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Crystallization of Electrospun Polymer Nanofibers

Author: SuFeng
Tutor: YuZuo
School: Donghua University
Course: Nanofibers and hybrid materials
Keywords: electrospun fiber crystallization glass transition temperature ambienttemperature
CLC: TQ340.1
Type: Master's thesis
Year: 2013
Downloads: 22
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Abstract


Electrospinning is a convenient, straightforward, and inexpensive method of preparing polymer fibers at submicron scales. Recently, with the development of nano-technology, electospinning method caught more sights, and was widely applied in many fields like environment engineering, tissue engineering and new energy materials. These potential applications of electrospun fibers depend on its properties, such as mechanical properties, thermal properties and piezoelectric properties. And the crystallization of fibers influenced these properties directly. From the reports, some kinds of electrospun polymer fibers were amorphous. And some other kinds of electrospun polymer fibers could crystallize. By concluding the results of other researchers, we found a relationship among glass transition temperature (Tg), ambient temperature and crystallization of electrospun fibers. Some polymer with lower Tg than ambient temperature still showed crystal structure after electrospinning process, such as polyoxyethylene (PEO), polyvinylidene fluoride (PVDF) and isotactic polybutene (i-PB). But the polymer with higher Tg than ambient temperature didn’t crystallize after electrospinning process, such as poly(L-lactide)(PLLA), polyethylene terephthalate (PET), poly(trimethylene terephthalate)(PTT), syndiotactic polystyrene (s-PS) and polyacrylonitrile (PAN). In order to prove this hypothesis, some experimental systems were used as follows.For verifying the correctness of the hypothesis above, crystallization of some other kinds of electrospun polymer fibers were studied. Some crystallized polymer with different Tg were electrospun, including polyoxyethylene (PEO), polycaprolactone (PCL), polyhydroxybutyrate (PHB), polyvinylidene fluoride (PVDF), poly(L-lactide)(PLLA) and polymethylmethacrylate (PMMA). The crystallization of these different polymer fibers was studied by XRD method. The result showed that crystallization of these electrospun polymer fibers still followed the hypothesis.For the polymer with lower Tg than ambient temperature, its electropun fibers still could crystallize, such as PEO, PCL, PHB, PVDF and PHBV. And for the polymer with higher Tg than ambient temperature, its electrospun fibers were almost amorphous, such as PLLA, PMMA, PET, PTT, PAN and isotactic polystyrene (i-PS). Thus the relationship between Tg and ambient temperature played an important role on crystallization of electrospun fibers.Meanwhile, for further proving the hypothesis, the influences of Tg and ambient temperature on crystallization of electrospun polymer fibers were explored from different standpoints.In order to get the information how ambient temperature influenced the crystallization of electrospun polymer fibers, crystallization of electrospun PLLA fibers was studied. The result showed that PLLA fibers were always amorphous when ambient temperature was lower than its glass transition temperature. And the fibers began to crystallize once the ambient temperature was higher than its glass transition temperature. The result indirectly proved the hypothesis that the relationship between Tg and ambient temperature played an important role on the crystallization of electrospun polymer fibers.Then, the influences of Tg on crystallization of electrospun polymer fibers were studied. By controlling the moisture of experimental environment, Tg of PVA could be changed. And crystallization of electrospun PVA fibers was changed with the change of its glass transition temperature. When the glass temperature of PVA was higher than ambient temperature, PVA fibers were amorphous. However, once the glass transition temperature was below ambient temperature, PVA fibers began to crystallize. This result also proved the hypothesis.Therefore, the influences of Tg and ambient temperature on the crystallization of electrospun polymer fibers followed the hypothesis. And it could be concluded that some polymer with lower Tg than ambient temperature still could crystallize after electrospinning process, but the other polymer with higher Tg than ambient temperature were amorphous after electrospinning process.

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CLC: > Industrial Technology > Chemical Industry > The chemical fiber industry > General issues > Basic theory
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