Y. TAO et al.: APPLICATION OF A THERMOPLASTIC POLYURETHANE/POLYLACTIC ACID COMPOSITE FILAMENT ...
71–76
APPLICATION OF A THERMOPLASTIC
POLYURETHANE/POLYLACTIC ACID COMPOSITE FILAMENT
FOR 3D-PRINTED PERSONALIZED ORTHOSIS
UPORABA VLAKEN KOMPOZITOV IZ TERMOPLASTI^NEGA
POLIURETANA IN POLILAKTI^NE KISLINE ZA 3D-TISKANJE
OPORNIC, PRILAGOJENIH OSEBNIM POTREBAM
Yubo Tao
1
, Jingjiao Shao
1
, Peng Li
1*
, Sheldon Q. Shi
2
1
College of Material Science and Engineering, Northeast Forestry University, Harbin 150040, China
2
Department of Mechanical and Energy Engineering, University of North Texas, Denton, TX 76203, USA
Prejem rokopisa – received: 2018-08-15; sprejem za objavo – accepted for publication: 2018-09-20
doi:10.17222/mit.2018.180
For designing and fabricating personalized, cost-effective and bio-degradable orthoses, a finger orthosis was chosen as an
example to explore a suitable material, personalized design method, and fabrication with a fuse-deposition-modeling (FDM)
open-source 3D printer. Thermoplastic polyurethane (TPU)/polylactic acid (PLA) composite filaments were explored for 3D
printing. The polymer composite compositions were TPU/PLA: 0 %/100 % (TP0), 25 %/75 % (TP25), and 50 %/50 % (TP50)
by weight, respectively. The mechanical performance, thermal properties, and structure of the TPU/PLA composite filaments
were assessed by tensile tests, thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC), and powder X-ray
diffraction (XRD) measurements. Compared to the neat PLA, the TP25 specimens exhibited almost the same tensile strength,
but its higher elongation at the break indicates that TP25 is more suitable for the material of orthoses. However, a further
increase of the TPU ratio to 50 % resulted in a sharp decrease of the tensile strength. The addition of TPU had little effect on the
starting thermal decomposition temperature, glass-transition temperature, and melting temperature of the composites. The com-
posite filaments can be printed through the normal 3D printing procedure. 3D scanning and open-source 3D printers can be used
to complete the design and fabrication of personalized orthoses.
Keywords: 3D printing, 3D scanning; orthosis, thermoplastic polyurethane, polylactic acid
Avtorji so se ukvarjali z oblikovanjem in izdelavo cenovno ugodnih, biorazgradljivih in individualnih (osebnim potrebam
prilagojenih) opornic. Na primeru opornice za prste so raziskovali ustreznost materiala, na~in izdelave s talilno-depozicijskim
modeliranjem (FDM; angl.: Fuse-Deposition-Modeling) na 3D printerju z odprtokodno programsko opremo, ter metodo
osebnega dizajna. Ugotavljali so primernost vlaken iz kompozita termoplasti~nega poliuretana (TPU) in polilakti~ne kisline
(PLA) za 3D tiskanje. Izbrane masne sestave polimernih kompozitov so bile TPU/PLA: 0 %/100 % (TP0), 25 %/75 % (TP25),
in 50 %/50 % (TP50). Mehanske, termi~ne in strukturne lastnosti vlaken iz TPU/PLA kompozitov so dolo~ili z nateznim
(trgalnim) preizkusom, termogravimetrijo (TGA), diferencialno vrsti~no kalorimetrijo (DSC) in pra{kovno rentgensko
difrakcijo (XRD). Primerjava med vzorci iz ~istega PLA in vzorci iz TP25 je pokazala skoraj enako natezno trdnost pri obeh, a
ve~ji raztezek pri TP25 ka`e na to, da je slednji primernej{i material za izdelavo opornic. Vendar pa je nadaljnje pove~anje
vsebnosti TPU na 50 % povzro~ilo mo~an padec natezne trdnosti vlaken. Dodatek TPU neznatno vpliva na temperaturo za~etka
termi~nega razpada, temperature prehoda v steklasto stanje in temperature taljenja kompozitov. Vlakna iz izbranih kompozitov
se lahko normalno izdelujejo s postopkom 3D tiskanja. Odprtokodni 3D tiskalniki omogo~ajo celovit dizajn in izdelavo
individualnih opornic.
Klju~ne besede: 3D tiskanje, 3D skeniranje, opornice, termoplasti~ni poliuretan, poliakti~na kislina
1 INTRODUCTION
In the medical field, orthoses are used for many pur-
poses. Depending on the patient’s impairment, they
might be used as braces for the rehabilitation of periphe-
ral nerves’ dysfunctions, the improvement of gait per-
formance for people with an impaired lower-limb func-
tion, or the optimization of the support of a limb used in
rheumatology, traumatology, or other articulations in-
flammatory processes.
1,2
3D printing (3DP), also known
as additive manufacturing (AM) technology, can be
defined as a technique for creating three-dimensional
objects in a layer-by-layer manner. Over the past few
years, 3DP has extended to areas of aerospace, auto-
motive, architecture, medical, education, and fashion.
Nowadays, 3DP is spreading in the orthosis field. Given
its low-cost and continuous materials evolution, its
diffusion is expected to rapidly increase in the near
future.
3
Fused deposition modelling (FDM) is one of the
most commonly used techniques in 3DP. The expiration
of early FDM patents has led to the growth of relatively
low-cost, open-source 3D printers. In essence, an FDM
printer consists of an engine, gear wheels, an extrusion
nozzle, and a building plate. The filament with a well-
defined and consistent diameter is loaded and pushed
towards the extrusion nozzle (which is set at an elevated
temperature) to be melted and deposited onto a building
Materiali in tehnologije / Materials and technology 53 (2019) 1, 71–76 71
UDK 615.477.3:678.664:655.3:531.259 ISSN 1580-2949
Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 53(1)71(2019)
*Corresponding author e-mail:
lptyb@aliyun.com

plate. Dictated by the slicing software, the extrusion
nozzle can be moved in different XY directions. Once
each individual cross-section of the desired object is
completed, the building plate can be moved down (Z
direction) to deposit different layers.
4
Polylactic acid (PLA) filaments are widely used as
bio-based feedstock for FDM. Although PLA filaments
are degradable and exhibit outstanding properties, its
brittleness restricts their suitability for orthosis applica-
tions. Preparing PLA composites by mixing PLA with an
elastomer offers a solution for ameliorating the tough-
ness of PLA.
5
Thermoplastic polyurethane (TPU) elasto-
mers are excellent biocompatible materials for many
applications in the medical field, such as blood bags and
surgical gloves, catheters, synthetic veins, and wound
dressings.
6
Based on the chemical structure of PLA and
TPU, it is possible to achieve better compatibility bet-
ween both polymers. PLA is compatible with the soft
polyester segments of TPU and can form hydrogen
bonds with the carbamates from hard segments of
TPU.
7,8
3DP’s most distinguishing feature is its ability to
construct complex spatial objects rapidly from a digital
model file. The design and production of personalized
products in the pharmaceutical field, such as medicines,
oral dosage forms, and medical devices, has benefitted
from the advantages of 3DP.
9,10
Computer-aided design
(CAD) and 3D scanning technology are commonly used
to generate 3D models. For personalized orthoses, 3D
scanning technology offers an ideal technique for ob-
taining patient-specific 3D models.
In this paper, a finger orthosis was chosen as an
example to explore the design and fabrication of a
personalized orthosis. The TPU/PLA composite
filaments were developed for FDM 3DP. The properties
of the TPU/PLA composite were investigated. The
feasibility of making personalized orthoses using 3D
scanning and an open-source 3D printer was explored.
2 EXPERIMENTAL PART
2.1 Preparation of TPU/PLA polymer composite fila-
ments
Virgin PLA (4032D) pellets were purchased from
NatureWorks LLC, USA. The density is 1.24 g cm
–3
and
the melting temperature is about 160 °C. TPU (1170A
Elastonllan) pellets were obtained from the BASF
Company, Germany. This is a polyether TPU with high
toughness and elongation at the break, and a density of
1.08 g cm
–3
.
The PLA and TPU pellets were initially dehydrated
(103 °C) for 4 hours to eliminate the moisture. After
drying, the TPU and PLA pellets were then blended with
different ratios of TPU/PLA (0 %/100 %(TP0), 25 %/75 %
(TP25), and 50 %/50 % (TP50) by weight and extruded
using a single screw extruder (C2 model, Wellzoom
LLC, Shenzhen, China) for fabricating neat PLA and
TPU/PLA polymer composite filaments.
The extruder has separate temperature (maximum
320 °C) controls for the mixture and the extrusion parts,
which offers a maximum extrusion speed of 2 m·min
–1
.
The extruded TPU/PLA filament was cut into smaller
particles and extruded again for three times to obtain a
well-mixed TPU/PLA composite filament with different
TPU blend proportions. During fabrication, 1.75 mm
filaments were used, the processing temperatures were
set at 180 °C (extrusion part) and 185 °C (mixture part),
with a filament yield (extrusion) speed of 1 m·min
–1
.
2.2 Property measurements of TPU/PLA composite
filaments
The tensile properties of the specimens were
measured with a universal testing machine (Changchun
Kexin instruments Co. Changchun, China). The speci-
mens were designed according to ASTM D638. Three
replicates were printed from each TPU/PLA ratio
composite filament for a mean value calculation. The
typical stress-strain curves and elasticity modulus were
obtained.
Thermal gravimetric analyses (TGA) and differential
scanning calorimetry (DSC) analyses of the specimens
were performed in a TA analyzer (Q 50, TA Instruments,
USA) and DSC analyzer (Q 20, TA Instruments, USA).
The samples were heated from 25 °C to 400 °C for the
TGA and to 300 °C for the DSC with an increase rate of
10 °C min
–1
to observe their thermal degradation beha-
viors. Throughout the whole procedure, the N
2
flow rate
was 30 mL·min
–1
.
Powder X-ray diffraction (XRD) measurements were
recorded using a D/max 220 analyzer (Rigaku, Japan).
The samples were scanned under conditions of a voltage
of 40 kV, a current of 30 mA, a starting angle of 5°, a
termination angle of 40°, and a step width of 0.02°.
2.3 3D scanning and printing
A Sense® 3D Scanner (3D Systems, Inc. USA) was
used to scan the finger to create a digital finger model of
an orthosis. As shown in Figure 1a, the lens of the
Y. TAO et al.: APPLICATION OF A THERMOPLASTIC POLYURETHANE/POLYLACTIC ACID COMPOSITE FILAMENT ...
72 Materiali in tehnologije / Materials and technology 53 (2019) 1, 71–76
Figure 1: 3D scanning and printing: a) the finger was scanned using a
3D scanner to obtain the digital finger model, b) the finger orthosis
was printed using an open-source 3D printer with FDM technology

scanner faced and slowly rotated around the finger until
the digital finger model was generated in the computer.
Geomagic Studio software (developed by Geomagic
Company) was used to edit the digital finger model, such
as deleting misplaced polygons, etc. Then the Boolean
operation of the 3DS MAX software (developed by
Autodesk) was used to design the matching orthosis mo-
del. The finger orthosis model was saved in STL
(Stereolithographic) format and transferred to the 3D
printer.
The specimens for the tensile properties and the
finger orthosis were printed with TP0, TP25, and TP50
filaments using an open-source 3D printer (605S model,
Shenzhen Aurora Technology Co, Shenzhen, China).
The nozzle diameter of the printer was 0.4 mm. The
CURA software (15.04 version, developed by Ultimaker)
was used to set the printing parameters. The printing
layer height was set to 0.3 mm, the shell thickness to 1.2
mm, the top and bottom thickness to 1.2 mm, the filling
density to 10 %, the printing speed to 30 mm s
–1
,t h e
printing temperature to 200 °C, the hot-bed temperature
to 60 °C, and the wire material flow rate to 100 %. The
printing process of the finger orthosis is shown in
Figure 1b.
3 RESULTS AND DISCUSSION
3.1 Filaments and test specimens
The neat PLA and TPU/PLA composite filaments
were manufactured successfully by the extruder with a
diameter of 1.75 mm, as shown in Figure 2a. The
TPU/PLA composite filaments showed a smooth surface
and a uniform diameter. Compared to the neat PLA, the
transparency of the TPU/PLA composite decreased. The
printed specimens of neat PLA and TPU/PLA composite
for the tensile property tests are shown in Figure 2b.
Through experimentation and observation, the TPU/PLA
composite filaments were determined to be suitable for
FDM printing.
3.2 Tensile properties
In Figure 3, the tensile stress-strain curves show that
the TP0 specimen has almost no plastic deformation
after the tensile yield point, and the neat PLA part under-
goes brittle fracture. Nevertheless, the TP25 and TP50
specimens exhibit plastic deformation and ductile frac-
ture after the tensile yield point. The fracture morphol-
ogy of the specimens shows that TP0 suffers breakage
without elongation. While the TP25 specimens can be
broken after the plastic deformation, and the fibers of the
TP50 specimen were stretched with no fracture. The
failure characteristics of the specimens revealed that a
higher TPU content results in a greater tensile toughness.
Table 1: Tensile properties of the specimens
Specimens
Tensile
modulus (MPa)
Tensile strength
(MPa)
Elongation at
break (%)
TP0 666.3 28.8 4.4
TP25 569.2 28.4 58.5
TP50 371.4 19.5 >100
Table 1 shows that the tensile modulus of the spe-
cimens decreases gradually with the increase of the TPU
content, and while the tensile strength of the TP25 speci-
mens undergoes insignificant changes, the elongation at
break increases over tenfold. However, the tensile
Y. TAO et al.: APPLICATION OF A THERMOPLASTIC POLYURETHANE/POLYLACTIC ACID COMPOSITE FILAMENT ...
Materiali in tehnologije / Materials and technology 53 (2019) 1, 71–76 73
Figure 3: Typical tensile stress-strain curves of the TP0, TP25, and
TP50 specimens as well as the fracture morphology of the specimens
Figure 2: Filaments and test specimens: a) neat PLA and TPU/PLA
composite filament, b) specimens for tensile property measurements

modulus and tensile strength of the TP50 specimens are
greatly reduced and the elongation at break is more than
100 %.
The alternating hard and soft segments of its mole-
cular chain endow the TPU with the unique properties of
flexibility and elasticity. When blended with the brittle
PLA, the TPU could contribute to the composite’s flexi-
bility. Furthermore, the hydrogen bond formed between
the PLA and TPU molecules guarantees that at an
optimized TPU addition ratio, the tensile strength of the
composite will be no less than that of the neat PLA. The
elongation determines the maximum deformation of a
material without breakage, which is especially important
from a manufacturing standpoint. Therefore, to obtain
optimal performance, it is necessary to prepare
PLA/TPU composites with tailored strength, modulus,
and elongation.
11
3.3 DSC analysis
As shown in Figure 4 and Table 2, the neat PLA can
be characterized with a T
g
at 57.9 °C, a cold crystalli-
zation temperature (T
c
) around 113.1 °C and a melting
temperature of (T
m
) 153.9 °C. Compared with the neat
PLA, the Tg of the two TPU/PLA composites slightly
decreased, which means that the TPU and PLA were
partially miscible. The compatibility of polymer blends
can be assessed by observing the shift in the Tg of the
phases in comparison with their original values.
12
The T
c
of the polymer composite decreased with an
increase of the TPU content, indicating that the TPU
affected the cold crystallization of the PLA. These
phenomena can be attributed to the added TPU, which
acts as a crystallization nucleation agent by providing
nucleation spots. Among the three filaments, both the
cold crystallization peak and the melting peak decreased
with an increase of the TPU content.
13
The melting
temperatures of TP0, TP25, and TP50 are about 153 °C.
Therefore, the printing temperature of TP25 and TP50
can equal that of the neat PLA.
Table 2: Thermal properties of neat PLA and TPU/PLA composite
filaments
Specimens T
g
(°C) T
c
(°C) T
m
(°C)
TP0 57.9 113.1 153.9
TP25 57.5 96.2 153.2
TP50 57.0 91.1 152.6
3.4 Thermal gravimetric analysis
As shown in Figure 5 and Table 3, the addition of
TPU has little effect on the initial decomposition
temperature (Ti) of the polymer composite. Compared to
the neat PLA, when the weight loss was 10 % (T10) of
TP25 and TP50, the decomposition temperatures
decreased less than 5 °C. The fast decomposition
temperature of the polymer composites shifted obviously
to lower temperature ranges, and the TPU/PLA
composites exhibited two fast decomposition peaks. The
increase of the TPU content had almost no effect on the
fast decomposition temperature. Compared to the neat
PLA, the heat stability of the polymer composite was
reduced; the initial decomposition temperatures of the
TPU/PLA composites were around 190 °C. The fast
decomposition temperature range was 270–280 °C,
which can fully meet the requirements of FDM 3D
printing.
Table 3: Decomposition temperature of the neat PLA and TPU/PLA
composite filaments
Specimens T
i
(°C) T
10
(°C) T
f
(°C)
TP0 188.2 250.4 292.6
TP25 187.9 245.6 273.1, 331.3
TP50 187.7 247.2 272.8, 331.1
3.5 X-ray diffraction spectra
In Figure 6, the XRD peak shape of the TPU/PLA
composite is similar to that of the neat PLA. The neat
PLA showed a broad amorphous halo at 2 = 16.9°,
Y. TAO et al.: APPLICATION OF A THERMOPLASTIC POLYURETHANE/POLYLACTIC ACID COMPOSITE FILAMENT ...
74 Materiali in tehnologije / Materials and technology 53 (2019) 1, 71–76
Figure 5: TGA and DTG curves of the neat PLA and TPU/PLA
composite filaments
Figure 4: DSC curves of neat PLA and TPU/PLA composite filaments

which is the characteristic diffraction peak of the PLA
crystallization. However, compared with the neat PLA,
due to the contribution of the TPU, the broad halo of the
diffraction peak 2 = 20.2°. The addition of TPU to PLA
has a heterogeneous nucleation effect on the crystalli-
zation of PLA. After 25 % TPU mixing, the peak inten-
sity decreases slightly, and the diffraction peak of 2 increases, indicating that the interplanar distance
decreases. When 50 % TPU is added, the peak width
decreases, as a result of the larger grain size.
3.6 Printed orthosis
The TP25 has more toughness than the neat PLA, but
a similar tensile strength and printing temperature with
the neat PLA. Therefore, it was chosen to print the
orthosis. The TP25 filament can be successively printed
through FDM 3D printing, and the finger orthosis
designed and printed can be a good fit, as shown in
Figure 7. This indicates that the TPU/PLA composite
filament is feasible for 3D printing orthoses.
4 CONCLUSIONS
The TPU/PLA composite filaments were prepared
and the potential of the composites for an application in
orthosis fabrication was evaluated. The research
demonstrated that the TPU/PLA composite filament is
compatible with the FDM process. Compared with the
neat PLA, the addition of TPU has little effect on the
starting thermal decomposition temperature, the glass-
transition temperature, and the melting temperature.
Without sacrificing any tensile strength, the composite
with 25 % TPU exhibited better toughness than the neat
PLA and can be printed smoothly, just like the PLA. The
results revealed that the TPU/PLA composite filament is
more suitable for the design of orthoses than the neat
PLA. 3D scanning and open-source 3D printers can be
used to complete the design and fabrication of per-
sonalized orthosis.
Acknowledgment
This project was supported by the Program for New
Century Excellent Talents in University of China
(NCET-13-0711). The authors would like to thank
Zelong Li for his help and advice.
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