber web is needle-punched to obtain a unidirectional moisture-wicking and heat-insulating polylactic acid (PLA) wadding with pore size increasing from the upper surface to the lower surface. The needle-punching includes upper needle plate needle-punching and lower needle plate needle-punching, or only upper needle plate needle-punching. The needle-punching conditions include: the needles in each row of the upper needle plate needle-punching are not evenly spaced, and the needle-punching depth varies; the needles in each row of the lower needle plate needle-punching are not evenly spaced, and the needle-punching depth varies; and the number of rows of lower needle plate needle-punching is less than the number of rows of upper needle plate needle-punching, the total needle-punching density of the lower needle plate is less than the total needle-punching density of the upper needle plate, the maximum needle-punching depth of both the lower and upper needle plate needle-punching is 1 / 2 the thickness of the unidirectional moisture-wicking and heat-insulating PLA wadding, and the sum of the needle-punching depths of the lower and upper needle plate needle-punching is less than the thickness of the unidirectional moisture-wicking and heat-insulating PLA wadding.

[0017] Preferably, the upper needle plate has 1 to 3 needle passes, the lower needle plate has 0 to 2 needle passes, and the total density of needle passes on the lower needle plate does not exceed 50% of the total density of needle passes on the upper needle plate.

[0018] Each needle insertion point of the upper needle plate is arranged with 2 to 6 rows of space, and each needle insertion point of the lower needle plate is arranged with 6 to 10 rows of space.

[0019] The needle depth difference of the upper needle plate is 0.5 to 4.5 mm, and the needle depth difference of the lower needle plate is 0.5 to 2 mm.

[0020] Preferably, the process after needle puncture further includes: hydrophilic treatment of the lower surface of the flocculation precursor obtained after needle puncture to obtain the unidirectional moisture-wicking and heat-insulating polylactic acid flocculation.

[0021] Preferably, the hydrophilic treatment is a corona treatment; the voltage of the corona treatment is 6-12kV and the time is 3-10s.

[0022] This invention provides the application of the unidirectional moisture-wicking and heat-insulating polylactic acid flocculant described in the above technical solution or the unidirectional moisture-wicking and heat-insulating polylactic acid flocculant prepared by the preparation method described in the above technical solution in the preparation of outdoor sportswear.

[0023] This invention provides a unidirectional moisture-wicking and heat-insulating polylactic acid (PLA) wadding, obtained by needle punching a fiber web. The raw material for preparing the fiber web includes hollow PLA fibers. The pore size increases from the upper surface to the lower surface of the unidirectional moisture-wicking and heat-insulating PLA wadding. This invention uses hollow PLA fibers as raw material to prepare the unidirectional moisture-wicking and heat-insulating PLA wadding via needle punching. It is a heterogeneous wadding with a porous structure of varying density, and the pore size increases from the upper surface to the lower surface. This results in a difference in moisture conduction from the lower surface to the upper surface compared to the upper surface to the lower surface, exhibiting unidirectional moisture-wicking characteristics. Specifically, the lower surface has larger pores, suitable for liquid water transfer, while the upper surface has smaller pores, suitable for vapor water transfer. The potential energy gradient of water and vapor after sweating during exercise also contributes to unidirectional moisture wicking. This invention uses hollow PLA fibers, which can store still air, and their high bulkiness and high resilience refine the pores of the wadding, blocking airflow and giving the wadding good heat retention.

[0024] Furthermore, the raw materials for preparing the fiber web in this invention also include non-hollow polylactic acid fibers. This invention uses a combination of hollow polylactic acid fibers and non-hollow polylactic acid fibers, which is beneficial to improve resilience and shape retention while ensuring good warmth retention.

[0025] Furthermore, the needle-punching process in this invention includes a hydrophilic treatment, which is applied to the lower surface of the unidirectional moisture-wicking and heat-insulating polylactic acid (PLA) wadding. The lower surface of the unidirectional moisture-wicking and heat-insulating PLA wadding in this invention has large pores; the hydrophilic treatment helps to improve moisture wicking capacity and maintain good heat-insulating performance. Attached Figure Description

[0026] Figure 1This is a diagram illustrating the structure and working principle of the unidirectional moisture-wicking and heat-insulating polylactic acid flocculant in this invention. Detailed Implementation

[0027] This invention provides a unidirectional moisture-wicking and heat-insulating polylactic acid (PLA) wadding, which is obtained by needle punching a fiber web. The raw material for preparing the fiber web includes hollow PLA fibers. The pore size increases from the upper surface to the lower surface of the unidirectional moisture-wicking and heat-insulating PLA wadding.

[0028] The unidirectional moisture-wicking and heat-insulating polylactic acid (PLA) wadding of this invention is obtained by needle punching a fiber web, the raw material of which includes hollow PLA fibers. Preferably, the raw material for preparing the fiber web also includes non-hollow PLA fibers, and the content of non-hollow PLA fibers in the raw material is preferably ≤90wt%. Polylactic acid (PLA) fiber is a completely biodegradable synthetic fiber. Its products, after being discarded, can be decomposed into carbon dioxide and water in soil or seawater through microbial action. It does not emit toxic gases when burned and does not cause pollution, making it a sustainable ecological fiber. In this invention, the raw material for preparing the fiber web can specifically be only hollow PLA fibers, or only hollow PLA fibers and non-hollow PLA fibers. Needle punching achieves bonding without the need for glue or ES fibers, and no other materials are added, which facilitates recycling and meets green environmental protection requirements. In this invention, specifically, the hollow polylactic acid fiber content in the unidirectional moisture-wicking and heat-insulating polylactic acid wadding is preferably 10-100 wt%, specifically 10 wt%, 20 wt%, 30 wt%, 40 wt%, 50 wt%, 60 wt%, 70 wt%, 80 wt%, 90 wt%, or 100 wt%.

[0029] In this invention, the cross-sections of both the hollow polylactic acid (PLA) fibers and the non-hollow PLA fibers are preferably circular. The specifications of the hollow PLA fibers include: a fineness preferably of 2.5–7D, more preferably 2.5–5D, and even more preferably 2.5–3.5D; a length preferably of 38–105 mm, more preferably 55–75 mm, and even more preferably 65 mm; and a hollowness preferably of 15–25%, more preferably 18–22%, and even more preferably 20%. The specifications of the non-hollow PLA fibers include: a fineness preferably of 0.8–7D, more preferably 1.5–4.5D, and even more preferably 1.5–3D; and a length preferably of 38–105 mm, more preferably 45–60 mm, and even more preferably 51 mm. In this invention, the hollow polylactic acid fiber preferably has a crimp count of 3 to 12 crimps / inch, more preferably 6.3 crimps / inch; the non-hollow polylactic acid fiber preferably has a crimp count of 3 to 12 crimps / inch, more preferably 4.7 crimps / inch. In this invention, the crimp count is an experimental test value, generally calculated based on the crimp count for a fiber length of 10 cm, with multiple sets averaged and one significant figure retained.

[0030] In this invention, the pore size increases from the upper surface to the lower surface of the unidirectional moisture-wicking and heat-insulating polylactic acid (PLA) wadding. The PLA wadding is a heterogeneous wadding with a porous structure of varying density, and the pore size increases from the upper surface to the lower surface. Macroscopically, it includes a dense layer (upper surface) and a sparse layer (lower surface). The unidirectional moisture-wicking effect is based on the difference between the amount of moisture wicked from the sparse layer to the dense layer (larger) and the amount of moisture wicked from the dense layer to the sparse layer (smaller); the greater the difference, the better the unidirectional moisture-wicking effect.

[0031] In this invention, the needle-punching process preferably includes a hydrophilic treatment, which is applied to the lower surface of the unidirectional moisture-wicking and heat-insulating polylactic acid (PLA) wadding. The lower surface of the unidirectional moisture-wicking and heat-insulating PLA wadding has large pores; the hydrophilic treatment helps to improve its moisture-wicking capacity.

[0032] In this invention, the amount of moisture conducted from the lower surface to the upper surface of the unidirectional moisture-wicking and heat-insulating polylactic acid (PLA) wadding is denoted as A1, and the amount of moisture conducted from the upper surface to the lower surface is denoted as A2. Specifically, the unidirectional moisture-wicking effect is evaluated by the ratio of the difference between A1 and A2 to A1, i.e., the rate of change in moisture conduction. Specifically, in this invention, the rate of change in moisture conduction of the unidirectional moisture-wicking and heat-insulating PLA wadding is calculated according to the formula shown in Equation I:

[0033] A=(A1-A2) / A1×100% Formula I;

[0034] In Formula I, A is the rate of change of moisture conduction of the unidirectional moisture-conducting and heat-insulating polylactic acid flocculant, A1 is the moisture conduction from the lower surface to the upper surface, and A2 is the moisture conduction from the upper surface to the lower surface.

[0035] In this invention, the moisture conduction change rate of the unidirectional moisture-wicking and heat-insulating polylactic acid flocculant is preferably 3-30%, more preferably 5-30%, further preferably 8-30%, even more preferably 10-30%, and still more preferably 12-30%; the greater the moisture conduction change rate, the better the unidirectional moisture-wicking effect of the unidirectional moisture-wicking and heat-insulating polylactic acid flocculant.

[0036] In this invention, the areal density of the unidirectional moisture-wicking and heat-insulating polylactic acid flocculant is preferably 30-350 g / m³. 2 More preferably 50–240 g / m 2 More preferably 90–180 g / m 2 More preferably, it is 100-120 g / m 2 The thickness is preferably 3 to 25 mm, more preferably 6.9 to 11.3 mm, even more preferably 7.6 to 10.1 mm, and even more preferably 8.0 to 9.0 mm.

[0037] This invention provides a method for preparing the unidirectional moisture-wicking and heat-insulating polylactic acid flocculant described in the above technical solution, comprising the following steps:

[0038] A fiber web is provided, wherein the raw material for preparing the fiber web includes hollow polylactic acid fibers;

[0039] The fiber web is needle-punched to obtain a unidirectional moisture-wicking and heat-insulating polylactic acid (PLA) wadding with pore size increasing from the upper surface to the lower surface. The needle-punching includes upper needle plate needle-punching and lower needle plate needle-punching, or only upper needle plate needle-punching. The needle-punching conditions include: the needles in each row of the upper needle plate needle-punching are not evenly spaced, and the needle-punching depth varies; the needles in each row of the lower needle plate needle-punching are not evenly spaced, and the needle-punching depth varies; and the number of rows of lower needle plate needle-punching is less than the number of rows of upper needle plate needle-punching, the total needle-punching density of the lower needle plate is less than the total needle-punching density of the upper needle plate, the maximum needle-punching depth of both the lower and upper needle plate needle-punching is 1 / 2 the thickness of the unidirectional moisture-wicking and heat-insulating PLA wadding, and the sum of the needle-punching depths of the lower and upper needle plate needle-punching is less than the thickness of the unidirectional moisture-wicking and heat-insulating PLA wadding.

[0040] This invention provides a fiber web, the raw material for which includes hollow polylactic acid (PLA) fibers, preferably only hollow PLA fibers, or a mixture of hollow PLA fibers and non-hollow PLA fibers. Preferably, the raw material is sequentially opened, carded, and laid into a web to obtain the fiber web. In this invention, the opening is preferably performed in an opening machine, specifically by feeding the raw material into the opening machine to open it, causing large fiber clumps and bundles to disintegrate, while simultaneously ensuring a uniform mixture of the various fiber components in the raw material. Specifically, the opening process aims to achieve uniform mixing and thorough opening of the raw material while minimizing fiber damage. In this invention, after opening in the opening machine, the raw material may still contain fiber clumps or bundles, and the fiber arrangement may be relatively disordered. In this case, carding is required to further loosen the opened fiber aggregates, increasing fiber separation while minimizing fiber damage, forming single fiber bundles, and further refining and arranging the fibers. The fiber web is then laid into a web. In this invention, the preferred method of web laying is cross-laying. This invention preferably improves the transverse strength of the fiber web by adjusting the fiber stacking direction to achieve cross-laying, thus resulting in good fiber web uniformity. This invention does not impose special limitations on the specific operation steps and process parameters of opening, carding, and web laying; any technical solution well-known to those skilled in the art can be used. In the embodiments of this invention, the important process parameters for opening and carding are shown in Table 1 (listed in the embodiments).

[0041] After obtaining the fiber web, the present invention needles the fiber web to obtain a unidirectional moisture-wicking and heat-insulating polylactic acid (PLA) wadding with pore size increasing from the upper surface to the lower surface. The needle wicking includes upper needle plate needle wicking and lower needle plate needle wicking, or only upper needle plate needle wicking. The needle wicking conditions include: the needles in each row of the upper needle plate needle wicking are not evenly spaced, and the needle wicking depth varies; the needles in each row of the lower needle plate needle wicking are not evenly spaced, and the needle wicking depth varies; and the number of rows of the lower needle plate needle wicking is less than the number of rows of the upper needle plate needle wicking, the total needle density of the lower needle plate needle wicking is less than the total needle density of the upper needle plate needle wicking, the maximum needle wicking depth of both the lower and upper needle plate needle wicking is 1 / 2 the thickness of the unidirectional moisture-wicking and heat-insulating PLA wadding, and the sum of the needle wicking depths of the lower and upper needle plate needle wicking is less than the thickness of the unidirectional moisture-wicking and heat-insulating PLA wadding.

[0042] In the acupuncture process described in this invention, the number of needle passes on the lower needle plate is less than the number of needle passes on the upper needle plate, and the difference between the two is preferably 1, 2, or 3. In this invention, the number of needle passes on the upper needle plate is preferably 1 to 3, specifically 1, 2, or 3; the number of needle passes on the lower needle plate is preferably 0 to 2, specifically 0, 1, or 2. In the acupuncture process described in this invention, the total density of needle passes on the lower needle plate is less than the total density of needle passes on the upper needle plate. The total density of needle passes on the lower needle plate is preferably no more than 50% of the total density of needle passes on the upper needle plate, more preferably no more than 35% of the total density of needle passes on the upper needle plate, and even more preferably no more than 30% of the total density of needle passes on the upper needle plate. Specifically, the needle density per pass on the upper needle plate is preferably 6 to 18 needles / cm. 2 More preferably, 8-12 stitches / cm 2 If the needle density of each needle on the upper needle plate is too high, the flocculent fibers are prone to clumping and have poor fluffiness; if the density is too low, the flocculent fibers are not firmly bonded and are prone to scattering. This invention controls the number of needles on the lower needle plate to be less than the number of needles on the upper needle plate, and controls the total needle density of the lower needle plate to be less than the total needle density of the upper needle plate, so that the unidirectional moisture-wicking and heat-insulating polylactic acid flocculent fibers have a dense-sparse structure, which helps to ensure that they have better unidirectional moisture-wicking and heat-insulating performance.

[0043] In the acupuncture process described in this invention, the needles in each row of the upper needle plate acupuncture are arranged with unequal density. Preferably, each row of needles in the upper needle plate acupuncture has 2 to 6 rows of independent space, specifically 2, 3, 4, 5, or 6 rows. Similarly, the needles in each row of the lower needle plate acupuncture are arranged with unequal density. Preferably, each row of needles in the lower needle plate acupuncture has 6 to 10 rows of independent space, specifically 6, 7, 8, 9, or 10 rows. This invention controls the unequal density of needles in both the upper and lower needle plate acupuncture, preventing the flocculent material from disintegrating and ensuring a better unidirectional moisture-wicking effect.

[0044] In the needle-punching process described in this invention, the needle-punching depth of the upper needle plate is different, wherein the difference in needle-punching depth of the upper needle plate is preferably 0.5–4.5 mm, more preferably 1.5–3.5 mm; the needle-punching depth of the lower needle plate is also different, wherein the difference in needle-punching depth of the lower needle plate is preferably 0.5–2 mm, more preferably 0.5–1.5 mm. This invention controls the difference in needle-punching depth between the upper and lower needle plates, which improves the bonding strength between the upper and lower surfaces, and facilitates the fabrication of outdoor sportswear through sewing.

[0045] In this invention, when the number of needles on the lower needle plate is not zero, the needles on the lower needle plate and the needles on the upper needle plate are misaligned. In this invention, the maximum piercing depth of both the lower and upper needle plate needles is half the thickness of the unidirectional moisture-wicking and heat-insulating polylactic acid (PLA) wadding. The sum of the piercing depths of the lower and upper needle plate needles is less than the thickness of the unidirectional moisture-wicking and heat-insulating PLA wadding, meaning it cannot pierce the PLA wadding to form convection channels, thus affecting its heat retention.

[0046] In this invention, the needle-punching process preferably further includes: hydrophilic treatment of the lower surface of the resulting floc precursor to obtain a unidirectional moisture-wicking and heat-insulating polylactic acid floc. In this invention, the hydrophilic treatment is preferably corona treatment; the voltage of the corona treatment is preferably 6–12 kV, more preferably 10–12 kV; the time is preferably 3–10 s, more preferably 4–8 s. This invention preferably performs corona treatment under the above conditions, which increases the adhesion of hollow polylactic acid fibers and non-hollow polylactic acid fibers to water and vapor, facilitating water molecule adsorption, improving hydrophilicity, and thus enhancing the unidirectional moisture-wicking effect.

[0047] This invention provides the application of the unidirectional moisture-wicking and heat-insulating polylactic acid (PLA) flocculant described in the above-described technical solution, or the unidirectional moisture-wicking and heat-insulating PLA flocculant prepared by the preparation method described in the above-described technical solution, in the preparation of outdoor sportswear. In this invention, the outdoor sportswear is preferably winter outdoor sportswear.

[0048] Figure 1 This is a diagram illustrating the structure and working principle of the unidirectional moisture-wicking and heat-insulating polylactic acid flocculant in this invention. Figure 1 As can be seen, the lower surface of the wadding is the layer closest to the human body, while the upper surface has loosely arranged fibers with larger pores, called the sparse layer. This facilitates the adsorption, storage, and transfer of liquid water and vapor. After hydrophilic treatment, the adsorption and storage capacity increases, allowing for the rapid absorption of sweat and vapor produced after exercise, keeping the skin dry. The upper surface has denser fibers with smaller pores, called the dense layer, which is beneficial for warmth retention. The sparse fibers on the side closest to the human body absorb heat energy from the body and transfer it to the dense layer, forming a temperature gradient. At the same time, after the body sweats, water and vapor form a humidity potential energy gradient, accelerating the movement of water molecules and facilitating the transfer of water and vapor outward from the body. Therefore, the sparse-dense layer structure of the wadding can achieve unidirectional moisture wicking.

[0049] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0050] The hollow polylactic acid (PLA) fibers used in the following embodiments and comparative examples of this invention have the following specifications: a fineness of 3.5D, a length of 65mm, a hollowness of 20%, and a crimp count of 6.3 crimps / inch (average); the non-hollow PLA fibers have the following specifications: a fineness of 3D, a length of 51mm, and a crimp count of 4.7 crimps / inch (average); both the hollow PLA fibers and the non-hollow PLA fibers have circular cross-sections.

[0051] Examples 1-7

[0052] The raw materials for preparing the fiber web are sequentially opened, combed, and cross-laid to obtain the fiber web;

[0053] The fiber web was needle-punched to obtain unidirectional moisture-wicking and heat-insulating polylactic acid flocculent sheets with increasing pore size from the upper surface to the lower surface. The samples were numbered sequentially from 1 to 7.

[0054] Examples 8-14

[0055] Needle punching was performed according to the methods of Examples 1 to 7 to obtain floc precursors with increasing pore size from the upper surface to the lower surface. Then, the lower surface of the floc precursors was subjected to corona treatment to obtain unidirectional moisture-wicking and heat-insulating polylactic acid flocs. The samples were numbered 1# to 7# in sequence.

[0056] Example 15

[0057] Polylactic acid flocs were prepared according to the method of Example 8, except for the raw materials used, the needle punching process, and the corona treatment conditions; the sample number of the polylactic acid flocs prepared in Example 15 is recorded as 15.

[0058] Comparative Examples 1-2

[0059] Polylactic acid flocs were prepared according to the method of Example 1, except for the raw materials used and the needle punching process; the polylactic acid flocs prepared in Comparative Examples 1 and 2 were numbered A and B respectively.

[0060] The opening and combing process parameters involved in each embodiment and comparative example are listed in Table 1. The parameters corresponding to different needle punching processes are listed in Table 2. The raw material ratio, needle punching process, and corona treatment conditions of the polylactic acid flocs in each embodiment and comparative example are listed in Table 3. The index parameters of the polylactic acid flocs in each embodiment and comparative example are listed in Table 4.

[0061] Table 1. Opening and carding process parameters in the examples and comparative examples.

[0062]

[0063] Table 2 Parameters corresponding to different acupuncture techniques

[0064]

[0065]

[0066] Table 3 shows the raw material ratios, needle punching process, and corona treatment conditions used in the examples and comparative examples.

[0067]

[0068]

[0069] Table 4. Indicators of polylactic acid flocculants in the examples and comparative examples.

[0070]

[0071]

[0072] In Table 4, the Clo value (CLO) is an engineering unit describing the thermal insulation performance of clothing or fabrics, i.e., "thermal resistance." The size of the Clo value indicates the degree of thermal insulation of the fabric. Thermal resistance reflects the ability to prevent heat transfer; a higher thermal resistance indicates better insulation. The change rate of moisture conduction refers to the percentage of the difference between the moisture conduction from the loose layer to the dense layer (higher) and the moisture conduction from the dense layer to the loose layer (lower), relative to the moisture conduction from the loose layer to the dense layer (higher). This reflects a difference in the direction of moisture conduction within the wadding, demonstrating the advantage of moisture conduction from the loose layer to the dense layer, i.e., a unidirectional moisture conduction effect.

[0073] Table 4 shows that the use of hollow PLA fibers can improve the warmth retention of the wadding, as evidenced by an increased CLO value. However, it also results in a bulkier and thicker wadding, leading to a bloated appearance in garments. For example, sample 1 has a high CLO value of 3.18509 and a high loft of 63.8 cm⁻¹. 3 / g; Non-hollow PLA fibers are less effective at insulating heat than hollow PLA fibers when used for wadding. For example, in sample 3, after adding 70% non-hollow PLA fibers, the CLO value decreased to 2.01735, and the loft also decreased to 47.1cm. 3 / g, but the compression resilience is not significantly different from that of hollow PLA fibers. This invention uses a combination of hollow PLA fibers and non-hollow PLA fibers, which helps to improve resilience and shape retention while ensuring good warmth retention of the wadding.

[0074] Furthermore, as shown in Table 4, the needle-punching process also affects the performance of the wadding. Higher needle-punching density and more needles result in more needles per unit area, leading to a thicker wadding. This also increases the number of needle-punched holes. Generally, the thicker the wadding, the better the insulation effect. The number of needle-punched holes affects the CLO value; for example, sample 5 has a CLO of 2.55141 and a loft of 53.7 cm⁻¹. 3 / g, the bulkiness decreases with increasing needle-punching density and number of needle punches. Furthermore, the needle-punching depth also affects the bulkiness of the flocs; for example, the bulkiness of samples 3 and 6 is 47.1 cm⁻¹. 3 / g and 49.2cm 3 / g. In addition, the total density difference between the upper and lower needle plates and the needle depth (the sum of the needle depths of the lower and upper needle plates) also affect the unidirectional moisture conduction effect. For example, the moisture conduction change rates of sample 1 and sample 3 were 12.83% and 6.10%, respectively.

[0075] Furthermore, as shown in Table 4, hydrophilic treatment is beneficial for improving the one-way moisture-wicking effect and thermal insulation performance of polylactic acid (PLA) flocs. Specifically, the one-way moisture-wicking and thermal insulation PLA flocs prepared in the embodiments of this invention have large pores on the lower surface. Corona treatment is beneficial for improving moisture wicking and maintaining good thermal insulation performance. For example, the moisture wicking change rate of sample 15 is 11.83%, and the CLO value is 3.51709, indicating that both one-way moisture wicking and thermal insulation performance remain at a high level.

[0076] Comparative Example 3

[0077] Homogeneous polylactic acid flocculent sheets, denoted as sample C, were prepared by needle punching process ⑤ using 100% non-hollow PLA fiber as raw material.

[0078] Comparative Example 4

[0079] Using 100% non-hollow PLA fiber as raw material, two layers of polylactic acid flocs were prepared by needle punching process ⑤. The two layers of polylactic acid flocs were stacked and placed together, and this was denoted as sample D.

[0080] The parameters of the polylactic acid flocs prepared in Comparative Examples 3 and 4 are listed in Tables 5 and 6.

[0081] Table 5. Specifications of polylactic acid flocs prepared in Comparative Examples 3 and 4

[0082]

[0083] Table 6. Specifications of polylactic acid flocs prepared in Comparative Examples 3 and 4

[0084]

[0085] As shown in Tables 5 and 6, Sample C is a homogeneous polylactic acid sheet, which does not have a one-way moisture-wicking effect and its warmth retention is also worse than that of Sample 1; Sample D uses two 60g / m² sheets. 2The composite polylactic acid flocs (layered) produced by this method also showed poorer unidirectional moisture-wicking and heat-insulating properties compared to sample 1. This indicates that, for flocs made from the same raw materials and with the same areal density, whether it is a homogeneous polylactic acid floc or a composite polylactic acid floc made by combining two flocs, the unidirectional moisture-wicking and heat-insulating properties are inferior to those of the unidirectional moisture-wicking and heat-insulating polylactic acid flocs prepared by the method of this invention.

[0086] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a unidirectional moisture-wicking and heat-insulating polylactic acid flocculant, characterized in that, Includes the following steps: Provide a fiber web, wherein the raw material for preparing the fiber web is only hollow polylactic acid fiber, or a mixture of hollow polylactic acid fiber and non-hollow polylactic acid fiber; The fiber web is needle-punched to obtain a unidirectional moisture-wicking and heat-insulating polylactic acid (PLA) wadding with pore size increasing from the upper surface to the lower surface. The needle-punching includes upper and lower needle plate needle-punching, or only upper needle plate needle-punching. The needle-punching conditions include: the needles in each pass of the upper needle plate needle-punching are not evenly spaced, and the needle-punching depth varies; the needles in each pass of the lower needle plate needle-punching are not evenly spaced, and the needle-punching depth varies; and the number of passes of the lower needle plate needle-punching is less than the number of passes of the upper needle plate needle-punching, and the total needle-punching density of the lower needle plate is less than the total needle-punching density of the upper needle plate needle-punching. The maximum needle penetration depth of both the upper and lower needle plates is half the thickness of the unidirectional moisture-wicking and heat-insulating polylactic acid (PLA) wadding. The sum of the needle penetration depths of the upper and lower needle plates is less than the thickness of the unidirectional moisture-wicking and heat-insulating PLA wadding. The upper needle plate has 1 to 3 needle passes, and the lower needle plate has 0 to 2 needle passes. The total needle density of the lower needle plate is less than that of the upper needle plate, and the total needle density of the lower needle plate does not exceed 50% of the total needle density of the upper needle plate. The needle density per pass on the upper needle plate is 6 to 18 needles / cm. 2 Each needle in the upper needle plate is arranged with 2-6 rows of needles, and each needle in the lower needle plate is arranged with 6-10 rows of needles. The needle depth difference of the upper needle plate is 0.5-4.5 mm, and the needle depth difference of the lower needle plate is 0.5-2 mm. The process after needle puncture also includes: subjecting the lower surface of the flocculation precursor obtained after needle puncture to corona treatment, wherein the voltage of the corona treatment is 6~12kV, to obtain the unidirectional moisture-wicking and heat-insulating polylactic acid flocculation; the pore size increases from the upper surface to the lower surface of the unidirectional moisture-wicking and heat-insulating polylactic acid flocculation.

2. The preparation method according to claim 1, characterized in that, The raw materials for preparation also include non-hollow polylactic acid fibers, and the content of non-hollow polylactic acid fibers in the raw materials is ≤90wt%.

3. The preparation method according to claim 2, characterized in that, The hollow polylactic acid fiber has the following specifications: fineness of 2.5~7D, length of 38~105mm, and hollowness of 15~25%; the non-hollow polylactic acid fiber has the following specifications: fineness of 0.8~7D, and length of 38~105mm.

4. The preparation method according to any one of claims 1 to 3, characterized in that, The areal density of the unidirectional moisture-wicking and heat-insulating polylactic acid flocculant is 30~350 g / m³. 2 The thickness is 3~25mm; The moisture conductivity change rate of the unidirectional moisture-wicking and heat-insulating polylactic acid (PLA) wadding is 3-30%, and the moisture conductivity change rate of the unidirectional moisture-wicking and heat-insulating PLA wadding is calculated according to the formula shown in Equation I: A=(A1-A2) / A1×100% formula I; In Formula I, A is the rate of change of moisture conduction of the unidirectional moisture-conducting and heat-insulating polylactic acid wadding, A1 is the amount of moisture conducted from the lower surface to the upper surface, and A2 is the amount of moisture conducted from the upper surface to the lower surface.

5. The preparation method according to claim 1, characterized in that, The corona treatment time is 3~10s.

6. The application of the unidirectional moisture-wicking and heat-insulating polylactic acid flocculant prepared by the preparation method according to any one of claims 1 to 5 in the preparation of outdoor sportswear.

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