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Citation: Liu, H.; Tian, J.; Pan, G.; Xie,
Y.; Yao, Q. Preparation of the Flexible
Green Body of YAG Ceramic Fiber by
Melt Spinning. Polymers 2022,14,
2096. https://doi.org/10.3390/
polym14102096
Academic Editors: Tao-Hsing Chen
and Shih-Chen Shi
Received: 18 April 2022
Accepted: 19 May 2022
Published: 20 May 2022
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polymers
Article
Preparation of the Flexible Green Body of YAG Ceramic Fiber
by Melt Spinning
Hongmei Liu 1,2, Junjie Tian 1, Gangwei Pan 3, Yongjin Xie 1and Qing Yao 1,*
1School of Mechanical Engineering, Nantong University, Nantong 226000, China; liu.hm@ntu.edu.cn (H.L.);
2009310006@stmail.ntu.edu.cn (J.T.); xieyongjin1030@163.com (Y.X.)
2School of Transportation and Civil Engineering, Nantong University, Nantong 226000, China
3School of Textile and Clothing, Nantong University, Nantong 226000, China; pangangwei@ntu.edu.cn
*Correspondence: yaoqing@ntu.edu.cn
Abstract:
YAG ceramic fiber, with its high thermal conductivity and easy to achieve limit size,
provides design flexibility as a laser gain medium. Its mainstream forming method was mainly
high-pressure extrusion, but there were disadvantages, such as lack of flexibility. In this work, the
flexible green body of YAG ceramic fiber was prepared by melt spinning. The melting characteristics
of TPU with four different Shore hardnesses were systematically investigated. The microstructure,
element homogeneity of the surface and fracture SEM images of the prepared ceramic fiber were
also analyzed in detail. The optimized process parameters of YAG ceramic fiber preparation were as
follows: the melting temperature was 220
◦
C, the screw feed rate of the double-cone screw extruder
was
F = 15.0 mm/min
and the TPU-95A# was used. The ceramic fiber with the mass ratio of TPU-
95A# to ceramic powder = 4:6 had the best microstructure quality. It had good flexibility and could
be knotted with a bending radius of about 2.5 mm, and the tensile strength reached approximately
20 MPa. These results are crucial for advancing YAG ceramic fiber applications.
Keywords: flexibility; YAG ceramic fiber; melt spinning; thermoplastic polyurethane (TPU)
1. Introduction
Since the invention of the first fiber laser in 1961 [
1
], fiber laser technology has been
developing from low power to high power. Now, the fiber laser is moving in the direction
of “any wavelength, any pulse duration and any power”. With its compact structure, high
conversion efficiency, convenient thermal management and flexible operation, the fiber
laser has been widely used in advanced manufacturing, energy exploration, biomedicine,
defense security and other fields [
2
]. Therefore, the further development of high-power
fiber laser technology has become urgent, and it is of great significance. The preparation of
the optical gain fiber as one of the core technologies is key.
Due to the low thermal conductivity of quartz glass (1.38 W/(m
·
K)), poor mechanical
performance and large bending radius, the traditional fiber laser is prone to large thermal
gradients, optical distortion, limited output power and mechanical damage during long-
time operation. Therefore, the application of high-power fiber lasers is limited by the
intrinsic properties of quartz glass [
3
]. Single crystal fibers, such as the Y
3
Al
5
O
12
(YAG)
crystal fiber, have the advantages of excellent physical and chemical properties of crystal
and thermal management. They can meet the application requirements of high-power
lasers [
4
]. In 2012, a French research team used the Yb: YAG single fiber prepared by
micro-pull-down to achieve the 251 W maximum continuous laser output power and 53%
slope efficiency at 1030 nm, which is the highest continuous laser output power and the
highest conversion efficiency obtained with the single crystal fiber thus far [
5
]. Researchers
of the Chinese Academy of Sciences have recently developed a new laser heating base
(LHPG) single crystal optical fiber growth furnace. They have successfully prepared a
Yb: YAG single crystal optical fiber with a diameter of 0.2 mm and a length of 710 mm. It
Polymers 2022,14, 2096. https://doi.org/10.3390/polym14102096 https://www.mdpi.com/journal/polymers
Polymers 2022,14, 2096 2 of 13
has the length–diameter ratio of a single crystal fiber >3000 and the diameter fluctuates
within
±
5%, with the highest aspect ratio among similar single crystal fibers in China [
6
].
Nevertheless, the preparation temperature of a single crystal optical fiber is generally above
the melting point. It has a complex production process, high equipment requirements, high
energy consumption and high cost. Especially, due to the separation coefficient of a single
crystal, high concentration doping is hindered, resulting in limited power improvement [
3
].
In 1995, Dr. Akio Ikesue prepared the world’s first laser transparent ceramics [
7
].
Transparent ceramics, with their high concentration of uniform doping, high thermal
conductivity and easy to achieve limit size, provide design flexibility as a laser gain
medium [
8
]. Accordingly, Kim and Fair from the U.S. Air Force Laboratory successfully
realized the preparation of a 30
µ
m diameter ceramic fiber using transparent ceramic
materials, verifying the feasibility of the fiber laser as a gain medium [
9
]. The materials
used in ceramic fiber are the most representative in yttrium aluminum garnet structure
(Y
3
Al
5
O
12
, YAG) transparent ceramics, with a wide range of uses, good optical performance
and high quantum efficiency advantages. Their good performance is well adapted to the
requirements of a high-power optical fiber laser [
10
–
12
]. For instance, Ikesue prepared
the Nd: YAG ceramic fiber that was 65 mm in length and 900 m in diameter by extrusion
and solid phase reaction [
13
,
14
]. Kim and Fair extruded a YAG fiber green body through
a 125 mm nozzle and sintered a highly transparent YAG transparent ceramic fiber with
hot isostatic pressure. The ceramic fiber diameter was about 20
µ
m and bend radius was
3 mm [
15
–
17
]. Recently, a novel route that combined aqueous gelcasting with a capillary
glass tube was designed to prepare a Yb: YAG transparent ceramic fiber with a diameter of
1.0 mm and length of 43.0 mm for the first time [18].
In addition to laser applications, YAG ceramic fiber is also of great interest in scintillator
research [
19
]. Dai and Wu prepared Ce: LuAG scintillation single crystal fibers (SCFs)
with excellent scintillation performance by adopting the laser-heated pedestal growth
(LHPG) method [
20
]. YAG ceramic fiber even has broad prospects in nuclear/fusion
applications [
21
]. Under different temperature radiation, the track diameters in both YAP
and YAG were very similar, and less energy was required for YAG [22].
However, due to the micron diameter, the preparation of YAG ceramic fiber was
difficult. Its mainstream forming method was mainly the high-pressure extrusion of Kim
and Fair and Ikesue et al. [
16
,
23
,
24
]. However, there are disadvantages to extrusion such
as metal ion impurities, organic matter residue and lack of flexibility. Therefore, it is very
necessary to explore new forming methods to overcome the shortcomings.
In this paper, a flexible green body of YAG transparent ceramic fiber was prepared by
the melt-spinning process for the first time. The process parameters under TPU with four
different Shore hardnesses, screw feed rates and melting temperatures were systematically
studied. The microstructure and uniformity of the green body were fully analyzed. In
particular, the mechanical properties such as strength, flexibility and bending radius were
researched in detail. The flexibility and bending strength of the YAG ceramic fiber were
significantly improved.
2. Experimental Procedure
The preparation process for the flexible green body of YAG ceramic fiber is shown in
Figure 1. It mainly consisted of two parts: the preparation of YAG ceramic powder and the
preparation of the flexible green body of YAG fiber by melt spinning.
Polymers 2022,14, 2096 3 of 13
Polymers2022,14,xFORPEERREVIEW3of14
Figure1.ProcessofpreparingtheflexiblegreenbodyofYAGceramicfiberbymeltspinning.
2.1.YAGCeramicPowderPreparation
Inthepresentstudy,Y2O3(99.99%purity,YuelongNewMaterialsCo.,Ltd.,Shang‐
hai,China),withanaverageparticlesizeof6.0μm,andα‐Al2O3(99.99%purity,Shanghai
YuelongChemicalCo.,Ltd.,Shanghai,China),withthemeanparticlesizeof160.0nm,
wereusedasstartingmaterials.Theabove‐mentionedpowderswithgooddispersionand
uniformwereweighedbasedonthestoichiometricratioofY3Al5O12.Thesinteringaddi‐
tivesweretetraethylorthosilicate(TEOS,99.99%purity,AlfaAesar,WardHill,Haverhill,
MA,USA)withanamountof0.5wt.%andMgO(99.99%purity,AlfaAesar,WardHill,
Haverhill,MA,USA)withanamountof0.1wt.%.Theyweremixedwithabsoluteethyl
alcoholandthenballmilledatarotationspeedof200r/minusinghigh‐purityAl2O3balls.
After12hofballmilling,themixedpowdershadgooduniformityandtheaverageparti‐
clesizewas360nm.Afterwards,themilledslurrywasdried,groundandsievedthrough
a200‐meshscreenthreetimes.Then,themixedpowderswerecalcinedat800°Cfor8h
inamufflefurnace.
2.2.MeltSpinningforFlexibleGreenBody
Thecommercialthermoplasticpolyurethane(TPU)particlesofdifferentShorehard‐
nesses75A,80A,90Aand95AwerelabelledTPU‐75A#,TPU‐80A#,TPU‐90A#andTPU‐
95A#,respectively.TheywerethoroughlymixedwiththepreparedYAGceramicpow‐
dersinamixer(HWV800,ShenzhenHasaiTechnologyCo.,Shenzhen,China)ataspeed
of100r/min.ThemassratioofTPUtoYAGceramicpowderwas4:6or3:7.Then,the
ceramic/TPUmixeswereputintoaminiaturetwin‐conescrewextruder(WLG10G,
ShanghaiXinshuoLtd.,Shanghai,China)andamatchingdrawingmachineformeltspin‐
ning(showninFigure2).Thetwin‐conescrewextruderwassetatdifferentscrewfeed
speeds(5mm/min,10mm/min,15mm/minand20mm/min),differentmelttemperatures
(160°C,180°C,200°Cand220°C),anddifferentnozzlediameters(0.2mm,0.3mmand
0.5mm)(Figure2a).Meanwhile,theextrudedfiberswerecooledinair(Figure2b)and
drawncontinuouslybyadrawingmachine(Figure2c).Finally,thecontinuousandflexi‐
blegreenbodyofYAGceramicfiberwasobtainedsuccessfullybymeltspinning.
Figure 1. Process of preparing the flexible green body of YAG ceramic fiber by melt spinning.
2.1. YAG Ceramic Powder Preparation
In the present study, Y
2
O
3
(99.99% purity, Yuelong New Materials Co., Ltd., Shanghai,
China), with an average particle size of 6.0
µ
m, and
α
-Al
2
O
3
(99.99% purity, Shanghai
Yuelong Chemical Co., Ltd., Shanghai, China), with the mean particle size of 160.0 nm,
were used as starting materials. The above-mentioned powders with good dispersion and
uniform were weighed based on the stoichiometric ratio of Y
3
Al
5
O
12
. The sintering addi-
tives were tetraethyl orthosilicate (TEOS, 99.99% purity, Alfa Aesar, Ward Hill, Haverhill,
MA, USA) with an amount of 0.5 wt.% and MgO (99.99% purity, Alfa Aesar, Ward Hill,
Haverhill, MA, USA) with an amount of 0.1 wt.%. They were mixed with absolute ethyl
alcohol and then ball milled at a rotation speed of 200 r/min using high-purity Al
2
O
3
balls.
After 12 h of ball milling, the mixed powders had good uniformity and the average particle
size was 360 nm. Afterwards, the milled slurry was dried, ground and sieved through a
200-mesh screen three times. Then, the mixed powders were calcined at 800
◦
Cfor8hina
muffle furnace.
2.2. Melt Spinning for Flexible Green Body
The commercial thermoplastic polyurethane (TPU) particles of different Shore hard-
nesses 75A, 80A, 90A and 95A were labelled TPU-75A#, TPU-80A#, TPU-90A# and TPU-
95A#, respectively. They were thoroughly mixed with the prepared YAG ceramic powders
in a mixer (HWV 800, Shenzhen Hasai Technology Co., Shenzhen, China) at a speed of
100 r/min. The mass ratio of TPU to YAG ceramic powder was 4:6 or 3:7. Then, the
ceramic/TPU mixes were put into a miniature twin-cone screw extruder (WLG10G, Shang-
hai Xinshuo Ltd., Shanghai, China) and a matching drawing machine for melt spinning
(shown in Figure 2). The twin-cone screw extruder was set at different screw feed speeds
(5 mm/min, 10 mm/min, 15 mm/min and 20 mm/min), different melt temperatures
(160
◦
C, 180
◦
C, 200
◦
C and 220
◦
C), and different nozzle diameters (0.2 mm, 0.3 mm and
0.5 mm) (Figure 2a). Meanwhile, the extruded fibers were cooled in air (Figure 2b) and
drawn continuously by a drawing machine (Figure 2c). Finally, the continuous and flexible
green body of YAG ceramic fiber was obtained successfully by melt spinning.
Polymers 2022,14, 2096 4 of 13
Polymers2022,14,xFORPEERREVIEW4of14
Figure2.Equipmentformeltspinninganddrawing:(a)nozzleofmeltspinningmachine,(b)YAG
ceramicfibercoolinginair,(c)drawingmechanismandformingprocess.
2.3.Characterizations
ThesurfacesandfractureoftheYAGfibergreenbodyandthedistributionofele‐
mentsintheYAGfiberwereobservedbyascanningelectronmicroscope(SEM,JSM‐6510,
JEOL,Kariya,Japan)withanenergydispersivespectrometer(EDS,Aztec,OxfordInstru‐
ments,Oxford,UK)system.
TheflowrateofmeltmassofTPUswithdifferentShorehardnesseswasdetermined
byameltindexmeter(XNR‐400C,Goettfert,Germany).TheTPUparticlesweremelted
intoaplasticfluidatameltingtemperatureof205°Candaloadof2.16kg.Thiswas
followedbythemassexitingthrougha2.1mmdiametercirculartubewithin10min.The
greaterthemass,thebetterthemeltflowoftheTPU,andviceversa.
ThediameterandtensilestrengthofYAGceramicfiberwithdifferentcomponents
weretestedbyamonofilamentstrengthmeterwithaloadingrateof2mm/min(YM‐06D,
NantongHongdaExperimentalInstrumentCo.,Ltd.,Nantong,China).
Figure 2.
Equipment for melt spinning and drawing: (
a
) nozzle of melt spinning machine, (
b
) YAG
ceramic fiber cooling in air, (c) drawing mechanism and forming process.
2.3. Characterizations
The surfaces and fracture of the YAG fiber green body and the distribution of elements
in the YAG fiber were observed by a scanning electron microscope (SEM, JSM-6510, JEOL,
Kariya, Japan) with an energy dispersive spectrometer (EDS, Aztec, Oxford Instruments,
Oxford, UK) system.
The flow rate of melt mass of TPUs with different Shore hardnesses was determined
by a melt index meter (XNR-400C, Goettfert, Germany). The TPU particles were melted
into a plastic fluid at a melting temperature of 205
◦
C and a load of 2.16 kg. This was
followed by the mass exiting through a 2.1 mm diameter circular tube within 10 min. The
greater the mass, the better the melt flow of the TPU, and vice versa.
The diameter and tensile strength of YAG ceramic fiber with different components
were tested by a monofilament strength meter with a loading rate of 2 mm/min (YM-06D,
Nantong Hongda Experimental Instrument Co., Ltd., Nantong, China).
Polymers 2022,14, 2096 5 of 13
3. Results and Discussion
TPU has excellent properties of good elasticity and high strength. The melting charac-
teristics of the organic polymer can be used as the “binder” of inorganic ceramic powder.
More importantly, TPU, with both excellent mechanical properties and melt fluidity, can
meet the forming demand of YAG ceramic fiber; thus, the prepared YAG ceramic fiber also
had high strength and good flexibility [
25
,
26
]. Therefore, TPU, with its high transparency
and purity, and different Shore hardnesses of 75A, 80A, 90A and 95A, was selected in this
study [27,28].
Figure 3shows the flow rate of melt mass and average flow rate of melt mass for
TPU with different Shore hardnesses under the same experimental conditions. Figure 3a
shows that the melt mass flow rate of TPU-75A# was 13.96 g/10 min, 13.90 g/10 min and
13.98 g/10 min
. Figure 3b displays the melt mass flow rate of TPU-80A# as 13.76 g/10 min,
13.74 g/10 min and 13.70 g/10 min. In Figure 3c, the melt mass flow rates of TPU-90A#
were 12.84 g/10 min, 12.88 g/10 min and 12.80 g/10 min. Lastly, in Figure 3d, it was
found that the melt mass flow rates of TPU-95A# were 15.72 g/10 min, 15.70 g/10 min and
15.74 g/10 min
. According to Figure 3a–d, it can be described that the melt mass flow rate
error of the four-hardness TPUs is very small after three tests. Consequently, it could be
expressed by the average flow rate of the corresponding melt mass. The average flow rates
were
13.95 g/10 min
, 13.73 g/10 min, 12.84 g/10 min and 15.72 g/10 min of TPU-75A#,
TPU-80A#, TPU-90A#, and TPU-95A#, respectively, as shown in Figure 3e. Obviously,
TPU-95A# had the highest average melt mass flow rate. TPU-90A# had a better hardness
value, but the melt mass flow rate was not as good as TPU-75A# and TPU-80A#. It could
be seen that the Shore hardness was not positively correlated with the flow rate of melt
mass, and TPU-95A # had the best hardness and melting characteristics in this experiment.
To further select the appropriate TPUs and optimize the process parameters of the
miniature twin-cone screw extruder, the performance of ceramic fiber under different
TPU types, screw feed rates and melting temperatures was tested by a single variable
method to obtain the best melt-spinning process conditions. Moreover, the melting rate,
flowability, formation of silk of molten mass and fiber tensile strength and flexibility were
set as “perceptual observation characteristics”. Table 1presents the concerned properties,
symbols and meanings of the molten mass and YAG ceramic fibers. Among them, the speed
of the melting rate is represented by the number of pentagrams, the intensity of tensile
strength is expressed by the number of circles, the difference in flexibility is represented
by the number of squares, the fluidity of the molten body is represented by the number of
triangles and the difficulty of filamentation is represented by the number of rhombuses.
Table 1. Concerned properties, symbols and meanings of the molten mass and YAG ceramic fibers.
Property Symbols and Meanings
Melting rate I(slow) →III (fast)
Tensile strength #(low) →### (high)
Flexibility (poor) → (good)
Flowability 4(poor) → 444 (good)
Forming silk 3(difficulty) →333 (easy)
Table 2provides the performance effects of different TPUs on ceramic fiber at the
melting temperature of 220
◦
C, feed speed of 15 mm/min and a nozzle diameter of 0.3 mm.
All four TPU types could melt and spin smoothly, but the TPU-95A# ceramic fiber had the
best melting rate, tensile strength and flexibility. The TPU-95A# served as the best TPU
option accordingly.
Polymers 2022,14, 2096 6 of 13
Polymers2022,14,xFORPEERREVIEW6of14
Figure3.Histogramsofflowrateofmeltmassandaverageflowrateofmeltmassfordifferent
TPUs:(a)TPU‐75A#,(b)TPU‐80A#,(c)TPU‐90A#,(d)TPU‐95A#;(e)averageflowrateoffourTPUs’
meltmass.
Table2providestheperformanceeffectsofdifferentTPUsonceramicfiberatthe
meltingtemperatureof220 °C,feedspeedof15mm/minandanozzlediameterof0.3mm.
AllfourTPUtypescouldmeltandspinsmoothly,buttheTPU‐95A#ceramicfiberhadthe
Figure 3.
Histograms of flow rate of melt mass and average flow rate of melt mass for different
TPUs: (
a
) TPU-75A#, (
b
) TPU-80A#, (
c
) TPU-90A#, (
d
) TPU-95A#; (
e
) average flow rate of four TPUs’
melt mass.
Polymers 2022,14, 2096 7 of 13
Table 2.
Performance effects of different TPUs on ceramic fiber at melting temperature of 220
◦
C,
feed speed of 15 mm/min and nozzle diameter of 0.3 mm.
No. TPU Label Samples Exhibition Characteristics and Analysis
1 75A
Polymers2022,14,xFORPEERREVIEW7of14
bestmeltingrate,tensilestrengthandflexibility.TheTPU‐95A#servedasthebestTPU
optionaccordingly.
Table2.PerformanceeffectsofdifferentTPUsonceramicfiberatmeltingtemperatureof220°C,
feedspeedof15mm/minandnozzlediameterof0.3mm.
No.TPULabelSamplesExhibitionCharacteristicsandAnalysis
175A
Meltingrate:☆☆
Tensilestrength:○○
Flexibility:□
280A
Meltingrate:☆☆
Tensilestrength:○○
Flexibility:□
390A
Meltingrate:☆
Tensilestrength:○○○
Flexibility:□□
495A
Meltingrate:☆☆☆
Tensilestrength:○○○
Flexibility:□□□
Table3demonstratestheperformanceeffectsofthedifferentfeedspeedsofscrews
ontheceramicfiberwithameltingtemperatureof220°C,TPU‐95A#andanozzlediam‐
eterof0.3mm.Itwasfoundthatwithinacertainrange(from5mm/minto15mm/min),
improvingthefeedspeednotonlyacceleratedthemeltingrate,butalsopromotedthe
tensilestrengthandflexibilityoftheceramicfiber.Nevertheless,whenthefeedspeedex‐
ceededacertainvalueandreached20mm/min,theincreasedshearratewoulddestroy
themolecularchainintheTPU[29,30].Itgraduallyuntiedandslidthemoleculesfrom
thenetworkstructure,anddecreasedtheconcentrationofthephysicalcrosslinkingpoint,
leadingtofurtherimprovementofthemeltingrate[31,32].However,theexcessivereduc‐
tionofmolecularweightreducedthemechanicalpropertiesofTPU,whichreducedthe
flexibilityandelasticityofthefinishedproduct.Therefore,thefeedspeedoftheoptimized
screwwas15mm/min.
Table3.Performanceeffectsofdifferentfeedspeedsofscrewsonceramicfiberatmeltingtemper‐
atureof220°C,TPU‐95A#andnozzlediameterof0.3mm.
No.FeedSpeed SamplesExhibitionCharacteristicsandAnalysis
15
Meltingrate:☆
Tensilestrength:○
Flexibility:□
210
Meltingrate:☆☆
Tensilestrength:○○
Flexibility:□□
Melting rate: II
Tensile strength: ##
Flexibility:
2 80A
Polymers2022,14,xFORPEERREVIEW7of14
bestmeltingrate,tensilestrengthandflexibility.TheTPU‐95A#servedasthebestTPU
optionaccordingly.
Table2.PerformanceeffectsofdifferentTPUsonceramicfiberatmeltingtemperatureof220°C,
feedspeedof15mm/minandnozzlediameterof0.3mm.
No.TPULabelSamplesExhibitionCharacteristicsandAnalysis
175A
Meltingrate:☆☆
Tensilestrength:○○
Flexibility:□
280A
Meltingrate:☆☆
Tensilestrength:○○
Flexibility:□
390A
Meltingrate:☆
Tensilestrength:○○○
Flexibility:□□
495A
Meltingrate:☆☆☆
Tensilestrength:○○○
Flexibility:□□□
Table3demonstratestheperformanceeffectsofthedifferentfeedspeedsofscrews
ontheceramicfiberwithameltingtemperatureof220°C,TPU‐95A#andanozzlediam‐
eterof0.3mm.Itwasfoundthatwithinacertainrange(from5mm/minto15mm/min),
improvingthefeedspeednotonlyacceleratedthemeltingrate,butalsopromotedthe
tensilestrengthandflexibilityoftheceramicfiber.Nevertheless,whenthefeedspeedex‐
ceededacertainvalueandreached20mm/min,theincreasedshearratewoulddestroy
themolecularchainintheTPU[29,30].Itgraduallyuntiedandslidthemoleculesfrom
thenetworkstructure,anddecreasedtheconcentrationofthephysicalcrosslinkingpoint,
leadingtofurtherimprovementofthemeltingrate[31,32].However,theexcessivereduc‐
tionofmolecularweightreducedthemechanicalpropertiesofTPU,whichreducedthe
flexibilityandelasticityofthefinishedproduct.Therefore,thefeedspeedoftheoptimized
screwwas15mm/min.
Table3.Performanceeffectsofdifferentfeedspeedsofscrewsonceramicfiberatmeltingtemper‐
atureof220°C,TPU‐95A#andnozzlediameterof0.3mm.
No.FeedSpeed SamplesExhibitionCharacteristicsandAnalysis
15
Meltingrate:☆
Tensilestrength:○
Flexibility:□
210
Meltingrate:☆☆
Tensilestrength:○○
Flexibility:□□
Melting rate: I I
Tensile strength: ##
Flexibility:
3 90A
Polymers2022,14,xFORPEERREVIEW7of14
bestmeltingrate,tensilestrengthandflexibility.TheTPU‐95A#servedasthebestTPU
optionaccordingly.
Table2.PerformanceeffectsofdifferentTPUsonceramicfiberatmeltingtemperatureof220°C,
feedspeedof15mm/minandnozzlediameterof0.3mm.
No.TPULabelSamplesExhibitionCharacteristicsandAnalysis
175A
Meltingrate:☆☆
Tensilestrength:○○
Flexibility:□
280A
Meltingrate:☆☆
Tensilestrength:○○
Flexibility:□
390A
Meltingrate:☆
Tensilestrength:○○○
Flexibility:□□
495A
Meltingrate:☆☆☆
Tensilestrength:○○○
Flexibility:□□□
Table3demonstratestheperformanceeffectsofthedifferentfeedspeedsofscrews
ontheceramicfiberwithameltingtemperatureof220°C,TPU‐95A#andanozzlediam‐
eterof0.3mm.Itwasfoundthatwithinacertainrange(from5mm/minto15mm/min),
improvingthefeedspeednotonlyacceleratedthemeltingrate,butalsopromotedthe
tensilestrengthandflexibilityoftheceramicfiber.Nevertheless,whenthefeedspeedex‐
ceededacertainvalueandreached20mm/min,theincreasedshearratewoulddestroy
themolecularchainintheTPU[29,30].Itgraduallyuntiedandslidthemoleculesfrom
thenetworkstructure,anddecreasedtheconcentrationofthephysicalcrosslinkingpoint,
leadingtofurtherimprovementofthemeltingrate[31,32].However,theexcessivereduc‐
tionofmolecularweightreducedthemechanicalpropertiesofTPU,whichreducedthe
flexibilityandelasticityofthefinishedproduct.Therefore,thefeedspeedoftheoptimized
screwwas15mm/min.
Table3.Performanceeffectsofdifferentfeedspeedsofscrewsonceramicfiberatmeltingtemper‐
atureof220°C,TPU‐95A#andnozzlediameterof0.3mm.
No.FeedSpeed SamplesExhibitionCharacteristicsandAnalysis
15
Meltingrate:☆
Tensilestrength:○
Flexibility:□
210
Meltingrate:☆☆
Tensilestrength:○○
Flexibility:□□
Melting rate: I
Tensile strength: ###
Flexibility:
4 95A
Polymers2022,14,xFORPEERREVIEW7of14
bestmeltingrate,tensilestrengthandflexibility.TheTPU‐95A#servedasthebestTPU
optionaccordingly.
Table2.PerformanceeffectsofdifferentTPUsonceramicfiberatmeltingtemperatureof220°C,
feedspeedof15mm/minandnozzlediameterof0.3mm.
No.TPULabelSamplesExhibitionCharacteristicsandAnalysis
175A
Meltingrate:☆☆
Tensilestrength:○○
Flexibility:□
280A
Meltingrate:☆☆
Tensilestrength:○○
Flexibility:□
390A
Meltingrate:☆
Tensilestrength:○○○
Flexibility:□□
495A
Meltingrate:☆☆☆
Tensilestrength:○○○
Flexibility:□□□
Table3demonstratestheperformanceeffectsofthedifferentfeedspeedsofscrews
ontheceramicfiberwithameltingtemperatureof220°C,TPU‐95A#andanozzlediam‐
eterof0.3mm.Itwasfoundthatwithinacertainrange(from5mm/minto15mm/min),
improvingthefeedspeednotonlyacceleratedthemeltingrate,butalsopromotedthe
tensilestrengthandflexibilityoftheceramicfiber.Nevertheless,whenthefeedspeedex‐
ceededacertainvalueandreached20mm/min,theincreasedshearratewoulddestroy
themolecularchainintheTPU[29,30].Itgraduallyuntiedandslidthemoleculesfrom
thenetworkstructure,anddecreasedtheconcentrationofthephysicalcrosslinkingpoint,
leadingtofurtherimprovementofthemeltingrate[31,32].However,theexcessivereduc‐
tionofmolecularweightreducedthemechanicalpropertiesofTPU,whichreducedthe
flexibilityandelasticityofthefinishedproduct.Therefore,thefeedspeedoftheoptimized
screwwas15mm/min.
Table3.Performanceeffectsofdifferentfeedspeedsofscrewsonceramicfiberatmeltingtemper‐
atureof220°C,TPU‐95A#andnozzlediameterof0.3mm.
No.FeedSpeed SamplesExhibitionCharacteristicsandAnalysis
15
Meltingrate:☆
Tensilestrength:○
Flexibility:□
210
Meltingrate:☆☆
Tensilestrength:○○
Flexibility:□□
Melting rate: III
Tensile strength: ###
Flexibility:
Table 3demonstrates the performance effects of the different feed speeds of screws on
the ceramic fiber with a melting temperature of 220
◦
C, TPU-95A# and a nozzle diameter
of 0.3 mm. It was found that within a certain range (from 5 mm/min to 15 mm/min),
improving the feed speed not only accelerated the melting rate, but also promoted the
tensile strength and flexibility of the ceramic fiber. Nevertheless, when the feed speed
exceeded a certain value and reached 20 mm/min, the increased shear rate would destroy
the molecular chain in the TPU [
29
,
30
]. It gradually untied and slid the molecules from the
network structure, and decreased the concentration of the physical crosslinking point, lead-
ing to further improvement of the melting rate [
31
,
32
]. However, the excessive reduction of
molecular weight reduced the mechanical properties of TPU, which reduced the flexibility
and elasticity of the finished product. Therefore, the feed speed of the optimized screw was
15 mm/min.
Table 3.
Performance effects of different feed speeds of screws on ceramic fiber at melting temperature
of 220 ◦C, TPU-95A# and nozzle diameter of 0.3 mm.
No. Feed Speed Samples Exhibition Characteristics and Analysis
1 5
Polymers2022,14,xFORPEERREVIEW7of14
bestmeltingrate,tensilestrengthandflexibility.TheTPU‐95A#servedasthebestTPU
optionaccordingly.
Table2.PerformanceeffectsofdifferentTPUsonceramicfiberatmeltingtemperatureof220°C,
feedspeedof15mm/minandnozzlediameterof0.3mm.
No.TPULabelSamplesExhibitionCharacteristicsandAnalysis
175A
Meltingrate:☆☆
Tensilestrength:○○
Flexibility:□
280A
Meltingrate:☆☆
Tensilestrength:○○
Flexibility:□
390A
Meltingrate:☆
Tensilestrength:○○○
Flexibility:□□
495A
Meltingrate:☆☆☆
Tensilestrength:○○○
Flexibility:□□□
Table3demonstratestheperformanceeffectsofthedifferentfeedspeedsofscrews
ontheceramicfiberwithameltingtemperatureof220°C,TPU‐95A#andanozzlediam‐
eterof0.3mm.Itwasfoundthatwithinacertainrange(from5mm/minto15mm/min),
improvingthefeedspeednotonlyacceleratedthemeltingrate,butalsopromotedthe
tensilestrengthandflexibilityoftheceramicfiber.Nevertheless,whenthefeedspeedex‐
ceededacertainvalueandreached20mm/min,theincreasedshearratewoulddestroy
themolecularchainintheTPU[29,30].Itgraduallyuntiedandslidthemoleculesfrom
thenetworkstructure,anddecreasedtheconcentrationofthephysicalcrosslinkingpoint,
leadingtofurtherimprovementofthemeltingrate[31,32].However,theexcessivereduc‐
tionofmolecularweightreducedthemechanicalpropertiesofTPU,whichreducedthe
flexibilityandelasticityofthefinishedproduct.Therefore,thefeedspeedoftheoptimized
screwwas15mm/min.
Table3.Performanceeffectsofdifferentfeedspeedsofscrewsonceramicfiberatmeltingtemper‐
atureof220°C,TPU‐95A#andnozzlediameterof0.3mm.
No.FeedSpeed SamplesExhibitionCharacteristicsandAnalysis
15
Meltingrate:☆
Tensilestrength:○
Flexibility:□
210
Meltingrate:☆☆
Tensilestrength:○○
Flexibility:□□
Melting rate: I
Tensile strength: #
Flexibility:
2 10
Polymers2022,14,xFORPEERREVIEW7of14
bestmeltingrate,tensilestrengthandflexibility.TheTPU‐95A#servedasthebestTPU
optionaccordingly.
Table2.PerformanceeffectsofdifferentTPUsonceramicfiberatmeltingtemperatureof220°C,
feedspeedof15mm/minandnozzlediameterof0.3mm.
No.TPULabelSamplesExhibitionCharacteristicsandAnalysis
175A
Meltingrate:☆☆
Tensilestrength:○○
Flexibility:□
280A
Meltingrate:☆☆
Tensilestrength:○○
Flexibility:□
390A
Meltingrate:☆
Tensilestrength:○○○
Flexibility:□□
495A
Meltingrate:☆☆☆
Tensilestrength:○○○
Flexibility:□□□
Table3demonstratestheperformanceeffectsofthedifferentfeedspeedsofscrews
ontheceramicfiberwithameltingtemperatureof220°C,TPU‐95A#andanozzlediam‐
eterof0.3mm.Itwasfoundthatwithinacertainrange(from5mm/minto15mm/min),
improvingthefeedspeednotonlyacceleratedthemeltingrate,butalsopromotedthe
tensilestrengthandflexibilityoftheceramicfiber.Nevertheless,whenthefeedspeedex‐
ceededacertainvalueandreached20mm/min,theincreasedshearratewoulddestroy
themolecularchainintheTPU[29,30].Itgraduallyuntiedandslidthemoleculesfrom
thenetworkstructure,anddecreasedtheconcentrationofthephysicalcrosslinkingpoint,
leadingtofurtherimprovementofthemeltingrate[31,32].However,theexcessivereduc‐
tionofmolecularweightreducedthemechanicalpropertiesofTPU,whichreducedthe
flexibilityandelasticityofthefinishedproduct.Therefore,thefeedspeedoftheoptimized
screwwas15mm/min.
Table3.Performanceeffectsofdifferentfeedspeedsofscrewsonceramicfiberatmeltingtemper‐
atureof220°C,TPU‐95A#andnozzlediameterof0.3mm.
No.FeedSpeed SamplesExhibitionCharacteristicsandAnalysis
15
Meltingrate:☆
Tensilestrength:○
Flexibility:□
210
Meltingrate:☆☆
Tensilestrength:○○
Flexibility:□□
Melting rate: II
Tensile strength: ##
Flexibility:
3 15
Polymers2022,14,xFORPEERREVIEW8of14
315
Meltingrate:☆☆☆
Tensilestrength:○○○
Flexibility:□□□
420
Meltingrate:☆☆☆
Tensilestrength:○
Flexibility:□□
Table4displaysthattheinfluenceofdifferentmeltingtemperaturesontheperfor‐
manceofYAGceramicfiberundertheconditionsofTPU‐95A#,ascrewfeedspeedof15
mm/minandanozzlediameterdependingonthesituation.Itwasclearlyfoundthatwith
thetemperatureincreasedfrom160°Cto220°C,theTPUmeltingrateandfluiditygrad‐
uallyimprovedandtheformationbymeltspinningalsowentfromdifficulttoeasy.In
addition,theoptionalnozzlediametercouldalsobesmallerandsmaller.Themelting
temperatureof220°CmettherequirementsforpreparingtheYAGceramicfiberinthis
experiment,andhence,220°Cwaspreferredastheoptimizedtemperatureparameter.
Thehighermeltingtemperaturewouldhavedamagedtheservicelifeoftheexperimental
equipment;asaresult,itwasnottested.
Table4.Performanceeffectsofdifferentmeltingtemperaturesonceramicfiberatfeedspeedof
screwof15mm/min,TPU‐95A#andnozzlediameterdependingonthesituation.
No.Temperature SamplesExhibitionCharacteristicsandAnalysis
1160°C
Meltingrate:☆
Flowability:△
Formingsilk:◇
2180°C
Meltingrate:☆
Flowability:△
Formingsilk:◇
3200°C
Meltingrate:☆☆
Flowability:△△
Formingsilk:◇◇
4220°C
Meltingrate:☆☆☆
Flowability:△△△
Formingsilk:◇◇◇
Throughtheaboveseriesofexperiments,itwasfoundthattheoptimizedprocess
parametersofYAGceramicfiberpreparationwereasfollows:themeltingtemperature
was220°C,thescrewfeedrateofthemicrodouble‐conescrewextruderwasF=15.0
mm/minandTPU‐95A#wasused.
Figure4showstheSEMimageofthesurfaceandfractureoftheYAGceramicfiber
withdifferentTPUtypesandtheratiosofTPUtoceramicpowder.Figure4a,brevealsthe
SEMimageofthesurfaceandfractureoftheceramicfiberwiththemassratioofTPU‐
75A#toceramicpowder=4:6,respectively.ThecomparisonofSEMimagesshowsthat
thesurfaceofceramicfiberinFigure4aiscoarserthanthatinFigure4b.Thiswasbecause
thehardnessofTPU‐75A#waslowerthanthatofTPU‐95A#.Thepreparationofthece‐
ramicfiberwasthroughthenozzle,formingthesilkthroughplasticdeformation;theplas‐
ticdeformationwasmainlycausedbytheresistanceoftheTPUmolecularchaintothe
Melting rate: III
Tensile strength: ###
Flexibility:
4 20
Polymers2022,14,xFORPEERREVIEW8of14
315
Meltingrate:☆☆☆
Tensilestrength:○○○
Flexibility:□□□
420
Meltingrate:☆☆☆
Tensilestrength:○
Flexibility:□□
Table4displaysthattheinfluenceofdifferentmeltingtemperaturesontheperfor‐
manceofYAGceramicfiberundertheconditionsofTPU‐95A#,ascrewfeedspeedof15
mm/minandanozzlediameterdependingonthesituation.Itwasclearlyfoundthatwith
thetemperatureincreasedfrom160°Cto220°C,theTPUmeltingrateandfluiditygrad‐
uallyimprovedandtheformationbymeltspinningalsowentfromdifficulttoeasy.In
addition,theoptionalnozzlediametercouldalsobesmallerandsmaller.Themelting
temperatureof220°CmettherequirementsforpreparingtheYAGceramicfiberinthis
experiment,andhence,220°Cwaspreferredastheoptimizedtemperatureparameter.
Thehighermeltingtemperaturewouldhavedamagedtheservicelifeoftheexperimental
equipment;asaresult,itwasnottested.
Table4.Performanceeffectsofdifferentmeltingtemperaturesonceramicfiberatfeedspeedof
screwof15mm/min,TPU‐95A#andnozzlediameterdependingonthesituation.
No.Temperature SamplesExhibitionCharacteristicsandAnalysis
1160°C
Meltingrate:☆
Flowability:△
Formingsilk:◇
2180°C
Meltingrate:☆
Flowability:△
Formingsilk:◇
3200°C
Meltingrate:☆☆
Flowability:△△
Formingsilk:◇◇
4220°C
Meltingrate:☆☆☆
Flowability:△△△
Formingsilk:◇◇◇
Throughtheaboveseriesofexperiments,itwasfoundthattheoptimizedprocess
parametersofYAGceramicfiberpreparationwereasfollows:themeltingtemperature
was220°C,thescrewfeedrateofthemicrodouble‐conescrewextruderwasF=15.0
mm/minandTPU‐95A#wasused.
Figure4showstheSEMimageofthesurfaceandfractureoftheYAGceramicfiber
withdifferentTPUtypesandtheratiosofTPUtoceramicpowder.Figure4a,brevealsthe
SEMimageofthesurfaceandfractureoftheceramicfiberwiththemassratioofTPU‐
75A#toceramicpowder=4:6,respectively.ThecomparisonofSEMimagesshowsthat
thesurfaceofceramicfiberinFigure4aiscoarserthanthatinFigure4b.Thiswasbecause
thehardnessofTPU‐75A#waslowerthanthatofTPU‐95A#.Thepreparationofthece‐
ramicfiberwasthroughthenozzle,formingthesilkthroughplasticdeformation;theplas‐
ticdeformationwasmainlycausedbytheresistanceoftheTPUmolecularchaintothe
Melting rate: III
Tensile strength: #
Flexibility:
Polymers 2022,14, 2096 8 of 13
Table 4displays that the influence of different melting temperatures on the perfor-
mance of YAG ceramic fiber under the conditions of TPU-95A#, a screw feed speed of
15 mm/min and a nozzle diameter depending on the situation. It was clearly found that
with the temperature increased from 160
◦
C to 220
◦
C, the TPU melting rate and fluidity
gradually improved and the formation by melt spinning also went from difficult to easy.
In addition, the optional nozzle diameter could also be smaller and smaller. The melting
temperature of 220
◦
C met the requirements for preparing the YAG ceramic fiber in this
experiment, and hence, 220
◦
C was preferred as the optimized temperature parameter.
The higher melting temperature would have damaged the service life of the experimental
equipment; as a result, it was not tested.
Table 4.
Performance effects of different melting temperatures on ceramic fiber at feed speed of screw
of 15 mm/min, TPU-95A# and nozzle diameter depending on the situation.
No. Temperature Samples Exhibition Characteristics and Analysis
1 160 ◦C
Polymers2022,14,xFORPEERREVIEW8of14
315
Meltingrate:☆☆☆
Tensilestrength:○○○
Flexibility:□□□
420
Meltingrate:☆☆☆
Tensilestrength:○
Flexibility:□□
Table4displaysthattheinfluenceofdifferentmeltingtemperaturesontheperfor‐
manceofYAGceramicfiberundertheconditionsofTPU‐95A#,ascrewfeedspeedof15
mm/minandanozzlediameterdependingonthesituation.Itwasclearlyfoundthatwith
thetemperatureincreasedfrom160°Cto220°C,theTPUmeltingrateandfluiditygrad‐
uallyimprovedandtheformationbymeltspinningalsowentfromdifficulttoeasy.In
addition,theoptionalnozzlediametercouldalsobesmallerandsmaller.Themelting
temperatureof220°CmettherequirementsforpreparingtheYAGceramicfiberinthis
experiment,andhence,220°Cwaspreferredastheoptimizedtemperatureparameter.
Thehighermeltingtemperaturewouldhavedamagedtheservicelifeoftheexperimental
equipment;asaresult,itwasnottested.
Table4.Performanceeffectsofdifferentmeltingtemperaturesonceramicfiberatfeedspeedof
screwof15mm/min,TPU‐95A#andnozzlediameterdependingonthesituation.
No.Temperature SamplesExhibitionCharacteristicsandAnalysis
1160°C
Meltingrate:☆
Flowability:△
Formingsilk:◇
2180°C
Meltingrate:☆
Flowability:△
Formingsilk:◇
3200°C
Meltingrate:☆☆
Flowability:△△
Formingsilk:◇◇
4220°C
Meltingrate:☆☆☆
Flowability:△△△
Formingsilk:◇◇◇
Throughtheaboveseriesofexperiments,itwasfoundthattheoptimizedprocess
parametersofYAGceramicfiberpreparationwereasfollows:themeltingtemperature
was220°C,thescrewfeedrateofthemicrodouble‐conescrewextruderwasF=15.0
mm/minandTPU‐95A#wasused.
Figure4showstheSEMimageofthesurfaceandfractureoftheYAGceramicfiber
withdifferentTPUtypesandtheratiosofTPUtoceramicpowder.Figure4a,brevealsthe
SEMimageofthesurfaceandfractureoftheceramicfiberwiththemassratioofTPU‐
75A#toceramicpowder=4:6,respectively.ThecomparisonofSEMimagesshowsthat
thesurfaceofceramicfiberinFigure4aiscoarserthanthatinFigure4b.Thiswasbecause
thehardnessofTPU‐75A#waslowerthanthatofTPU‐95A#.Thepreparationofthece‐
ramicfiberwasthroughthenozzle,formingthesilkthroughplasticdeformation;theplas‐
ticdeformationwasmainlycausedbytheresistanceoftheTPUmolecularchaintothe
Melting rate: I
Flowability: 4
Forming silk: 3
2 180 ◦C
Polymers2022,14,xFORPEERREVIEW8of14
315
Meltingrate:☆☆☆
Tensilestrength:○○○
Flexibility:□□□
420
Meltingrate:☆☆☆
Tensilestrength:○
Flexibility:□□
Table4displaysthattheinfluenceofdifferentmeltingtemperaturesontheperfor‐
manceofYAGceramicfiberundertheconditionsofTPU‐95A#,ascrewfeedspeedof15
mm/minandanozzlediameterdependingonthesituation.Itwasclearlyfoundthatwith
thetemperatureincreasedfrom160°Cto220°C,theTPUmeltingrateandfluiditygrad‐
uallyimprovedandtheformationbymeltspinningalsowentfromdifficulttoeasy.In
addition,theoptionalnozzlediametercouldalsobesmallerandsmaller.Themelting
temperatureof220°CmettherequirementsforpreparingtheYAGceramicfiberinthis
experiment,andhence,220°Cwaspreferredastheoptimizedtemperatureparameter.
Thehighermeltingtemperaturewouldhavedamagedtheservicelifeoftheexperimental
equipment;asaresult,itwasnottested.
Table4.Performanceeffectsofdifferentmeltingtemperaturesonceramicfiberatfeedspeedof
screwof15mm/min,TPU‐95A#andnozzlediameterdependingonthesituation.
No.Temperature SamplesExhibitionCharacteristicsandAnalysis
1160°C
Meltingrate:☆
Flowability:△
Formingsilk:◇
2180°C
Meltingrate:☆
Flowability:△
Formingsilk:◇
3200°C
Meltingrate:☆☆
Flowability:△△
Formingsilk:◇◇
4220°C
Meltingrate:☆☆☆
Flowability:△△△
Formingsilk:◇◇◇
Throughtheaboveseriesofexperiments,itwasfoundthattheoptimizedprocess
parametersofYAGceramicfiberpreparationwereasfollows:themeltingtemperature
was220°C,thescrewfeedrateofthemicrodouble‐conescrewextruderwasF=15.0
mm/minandTPU‐95A#wasused.
Figure4showstheSEMimageofthesurfaceandfractureoftheYAGceramicfiber
withdifferentTPUtypesandtheratiosofTPUtoceramicpowder.Figure4a,brevealsthe
SEMimageofthesurfaceandfractureoftheceramicfiberwiththemassratioofTPU‐
75A#toceramicpowder=4:6,respectively.ThecomparisonofSEMimagesshowsthat
thesurfaceofceramicfiberinFigure4aiscoarserthanthatinFigure4b.Thiswasbecause
thehardnessofTPU‐75A#waslowerthanthatofTPU‐95A#.Thepreparationofthece‐
ramicfiberwasthroughthenozzle,formingthesilkthroughplasticdeformation;theplas‐
ticdeformationwasmainlycausedbytheresistanceoftheTPUmolecularchaintothe
Melting rate: I
Flowability: 4
Forming silk: 3
3 200 ◦C
Polymers2022,14,xFORPEERREVIEW8of14
315
Meltingrate:☆☆☆
Tensilestrength:○○○
Flexibility:□□□
420
Meltingrate:☆☆☆
Tensilestrength:○
Flexibility:□□
Table4displaysthattheinfluenceofdifferentmeltingtemperaturesontheperfor‐
manceofYAGceramicfiberundertheconditionsofTPU‐95A#,ascrewfeedspeedof15
mm/minandanozzlediameterdependingonthesituation.Itwasclearlyfoundthatwith
thetemperatureincreasedfrom160°Cto220°C,theTPUmeltingrateandfluiditygrad‐
uallyimprovedandtheformationbymeltspinningalsowentfromdifficulttoeasy.In
addition,theoptionalnozzlediametercouldalsobesmallerandsmaller.Themelting
temperatureof220°CmettherequirementsforpreparingtheYAGceramicfiberinthis
experiment,andhence,220°Cwaspreferredastheoptimizedtemperatureparameter.
Thehighermeltingtemperaturewouldhavedamagedtheservicelifeoftheexperimental
equipment;asaresult,itwasnottested.
Table4.Performanceeffectsofdifferentmeltingtemperaturesonceramicfiberatfeedspeedof
screwof15mm/min,TPU‐95A#andnozzlediameterdependingonthesituation.
No.Temperature SamplesExhibitionCharacteristicsandAnalysis
1160°C
Meltingrate:☆
Flowability:△
Formingsilk:◇
2180°C
Meltingrate:☆
Flowability:△
Formingsilk:◇
3200°C
Meltingrate:☆☆
Flowability:△△
Formingsilk:◇◇
4220°C
Meltingrate:☆☆☆
Flowability:△△△
Formingsilk:◇◇◇
Throughtheaboveseriesofexperiments,itwasfoundthattheoptimizedprocess
parametersofYAGceramicfiberpreparationwereasfollows:themeltingtemperature
was220°C,thescrewfeedrateofthemicrodouble‐conescrewextruderwasF=15.0
mm/minandTPU‐95A#wasused.
Figure4showstheSEMimageofthesurfaceandfractureoftheYAGceramicfiber
withdifferentTPUtypesandtheratiosofTPUtoceramicpowder.Figure4a,brevealsthe
SEMimageofthesurfaceandfractureoftheceramicfiberwiththemassratioofTPU‐
75A#toceramicpowder=4:6,respectively.ThecomparisonofSEMimagesshowsthat
thesurfaceofceramicfiberinFigure4aiscoarserthanthatinFigure4b.Thiswasbecause
thehardnessofTPU‐75A#waslowerthanthatofTPU‐95A#.Thepreparationofthece‐
ramicfiberwasthroughthenozzle,formingthesilkthroughplasticdeformation;theplas‐
ticdeformationwasmainlycausedbytheresistanceoftheTPUmolecularchaintothe
Melting rate: II
Flowability: 44
Forming silk: 33
4 220 ◦C
Polymers2022,14,xFORPEERREVIEW8of14
315
Meltingrate:☆☆☆
Tensilestrength:○○○
Flexibility:□□□
420
Meltingrate:☆☆☆
Tensilestrength:○
Flexibility:□□
Table4displaysthattheinfluenceofdifferentmeltingtemperaturesontheperfor‐
manceofYAGceramicfiberundertheconditionsofTPU‐95A#,ascrewfeedspeedof15
mm/minandanozzlediameterdependingonthesituation.Itwasclearlyfoundthatwith
thetemperatureincreasedfrom160°Cto220°C,theTPUmeltingrateandfluiditygrad‐
uallyimprovedandtheformationbymeltspinningalsowentfromdifficulttoeasy.In
addition,theoptionalnozzlediametercouldalsobesmallerandsmaller.Themelting
temperatureof220°CmettherequirementsforpreparingtheYAGceramicfiberinthis
experiment,andhence,220°Cwaspreferredastheoptimizedtemperatureparameter.
Thehighermeltingtemperaturewouldhavedamagedtheservicelifeoftheexperimental
equipment;asaresult,itwasnottested.
Table4.Performanceeffectsofdifferentmeltingtemperaturesonceramicfiberatfeedspeedof
screwof15mm/min,TPU‐95A#andnozzlediameterdependingonthesituation.
No.Temperature SamplesExhibitionCharacteristicsandAnalysis
1160°C
Meltingrate:☆
Flowability:△
Formingsilk:◇
2180°C
Meltingrate:☆
Flowability:△
Formingsilk:◇
3200°C
Meltingrate:☆☆
Flowability:△△
Formingsilk:◇◇
4220°C
Meltingrate:☆☆☆
Flowability:△△△
Formingsilk:◇◇◇
Throughtheaboveseriesofexperiments,itwasfoundthattheoptimizedprocess
parametersofYAGceramicfiberpreparationwereasfollows:themeltingtemperature
was220°C,thescrewfeedrateofthemicrodouble‐conescrewextruderwasF=15.0
mm/minandTPU‐95A#wasused.
Figure4showstheSEMimageofthesurfaceandfractureoftheYAGceramicfiber
withdifferentTPUtypesandtheratiosofTPUtoceramicpowder.Figure4a,brevealsthe
SEMimageofthesurfaceandfractureoftheceramicfiberwiththemassratioofTPU‐
75A#toceramicpowder=4:6,respectively.ThecomparisonofSEMimagesshowsthat
thesurfaceofceramicfiberinFigure4aiscoarserthanthatinFigure4b.Thiswasbecause
thehardnessofTPU‐75A#waslowerthanthatofTPU‐95A#.Thepreparationofthece‐
ramicfiberwasthroughthenozzle,formingthesilkthroughplasticdeformation;theplas‐
ticdeformationwasmainlycausedbytheresistanceoftheTPUmolecularchaintothe
Melting rate: III
Flowability: 444
Forming silk: 333
Through the above series of experiments, it was found that the optimized process
parameters of YAG ceramic fiber preparation were as follows: the melting temperature was
220
◦
C, the screw feed rate of the micro double-cone screw extruder was F = 15.0 mm/min
and TPU-95A# was used.
Figure 4shows the SEM image of the surface and fracture of the YAG ceramic fiber
with different TPU types and the ratios of TPU to ceramic powder. Figure 4a,b reveals the
SEM image of the surface and fracture of the ceramic fiber with the mass ratio of TPU-75A#
to ceramic powder = 4:6, respectively. The comparison of SEM images shows that the
surface of ceramic fiber in Figure 4a is coarser than that in Figure 4b. This was because the
hardness of TPU-75A# was lower than that of TPU-95A#. The preparation of the ceramic
fiber was through the nozzle, forming the silk through plastic deformation; the plastic
deformation was mainly caused by the resistance of the TPU molecular chain to the friction
shear force [
33
]. In other words, the higher the hardness of TPU, the more conducive it
was to resist friction and shear force [
34
,
35
]. This would make the wear of the ceramic
fiber surface lower, and the prepared ceramic fiber surface smoother. Accordingly, it can be
seen from Figure 4d that when the melting index and hardness of TPU-75A# were low, the
fracture SEM image of the prepared ceramic fiber had microporosity. This led to a reduction
in density and strength of the ceramic fiber.
Polymers 2022,14, 2096 9 of 13
Polymers2022,14,xFORPEERREVIEW9of14
frictionshearforce[33].Inotherwords,thehigherthehardnessofTPU,themorecondu‐
civeitwastoresistfrictionandshearforce[34,35].Thiswouldmakethewearofthece‐
ramicfibersurfacelower,andthepreparedceramicfibersurfacesmoother.Accordingly,
itcanbeseenfromFigure4dthatwhenthemeltingindexandhardnessofTPU‐75A#were
low,thefractureSEMimageofthepreparedceramicfiberhadmicroporosity.Thisledto
areductionindensityandstrengthoftheceramicfiber.
Figure4.SEMimagesofthesurfaceandfractureofYAGceramicfiberwithdifferentTPUtypesand
theratiosofTPUtoceramicpowder:(a,d)surfaceandfractureoftheceramicfiberwiththemass
ratioofTPU‐75A#toceramicpowder=4:6,respectively;(b,e)surfaceandfractureoftheceramic
fiberwiththemassratioofTPU‐95A#toceramicpowder=4:6,respectively;(c,f)surfaceandfrac‐
tureoftheceramicfiberwiththemassratioofTPU‐95A#toceramicpowder=3:7,respectively.
ThecomparisonbetweenFigure4b,cshowsthatthesurfaceoftheceramicfiberin
Figure4bissmootherthanthatinFigure4c;thatis,thesurfaceoftheceramicfiberwith
themassratioofTPU‐95A#toceramicpowder=3:7isrougher(asshowninFigure4c).
Thiswasbecausetheceramicpowderusedinthisexperimentwasmainlycomposedof
Y2O3andAl2O3.Excessivemetaloxidepowderabsorbsheatatahightemperature.Asa
result,themeltingoftheTPUpolymerwasnotsufficientforittoremainonthesurfaceof
thefiber,resultinginaroughsurfaceontheceramicfiber.
Accordingly,bycomparingFigure4e,f,itcanbefoundthattheSEMfractureofFig‐
ure4ewassmootherthanthatofFigure4f.Botharemorecompleteandnonporousthan
inFigure4d,mainlybecausethehardnessandmeltingcharacteristicsofTPU‐95A#were
betterthanTPU‐75A#,whichcoincideswiththeconclusionofFigure3.Inaddition,the
SEMfractureoftheceramicfiberinFigure4fseemedtohaveacertainincompletemolten
sheetofTPU‐95A#.Thisindicatedthatwiththeincreaseinthemassratioofceramicpow‐
der,thepowderwasnotonlynotabletobecompletelywrappedbythemeltingTPU,but
alsoeasilyledtoinsufficientTPUmelting[36,37].Thepreparedceramicfiberwasnotas
highinqualityasthequalityinFigure4e.
Therefore,accordingtothesurfaceandfractureSEMimagesinFigure4,theceramic
fiberwiththemassratioofTPU‐95A#toceramicpowder=4:6hasthebestmicrostructure
quality.
Figure5demonstratestheEDSanalysisoftheceramicfiber(TPU‐95A#,themass
ratioofTPU‐75A#toceramicpowder=4:6).Figure5ashowsthesurfaceSEMimagefrom
thesurfacescanningoftheceramicfiber.Figure5bdisplaysthehistogramoftheelemental
quantitativeanalysis,andFigure5cplotsthetypesandintensitiesofelementsdetected
(embeddedtable:themassandatomicspecificgravityofthefourelements).InFigure5c,
Figure 4.
SEM images of the surface and fracture of YAG ceramic fiber with different TPU types and
the ratios of TPU to ceramic powder: (
a
,
d
) surface and fracture of the ceramic fiber with the mass
ratio of TPU-75A# to ceramic powder = 4:6, respectively; (
b
,
e
) surface and fracture of the ceramic
fiber with the mass ratio of TPU-95A# to ceramic powder = 4:6, respectively; (
c
,
f
) surface and fracture
of the ceramic fiber with the mass ratio of TPU-95A# to ceramic powder = 3:7, respectively.
The comparison between Figure 4b,c shows that the surface of the ceramic fiber in
Figure 4b is smoother than that in Figure 4c; that is, the surface of the ceramic fiber with
the mass ratio of TPU-95A# to ceramic powder = 3:7 is rougher (as shown in Figure 4c).
This was because the ceramic powder used in this experiment was mainly composed of
Y
2
O
3
and Al
2
O
3
. Excessive metal oxide powder absorbs heat at a high temperature. As a
result, the melting of the TPU polymer was not sufficient for it to remain on the surface of
the fiber, resulting in a rough surface on the ceramic fiber.
Accordingly, by comparing Figure 4e,f, it can be found that the SEM fracture of
Figure 4e was smoother than that of Figure 4f. Both are more complete and nonporous
than in Figure 4d, mainly because the hardness and melting characteristics of TPU-95A#
were better than TPU-75A#, which coincides with the conclusion of Figure 3. In addition,
the SEM fracture of the ceramic fiber in Figure 4f seemed to have a certain incomplete
molten sheet of TPU-95A#. This indicated that with the increase in the mass ratio of ceramic
powder, the powder was not only not able to be completely wrapped by the melting TPU,
but also easily led to insufficient TPU melting [
36
,
37
]. The prepared ceramic fiber was not
as high in quality as the quality in Figure 4e.
Therefore, according to the surface and fracture SEM images in Figure 4, the ceramic
fiber with the mass ratio of TPU-95A# to ceramic powder = 4:6 has the best microstruc-
ture quality.
Figure 5demonstrates the EDS analysis of the ceramic fiber (TPU-95A#, the mass ratio
of TPU-75A# to ceramic powder = 4:6). Figure 5a shows the surface SEM image from the
surface scanning of the ceramic fiber. Figure 5b displays the histogram of the elemental
quantitative analysis, and Figure 5c plots the types and intensities of elements detected
(embedded table: the mass and atomic specific gravity of the four elements). In Figure 5c,
the weight percentages of the C, O, Al and Y elements were 48.70, 32.60, 7.44 and 11.26,
respectively, and the atomic percentages were 62.43, 31.38, 4.24 and 1.95, respectively. The
sum of the weight percentage and the atomic percentage of each element was 100. Among
them, C, O and undetected H elements were mainly provided by the polymer TPU, whereas
Al, Y and O elements were provided by the Y
2
O
3
and Al
2
O
3
ceramic powder, with no other
elements. It can be inferred that there were no other impurity elements in the preparation
Polymers 2022,14, 2096 10 of 13
process of the ceramic fiber in this experiment. The process of melt spinning adopted in
this study can prepare the high-quality and pure ceramic fiber.
Polymers2022,14,xFORPEERREVIEW10of14
theweightpercentagesoftheC,O,AlandYelementswere48.70,32.60,7.44and11.26,
respectively,andtheatomicpercentageswere62.43,31.38,4.24and1.95,respectively.The
sumoftheweightpercentageandtheatomicpercentageofeachelementwas100.Among
them,C,OandundetectedHelementsweremainlyprovidedbythepolymerTPU,
whereasAl,YandOelementswereprovidedbytheY2O3andAl2O3ceramicpowder,with
nootherelements.Itcanbeinferredthattherewerenootherimpurityelementsinthe
preparationprocessoftheceramicfiberinthisexperiment.Theprocessofmeltspinning
adoptedinthisstudycanpreparethehigh‐qualityandpureceramicfiber.
Figure5.EDSanalysisoftheceramicfiber(TPU‐95A#,themassratioofTPU‐75A#toceramicpow‐
der=4:6):(a)surfaceSEMimagefromsurfacescanningofceramicfiber,(b)histogramofelemental
quantitativeanalysis,(c)plotoftypesandintensitiesofelementsdetected(embeddedtable:the
massandatomicspecificgravityofthefourelements).
Figure6demonstratesthetensilestrengthofdifferentTPUtypesandcomponents.
Thetensilestrengthoftheceramicfiberwasmeasuredataloadingrateof2mm/minina
monofilamentsstrengthtester.Figure6ashowsthatthetensilestrengthsofTPU‐75A#and
ceramicpowder=4:6were13.55mpa,15.75mpaand14.47mpa.Thetensilestrengthsof
TPU‐95A#andceramicpowder=4:6were19.45MPa,20.06MPaand19.85MPa.Theten‐
silestrengthsofTPU‐95A#andceramicpowder=3:7were13.09MPa,14.09MPaand13.95
MPa.Thehistogramoftwogroups(TPU‐75A#andceramicpowder=4:6andTPU‐95A#
andceramicpowder=4:6)showsthatundertheconditionofaconstantmassratioof
ceramicpowder,thetensilestrengthofceramicfibermadebyTPU‐95A#withahighhard‐
nesswashigherthanthatmadebyTPU‐75A#withalowhardness.Itfurtherconfirmed
thatforTPU,havingahighhardnessimprovesthetoughnessandtensilestrengthofce‐
ramicfiber.Inaddition,thehistogramoftwogroups(TPU‐95A#andceramicpowder=
4:6andTPU‐95A#andceramicpowder=3:7)displaysthatwhentheTPUhardnesswas
thesame,thetensilestrengthdecreasedsignificantlywiththedecreaseintheTPUratio.
Figure 5.
EDS analysis of the ceramic fiber (TPU-95A#, the mass ratio of TPU-75A# to ceramic
powder = 4:6
): (
a
) surface SEM image from surface scanning of ceramic fiber, (
b
) histogram of
elemental quantitative analysis, (
c
) plot of types and intensities of elements detected (embedded
table: the mass and atomic specific gravity of the four elements).
Figure 6demonstrates the tensile strength of different TPU types and components.
The tensile strength of the ceramic fiber was measured at a loading rate of 2 mm/min in a
monofilaments strength tester. Figure 6a shows that the tensile strengths of TPU-75A# and
ceramic powder = 4:6 were 13.55 MPa, 15.75 MPa and 14.47 MPa. The tensile strengths of
TPU-95A# and ceramic powder = 4:6 were 19.45 MPa, 20.06 MPa and 19.85 MPa. The tensile
strengths of TPU-95A# and ceramic powder = 3:7 were 13.09 MPa, 14.09 MPa and 13.95 MPa.
The histogram of two groups (TPU-75A# and ceramic powder = 4:6 and TPU-95A# and
ceramic powder = 4:6) shows that under the condition of a constant mass ratio of ceramic
powder, the tensile strength of ceramic fiber made by TPU-95A# with a high hardness
was higher than that made by TPU-75A# with a low hardness. It further confirmed that
for TPU, having a high hardness improves the toughness and tensile strength of ceramic
fiber. In addition, the histogram of two groups (TPU-95A# and ceramic powder = 4:6 and
TPU-95A# and ceramic powder = 3:7) displays that when the TPU hardness was the same,
the tensile strength decreased significantly with the decrease in the TPU ratio. Excessive
metal oxides in ceramic powders may also lead to the incomplete melting of TPU.
Figure 6b exhibits the average tensile strength calculated based on Figure 6a from
the results of TPU-75A# and ceramic powder = 4:6, TPU-95A# and ceramic
powder = 4:6
and TPU-95A# and ceramic powder = 3:7. Their average tensile strengths were 14.59 MPa,
19.79 MPa and 13.71 MPa, respectively. Apparently, the average tensile strength of TPU-
95A# and ceramic powder = 4:6 was larger than that of the other TPU types and components,
Polymers 2022,14, 2096 11 of 13
and the error fluctuation was smaller than that of the others. Therefore, Figure 6adequately
shows that the ceramic fiber with TPU-95A# and ceramic powder = 4:6 had the best
flexibility and uniformity, which was also consistent with the microstructure of Figure 4.
Polymers2022,14,xFORPEERREVIEW11of14
Excessivemetaloxidesinceramicpowdersmayalsoleadtotheincompletemeltingof
TPU.
Figure6.TensilestrengthofdifferentTPUtypesandcomponents:(a)threetensilestrengthtestsof
differentTPUtypesandcomponents(TPU‐75A#andceramicpowder=4:6,TPU‐95A#andceramic
powder=4:6,TPU‐95A#andceramicpowder=3:7;inset:thetestsituationbythemonofilament
strengthtester),(b)averagetensilestrengthofdifferentTPUtypesandcomponents.
Figure6bexhibitstheaveragetensilestrengthcalculatedbasedonFigure6afromthe
resultsofTPU‐75A#andceramicpowder=4:6,TPU‐95A#andceramicpowder=4:6and
TPU‐95A#andceramicpowder=3:7.Theiraveragetensilestrengthswere14.59MPa,
19.79MPaand13.71MPa,respectively.Apparently,theaveragetensilestrengthofTPU‐
95A#andceramicpowder=4:6waslargerthanthatoftheotherTPUtypesandcompo‐
nents,andtheerrorfluctuationwassmallerthanthatoftheothers.Therefore,Figure6
adequatelyshowsthattheceramicfiberwithTPU‐95A#andceramicpowder=4:6had
thebestflexibilityanduniformity,whichwasalsoconsistentwiththemicrostructureof
Figure4.
Figure7showsasampleoftheYAGceramicfiberpreparedbymeltspinning.Figure
7adisplaystheflexiblegreenbodyofYAGceramicfiberwiththemassratioofTPU‐95A#
toceramicpowder=4:6.Thisgreenbodyhadgoodflexibilityandcouldbebentandknot‐
tedwithabendingradiusofabout2.5mm.Figure7bshowsthefiberpreparedbyTPU‐
95A#,withabendingradiusofabout2.5mm.Therefore,meltspinningwasaneffective
waytoprepareceramicfiberwithhighflexibilityandhighstrength.Inthefuture,further
researchonthesinteringandpolishingofceramicfiberwillbecarriedout.
Figure7.SampleofYAGceramicfiberbymeltspinning:(a)flexiblegreenbodyofceramicfiber
withthemassratioofTPU‐95A#toceramicpowder=4:6,(b)TPU‐95A#meltspinning.
Figure 6.
Tensile strength of different TPU types and components: (
a
) three tensile strength tests of
different TPU types and components (TPU-75A# and ceramic powder = 4:6, TPU-95A# and ceramic
powder = 4:6, TPU-95A# and ceramic powder = 3:7; inset: the test situation by the monofilament
strength tester), (b) average tensile strength of different TPU types and components.
Figure 7shows a sample of the YAG ceramic fiber prepared by melt spinning. Figure 7a
displays the flexible green body of YAG ceramic fiber with the mass ratio of TPU-95A# to
ceramic powder = 4:6. This green body had good flexibility and could be bent and knotted
with a bending radius of about 2.5 mm. Figure 7b shows the fiber prepared by TPU-95A#,
with a bending radius of about 2.5 mm. Therefore, melt spinning was an effective way to
prepare ceramic fiber with high flexibility and high strength. In the future, further research
on the sintering and polishing of ceramic fiber will be carried out.
Polymers2022,14,xFORPEERREVIEW11of14
Excessivemetaloxidesinceramicpowdersmayalsoleadtotheincompletemeltingof
TPU.
Figure6.TensilestrengthofdifferentTPUtypesandcomponents:(a)threetensilestrengthtestsof
differentTPUtypesandcomponents(TPU‐75A#andceramicpowder=4:6,TPU‐95A#andceramic
powder=4:6,TPU‐95A#andceramicpowder=3:7;inset:thetestsituationbythemonofilament
strengthtester),(b)averagetensilestrengthofdifferentTPUtypesandcomponents.
Figure6bexhibitstheaveragetensilestrengthcalculatedbasedonFigure6afromthe
resultsofTPU‐75A#andceramicpowder=4:6,TPU‐95A#andceramicpowder=4:6and
TPU‐95A#andceramicpowder=3:7.Theiraveragetensilestrengthswere14.59MPa,
19.79MPaand13.71MPa,respectively.Apparently,theaveragetensilestrengthofTPU‐
95A#andceramicpowder=4:6waslargerthanthatoftheotherTPUtypesandcompo‐
nents,andtheerrorfluctuationwassmallerthanthatoftheothers.Therefore,Figure6
adequatelyshowsthattheceramicfiberwithTPU‐95A#andceramicpowder=4:6had
thebestflexibilityanduniformity,whichwasalsoconsistentwiththemicrostructureof
Figure4.
Figure7showsasampleoftheYAGceramicfiberpreparedbymeltspinning.Figure
7adisplaystheflexiblegreenbodyofYAGceramicfiberwiththemassratioofTPU‐95A#
toceramicpowder=4:6.Thisgreenbodyhadgoodflexibilityandcouldbebentandknot‐
tedwithabendingradiusofabout2.5mm.Figure7bshowsthefiberpreparedbyTPU‐
95A#,withabendingradiusofabout2.5mm.Therefore,meltspinningwasaneffective
waytoprepareceramicfiberwithhighflexibilityandhighstrength.Inthefuture,further
researchonthesinteringandpolishingofceramicfiberwillbecarriedout.
Figure7.SampleofYAGceramicfiberbymeltspinning:(a)flexiblegreenbodyofceramicfiber
withthemassratioofTPU‐95A#toceramicpowder=4:6,(b)TPU‐95A#meltspinning.
Figure 7.
Sample of YAG ceramic fiber by melt spinning: (
a
) flexible green body of ceramic fiber with
the mass ratio of TPU-95A# to ceramic powder = 4:6, (b) TPU-95A# melt spinning.
4. Conclusions
In this study, the flexible ceramic fiber was prepared by melt spinning. The melting
characteristics with TPUs and four different Shore hardnesses were systematically investi-
gated. The tensile strength and flexibility of ceramic fiber was tested. The microstructure,
element types and homogeneity of the surface and fracture SEM images were also analyzed
in detail. Through the above series of experiments, the optimized process parameters
of YAG ceramic fiber preparation were as follows: the melting temperature was 220
◦
C,
the screw feed rate of the micro double-cone screw extruder was F = 15.0 mm/min and
the TPU-95A# was used. In addition, according to the surface and fracture SEM images,
Polymers 2022,14, 2096 12 of 13
the ceramic fiber with the mass ratio of TPU-95A# to ceramic powder = 6:4 had the best
microstructure quality, and there were no other impurity elements. The resulting flexible
green body of YAG ceramic fiber had good flexibility and could be bent and knotted with a
bending radius of about 2.5 mm, and the tensile strength reached approximately 20 MPa.
Therefore, melt spinning provided a novel path to prepare the green body of YAG ceramic
fiber. The popular application and development of ceramic fibers in lasers can be greatly
enhanced by this new preparation method.
Author Contributions:
Conceptualization, H.L. and Q.Y.; methodology, H.L.; software, J.T.; valida-
tion, H.L., J.T. and G.P.; formal analysis, H.L. and J.T.; investigation, Q.Y. and Y.X.; resources, Q.Y.;
data curation, Y.X.; writing—original draft preparation, H.L. and J.T.; writing—review and editing,
H.L. and J.T.; visualization, Y.X.; supervision, Q.Y.; project administration, Q.Y.; funding acquisition,
Q.Y. All authors have read and agreed to the published version of the manuscript.
Funding:
This research was funded by the National Natural Science Foundation of China (62005133)
and Talent Introduction Project of Nantong University (135420610063). And The APC was funded
by the National Natural Science Foundation of China (62005133) and Talent Introduction Project of
Nantong University (135420610063).
Data Availability Statement:
Data will be made available from the corresponding authors on rea-
sonable request.
Acknowledgments:
The authors acknowledge the generous financial support from the National Nat-
ural Science Foundation of China (62005133) and Talent Introduction Project of Nantong University
(135420610063).
Conflicts of Interest: The authors declare no conflict of interest.
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