CN112280266A

CN112280266A - Synchronous preparation process of reactive cellulose nano-fibril/polylactic acid composite material

Info

Publication number: CN112280266A
Application number: CN202011200020.5A
Authority: CN
Inventors: 李群; 段燕; 孟凡盛
Original assignee: Tianjin University of Science and Technology
Current assignee: Tianjin University of Science and Technology
Priority date: 2020-11-02
Filing date: 2020-11-02
Publication date: 2021-01-29

Abstract

The invention discloses a synchronous preparation process of a reactive cellulose nano-fibril/polylactic acid composite material, belonging to the field of preparation of plant-based nano-composite materials. The preparation method is basically characterized in that polylactic acid is used as a matrix polymer, modified fibers are used as a reinforcing phase, and a double-screw extrusion method is adopted to complete the preparation of the composite material. Through silanization modification of paper pulp fibers, hydrophilicity of the paper pulp fibers is reduced, and meanwhile, dissociation of fibrils is achieved through high shear and high temperature of a double-screw extruder, so that the fibers are dissociated into a nanometer grade, and a functional group (-NH) on a silane coupling agent₂) The polylactic acid/polylactic acid composite material can better react with carboxyl in a polylactic acid matrix to form a chemical bond, the interface effect is obviously improved, the production process of the composite material is simplified, and the mechanical property of the composite material is greatly improved.

Description

Synchronous preparation process of reactive cellulose nano-fibril/polylactic acid composite material

Technical Field

The invention belongs to the field of preparation of plant-based nano composite materials, and particularly relates to a synchronous preparation process of a reactive cellulose nano fibril/polylactic acid composite material.

Background

With the increasing exhaustion of mineral resources such as petroleum and the problem of "white pollution" caused by petroleum-based plastics in the world, polylactic acid (PLA) has attracted much attention as a biodegradable material. Can be completely degraded into carbon dioxide and water under the specific condition of microorganisms in the nature, thereby effectively protecting the environment. However, some of the disadvantages of polylactic acid itself, such as: its wide use is limited by its great brittleness, poor crystallinity and low thermal stability. Often, the composite material is compounded with other materials, so that the advantages of each base material are fully exerted, and the application range of the polylactic acid is expanded, so that the solution is considered to be realized by using the cellulose nano-fibrils which have degradability and high strength as the reinforcing phase.

The Cellulose Nanofibrils (CNF) have the advantages of wide raw material source, high length-diameter ratio, good mechanical property, good biocompatibility, degradability and the like. CNF has higher mechanical strength than Cellulose Nanocrystals (CNC) at the same fiber content. The CNF is entangled to form a three-dimensional network structure due to the high length-diameter ratio of the CNF, can limit the violent movement of polymer molecules to a certain extent, improves the thermodynamic property of the polymer molecules, and has wide application prospect in the field of nano composite reinforced materials.

CNF has poor compatibility with weakly polar polylactic acid due to a large number of free hydroxyl groups on its surface. The current research work mainly aims to reduce the hydrophilicity of the CNF through modification, improve the dispersibility and interfacial compatibility of the CNF in the polylactic acid, and achieve certain results. Wherein, Bulota and the like compound esterified microfibrillated cellulose (MFC) and polylactic acid to prepare the MFC/polylactic acid composite material, and the mechanical property of the composite material is improved. Kahavita et al silanize and modify CNF, melt and mix modified CNF and polypropylene (PP) with internal mixer, then press and mold to make modified CNF/PP nano composite material, the composite material has higher mechanical property. In the above method, the modified fiber and the base material are simply and physically blended, no chemical reaction occurs, the interface compatibility between the fiber and the polylactic acid is limited, the preparation method is complex, the cost is high, and the processes of CNF preparation-modification-compounding and the like are required. Therefore, it is a challenge to form chemical bonds between the fibers and the polylactic acid, further improve the interfacial compatibility between the fibers and the polylactic acid, and develop a simple and easy preparation method of the CNF/polylactic acid composite material.

Disclosure of Invention

Aiming at the problems of poor compatibility of hydrophilic CNF and polylactic acid matrix, poor mechanical property of composite material, complex composite process and the like, the invention takes paper pulp fiber as raw material, gamma-aminopropyl triethoxysilane (APS) as coupling agent to perform silanization modification on the paper pulp fiber, and the modified coupling agent and the paper pulp fiberThe hydroxyl on the fiber is dehydrated and condensed to form ether bond, so that the number of exposed hydroxyl on the surface of the fibril is reduced, on one hand, the hydrophilicity of the fibril is reduced, on the other hand, the dissociation of the fibril is realized by the high shear and high temperature of a double-screw extruder, the fiber is dissociated into nanometer grade, and the functional group (-NH) on the silane coupling agent is formed when the fiber is melted and extruded with polylactic acid₂) The composite material can better react with carboxyl in a polylactic acid matrix, chemical bonds are formed between silanized CNF and polylactic acid, the interface effect is obviously improved, and the mechanical property of the composite material is improved. Meanwhile, the method combines the preparation of the CNF and the preparation of the composite material into one step, simplifies the production process of the composite material, improves the production efficiency and reduces the production energy consumption.

The invention is implemented by the following technical scheme:

(1) shredding paper pulp fiber raw materials, soaking in sodium hydroxide solution at room temperature for 2 hours, then washing the filtrate to neutrality by using distilled water containing a few drops of acetic acid, and drying for later use.

(2) Adding 3-50% APS (mass percentage relative to fiber) into the water-ethanol mixed solution (V)_{Water (W)}∶V_Ethanol40: 60), placing the mixture into a three-neck flask, adding a proper amount of the dry paper pulp fiber obtained in the step (1), magnetically stirring the mixture for 1 to 3 hours at the temperature of between 80 and 100 ℃, after the reaction is finished, carrying out suction filtration, washing the mixture by using distilled water, and washing away the unreacted coupling agent. After washing, the fiber was left at room temperature for 1 day, and then dried and pulverized at 60 ℃ to prepare a modified fiber.

(3) Crushing polylactic acid, sieving with a 100-mesh sieve, accurately weighing 40g of polylactic acid powder, adding 2-16 g of modified fiber, and uniformly mixing. Adding the mixture into a Haake torque rheometer to melt and mix for 10min, wherein the rotating speed of a screw is 30rpm, and the mixing temperature is 180-200 ℃. And after cooling and granulation, adding the granules into a Haake rheometer again for mixing, repeating the process for 1-3 times, transferring the mixed granules into a rectangular mould, preheating at 180-200 ℃ and 0MPa for 5min, hot-pressing at 180-200 ℃ and 10MPa for 10min, and cold-pressing at room temperature and 10MPa for 5min to obtain the silanization modified CNF/PLA composite material.

Compared with the prior art, the invention has the following advantages:

the invention realizes the dissociation of fibril by means of high shearing and high temperature of a double-screw extruder, dissociates fiber into nanometer grade, fully exerts nanometer size effect, and leads functional groups (-NH) on a silane coupling agent to be melted and extruded with polylactic acid₂) The composite material can better react with carboxyl/hydroxyl in a polylactic acid matrix, a chemical bond is formed between silanized CNF and polylactic acid, the interface effect is obviously improved, the mechanical property, the thermal stability and the like of the composite material are further improved, and the application range of the polylactic acid is expanded. Meanwhile, the method combines the preparation of the CNF and the preparation of the composite material into one step, simplifies the production process of the composite material, improves the production efficiency, reduces the production energy consumption and provides technical support for the high-efficiency industrial production of the composite material.

Detailed Description

The best mode for carrying out the invention is described in further detail below by way of specific examples.

(1) 200g of pulp fiber raw material is shredded, soaked in sodium hydroxide solution for 2 hours at room temperature, and then the filtrate is washed to neutrality by distilled water containing a few drops of acetic acid and dried for standby.

(2) 30 percent of APS (mass percent relative to the fiber) is added into the water-ethanol mixed solution (V)_{Water (W)}∶V_Ethanol40: 60), placing in a three-neck flask, adding 20g of the dried pulp fiber obtained in the step (1), magnetically stirring for 2h at 90 ℃, after the reaction is finished, carrying out suction filtration, washing with distilled water, and washing away unreacted coupling agent. After washing, the fiber was left at room temperature for 1 day, and then dried and pulverized at 60 ℃ to prepare a modified fiber.

(3) Crushing polylactic acid (PLA), sieving with a 100-mesh sieve, accurately weighing 40g of polylactic acid powder, adding 12g of modified fiber, and uniformly mixing. Adding the mixture into a Haake torque rheometer to melt and mix for 10min, wherein the rotating speed of a screw is 30rpm, and the mixing temperature is 190 ℃. And after cooling and granulation, adding the granules into a Haake rheometer again for mixing, repeating the process for 1-3 times, transferring the mixed granules into a rectangular mould, preheating at 190 ℃ and 0MPa for 5min, hot-pressing at 190 ℃ and 10MPa for 10min, and cold-pressing at room temperature and 10MPa for 5min to obtain the silanization modified CNF/PLA composite material.

Compared with the prior art, the invention has the following advantages:

(1) the invention realizes the dissociation of fibril by means of high shearing and high temperature of a double-screw extruder, dissociates fiber into nanometer grade, fully exerts nanometer size effect, and leads functional groups (-NH) on a silane coupling agent to be melted and extruded with polylactic acid₂) The composite material can better react with carboxyl in a polylactic acid matrix, chemical bonds are formed between silanized CNF and polylactic acid, the interface effect is obviously improved, the mechanical property, the thermal stability and the like of the composite material are further improved, and the application range of the polylactic acid is expanded.

(2) The preparation method integrates the preparation of the CNF and the preparation of the composite material into one step, simplifies the production process of the composite material, improves the production efficiency, reduces the production energy consumption and provides technical support for the high-efficiency industrial production of the composite material.

Claims

1. A synchronous preparation process of a reactive cellulose nanofibril/polylactic acid composite material is characterized by comprising the following steps:

(2) 3 to 50 percent of gamma-aminopropyl triethoxy silane coupling agent (mass percent relative to the fiber) is added into the water-ethanol mixed solution (V)_{Water (W)}∶V_Ethanol40: 60), placing the mixture into a three-neck flask, adding a proper amount of the dried paper pulp fiber obtained in the step (1), magnetically stirring the mixture for 1 to 3 hours at a temperature of between 80 and 100 ℃, after the reaction is finished, carrying out suction filtration and washing the mixture by using distilled water, washing off unreacted coupling agent, placing the washed mixture at room temperature for 1 day, and then drying and crushing the washed mixture at a temperature of 60 ℃ to prepare the modified fiber.

(3) Crushing polylactic acid (PLA), sieving with a 100-mesh sieve, accurately weighing 40g of polylactic acid powder, adding 2-16 g of modified fiber, and uniformly mixing. Adding the mixture into a Haake torque rheometer to melt and mix for 10min, wherein the rotating speed of a screw is 30rpm, and the mixing temperature is 180-200 ℃. And after cooling and granulation, adding the granules into a Haake rheometer again for mixing, repeating the process for 1-3 times, transferring the mixed granules into a rectangular mould, preheating at 180-200 ℃ and 0MPa for 5min, hot-pressing at 180-200 ℃ and 10MPa for 10min, and cold-pressing at room temperature and 10MPa for 5min to obtain the silanization modified CNF/PLA composite material.

2. The process for the simultaneous preparation of reactive cellulose nanofibrils/polylactic acid composite according to claim 1, characterized in that: directly modifying the fiber, realizing the dissociation of fibril by means of the high shearing and high temperature of a double-screw extruder, and dissociating the fiber into nanometer grade to modify the functional group (-NH) on the CNF₂) Reacts with carboxyl in polylactic acid matrix, and combines the preparation of CNF and the preparation of composite material into one step.