Key Engineering Materials Vol. 561 (2013) pp 8-12 Online available since 2013/Jul/15 at www.scientific.net © (2013) Trans Tech Publications, Switzerland doi:10.4028/www.scientific.net/KEM.561.8
The Preparation of Polypropylene/Polyvinyl Alcohol Ultra-fine Fibers Using Melt Electrospinning Method LI Haoyi1,a, DING Yumei1,b, LIU Yong1,c, ZHANG Youchen1,d, YANG Weimin1,2,e* 1
College of Mechanical and Electrical Engineering, Beijing University of Chemical Technology, Beijing 100029, China
2
State Key Laboratory of Organic-Inorganic Composites, Beijing University of Chemical Technology, Beijing 100029, China a
[email protected],
[email protected],
[email protected], d
[email protected],
[email protected]
Keywords: melt electrospinning；PP/PVA compound；plasticizer；polymer paper；
Abstract. Some polymers like polypropylene (PP), polyethylene (PE), polyphenylene sulfide (PPS) are very hard to be solute in conventional solvents at room temperature, and impossible to be solution electrospun, but they can be easily fabricated into ultra-fine fibers using melt electrospinning. In this study, PP/PVA compound ultra-fine fibers were produced using mlet electrospinning. The effect of PVA content in PP/PVA compound on the properities of resultant fibers was studied. Different plasticizers were added into the compound to find the most effective plasticizer reducing the melt viscosity. It was shown that PP/PVA compound with content of 5% PVA can produce the finest fiber while adding 8% hyper-branched polyester (HBP). In addition, the resultant fibers were made into thin paper using compaction processing, and water absorbability was tested. The results were expected to be used in dyeable PP cloth production and degradable polymer paper production. Introduction Eletrospinning process is a widely used method to produce fine fibers of polymer solution or melt using electrostatic forces [0]. Electrospinning can be conducted in two methods: solution electrospinning and melt electrospinning [2, 3]. In recent twenty years, solution electrospinning was paid more attention due to its mild preparation condition and multiple materials applicability [4], but the use of toxic solvent caused many disadvantage : such as need of extra solvent recycler, harm to human body [5] of the residual solvent[5], and limited production [6]. Research on melt electrospinning is relatively few because of requirement of high processing temperature and low melt viscosity [7]. But the advantage of melt electrospinning has been more and more highlighted with the improvements of heating system, inventions of new devices and the use of high quality viscosity reducers. Especially, melt electrospinning can process some insoluble polymers like PP, PE [8], PPS into ultra-fine fibers which are smaller than conventional melt-blowing method. PP is a common used material for melt electrospinning. As nopolar material, it has poor hygroscopicity and dyeability, which limits its use in many areas. PVA is a kind of polar polymer possessing abundant hydroxyl, the composites of polyvinyl alcohol (PVA) and other materials can significantly improve their hygroscopicity and dyeability. In this study, ultra-fine fibers were got by PP/PVA composite using melt electrospinning method. The effect of typical plasticizers as PP/PVA compound viscosity reducer was studied, and the hygroscopicity of polymer paper made of resultant fabrics was also investigated. Experimental Equipments. As Fig.1 shows, melt electrospinning device was specifically designed for melt electrospinning by authors’ research team. This device was mainly composed of steel cylinder, piston, sprayer, heating system, receiver, and a high voltage supplier, in which, the heating system is All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of TTP, www.ttp.net. (ID: 123.235.8.198-06/09/13,11:28:04)
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consisted of electrical heating rings, thermal sensors, and a temperature controller. The sprayer was cone-shaped umbrella-like sprayer instead of the traditional capillary. The melts flowed onto the surface of sprayer and then formed Taylor 's cones spontaneously at the bottom edge of the sprayer in the high voltage electrostatic field.
Fig.1 Schematic illustration of melt electrospinning device and the photograph of the model machine Miniature twin-screw extruder (PRISM Company) was used to blend PP/PVA. The processing temperature was 220℃, screw rotate speed was 50 rpm. Every sample was compounded for twice. Marerials. PP 6315 was bought from China Petrochemical Corporation, Beijing Yanshan branch Co. PVA-500 was bought from Tai Wan Chang Chun Group. Glycerol and Calcium stearate (CaSA) were bought from Beijing Additive Institute. The HBP (H203) was bought from Suzhou Haibao resin technology Co, LTD. Processing. The PVA pellets were dried at 50℃ for two days. Then PP and PVA pellets were grinded separately. The resultant powders were sieved with mesh 100 and powders smaller than 200µm were obtained. Compound the PP and PVA powders with certain proportion and then add them into miniature twin-screw extruder, the set processing temperature was 220℃，the set rotate speed was 50 rpm. Extrude materials for twice at the same condition. The resultant pellets were grinded again for melt electrospinning. Then, the cylinder was heated to target temperature (220℃). The sprayer was fixed to the tip of the cylinder. Distance between sprayer and receiver was set to 12cm, then the polymer powder were added into the cylinder. After 5-10 mins, the material was totally melt and flew out to the rim of the sprayer uniformly. Then high voltage supplier was switched on and adjusted to the optimum voltage (40kv), thus tens of Taylor cones were found around the rim of the sprayer, and jets flew towards to the receiver. Finally a thin non-woven fabric was collected. When electrospinning, the receiver was moved in constant speed of 0.3m/h in X-Y directions, uniform fabrics was were obtained. At last, The sample fabrics were cut into 30×30mm square and kept the weight of samples were kept at 0.105g. Then fixed them between two A4 papers for protection, and pressed it them within two steel plates weighing 4kg at 120℃ for 3mins. This process was proceeded in a vacuum drying chamber. Characterization. The morphologies of the electrospinning fibers were observed by scanning electron microscopy (SEM, Hitachi S4700). Fiber samples were coated with a layer of 10 nm platinum before observation. Scanning voltage was 20 KV. PP/PVA polymer papers of varies compositions with the same area and quality were immersed into demonized water for two hours. Then each sample was picked out and weighed separately. Quality of water it absorbed was figured out. Results and Discussion Effect of plasticizers on PP/PVA fibers. Pure PVA was impossible to be melt electrospun due to its high viscosity of 4-5mPa.s. Considering raising the spinning temperature may cause severe degradation, several typical plasticizers were used to decrease the viscosity of PVA, especially the viscosity of PP/PVA compounds. Here PP/PVA compounds with different content of glycerol, CaSA,
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Advanced Polymer Processing III
current(mA)
HBP were melt electrospun into fibers. It was found that PP/PVA with glycerol or CaSA can hardly produce fibers. It was observed that glycerol powders were electrospun solely to the receiver while PP/PVA melt remained in the chamber when PVA content in PP/PVA compound exceeded 10%, which may be because that the great melt temperature difference between glycerol and PP/PVA compound lead to a inadequate distribution of glycerol and PP/PVA compound. And the addition of HBP in PP/PVA compound produced the smallest and most uniform fibers. That’s because HBP has a three dimensional spherical structure, and it could easily permeate into the entangled PP and PVA chains and play a role as slid balls between molecules. This effect greatly improved the melt fluidity of PP/PVA compound. The nature of electrospinning is the interaction of charges or dipole loaded on the polymer chains. So connection between jet current and the fiber property is worthy to know. As fig.2 shows, when the added HBP content is constant, the current decreases with the increase of PVA content in PP/PVA compounds. It means the increase of PVA content in compound causes the increase of material viscosity and thus the jets velocity decreases and thicker fibers are got, all these facts lead to the decrease of jet current.
0.13 0.12 0.11 0.1 0.09 0.08 0
5
10
15
20
PVA content(%)
Fig.2 The processing jet current when different content PVA was added into PP/PVA.
Current(mA)
Fig.3 told that when different contents of HBP were added into the same PP/PVA compound, the current decreased with the increase of HBP content. That because the more HBP (
