A composite material for enhancing the strength of PLA melt and a preparation method and application thereof

Abstract

The application discloses a kind of composite for enhancing PLA melt strength and its preparation method and application, the composite is made of the following weight parts of component:SEBS 10-20 parts, polyester-polyether block copolymer 5-10 parts, SEBS-g-MAH 5-8 parts, oxidized PE wax 0.5-2 parts;By twin-screw extruder melt blending, extrusion granulation, obtain the white or milky white granules SEBS / polyester-polyether block copolymer / SEBS-g-MAH composite material.It is prepared by high melt strength PLA that PLA, the composite of the application and oxidized PE wax are melt blended by twin-screw extruder according to weight fraction.The enhanced PLA has the following characteristics: chain entanglement degree is 3.5-4.1 mol / cm 3 , melt strength is 13.6-16.8 cN, tensile strength is 49.5-64.2 MPa, and elongation at break is 25.4-64.5%.

Description

Technical Field

[0001] This invention relates to the field of polymer composite materials technology, specifically to a PLA composite material for the production of disposable plastic films, its preparation method, and its application. Background Technology

[0002] With the rapid development of the logistics economy, the demand for disposable plastic film products has increased dramatically, becoming an indispensable flexible packaging material in the modern logistics industry. Currently, the disposable plastic films used on a large scale are petroleum-based polyethylene and polypropylene films. Petroleum is a non-renewable resource, and its price has recently continued to rise, leading to an increase in the cost of polyethylene and polypropylene films. Furthermore, polyethylene and polypropylene films are difficult to recycle and reuse after use, and are also difficult to degrade naturally, causing significant pollution to the ecological environment.

[0003] Polylactic acid (PLA) is the most promising biodegradable bio-based material for large-scale replacement of polyethylene and polypropylene films. However, due to the large critical entanglement molecular weight of PLA chains, its melt strength is low, and the melt exhibits strain softening during tensile testing, which restricts its processing on blow molding equipment such as extrusion blow molding and stretch blow molding, and also results in low tensile strength of the film. To achieve the required mechanical strength for use, manufacturers can only increase the film thickness, which undoubtedly increases the cost of using PLA films. Therefore, reducing the entanglement molecular weight of PLA chains in the melt during PLA forming and processing can fundamentally improve its melt strength and the mechanical strength of the PLA film.

[0004] Long-chain branched PLA prepared by polymerization can improve the chain entanglement of PLA melt, thereby increasing its melt strength. However, the preparation of long-chain branched PLA by polymerization is complicated by two factors: the process is complex and the investment cost of polymerization production lines is too high, which limits the large-scale production of long-chain branched PLA. Summary of the Invention

[0005] One of the objectives of this invention is to provide a composite material for enhancing the melt strength of PLA, which can effectively improve the melt strength and mechanical strength of PLA.

[0006] The second objective of this invention is to provide a method for preparing the above-mentioned composite material for enhancing the melt strength of PLA, which has a simple process and low production cost.

[0007] A third objective of this invention is to provide the application of the aforementioned composite material for enhancing the melt strength of PLA.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0009] In a first aspect, the present invention provides a composite material for enhancing the melt strength of PLA, comprising the following components in parts by weight: 10-20 parts of hydrogenated styrene-butadiene-styrene block copolymer (SEBS); 5-10 parts of polyester-polyether block copolymer; 5-8 parts of maleic anhydride-grafted hydrogenated styrene-butadiene-styrene block copolymer (SEBS-g-MAH); and 0.5-2 parts of oxidized PE wax; wherein the SEBS has a star-shaped chain structure and the styrene / rubber ratio is 30 / 70.

[0010] Preferably, the polyester-polyether block copolymer has a linear chain structure and a polyester / polyether ratio of 38 / 62.

[0011] Preferably, the SEBS-g-MAH has a linear chain structure, a maleic anhydride grafting rate of 1.5%, and a styrene / rubber ratio of 30 / 70.

[0012] Preferably, the molecular weight of the oxidized PE wax is 2500-3200.

[0013] Secondly, the present invention provides a method for preparing the above-mentioned composite material for enhancing the melt strength of PLA, comprising the following steps:

[0014] (1) Weigh SEBS, polyester-polyether block copolymer, SEBS-g-MAH and oxidized PE wax according to the proportion, add them to the mixer and mix evenly to obtain a premix;

[0015] (2) The premix obtained in step (1) is added to a twin-screw extruder for melt blending and extrusion granulation. The temperature settings of each working section of the twin-screw extruder are 180℃, 190℃, 195℃, 190℃, 185℃ and 170℃ respectively, the die head temperature is 170℃ and the screw speed is 300 rpm.

[0016] Thirdly, the present invention provides the application of the above-mentioned composite material in the preparation of high melt strength polylactic acid, including the following steps: weighing 100 parts of PLA, 10-25 parts of composite material, and 0.5 parts of oxidized PE wax, mixing them evenly, and then melt-blending and extruding them into granules in a twin-screw extruder; the temperature settings of each working section of the twin-screw extruder are 175℃, 180℃, 175℃, 165℃, 165℃, and 165℃, respectively, the die head temperature is 165℃, and the screw speed is 200 rpm.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] 1. The present invention introduces SEBS / polyester-polyether block copolymer / SEBS-g-MAH composite material into existing PLA, using it as the three-dimensional chain entanglement center of the composite melt, thereby controlling the melt chain entanglement degree and thus controlling the melt strength of the composite material, thereby giving the PLA composite material good blow molding processing performance and excellent tensile strength.

[0019] 2. SEBS / polyester-polyether block copolymer / SEBS-g-MAH composite reinforced PLA has the following characteristics: chain entanglement degree of 3.5-4.1 mol / cm 3 The melt strength is 13.6-16.8 cN, the tensile strength is 49.5-64.2 MPa, and the elongation at break is 25.4-64.5%. Detailed Implementation

[0020] The present invention will be further described in detail below with reference to specific embodiments.

[0021] Example 1

[0022] Weigh 10 kg of SEBS, 7.5 kg of polyester-polyether block copolymer, 5 kg of SEBS-g-MAH, and 0.5 kg of oxidized PE wax, and premix them in a mixer. Add the premixed material to a twin-screw extruder for melt blending, extrusion, and granulation. The temperatures of each working section of the twin-screw extruder are set to 180℃, 190℃, 195℃, 190℃, 185℃, and 170℃, with the die head temperature at 170℃. The screw speed is 300 rpm.

[0023] Example 2

[0024] Weigh 15 kg of SEBS, 7.5 kg of polyester-polyether block copolymer, 6 kg of SEBS-g-MAH, and 1.5 kg of oxidized PE wax, and premix them in a mixer. Then, add the premixed material to a twin-screw extruder for melt blending, extrusion, and granulation. The temperatures of each working section of the twin-screw extruder are set to 180℃, 190℃, 195℃, 190℃, 185℃, and 170℃, with the die head temperature at 170℃. The screw speed is 300 rpm.

[0025] Example 3

[0026] Weigh 20 kg of SEBS, 10 kg of polyester-polyether block copolymer, 8 kg of SEBS-g-MAH, and 2 kg of oxidized PE wax, and premix them in a mixer. Add the premixed material to a twin-screw extruder for melt blending, extrusion, and granulation. The temperatures of each working section of the twin-screw extruder are set to 180℃, 195℃, 200℃, 195℃, 185℃, and 170℃, with the die head temperature at 170℃. The screw speed is 300 rpm.

[0027] Example 4

[0028] Weigh 12.5 kg of SEBS, 5 kg of polyester-polyether block copolymer, 7 kg of SEBS-g-MAH, and 1.5 kg of oxidized PE wax, and premix them in a mixer. Add the premixed material to a twin-screw extruder for melt blending, extrusion, and granulation. The temperatures of each working section of the twin-screw extruder are set to 180℃, 190℃, 195℃, 190℃, 185℃, and 170℃, with the die head temperature at 170℃. The screw speed is 300 rpm.

[0029] In the above embodiments, the SEBS used has a star-shaped chain structure and a styrene / rubber ratio of 30 / 70.

[0030] In the above embodiments, the polyester-polyether block copolymer used has a linear chain structure and a polyester / polyether ratio of 38 / 62.

[0031] In the above embodiments, the maleic anhydride grafting rate of the SEBS-g-MAH used was 1.5%, and the styrene / rubber ratio was 30 / 70.

[0032] In the above embodiments, the molecular weight of the oxidized PE wax used was 2500-3200.

[0033] The present invention describes the application of a composite material for enhancing the melt strength of PLA. The materials are weighed and mixed evenly according to the following method: 100 parts PLA, 10-25 parts composite material, and 0.5 parts oxidized PE wax. The mixture is then melt-blended and extruded into granules using a twin-screw extruder. The temperatures of each working section of the twin-screw extruder are set to 175℃, 180℃, 175℃, 165℃, 165℃, and 165℃, respectively. The die head temperature is 165℃, and the screw speed is 200 rpm.

[0034] The storage modulus (G′) and loss modulus (G″) of PLA composites were tested using an AR 1500ex rheometer. The plateau modulus was calculated from G′, G″, and the PLA molecular weight. Calculate the molecular weight of chain entanglement (M) according to equation (2). e ):

[0035]

[0036] In the formula: ρ is the density, g / cm³ 3 R is the gas constant, J / (mol·K); T is the temperature, K; Pa.

[0037] The degree of entanglement of the melt chain is calculated according to formula (2).

[0038]

[0039] The melt strength of the composite material was tested using a melt tensile rheometer with an initial velocity of 20 mm / s and an acceleration of 2 mm / s². 2 .

[0040] According to GB / T1040.3-2006, the tensile strength and elongation at break of the composite material were tested at a tensile rate of 5 mm / min. Each group of samples was measured in parallel 5 times and the average value was taken.

[0041] The table below shows the performance test results of the composite material-reinforced PLA of this invention.

[0042]

[0043] The weight-average molecular weight of PLA used in the above examples and *comparative examples is 80,000.

[0044] Unreinforced PLA has a melt strength of 5.2 cN, a tensile strength of 31.3 MPa, and an elongation at break of 22.6%. The composite material for enhancing PLA melt strength described in this invention can effectively improve the chain entanglement of the PLA melt. Compared to unreinforced PLA, the melt strength and mechanical properties of the reinforced PLA are greatly improved, with a melt strength of 13.6-16.8 cN, a tensile strength of 49.5-64.2 MPa, and an elongation at break of 25.4-64.5%.

[0045] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications, equivalent substitutions, and improvements made by those skilled in the art within the scope of the technology disclosed in the present invention, and within the spirit and principles of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A composite material for enhancing the melt strength of PLA, characterized in that, It is made from the following components in parts by weight: 10-20 parts of hydrogenated styrene-butadiene-styrene block copolymer; 5-10 parts of polyester-polyether block copolymer; 5-8 parts of maleic anhydride-grafted hydrogenated styrene-butadiene-styrene block copolymer; and 0.5-2 parts of oxidized PE wax; wherein the hydrogenated styrene-butadiene-styrene block copolymer has a star-shaped chain structure and the styrene / rubber ratio is 30 / 70.

2. The composite material for enhancing the melt strength of PLA according to claim 1, characterized in that, The polyester-polyether block copolymer has a linear chain structure and a polyester / polyether ratio of 38 / 62.

3. The composite material for enhancing the melt strength of PLA according to claim 1, characterized in that, The maleic anhydride-grafted hydrogenated styrene-butadiene-styrene block copolymer has a linear chain structure, a maleic anhydride grafting rate of 1.5%, and a styrene / rubber ratio of 30 / 70.

4. A composite material for enhancing the melt strength of PLA according to claim 1, characterized in that, The molecular weight of the oxidized PE wax is 2500-3200.

5. A method for preparing a composite material for enhancing the melt strength of PLA according to any one of claims 1 to 4, characterized in that, Includes the following steps: (1) Weigh the hydrogenated styrene-butadiene-styrene block copolymer, polyester-polyether block copolymer, maleic anhydride-grafted hydrogenated styrene-butadiene-styrene block copolymer and oxidized PE wax according to the proportion, add them to the mixer and mix evenly to obtain a premix. (2) The premix obtained in step (1) is added to a twin-screw extruder for melt blending and extrusion granulation. The temperature settings of each working section of the twin-screw extruder are 180℃, 190℃, 195℃, 190℃, 185℃ and 170℃ respectively, the die head temperature is 170℃ and the screw speed is 300 rpm.

6. The application of the composite material according to any one of claims 1 to 4 in the preparation of high melt strength polylactic acid, characterized in that, The process includes the following steps: Weigh 100 parts of PLA, 10-25 parts of composite material, and 0.5 parts of oxidized PE wax, mix them evenly, and then melt-blend and extrude them into granules in a twin-screw extruder; The temperature settings for each working section of the twin-screw extruder are 175℃, 180℃, 175℃, 165℃, 165℃, and 165℃, respectively, with the die head temperature at 165℃ and the screw speed at 200 rpm.

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