A polylactic acid blend composition and its preparation method

Abstract

The present invention provides a polylactic acid blend composition and a preparation method thereof, as well as a flame-retardant polylactic acid fiber spun from the composition. The polylactic acid blend composition is prepared by blending raw materials including polylactic acid and a phosphorus-containing flame retardant. The addition of the phosphorus-containing flame retardant not only endows polylactic acid with good flame-retardant properties, but also improves the melt fluidity of polylactic acid, greatly reduces the spinning temperature and fineness of polylactic acid, and at the same time, the polylactic acid fiber prepared therefrom still has good mechanical properties.

Description

Technical Field

[0001] The present invention belongs to the technical field of polylactic acid materials, and particularly relates to a polylactic acid blend composition, a heat-resistant flame-retardant polylactic acid fiber and a preparation method thereof. Background Art

[0002] As a biobased polymer, poly-L-lactic acid (PLLA) has a very wide range of application fields. At the beginning of its discovery, the application of PLLA focused on the biodegradable field, such as disposable medical supplies, disposable tableware, personal care hygiene materials, textile clothing, agriculture and packaging materials, etc. Especially after the country prohibited the use of non-degradable garbage bags and packaging materials, the consumption increased rapidly. The limiting oxygen index (LOI) of PLLA is about 19, which is relatively flammable. The flammability problem of its products as materials is related to storage safety, production and life safety and people's health. Therefore, it is urgent to solve the flame retardancy problem of PLLA.

[0003] In recent years, researchers have tried various methods to improve the flame retardant performance of PLLA. For example, nano-inorganic flame retardants, phosphorus-based flame retardants and intumescent flame retardants are often used as flame retardant modifiers for PLLA, and some new effective flame retardant systems have also been developed. Grégory Stoclet et al. added 17 wt% halloysite to PLLA and reduced the peak heat release rate (pHRR) of PLLA by 40%. Lei Song et al. found the synergistic effect of intumescent flame retardants (pentaerythritol phosphate (PEPA) and melamine phosphate (MP)) and polyhedral oligomeric silsesquioxane (POSS) on the PLLA matrix. Only 25 wt% of the IFR material made PLLA reach the V-1 grade, while PLLA with 20 wt% of IFR plus 5 wt% of POSS passed the UL94 V-0 grade. PingWei et al. added 5 wt% of sulfuric acid intercalated modified expanded graphite to PLLA, and then PLLA / CEPPA passed the UL94 V-0 grade. Qian Yong et al. added 0.5 wt% of flame retardant (Al-SBA-15) to PLLA and it passed the UL94 V-0 grade, and the LOI reached 30%. Wang et al. synthesized flame retardant PPLA through the chain growth reaction of a dihydroxy-terminated prepolymer (lactic acid) using ethyl dichlorophosphate as a chain extender. Adding 5 wt% of PPLA can endow PLLA with a 25% LOI value and the UL94 V-0 grade.

[0004] However, adding a large amount of flame retardant will have a greater impact on the mechanical properties and processability of the polymer. Therefore, how to balance the flame retardancy and processability of PLLA so that its processability is not reduced while improving the flame retardancy has become a problem to be solved at present. Summary of the Invention

[0005] Based on the above technical background, the inventor made unremitting efforts and found that: the polylactic acid blend composition obtained by adding a phosphorus-containing flame retardant to polylactic acid not only has good flame retardancy, but also has better melt fluidity than the melt of polylactic acid without the addition of the phosphorus-containing flame retardant, so that its spinning temperature is lower than that of polylactic acid. At the same time, compared with polylactic acid, the mechanical properties of the polylactic acid blend composition and the flame-retardant polylactic acid fiber prepared therefrom have not changed significantly, and it has good fineness and mechanical properties, thus completing the present invention.

[0006] The first aspect of the present invention is to provide a polylactic acid blend composition, which comprises polylactic acid and a phosphorus-containing flame retardant;

[0007] The mass ratio of the phosphorus-containing flame retardant to polylactic acid is (0.1-30):(70-200).

[0008] The second aspect of the present invention is to provide a method for preparing the flame-retardant polylactic acid fiber described in the first aspect of the present invention, and the preparation method comprises the following steps:

[0009] Step 1: Blend polylactic acid and a phosphorus-containing flame retardant to obtain a flame-retardant polylactic acid masterbatch;

[0010] Step 2: Mix the flame-retardant polylactic acid masterbatch, PLLA / ZnO masterbatch and PLLA to obtain a polylactic acid blend composition.

[0011] The third aspect of the present invention is to provide a flame-retardant polylactic acid fiber, which is prepared by spinning the polylactic acid blend composition described in the first aspect of the present invention or the polylactic acid blend composition prepared according to the preparation method described in the second aspect of the present invention.

[0012] The polylactic acid blend composition, heat-resistant flame-retardant polylactic acid fiber and preparation method thereof provided by the present invention have the following advantages:

[0013] (1) In the present invention, blending a phosphorus-containing flame retardant with polylactic acid not only improves the flame retardancy of polylactic acid, but also improves the melt fluidity of polylactic acid, and reduces the spinning temperature of polylactic acid;

[0014] (2) The heat-resistant flame-retardant polylactic acid fiber prepared from the polylactic acid blend composition has a lower fineness and excellent antibacterial properties. Description of the Drawings

[0015] Figure 1 DSC test spectra showing the heating process of PLLA, CEPPA and the polylactic acid blend compositions prepared in Examples 1-7;

[0016] Figure 2 DSC test spectra showing the cooling process of PLLA, CEPPA and the polylactic acid blend compositions prepared in Examples 1-7;

[0017] Figure 3 Show the DSC test spectra of the fibers prepared from PLLA, CEPPA, Example 8 and Example 12 during the heating process;

[0018] Figure 4 Show the DSC test spectra of the fibers prepared from PLLA, CEPPA, Example 8 and Example 12 during the cooling process;

[0019] Figure 5 Show the TGA test spectra of CEPPA, PLLA, Example 2, Example 4 and Example 6;

[0020] Figure 6 Show the graph of the heat release rate varying with time of the polylactic acid blend composition prepared from PLLA, Example 5 and Example 7;

[0021] Figure 7 Show the graph of the total heat release varying with time of the polylactic acid blend composition prepared from PLLA, Example 5 and Example 7;

[0022] Figure 8 Show the graph of the total smoke release varying with time of the polylactic acid blend composition prepared from PLLA, Example 5 and Example 7;

[0023] Figure 9 Show the photos of the cone calorimeter residue of PLLA;

[0024] Figure 10 Show the photos of the cone calorimeter residue of the polylactic acid blend composition prepared from Example 5;

[0025] Figure 11 Show the photos of the cone calorimeter residue of the polylactic acid blend composition prepared from Example 7. Detailed implementation manners

[0026] The present invention will be described in detail below, and the features and advantages of the present invention will become clearer and more definite along with these descriptions.

[0027] The first aspect of the present invention lies in providing a polylactic acid blend composition, which comprises polylactic acid and a phosphorus-containing flame retardant.

[0028] In the present invention, the polylactic acid is L-polylactic acid.

[0029] The phosphorus-containing flame retardant is selected from one or more of diethyl ethylphosphonate, resorcinol bis(di(2,6-dimethylphenyl)phosphate), pentaerythritol phosphate, 2-carboxyethylphenylphosphinic acid (CEPPA), and tris(2,3-dibromopropyl) phosphate. Through experiments, it is found that the addition of the above phosphorus-containing flame retardants can not only improve the flame retardancy of polylactic acid, but also plasticize polylactic acid, improve the melt fluidity of polylactic acid, reduce the spinning temperature of polylactic acid, reduce energy consumption, facilitate the increase of the spinning speed, increase the production capacity per unit time, save costs. At the same time, the addition of this phosphorus-containing flame retardant will not reduce the mechanical properties of the polylactic acid fiber obtained by spinning, and has good application prospects.

[0030] Preferably, the phosphorus-containing flame retardant is selected from one or more of diethyl ethylphosphonate, pentaerythritol phosphate, and 2-carboxyethylphenylphosphinic acid, and more preferably 2-carboxyethylphenylphosphinic acid.

[0031] During the combustion process of polylactic acid, 2-carboxyethylphenylphosphinic acid (CEPPA) can act simultaneously in the gas phase and the condensed phase. In the gas phase, it generates free radical scavengers to inhibit the further occurrence of combustion. In the condensed phase, it promotes carbonization to form a closed carbon layer, slowing down the mass transfer and heat transfer between the flame and the polylactic acid matrix, achieving the purpose of inhibiting combustion. Especially the addition of CEPPA will not only improve the flame retardancy effect, but also will not reduce the mechanical properties of the polylactic acid fiber. At the same time, it has a good plasticizing effect on polylactic acid and can effectively reduce the spinning temperature of polylactic acid.

[0032] The mass ratio of the phosphorus-containing flame retardant to polylactic acid is (0.1 - 30):(70 - 200), preferably (0.15 - 20):(80 - 150), and more preferably (0.2 - 10):(90 - 100).

[0033] Too much addition of the phosphorus-containing flame retardant will not only affect its flame retardancy effect on polylactic acid, but also reduce the mechanical properties of the polylactic acid fiber. Through experiments, it is found that when the addition amount of the phosphorus-containing flame retardant exceeds the above range, the breaking strength and elongation at break of polylactic acid decrease. While within the above range, due to the crystallization-promoting effect of the above phosphorus-containing flame retardant, the crystallinity of polylactic acid increases, which can improve the flame retardancy of the polylactic acid fiber without reducing its mechanical properties, and at the same time reduce the spinning temperature. It is found through experiments that when the addition amount of the phosphorus-containing flame retardant is within the above range, the spinning temperature of polylactic acid can be reduced by 5 - 30 °C.

[0034] In the present invention, the raw materials further include zinc oxide. Adding an appropriate amount of zinc oxide to polylactic acid can not only improve the mechanical properties of polylactic acid, but also be beneficial to improving the antibacterial property of the polylactic acid textile material prepared therefrom. After adding zinc oxide, the antibacterial rates against Escherichia coli and Staphylococcus aureus can reach more than 90%.

[0035] The mass ratio of the zinc oxide to the polylactic acid is 1:(500 - 700), preferably 1:(550 - 650), and more preferably 1:(570 - 600).

[0036] The polylactic acid blend composition of the present invention is prepared by blending raw materials including polylactic acid and a phosphorus-containing flame retardant.

[0037] According to a preferred embodiment of the present invention, the polylactic acid blend composition of the present invention is prepared by blending polylactic acid and a phosphorus-containing flame retardant to obtain a masterbatch, and then mixing it with a PLLA / ZnO masterbatch and PLLA. By blending with the phosphorus-containing flame retardant first and then mixing with the PLLA / ZnO masterbatch and PLLA, the phosphorus-containing flame retardant and polylactic acid can be more evenly mixed and have better compatibility.

[0038] The blending of polylactic acid and the phosphorus-containing flame retardant is preferably carried out in a twin-screw extruder, and the temperatures in each blending zone are (180 - 220)°C - (170 - 210)°C - (160 - 200)°C - (150 - 190)°C - (150 - 170)°C - (140 - 160)°C.

[0039] According to the present invention, the mixing is preferably carried out in a single-screw extruder, and the temperatures in each zone of the single-screw extruder are (140 - 200)°C - (170 - 210)°C - (170 - 220)°C - (180 - 220)°C.

[0040] The limiting oxygen index of the polylactic acid blend composition of the present invention is 22% - 35%, and the UL-94 can reach V0 grade at most. The spinning temperature of the polylactic acid blend composition is 5 - 30°C lower than that of polylactic acid. Moreover, the fibers obtained by spinning the polylactic acid blend composition have mechanical properties equivalent to those of polylactic acid fibers, greatly reducing the preparation cost and energy consumption of polylactic acid fibers.

[0041] The second aspect of the present invention is to provide a method for preparing the flame-retardant polylactic acid fiber described in the first aspect of the present invention, and the preparation method includes the following steps:

[0042] Step 1: Blend polylactic acid and a phosphorus-containing flame retardant to obtain a flame-retardant polylactic acid masterbatch;

[0043] Step 2: Mix the flame-retardant polylactic acid masterbatch, PLLA / ZnO masterbatch and PLLA to obtain a polylactic acid blend composition.

[0044] The following is a specific description and explanation of this step.

[0045] Step 1: Blend polylactic acid and a phosphorus-containing flame retardant to obtain a flame-retardant polylactic acid masterbatch.

[0046] The phosphorus-containing flame retardant is selected from one or more of diethyl ethylphosphonate, resorcinol bis(di(2,6-dimethylphenyl)phosphate), pentaerythritol phosphate, 2-carboxyethylphenylphosphinic acid (CEPPA), and tris(2,3-dibromopropyl) phosphate, preferably selected from one or more of diethyl ethylphosphonate, pentaerythritol phosphate, and 2-carboxyethylphenylphosphinic acid, and more preferably 2-carboxyethylphenylphosphinic acid.

[0047] The addition of the phosphorus-containing flame retardant can not only improve the flame retardancy of polylactic acid but also improve the melt fluidity of polylactic acid, acting as a plasticizer. Among them, CEPPA has the best flame retardancy and plasticizing effect on polylactic acid.

[0048] The mass ratio of the phosphorus-containing flame retardant to polylactic acid is (0.1 - 0.6):1, preferably (0.2 - 0.5):1, and more preferably (0.3 - 0.45):1.

[0049] With the increase in the addition amount of the phosphorus-containing flame retardant, the melt fluidity of polylactic acid gradually increases, its spinning temperature gradually decreases, the spinning speed increases, and at the same time, the limiting oxygen index of polylactic acid increases and the vertical burning performance improves. However, further increasing the amount of the phosphorus-containing flame retardant will reduce the mechanical properties of polylactic acid.

[0050] In the present invention, the blending is carried out in a twin-screw extruder. It is found in the experiment that under the processing conditions of polylactic acid, CEPPA is a liquid and cannot be spun by single-screw conveying, and the CEPPA liquid is difficult to be mixed evenly with polylactic acid chips, resulting in uneven dispersion in PLLA. By using a twin-screw extruder to prepare the flame-retardant polylactic acid masterbatch, the problems of single-screw processing and uneven dispersion are solved.

[0051] The temperatures of each zone in the twin-screw extruder are (180 - 220)°C - (170 - 210)°C - (160 - 200)°C - (150 - 190)°C - (150 - 170)°C - (140 - 160)°C, preferably (190 - 210)°C - (180 - 200)°C - (170 - 190)°C - (160 - 180)°C - (155 - 165)°C - (145 - 155)°C, and more preferably 200°C - 190°C - 180°C - 170°C - 160°C - 150°C.

[0052] The blending time is 1 - 10 min, preferably 1 - 5 min, and more preferably 1 - 3 min.

[0053] The screw speed is 20 - 70 r / min, preferably 40 - 60 r / min, and more preferably 50 r / min.

[0054] The screw speed and blending time can affect the uniformity and compatibility of the mixture of the phosphorus-containing flame retardant and polylactic acid, and further affect the flame retardant and plasticizing effects of the phosphorus-containing flame retardant. If the screw speed is too low and the blending time is too short, the flame retardant and plasticizing effects of the phosphorus-containing flame retardant on polylactic acid are poor. If the screw speed is too high and the blending time is too long, partial degradation of polylactic acid will occur.

[0055] Step 2: Mix the flame-retardant polylactic acid masterbatch, PLLA / ZnO masterbatch and PLLA to obtain a polylactic acid blend composition.

[0056] The PLLA / ZnO masterbatch is purchased from Xi'an Mingbo Chemical Technology Co., Ltd., and the zinc oxide content is 17%. Adding an appropriate amount of zinc oxide to polylactic acid can improve the antibacterial rate of the polylactic acid fiber obtained by spinning the blend composition without reducing other properties of polylactic acid.

[0057] The mass ratio of the flame-retardant polylactic acid masterbatch, PLLA / ZnO masterbatch and PLLA is (0.01 - 30):(0.5 - 10):(60 - 100), preferably the mass ratio is (0.05 - 10):(0.5 - 7):(83 - 99.9), and more preferably the mass ratio is (0.1 - 5):(0.5 - 5):(90 - 99.9).

[0058] In the present invention, the mixing is preferably carried out in a single-screw extruder. The temperatures of each zone in the single-screw extruder are (140 - 200)°C - (170 - 210)°C - (170 - 220)°C - (180 - 220)°C. Preferably, the temperatures of each zone are (150 - 180)°C - (180 - 200)°C - (190 - 210)°C - (190 - 210)°C, and more preferably the temperatures of each zone are 160°C - 190°C - 200°C - 200°C.

[0059] The mixing time is 1 - 10 min, preferably the mixing time is 1 - 5 min, and more preferably the mixing time is 1 - 3 min.

[0060] The mixing temperature and time can affect the homogeneity of the mixture of substances, and further affect their compatibility. The better the compatibility, the better the flame retardant and plasticizing effects of the phosphorus-containing flame retardant on polylactic acid.

[0061] The screw speed is 20 - 100 r / min, preferably 30 - 70 r / min, and more preferably 40 - 50 r / min.

[0062] The third aspect of the present invention is to provide a flame-retardant polylactic acid fiber, which is prepared by spinning the polylactic acid blend composition described in the first aspect of the present invention or the polylactic acid blend composition prepared according to the preparation method described in the second aspect of the present invention.

[0063] Before spinning, the blend composition is preferably dried. The drying temperature is preferably 80-120 °C, more preferably 100 °C, and the drying time is preferably 500-700 min, more preferably 600 min.

[0064] Spinning is preferably carried out in a single-screw spinning machine. The temperatures in each zone of the single-screw spinning machine are (140-180) °C-(170-210) °C-(180-220) °C-(180-220) °C, preferably (150-170) °C-(180-200) °C-(190-210) °C-(190-210) °C, and more preferably 160 °C-190 °C-200 °C-(190-200) °C.

[0065] The temperature of the pipeline is 170-210 °C, preferably 180-205 °C, and more preferably 185-205 °C.

[0066] The temperature of the spinning pack is 170-220 °C, preferably 180-215 °C, and more preferably 181-210 °C.

[0067] The present inventors have found that adding the above-mentioned phosphorus-containing flame retardant, especially CEPPA, to polylactic acid, which has a relatively close melting point to polylactic acid and certain compatibility with polylactic acid. The addition of CEPPA can not only improve the flame retardancy of polylactic acid, but also act as a plasticizer for the polylactic acid melt during the spinning process, reducing the spinning temperature of polylactic acid by 5-30 °C.

[0068] The pressure of the spinning pack is 5.5-7 MPa, preferably 6-7 MPa, and more preferably 6.5 MPa. During the spinning process, adjust the spinning temperature to ensure that the pressure of the spinning pack is about in the above range.

[0069] The winding speed is 800-1200 m / min, preferably 900-1100 m / min, and more preferably 1000 m / min.

[0070] After spinning, the as-spun fibers are preferably drawn using a parallel draw frame. During the drawing process, keep the drawing temperature and speed constant, and adjust the draw ratio to keep the elongation at break at about 30%.

[0071] The draw winding speed is 300-500 m / min, preferably 350-450 m / min, and more preferably 400 m / min.

[0072] The temperatures of the first draw roll, the second draw roll, and the setting box are (60-90) °C-(90-110) °C-(120-150) °C respectively. The preferred temperatures are (70-80) °C-(95-105) °C-(130-145) °C, and the more preferred temperatures are 75 °C-100 °C-140 °C.

[0073] The draft ratio is 2 to 3.5, preferably 2.5 to 3.1.

[0074] The fineness of the flame-retardant polylactic acid fiber described in the present invention is 110 to 135 dtex / 96f, the breaking strength is 2.7 to 3.1 cN / dtex, and the elongation at break is 28 to 35%.

[0075] The beneficial effects of the present invention are as follows:

[0076] (1) The LOI value of the polylactic acid blend composition described in the present invention can reach 32, the burning time of UL-94 with flame is significantly shortened, the flame-retardant level reaches V-0 grade, its ignition time is prolonged, and both the heat release rate and the total amount are significantly reduced;

[0077] (2) The addition of the flame retardant has little effect on the thermal stability of PLLA and the residue amount at 700 °C. After adding the flame retardant, its glass transition temperature, cold crystallization temperature, and thermal crystallization temperature change little. Due to the melting induction effect of the flame retardant, its melting point decreases slightly;

[0078] (3) The PLLA blend composition added with the flame retardant has good spinnability and drawability, and the prepared fiber has good mechanical properties. The flame retardant has a certain plasticizing effect on PLLA. As the addition amount of the flame retardant increases, the spinning temperature of the polylactic acid fiber gradually decreases, and the draw ratio gradually increases, which is beneficial to the preparation of fine PLLA fibers with certain flame retardancy;

[0079] (4) Adding a phosphorus-containing flame retardant is beneficial to improving the thermal crystallization performance of PLLA, and can be used to solve the problem of non-woven fabric shrinkage caused by slow crystallization speed during the meltblowing process of PLLA;

[0080] (5) The antibacterial rate of the added zinc oxide against Escherichia coli and Staphylococcus aureus reaches 99%, and the addition amount of the phosphorus-containing flame retardant has no effect on its antibacterial property.

[0081] Examples

[0082] The present invention will be further elaborated through specific examples below. These examples are only for illustrating the present invention and are not used to limit the scope of the present invention.

[0083] Example 1

[0084] 70 parts by weight of PLLA and 30 parts by weight of CEPPA were placed in a DZF-6050 vacuum drying oven and vacuum dried at 100 °C for 12 h. Then they were placed in a twin-screw extruder (Poly OS, HAAKE, Germany) for melt blending. The screw speed was 50 r / min, and the temperatures of each zone of the screw were 200 °C, 190 °C, 180 °C, 170 °C, 160 °C, and 150 °C in sequence. The blending time was 3 min to obtain the PLLA / CEPPA masterbatch.

[0085] 0.2 parts by weight of the PLLA / CEPPA masterbatch, 1 part by weight of the PLLA / ZnO masterbatch (purchased from Xi'an Mingbo Chemical Technology Co., Ltd., with a zinc oxide content of 17%, the same below), and 99.8 parts by weight of PLLA were mixed. The temperatures of each zone of the single-screw extruder were 160 °C - 190 °C - 200 °C - 200 °C, the mixing time was 3 min, and the screw speed was 50 r / min to obtain the polylactic acid blend composition, named PLLA / CEPPA0.2.

[0086] Example 2

[0087] The polylactic acid blend composition was prepared in a similar manner to Example 1, except that: 1 part by weight of the PLLA / ZnO masterbatch, 99.6 parts by weight of PLLA, and 0.4 parts by weight of the PLLA / CEPPA masterbatch were placed in a DZF-6050 vacuum drying oven and vacuum dried at 100 °C for 12 h. The product was named PLLA / CEPPA0.4.

[0088] Example 3

[0089] The polylactic acid blend composition was prepared in a similar manner to Example 1, except that: 1 part by weight of the PLLA / ZnO masterbatch, 99.4 parts by weight of PLLA, and 0.6 parts by weight of the PLLA / CEPPA masterbatch were placed in a DZF-6050 vacuum drying oven and vacuum dried at 100 °C for 12 h. The product was named PLLA / CEPPA0.6.

[0090] Example 4

[0091] The polylactic acid blend composition was prepared in a similar manner to Example 1, except that: 1 part by weight of the PLLA / ZnO masterbatch, 99.2 parts by weight of PLLA, and 0.8 parts by weight of the PLLA / CEPPA masterbatch were placed in a DZF-6050 vacuum drying oven and vacuum dried at 100 °C for 12 h. The product was named PLLA / CEPPA0.8.

[0092] Example 5

[0093] The preparation of the polylactic acid blend composition was carried out in a similar manner to Example 1, except that: 1 part by weight of PLLA / ZnO masterbatch, 99.0 parts by weight of PLLA, and 1.0 part by weight of PLLA / CEPPA masterbatch were placed in a DZF-6050 type vacuum dryer and dried under vacuum at 100 °C for 12 h, and the product was named PLLA / CEPPA1.0.

[0094] Example 6

[0095] The preparation of the polylactic acid blend composition was carried out in a similar manner to Example 1, except that: 1 part by weight of PLLA / ZnO masterbatch, 98.5 parts by weight of PLLA, and 1.5 parts by weight of PLLA / CEPPA masterbatch were placed in a DZF-6050 type vacuum dryer and dried under vacuum at 100 °C for 12 h, and the product was named PLLA / CEPPA1.5.

[0096] Example 7

[0097] The preparation of the polylactic acid blend composition was carried out in a similar manner to Example 1, except that: 1 part by weight of PLLA / ZnO masterbatch, 98 parts by weight of PLLA, and 2 parts by weight of PLLA / CEPPA masterbatch were placed in a DZF-6050 type vacuum dryer and dried under vacuum at 100 °C for 12 h, and the product was named PLLA / CEPPA2.0.

[0098] Experimental Example 8

[0099] The polylactic acid blend composition prepared in Example 1 was dried at 100 °C for 600 min, and after drying, it was placed in a single-screw spinning machine for spinning. During the spinning process, the spinning temperatures of Zone Ι,

[0100] Zone Ⅱ, Zone Ⅲ, Zone Ⅳ, the pipe and the spinneret were adjusted to 160 °C, 190 °C, 200 °C, 200 °C, 205 °C and 210 °C respectively, the spinneret pressure was adjusted to 6.5 MPa, the winding speed was 1000 m / min, and a parallel drafting machine was used to draft the as-spun fibers. During the drafting process, the drafting temperature and speed were kept constant, the drafting winding speed was 400 m / min, the temperatures of the first drafting roller, the second drafting roller and the setting box were 75 °C, 100 °C and 140 °C respectively, and the drafting ratio was 2.7.

[0101] Example 9

[0102] The preparation of the flame-retardant polylactic acid fiber was carried out in a similar manner to Example 8, except that: the polylactic acid blend composition prepared in Example 2 was used for spinning, and during the spinning process, the spinning temperatures of Zone Ι, Zone Ⅱ, Zone Ⅲ, Zone Ⅳ, the pipe and the spinneret were adjusted to 160 °C, 190 °C, 200 °C, 200 °C, 205 °C and 203 °C respectively, and the drafting ratio was 2.7.

[0103] Example 10

[0104] The flame-retardant polylactic acid fiber was prepared in a similar manner to Example 8, except that: the polylactic acid blend composition prepared in Example 3 was used for spinning, and the spinning temperatures of Zone Ι, Zone Ⅱ, Zone Ⅲ, Zone Ⅳ, the pipe and the spinneret were adjusted to 160 °C, 190 °C, 200 °C, 200 °C, 200 °C and 200 °C respectively during the spinning process, and the draft ratio was 2.9.

[0105] Example 11

[0106] The flame-retardant polylactic acid fiber was prepared in a similar manner to Example 8, except that: the polylactic acid blend composition prepared in Example 4 was used for spinning, and the spinning temperatures of Zone Ι, Zone Ⅱ, Zone Ⅲ, Zone Ⅳ, the pipe and the spinneret were adjusted to 160 °C, 190 °C, 200 °C, 200 °C, 195 °C and 198 °C respectively during the spinning process, and the draft ratio was 2.9.

[0107] Example 12

[0108] The flame-retardant polylactic acid fiber was prepared in a similar manner to Example 8, except that: the polylactic acid blend composition prepared in Example 5 was used for spinning, and the spinning temperatures of Zone Ι, Zone Ⅱ, Zone Ⅲ, Zone Ⅳ, the pipe and the spinneret were adjusted to 160 °C, 190 °C, 200 °C, 200 °C, 190 °C and 190 °C respectively during the spinning process, and the draft ratio was 2.9.

[0109] Example 13

[0110] The flame-retardant polylactic acid fiber was prepared in a similar manner to Example 8, except that: the polylactic acid blend composition prepared in Example 6 was used for spinning, and the spinning temperatures of Zone Ι, Zone Ⅱ, Zone Ⅲ, Zone Ⅳ, the pipe and the spinneret were adjusted to 160 °C, 190 °C, 200 °C, 190 °C, 190 °C and 186 °C respectively during the spinning process, and the draft ratio was 3.1.

[0111] Example 14

[0112] The flame-retardant polylactic acid fiber was prepared in a similar manner to Example 8, except that: the polylactic acid blend composition prepared in Example 7 was used for spinning, and the spinning temperatures of Zone Ι, Zone Ⅱ, Zone Ⅲ, Zone Ⅳ, the pipe and the spinneret were adjusted to 160 °C, 190 °C, 200 °C, 190 °C, 185 °C and 181 °C respectively during the spinning process, and the draft ratio was 3.1.

[0113] Comparative Example

[0114] Comparative Example 1

[0115] The PLLA was placed in a DZF-6050 vacuum drying oven and dried under vacuum at 100 °C for 12 h. Then it was placed in a twin-screw extruder (Poly OS, HAAKE, Germany) for melt blending. The screw speed was 50 r / min, and the temperatures of each zone of the screw were 200 °C, 190 °C, 180 °C, 170 °C, 160 °C, and 150 °C in sequence. The blending time was 3 min to obtain the PLLA masterbatch.

[0116] 1 part by weight of PLLA / ZnO masterbatch and 100 parts by weight of PLLA were mixed at a mixing temperature of 160 °C - 190 °C - 200 °C - 200 °C), with a mixing time of 3 min and a screw speed of 50 r / min to obtain the blend composition.

[0117] The blend composition was placed in a single-screw spinning machine for spinning. During the spinning process, the spinning temperatures of Zone Ι, Zone Ⅱ, Zone Ⅲ, Zone Ⅳ, the pipe, and the spinneret were adjusted to 160 °C, 190 °C, 200 °C, 200 °C, 205 °C, and 210 °C respectively. The spinneret pressure was adjusted to 6.5 MPa, and the winding speed was 1000 m / min. The as-spun fibers were drawn using a parallel drawing machine. During the drawing process, the drawing temperature and speed were kept constant, the drawing winding speed was 400 m / min, the temperatures of the first drawing roller, the second drawing roller, and the setting box were 75 °C, 100 °C, and 140 °C respectively, and the drawing ratio was 2.1.

[0118] Experimental Example

[0119] The flame-retardant test specimens were prepared from the polylactic acid blend compositions prepared in Examples 1 - 7 and the blend composition prepared in Comparative Example 1 using a JPH30 injection molding machine (screw diameter 25 mm, Guangdong Hongli Machinery Co., Ltd.) for flame-retardant performance testing.

[0120] Experimental Example 1 DSC Test

[0121] The samples were heated on a hot stage and quenched to eliminate the thermal history (the fiber samples were not treated for removing the thermal history). DSC tests were carried out using a Q2000 from TA Instruments, USA, in the temperature range of 0 - 200 °C, with a heating rate of 20 °C / min under a nitrogen atmosphere.

[0122] The DSC test spectra of PLLA, CEPPA, and the polylactic acid blend compositions prepared in Examples 1 - 7 are shown respectively as Figure 1 (during the heating process) and Figure 2 (during the cooling process). The DSC test spectra of the fiber products prepared from PLLA, CEPPA, Example 8, and Example 12 are shown respectively as Figure 3 (during the heating process) and Figure 4 (during the cooling process).

[0123] Figure 1 andFigure 2 It can be seen that part of CEPPA is dispersed in the form of molecules between the PLLA molecular chains, which hinders the crystallization of PLLA and reduces the influence on the molecular motion of PLLA. Therefore, when the addition amount of PLLA / CEPPA is not more than 2%, the glass transition temperature of the polylactic acid blend composition decreases slightly with the increase of the addition amount of PLLA / CEPPA, which is beneficial to improving the drawability of the polylactic acid blend composition. During the cooling process, the thermal crystallization peak of CEPPA is about 120 °C, and there is no thermal crystallization peak when PLLA is cooled at a rate of 20 °C / min. With the increase of the addition amount of PLLA / CEPPA, due to the induction of CEPPA crystallization, the PLLA molecular chains crystallize with the crystallization of CEPPA as the crystal nucleus. Therefore, the thermal crystallization peak area of the polylactic acid blend composition gradually increases, showing the promotion of PLLA thermal crystallization.

[0124] From Figure 3 and Figure 4 It can be seen that the glass transition temperatures of the flame-retardant polylactic acid fibers prepared in Example 8 and Example 12 both disappear. When the addition amount of PLLA / CEPPA is 0.2%, there is no obvious influence on the melting point of the polylactic acid fiber. When the addition amount of PLLA / CEPPA is increased to 1%, due to the melting induction of CEPPA, its melting point is reduced to 168 °C. It can be seen from the cooling process that there is no thermal crystallization phenomenon in PLLA, and the flame-retardant polylactic acid fibers prepared in Example 8 and Example 12 show thermal crystallization peaks, indicating that the addition of 0.2% of CEPPA can promote the thermal crystallization of PLLA, which can be used to prepare meltblown polylactic acid nonwovens to solve the problem of slow crystallization rate of PLLA during the meltblowing process, resulting in cloth surface shrinkage.

[0125] Experimental Example 2 TGA Test

[0126] The test was carried out using Netzsch TG 209F1 from Germany, in a nitrogen atmosphere, the test temperature range was from room temperature to 600 °C, and the heating rate was 10 °C / min.

[0127] The test results of CEPPA, PLLA, Example 2, Example 4 and Example 6 are as Figure 5 shown.

[0128] From Figure 5 it can be seen that the thermal decomposition temperatures of CEPPA and PLLA are 185 °C and 300 °C respectively. The thermal decomposition temperature of the polylactic acid blend composition prepared after adding the flame retardant CEPPA is reduced to about 260 °C, which is related to the low decomposition temperature of the flame retardant CEPPA. However, the processing temperature of PLLA is generally not more than 220 °C. Therefore, the polylactic acid blend composition prepared in the present invention meets the requirements of thermal processing.

[0129] Experimental Example 3 Limiting Oxygen Index Test

[0130] The splines prepared in Examples 1-7 and Comparative Example 1 were subjected to limiting oxygen index tests using an American Dynisco oxygen index tester. The size of the splines was 100 mm × 6.5 mm × 4 mm, and the test was carried out in accordance with GB / T 2406.2-2009. The test results are shown in Table 1.

[0131] Table 1

[0132]

[0133] As can be seen from Table 1, when the addition amount of PLLA / CEPPA is not more than 1 wt%, with the increase of the addition amount of CEPPA, the LOI value of the polylactic acid blend composition increases from 19% to 32%, indicating that CEPPA has the effect of improving the flame retardant performance of PLLA. Further increasing the dosage of CEPPA, its LOI value does not increase significantly.

[0134] Experimental Example 4 Vertical Burning Performance Test

[0135] The splines prepared in Examples 1-7 and Comparative Example 1 were subjected to vertical burning tests using a CZF-3 horizontal and vertical burning tester produced by Nanjing Jiangning Analytical Instrument Co., Ltd. The size of the splines was 100 mm × 13 mm × 4 mm, and the test standard was GB / T 2408-2008. The test results are shown in Table 1.

[0136] In Table 1, the afterflame self-extinguishing time t 1 and t 2 of the polylactic acid blend composition decrease with the increase of the addition amount of CEPPA. There is a molten drop phenomenon during the ignition process, but the absorbent cotton is not ignited, and it no longer drips after leaving the ignition source. The polylactic acid blend composition with 1 wt% PLLA / CEPPA can reach the V0 level of UL-94. Further increasing the addition amount of CEPPA, its vertical burning performance does not improve significantly.

[0137] Experimental Example 5 Cone Calorimetry Test

[0138] The test was carried out using a British FTT Standard Corn Calorimeter cone calorimeter, with a heat radiation power of 35 kW / m 2 , the sample size was 100 × 100 × 3 mm, and the test standard was ISO 5660-1:2016. The graphs of the heat release rate (HRR), total heat release (THR), and total smoke release (TSR) of PLLA, the polylactic acid blend compositions prepared in Example 5 and Example 7, varying with time are shown respectively as Figure 6 , Figure 7 and Figure 8 shown. The cone calorimetry residues are shown respectively as Figures 9 - 11 shown.

[0139] The cone calorimeter test is an effective method for evaluating the heat radiation resistance of materials under the heat radiation condition of 35 kW / m² in the atmospheric environment. As can be seen from 2 it, compared with the polylactic acid without CEPPA added, the ignition time of the polylactic acid blend composition prepared in Example 5 is delayed from 68 s to 76 s, an extension of 8 s, and the maximum heat release rate is reduced from 440 kW / m² Figure 6 to 343 kW / m² 2 , and the maximum heat release rate is reduced by 22%. The ignition time of the polylactic acid blend composition prepared in Example 7 is extended to 85 s, an extension of 17 s, and the maximum heat release rate is reduced from 440 kW / m² 2 to 325 kW / m² 2 , and the maximum heat release rate is reduced by 26%. 2

[0140] Figure 7 In 2 , the total heat release amounts of the polylactic acid blend compositions in Example 5 and Example 7 are 60.4 MJ / m² 2 and 63.1 MJ / m²

[0141] respectively, which are reduced by 22.6% and 19.1% compared with the polylactic acid without CEPPA added. Figure 8 As can be seen from 2 it, after adding 1% and 2% of PLLA / CEPPA, the smoke release amounts of the polylactic acid blend compositions increase from 148.2 m² / m² 2 to 416.5 m² / m² 2 and 769.0 m² / m² 2 respectively, but are still much smaller than the smoke release amount (2092.7 m² / m² 2 ) of the commonly used PET material with benzene rings in the molecular chain at present. 2 2 / m² 2

[0142] As can be seen from Figures 9 - 11 , compared with PLLA, the polylactic acid blend composition has certain char-forming properties, indicating that CEPPA promotes the char formation of PLLA during combustion, causes the surface of the blend to expand during combustion, forms a carbon layer that is difficult to burn, and at the same time reduces the contact between the blend and oxygen and reduces the total heat release.

[0143] Experimental Example 6 Fiber fineness and strength test

[0144] The fiber fineness was tested using a YG086 lea strength tester (Changzhou No. 1 Textile Equipment Co., Ltd.), and the test standard was GB / T 14343-2008. The fiber strength was tested using an HD021N electronic single yarn strength tester (Nantong Hongda Experimental Instrument Co., Ltd.), and the test standard was GB / T 14344-2008. The fineness and strength test results are shown in Table 2.

[0145] Table 2

[0146]

[0147] As can be seen from Table 2, after adding CEPPA, the fineness of the polylactic acid fiber decreased from 168.3 dtex / 96f to 122 - 133 dtex / 96f, indicating that after adding CEPPA, the draw ratio of the polylactic acid fiber increased and the fineness decreased.

[0148] As can be seen from Table 2, compared with PLLA fiber, after adding 1% of PLLA / CEPPA, the breaking strength of the fiber decreased from 3.11 cN / dtex to 2.78 cN / dtex. This may be because the PLLA / CEPPA masterbatch underwent one heat treatment, and PLLA had a certain degree of degradation, resulting in a slight decrease in the breaking strength. However, its fiber can still meet the textile processing requirements.

[0149] Mechanical Property Test of Experimental Example 7

[0150] The mechanical properties of the polylactic acid blend compositions of Example 1, Example 3, Example 5, Example 7 and PLLA in Comparative Example 1 were tested, and the test results are shown in Table 3.

[0151] Table 3

[0152] Sample Name Breaking Strength / MPa Elongation at Break / % Initial Modulus / GPa PLLA 64.51 6.25 1.209 Example 1 63.65 4.84 1.359 Example 3 60.93 3.99 1.638 Example 5 58.29 2.82 1.882 Example 7 56.24 2.91 2.078

[0153] As can be seen from Table 3, with the increase in the addition amount of CEPPA, the breaking strength and elongation at break of polylactic acid gradually decreased. However, when the addition amount of PLLA / CEPPA was not more than 1%, the influence on the mechanical properties of polylactic acid was not significant.

[0154] Antibacterial Property Test of Experimental Example 8

[0155] The flame-retardant polylactic acid fibers prepared in Example 8 and Example 12 were woven into sock tubes on a hosiery machine, and the antibacterial properties were tested. The test results are shown in Table 4.

[0156] Table 4

[0157]

[0158] As can be seen from Table 4, the antibacterial rate of adding 1% PLLA / ZnO against Escherichia coli and Staphylococcus aureus reaches 99%, and the addition amount of CEPPA has no effect on its antibacterial performance.

[0159] The present invention has been described in detail above in conjunction with specific embodiments and exemplary examples, but these descriptions should not be construed as limiting the present invention. Those skilled in the art understand that without departing from the spirit and scope of the present invention, various equivalent substitutions, modifications or improvements can be made to the technical solutions and implementation manners of the present invention, and these all fall within the scope of the present invention. The protection scope of the present invention is subject to the appended claims.

Claims

1. A preparation method of a polylactic acid blend composition, characterized in that, the polylactic acid blend composition comprises polylactic acid and a phosphorus-containing flame retardant; the polylactic acid is L-polylactic acid; the phosphorus-containing flame retardant is 2-carboxyethylphenylphosphinic acid, the blend composition further comprises zinc oxide, and the mass ratio of the zinc oxide to the polylactic acid is 1:(570-600), the preparation method comprises the following steps: Step 1: Blend the polylactic acid and the phosphorus-containing flame retardant to obtain a flame-retardant polylactic acid masterbatch. The mass ratio of the phosphorus-containing flame retardant to the polylactic acid is (0.2-0.5):

1. The blending is carried out in a twin-screw extruder, and the temperatures of each zone in the twin-screw extruder are (190-210)°C-(180-200)°C-(160-180)°C-(155-165)°C-(155-165)°C-(145-155)°C. The blending time is 1-5 min, and the screw speed is 40-60 r / min; Step 2: Mix the flame-retardant polylactic acid masterbatch, PLLA / ZnO masterbatch and PLLA to obtain a polylactic acid blend composition. The mass ratio of the flame-retardant polylactic acid masterbatch, PLLA / ZnO masterbatch and PLLA is (0.1-5):(0.5-5):(90-99.9). The mixing is carried out in a single-screw extruder, and the temperatures of each zone in the single-screw extruder are (150-180)°C-(180-200)°C-(190-210)°C-(190-210)°C. The mixing time is 1-5 min; the spinning temperature of the polylactic acid blend composition is 5-30°C lower than that of the polylactic acid; the limiting oxygen index of the polylactic acid blend composition is 22%-35%.

2. The preparation method according to claim 1, characterized in that, in Step 1, the mass ratio of the phosphorus-containing flame retardant to the polylactic acid is (0.3-0.45):1.

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