靜電紡絲—循環熱壓法製備PVDF膜之多態結晶相分析｜國立臺灣科技大學博碩士論文系統

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研究生：	蘇柏諺 Po-Yan Su
論文名稱：	靜電紡絲—循環熱壓法製備PVDF膜之多態結晶相分析 Polymorphic Structures Analysis of Poly(vinylidene fluoride) (PVDF) Fabricated by Electrospinning—Cyclic Hot-Pressing Technique
指導教授：	周振嘉 Chen-Chia Chou
口試委員:	蔡大翔 Dah-Shyang Tsai 吳昌謀 Chang-Mou Wu
學位類別：	碩士 Master
系所名稱：	工程學院 - 機械工程系 Department of Mechanical Engineering
論文出版年：	2022
畢業學年度：	110
語文別：	英文
論文頁數：	148
中文關鍵詞：	靜電紡絲、PVDF 、熱壓、相含量、單相結晶度、熱穩定性
外文關鍵詞：	Electrospinning, PVDF, Hot-Pressing, Phase fraction, Crystallinity of each phase, Thermal stability
相關次數：	點閱：208 下載：0
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本研究先將聚偏二氟乙烯(PVDF)以靜電紡絲之製程產生一定量的β相，然後再使用循環熱壓的方式來探討其對於PVDF生成β相之影響及三相(α、β、γ)的相變化與熱穩定性。其中的重點在於循環熱壓法可否影響靜電紡絲PVDF的極性相(β、γ)之生成。本研究分成兩部分，第一部分先利用機械壓縮的方式來探討在何種壓力(50 ~ 500 MPa)的條件下最有利於靜電紡絲PVDF中極性相的生成；第二部分則沿用第一部分的最佳壓力(300 MPa)來對靜電紡絲PVDF進行循環熱壓的實驗。試片表面形貌由SEM觀察，而DSC與FTIR可以分別計算總結晶度(Xc)與個別的相含量(F(α)、F(β)、F(γ))，且總結晶度與相含量相乘可得到單相結晶度(Xα、Xβ、Xγ)最後在使用XRD來推估試片的應變與晶粒大小。

首先，第一部分中以機械壓力對電紡PVDF進行壓縮，由FTIR的計算結果發現在壓力為300MPa的條件下PVDF的F(β)由原本電紡的56.22 %上升到最高值66.94 %，因此後續循環熱壓便全部在壓力為300 MPa的固定壓力下進行。

第二部分實驗中的SEM圖表現出在熱壓溫度大於100 oC時，試片會有較低的孔隙率。但是因為電紡PVDF初始孔隙較多，因此有機會出現空氣團聚而形成孔洞。從DSC計算的結晶性中可以發現所有試片均在熱壓溫度為140 oC時有最高的結晶性，表示PVDF在此溫度最容易生成穩定的結晶型態，其中最高結晶度為試140 oC熱壓1循環(140-1)的58.74 %。此外，在FTIR中我們不只單純計算出各相的含量，我們必須將DSC計算的結晶度(Xc)與各別相含量(F(α)、F(β)及F(γ))相乘，從而得到真正的單相結晶度(Xα、Xβ及Xγ)，以便更好觀察循環熱壓法對於電紡PVDF的影響。而其中試片160-1有最高的Xβ = 43.7 %，試片140-1有最高的Xα = 15.4 %以及第二高的Xβ = 43.3 %。另外，在熱壓溫度低於165 oC時Xβ會隨熱壓溫度增加而增加。由此可知在140 oC ~ 165 oC時我們可以此為基礎來增加更多的β相結晶度。然而，本研究中的循環熱壓法的Xβ與Xc會隨著熱壓的循環次數增加而急遽減少，就像是在4循環實驗中熱壓溫度高於140 oC時的各相結晶性皆不超過15 %，在8循環中更是不超過10 %。在DSC與FTIR的資料整合中，我們還可以整理出在電紡PVDF的熱壓製程後對各相熱穩定性的影響。從試片165-2與170-2的DSC圖中可以發現γ相的吸熱峰值最低點為172.69 oC，也是本研究中發現的γ相存在的最低熔點。另外，在試片165-8中觀察到兩個吸熱峰(174.87 oC及176.37 oC)，再加上此試片中的β相結晶度大於α相結晶度，推斷β相在此條件下的熱穩定性是大於α相的，所以174.87 oC為β相的最高熔點。再由XRD的分析結果中我們得知α相的應變一直高於β相，並且隨著循環次數增加而略為增加，符合文獻資料中提到的β相可以由受應力影響的α相變化而來。雖然電紡PVDF的結晶度會隨熱壓溫度及循環次數增加而降低，而由Scherrer’s 方程式估算的晶粒大小中顯示各相的平均晶粒大小會隨著熱壓的溫度及循環次數提高而增加。

綜上所述，相較於原始的電紡纖維膜，循環熱壓製程可以有效增加試片的密度以及降低試片的缺陷。當熱壓溫度低於或等於140 oC時，熱壓循環次數的增加亦同時增加Xc與Xβ；而當熱壓溫度高於140 oC時會增加高分子鏈的活動性從而使Xc與Xβ呈現相反的趨勢。在140 oC及160 oC的1循環熱壓條件下可得到最佳的Xβ為43.5 %，因為此溫度最接近PVDF的再結晶溫度。為獲得大晶粒與高結晶度的β相，熱壓溫度應該要低於 165 oC且低於4次循環；而大晶粒與高結晶度的γ相熱壓溫度則是要大於160 oC且循環約2 ~ 4次。

This research aims to obtain a higher amount of the β phase, the phase transition, and their thermal stability in PVDF produced by the electrospinning and hot-pressing approach. To have a better investigation of the effects of the cyclic hot-pressing (HP) process, two series of experiments were conducted. First, the electrospun (ES) PVDF membranes were compressed under various pressures (50 ~ 500 MPa). Secondly, the cyclic HP was conducted at various temperatures (60 ~ 170 oC) for various cycles (1 ~ 8 cycles). For calculating the crystallinity of each phase (Xα, Xβ, and Xγ), we multiply the phase fraction (F(α), F(β), and F(γ)) with the total crystallinity (Xc) which was obtained from FTIR spectra and DSC curves, respectively.

In the first series of experiments, the ES PVDF membranes were mechanically pressed and investigated the maximum electroactive phase fraction within the PVDF membranes. According to the FTIR spectra, the fraction of the β phase, F(β), reaches the optimal value of 66.94 % under 300 MPa, while that of the raw ES PVDF shows a value of 56.22 %.

In the second series of experiments, we conducted the HP process at various temperatures for various cycles under the optimal pressure of 300 MPa from the first series of results. The SEM micrographs show the surface morphology with low porosity and high packing density as the HP temperature is higher than 100 oC; however, some aggregated air bubbles are observed due to the agglomeration of the primitive air gaps within the ES PVDF nanofibers. From DSC curves, it is noteworthy that the highest Xc in each cycle is achieved at an HP temperature of 140 oC. The optimal Xβ of 43.7 % is reached in the sample hot-pressed at 160 oC for 1 cycle (160-1), while the optimal Xα of 15.4 % and the second-highest Xβ of 43.3 % are obtained in sample 140-1. On the other hand, when the HP temperature is lower than 165 oC, the Xβ increases with the increase of the HP temperature. We find out that the Xc will dramatically decrease with the increasing HP cycle, implying that the Xα and Xβ decreased as well. Furthermore, we thoroughly investigate the thermal stability of each phase in hot-pressed ES PVDF by analyzing the DSC curves and the FTIR spectra. The β phase has a melting temperature (Tm) of 174.9 oC which shows higher thermal stability than that of the α phase. From the XRD results, we know that the calculated strain of the α phase is always higher than that of the β phase and increases with the increasing HP cycle. As literature reported, the β phase is stress induced by the deformation of the α phase. Notwithstanding that the total crystallinity will decrease with the increase of the HP temperature and the cycle, the crystallites sizes of each phase (Dc) increase with the increasing HP temperature and the cycle.

In summary, the cyclic HP process produces the PVDF membrane with higher density and lower defects as we compare it with the virgin ES PVDF. Furthermore, the increase of the HP cycle also improves the Xc and the Xβ when the HP temperature is lower than 140 oC, while that of hot-pressed at the temperature higher than 140 oC shows a decreasing tendency due to the increase of the HP temperature improve the polymer chain mobility of the PVDF. The optimal Xβ around 43.5 % is obtained by HP at 140 or 160 oC for 1 cycle owing to this HP temperature contributing to the recrystallization of the PVDF. To obtain high β phase’s crystallinity with large crystallites sizes, the ES PVDF should be hot-pressed at a temperature within 140 ~ 160 oC for the cycle no more than 4 times, while that of the γ phase should be conducted at an HP temperature that is higher than 160 oC for 2 ~ 4 cycles.

Abstract    I
中文摘要    III
Acknowledgments    V
Table of Contents    VII
List of Figures    X
List of Tables    XVII
Chapter 1  Introduction    1
Chapter 2  Literature Review    3
2-1 Piezoelectric Materials    3
2-2 Polyvinylidene Difluoride (PVDF)    5
2-2-1 Crystalline Structures of PVDF    6
2-3 Electrospinning Technology    10
2-3-1 Polymer Solution Properties    14
2-3-1-1 Molecular Weight, Polymer Concentration, and Solution Viscosity    14
2-3-1-2 Surface Tension    16
2-3-2 Process Parameters    17
2-3-2-1 Applied Voltage    17
2-3-2-2 Feeding Rate    19
2-3-2-3 Effect of Collector    19
2-3-2-4 Diameter of Pipette Orifice / Needle    20
2-3-2-5 Distance between Tip and Collector    21
2-4 Hot Pressing for PVDF    21
2-5 Fourier Transform Infrared Spectrometer (FTIR) [43]    24
2-6 Differential Scanning Calorimetry (DSC)    26
Chapter 3  Experimental Procedures and Measurement Methods    29
3-1 Experimental Procedures    29
3-1-1 Preparation of PVDF Solution    31
3-1-2 Electrospinnig Parameters    32
3-1-3 Hot Pressing Procedures    33
3-2 Measurements and Analysis    35
3-2-1 Fourier Transform Infrared Spectrometer (FTIR)    35
3-2-2 Differential Scanning Calorimetry (DSC)    39
3-2-3 Scanning Electron Microscopy (SEM)    41
3-2-4 X-Ray Diffractometer (XRD)    41
Chapter 4  Results and Discussion    42
4-1 Crystallinity and Polymorphisms in Electrospun PVDF    42
4-2 Optimized Mechanical Pressure for Electrospun PVDF Membrane    46
4-3 1 Cycle Hot-Pressing at Various Temperatures    52
4-3-1 SEM Evolution    52
4-3-2 DSC & FTIR    54
4-3-3 XRD Analysis    59
4-4 2 Cycles Hot-Pressing at Various Temperatures    62
4-4-1 SEM Evolution    63
4-4-2 DSC & FTIR    64
4-4-3 XRD Analysis    70
4-5 4 Cycles Hot-Pressing at Various Temperatures    73
4-5-1 SEM Evolution    74
4-5-2 DSC & FTIR    75
4-5-3 XRD Analysis    81
4-6 8 Cycles Hot-Pressing at Various Temperatures    84
4-6-1 SEM Evolution    84
4-6-2 DSC & FTIR    86
4-6-3 XRD Analysis    92
4-7 Effects of the Cyclic Hot-Pressing on ES PVDF Membrane    95
4-7-1 Surface Morphology Evolution in Hot-Pressed ES PVDF    95
4-7-2 Phases’ Transitions and Their Crystallinity    96
4-7-3 Thermal Stability Enhancement    100
4-7-4 Crystallites Size and Strain    103
Chapter 5  Conclusions    106
Bibliography    108
Appendix    114
Appendix I － α Phase    114
Appendix II － β Phase    116
Appendix III － γ Phase    117
Appendix IV － XRD Pattern of Sample 170-2 Plot With the PDF Cards of Three Phases    118
Appendix V － All Crystallites Size from XRD Patterns for 1 cycle    119
Appendix VI － All Crystallites Size from XRD Patterns for 2 cycles    121
Appendix VII － All Crystallites Size from XRD Patterns for 4 cycles    123
Appendix VIII － All Crystallites Size from XRD Patterns for 8 cycles    125
Appendix IX － All of the Thicknesses of the Hot-Pressed ES PVDF membranes    127
                                

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全文公開日期 2025/01/24 (校內網路)
全文公開日期 2028/01/24 (校外網路)
全文公開日期 2028/01/24 (國家圖書館：臺灣博碩士論文系統)

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