Huang Qian, Li Jing, Yu Junrong, Wang Yan, Zhu Jing, Hu Zuming

(State Key Laboratory for Modification of Chemical Fibers and Polymer Materials, College of Materials Science and Engineering, Donghua University, Shanghai 201620)

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Preparation of PMIA/MWNTs nanofiber via solution blow spinning process

Huang Qian, Li Jing, Yu Junrong*, Wang Yan, Zhu Jing, Hu Zuming

(State Key Laboratory for Modification of Chemical Fibers and Polymer Materials, College of Materials Science and Engineering, Donghua University, Shanghai 201620)

Poly-m-phenylene isophthalamide/multi-wall carbon nanotubes (PMIA/MANTs) nanofibers were prepared via solution blow spinning technique.The change of the surface morphology and diameter distribution of the nanofibers with the spinning parameters was discussed. The effect of MWNTs on the crystallization property and mechanical properties of PMIA nanofibers membrane was discussed.The results showed that the PMIA/MWNTs nanofibers could be produced with good morphology as the drawing air pressure was 0.12 MPa and the inner diameter of the spinneret nozzle was 0.4-0.5 mm;as the load of MWNTs was increased, the average diameter and crystallinity of the nanofibers increased, the tensile strength of the nanofibers membrane increased and the elongation at break decreased; the PMIA/MWNTs nanofibers had uniform morphology and fine diameter with the average value of 372 nm, the tensile strength of the nanofibers membrane reached 41.85 MPa with a growth more than 86% as compared with that of pure PMIA nanofibers membrane as the MWNTs load was optimized as 0.3%.

poly-m-phenylene isophthalamide; multi-wall carbon nanotubes; solution blow spinning; surface morphology; mechanical properties

Solution blow spinning is a new method to produce micro and nanofibers from polymer solution[1]. This technique applies a high speed gas through the airjet nozzle on the polymer solution extruded from a spinneret nozzle, then the polymer solution is stretched by the high speed gas flow, and the solvent rapidly evaporates, finally forming a web of micro and nanofibers. The solution blow spinning technique is superior to traditional electrospinning in the commercial production due to its simple process, high efficiency, low energy consumption and high safety[2-3].

Poly-m-phenylene isophthalamide (PMIA) nanofibers are considered as a satisfying material for high-temperature high-efficiency filtration and lithium battery separator due to its excellent heat resistance, flame resistance, chemical resistance and electrical insulation property[4-5]. But the tensile strength of PMIA nanofibers membrane is low because of its flexible macromolecular structure, restricting its application in the high-performance field. Indeed, it has been reported that a rational amount of multi-wall carbon nanotubes (MWNTs) could well reinforce PMIA nanofibers. He Suwen[6]et al. have produced a PMIA nanofibers membrane with the mechanical properties considerably improved as incorporated with MWNTs during the electrospinning process. And the fiber average diameter is obviously decreased while raising the load of MWNTs. However, the incorporation of MWNTs provides the effect on the solution blow spinning process different from the electrospinning process owing to their different spinning mechanism. Currently, researchers have primarily studied the effects of spinning parameters on the morphology of the produced nanofibers[7]while the stability of the solution jet flow is rarely reported.

Here we discuss the stability of PMIA/MWNTs solution jet flow under different stretch gas pressure and investigate the effect of the incorporation of MWNTs on the solution blow spinning performance of PMIA solution and the mechanical properties of the nanofibers membrane thereof.

1 Experiment

1.1 Raw material

PMIA solution: 15.66% PMIA by mass fraction, weight average relative molecular mass (MW) 1.04×105, purchased from X-FIPER New Material Co.,Ltd; N,N- dimethylacetamide (DMAc): analytical grade, purchased from Yonghua Chemical Sci & Tech Company;MWNTs:10-15 nm

in diameter,10-20 μm in length,purchased from Chengdu Organic Chemical Company.

1.2 Preparation of PMIA/MWNTs spinning solution

An appropriate amount of acid-treated MWNTs[8]was dispersed in DMAc under ultrasonication, then the MWNTs dispersion was mixed with PMIA solution at a specific ratio and formed PMIA/MWNTs solution in which the mass fraction of PMIA was 12% and the load of MWNTs ranged from 0.1% to 0.5% in PMIA.

1.3 Preparation of PMIA/MWNTs nanofiber by solution blow spinning

Fig.1 showed a self-made solution blow spinning experimental apparatus. This apparatus uses a syringe pump to quantitatively deliver a polymer solution. The gas flow unit comprises a nitrogen gas steel container and a decompression buffer tank. The spinneret unit consists of concentric nozzles whereby the polymer solution is pumped out through the inner nozzle while a constant, high speed gas flow is blown out through the outer nozzle of 1.2 mm in inner diameter. The protrusion distance of the inner nozzle was 8 mm. The PMIA/MWNTs nanofibers could be prepared with the thickness of 100 μm by adjusting the gas pressure and spinneret nozzle diameter under the solution injection rate 1.0 mL/h, room temperature, relative humidity about 50%, collection distance 40 cm and rotating drum velocity 200 r/min.

Fig.1 Diagram of an apparatus preparing nanofiber membrane via solution blow spinning process1—Polymer solution；2—Tee pipe coupling；3—High pressure gas；4—Spinneret nozzle；5—Airjet nozzle；6—Collector

1.4 Test and characterization

The morphology of the produced composite nanofibers

was observed with Quanta-250 scanning electron microscope (SEM) manufactured by FEI Co., Czech. The fiber diameter distribution was measured by taking 100 nanofibers with an Image Tool software. The crystalline structure of the nanofibers was determined with a D/max-2550 PC X-ray diffraction analysis (XRD) manufactured by Rigaku Co., Japan. The determination conditions were as followed: powder diffraction sample making, CuKα target, voltage 40 kV, electric current 300 mA, 2θ range 5°-60° in steps of 2(°)/min. The mechanical properties of the nanofibers membrane were measured with an XQ-1C single fiber tensile tester manufactured by Shanghai New Fiber Instrument Co., Ltd. The clamp distance was 10 mm, drawing speed 10 mm/min, strength 0-200 cN, elongation 100%.

2 Results and discussion

2.1 Gas flow pressure

As shown in Fig.2, the nanofibers was poor in the morphology with droplets and serious doublings and relatively high in diameter at the gas pressure of 0.08 MPa; when the gas pressure was 0.10 MPa, the surface morphology of nanofibers became better, there were still some obvious doublings and the fiber diameter was uneven, which was attributed to the fact that the gas pressure was too low to completely disperse the extruded solution jet and led to low volatilizing speed of solvents, resulting in the adhesion of multiple strands; when the gas pressure was 0.12 MPa, the solution jet was blown into a completely dispersed state and the doublings was greatly depressed, which indicated that the high-speed gas flow could efficiently stretch the solution jet and make the solvents volatilize, and the obtained nanofibers exhibited smooth surface and uniform diameter distribution ranging 300-400 nm; however, the doublings formed again at the gas pressure of 0.14 MPa and the droplets appeared at the gas pressure of 0.16 MPa, which was because the gas speed was so high that the solvents couldn′t volatilize in time and might fall on the collector resulting in the fiber adhesion and poor morphology of nanofibers membrane. Therefore, the optimal gas pressure was considered as 0.12 MPa.

Fig.2 SEM images of PMIA/MWNTs nanofibers membrane at different gas pressureMWNTs load 0.3%, spinneret nozzle inner diameter 0.51 mm.

2.2 Spinneret nozzle inner diameter

As shown in Fig.3,the nanofibers membrane had a high fiber average diameter and a great many doublings at the inner diameter of spinneret nozzle of 0.62 mm because the extruded solution jet was too thick to be dispersed efficiently; the nanofibers exhibited the uniform morphology with no obvious doublings and the diameter ranging 300-400 nm as the inner diameter of the spinneret nozzle was decreased to 0.51 mm or 0.41 mm, because the solution jet was completely dispersed and well stretched so as to acquire fine and uniform fiber diameter; the morphology of the nanofibers became poor and the fiber adhesion and doubling appeared again as the inner diameter of spinneret nozzle was decreased to 0.33 mm, and the doubling phenomenon became serious as the inner diameter of spinneret nozzle was 0.25 mm, which was because smaller spinneret nozzle diameter caused higher extrusion rate of spinning solution and then the relative speed between the gas flow and extruded solution was not so high enough to well stretch the nanofibers. Therefore, the optimal spinneret nozzle diameter was considered as 0.4-0.5 mm.

Fig.3 SEM images of PMIA/MWNTs nanofibers membrane at different spinneret nozzle inner diameter Gas pressure 0.12 MPa; MWNTs load 0.3%.

2.3 MWNTs load

As shown in Fig.4, the PMIA/MWNTs nanofibers possessed the fairly good surface morphology and uniform diameter distribution with the average diameter below 400 nm as the MWNTs load was lower than 0.3%; the nanofibers became thicker and the doublings appeared as the MWNTs load was increased to 0.4%; the doubling phenomenon became serious, the fiber morphology was poor and the droplets formed as the load was increased to 0.5%, which was because the solution viscosity was increased to a specific degree due to the polar interaction between PMIA molecules and carboxyl group on the surface of acid-treated MWNTs[9], making the solution blow spinning difficult and the fiber thicker; moreover, the aggregation of MWNTs was not obviously observed on the surface of PMIA/MWNTs nanofibers, which indicated that acid-treated MWNTs could be well dispersed in PMIA solution.

Fig.4 SEM images of PMIA/MWNTs nanofibers membrane under different MWNTs load Gas pressure 0.12 MPa; spinneret nozzle inner diameter 0.51 mm.

It can be seen from Fig.5 that the PMIA/MWNTs nanofibers with different MWNTs load had similar XRD patterns and each showed an obvious diffraction peak at 2θ of about 24°, which indicated that the incorporation of MWNTs did not change the crystalline structure of PMIA; the diffraction peaks profoundly became intensive and the crystallinity of the nanofibers rose as the MWNTs load was increased to more than 0.2%, which indicated that MWNTs promoted the crystallization of PMIA molecules as a nucleating agent.

It can be seen from Tab.1 that the strength of the nanofibers membrane was gradually increased and the elongation at break was gradually decreased as the MWNTs load was increased; the tensile strength of the nanofibers membrane was increased to 41.85 MPa with a growth of more than 86% as compared with that of pure PMIA nanofibers membrane at the MWNTs load of 0.3%,which proved that incorporated MWNTs contributed a good reinforcement effect to the PMIA nanofibers; when continuously increased the MWNTs load, the mechanical properties of the nanofibers membrane did not change, but the fiber got thicker and the morphology became poor with doublings and droplets. Therefore, the optimal MWNTs load was considered as 0.3% for preparing PMIA/MWNTs nanofibers.

Fig.5 XRD patterns of PMIA/MWNTs nanofibers under different MWNTs load1—0；2—0.1%；3—0.2%；4—0.3%；5—0.4%；6—0.5%

Tab.1 Mechanical properties and average diameter of PMIA/MWNTs nanofiber with different MWNTs load

MWNTsload，%Fiberaveragediameter/nmTensilestrength/MPaElongationatbreak，%034322．4864．400．134631．2863．640．236329．0161．880．337241．8538．160．442742．7339．530．543240．1539．58

3 Conclusions

a. The stability of the spinning jet was gradually improved when the gas flow pressure was increased during the solution blow spinning process. The PMIA/MWNTs nanofibers membrane could be produced with fairly good morphology and average diameter of 372 nm when the gas flow pressure was 0.12 MPa and the inner diameter of the spinneret nozzle was 0.51 mm.

b. The diameter, crystallinity and mechanical properties of the nanofibers were increased when the MWNTs load was increased. The tensile strength of the nanofibers membrane was increased by 86% and above when the MWNTs load was up to 0.3%, as compared with that of pure PMIA nanofibers membrane. The nanofibers got thick and the nanofibers membrane became poor in morphology while continuously increasing MWNTs load.

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溶液噴射紡絲制備PMIA/MWNTs納米纖維的研究

黃 千，李 靜，于俊榮，王 彥，諸 靜，胡祖明

(東華大學(xué)材料科學(xué)與工程學(xué)院纖維材料改性國家重點實驗室，上海 201620)

采用溶液噴射紡絲技術(shù)制備間位芳綸/多壁碳納米管(PMIA/MWNTs)納米纖維，探討了不同工藝參數(shù)下納米纖維表觀形貌和直徑分布的變化，研究了MWNTs對PMIA納米纖維膜結(jié)晶性能和力學(xué)性能的影響。結(jié)果表明：在拉伸風(fēng)壓為0.12 MPa、噴絲孔內(nèi)徑為0.4～0.5 mm時，可以制得形貌較好的PMIA/MWNTs納米纖維；隨MWNTs負(fù)載量的增加，制得納米纖維的平均直徑變粗，結(jié)晶度變大，纖維膜拉伸強度增大，斷裂伸長率則下降；MWNTs的最佳負(fù)載量為0.3%，此時可制得形貌結(jié)構(gòu)均勻，直徑較細(xì)的PMIA/MWNTs納米纖維，纖維平均直徑為372 nm，纖維膜拉伸強度達(dá)到41.85 MPa，較純PMIA納米纖維膜提高了86%以上。關(guān)鍵詞：間位芳綸多壁碳納米管 溶液噴射紡絲 表觀形貌 力學(xué)性能

Foundation item: Natural Science Foundation of Shanghai (15ZR1401100). * Corresponding author: yjr@dhu.edu.cn.

TQ342+.72 Document code:A Article ID: 1001- 0041(2016)05- 0046- 04

Received date:09- 10- 2016; revised date: 25- 10- 2016.

Biography: Huang Qian(1992-),male, postgraduate, is engaged in nanofibers membrane. E-mail：hq65743889@163.com.