materials
ArticleAdditive Manufacturing of Plastics Used for Protection against
COVID19—The Influence of Chemical Disinfection by Alcoholon the Properties of ABS and PETG Polymers
Krzysztof Grzelak , Julia Łaszcz, Jakub Polkowski, Piotr Mastalski, Janusz Kluczyński * , Jakub Łuszczek
Janusz Torzewski , Ireneusz Szachogłuchowicz and Rafał Szymaniuk,

Institute of Robots & Machine Design, Faculty of Mechanical Engineering, Military University of Technology,
2 Gen. S. Kaliskiego St., 00-908 Warsaw 49, Poland; krzysztof.grzelak@wat.edu.pl (K.G.);
julia.laszcz@student.wat.edu.pl (J.Ł.); jakub.polkowski@student.wat.edu.pl (J.P.);
piotr.mastalski@student.wat.edu.pl (P.M.); jakub.luszczek@wat.edu.pl (J.Ł.); janusz.torzewski@wat.edu.pl (J.T.);
ireneusz.szachogluchowicz@wat.edu.pl (I.S.); rafal.szymaniuk@student.wat.edu.pl (R.S.)* Correspondence: janusz.kluczynski@wat.edu.pl; Tel.: +48-261-837-646

 
Citation: Grzelak, K.; Łaszcz, J.;
Polkowski, J.; Mastalski, P.;
Kluczyński, J.; Łuszczek, J.;
Torzewski, J.; Szachogłuchowicz, I.;
Szymaniuk, R. Additive

Abstract: In this paper, the influence of disinfection on structural and mechanical properties ofadditive manufactured (AM) parts was analyzed. All AM parts used for a fight against COVID19
were disinfected using available methods—including usage of alcohols, high temperature, ozonation,
etc.—which influence on AM parts properties has not been sufficiently analyzed. During thisresearch, three types of materials dedicated for were tested in four different disinfection times andtwo disinfection liquid concentrations. It has been registered that disinfection liquid penetrated
void into material’s volume, which caused an almost 20% decrease in tensile properties in parts
manufactured using a glycol-modified version of polyethylene terephthalate (PETG).

Manufacturing of Plastics Used forProtection against COVID19—The

Keywords: additive manufacturing; structural analysis; mechanical properties; polymers; COVID19

Influence of Chemical Disinfection by
Alcohol on the Properties of ABS and
PETG Polymers. Materials 2021, 14,4823. https://doi.org/10.3390/

1. Introduction

ma14174823

COVID19 pandemic caused a massive gap in deliveries of first-aid tools for humanlife and health protection against the virus. At the beginning of lockdown in 2020 allcompanies, freelancers, and hobbyists connected with additive manufacturing (AM) of
polymers started to produce face shields, diving masks high-efficiency particulate air(HEPA) connectors, anti-dust masks HEPA connectors, and other different tools.
Material extrusion additive manufacturing (ME-AM) plays a significant role in manyindustries because of its advantages, such as easy digitization based on three-dimensional
CAD data, fast, and low-cost efficient creation of customized, on-demand, and prototype
products, and reflecting accurately very complex geometries. One of the most common
and popular methods is fused filament fabrication (FFF), where thermoplastic material(filament) is heated in a range of 175–265 ◦ C (depends on material type). The plasticizedfilament is being deposited layer by layer in the building plate in such a way to allow
reaching the desired shape of the same part. There is a variety of filaments used in thistechnology. Poly(lactic acid) (PLA) and acrylonitrile butadiene styrene (ABS) are the mostcharacteristic materials used in that type of ME-AM. PLA is non-toxic, biodegradable,
biocompatible therefore, it is used in the field of medicine [1–5]. However, objects madeof PLA are characterized by low mechanic properties [6], especially at a temperature nearplasticizing point (about 60 ◦ C) [7] and are influenced by low fatigue resistance, too [4].
That is why this material has not been used during AM of parts dedicated for protection
against COVID19 [2].
Many researchers analyzed the influence of FFF technology parameters (layer thickness, infill density, and pattern) on the final product properties and used the material itself.
One material commonly used is polyethylene terephthalate glycol (PETG), which is more

Academic Editors: Juergen Stampfl
and Filippo Berto
Received: 6 July 2021
Accepted: 23 August 2021
Published: 25 August 2021

Publisher’s Note: MDPI stays neutral
with regard to jurisdictional claims inpublished maps and institutional affiliations.

Copyright: © 2021 by the authors.
Licensee MDPI, Basel, Switzerland.
This article is an open access article
distributed under the terms andconditions of the Creative Commons
Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).

Materials 2021, 14, 4823. https://doi.org/10.3390/ma14174823

https://www.mdpi.com/journal/materials

Materials 2021, 14, 4823

2 of 21flexibly and resistant to temperature than PLA, and has high durability, low shrinkage, andis hydrophobic [8]. These specific properties of polyethylene terephthalate glycol led to it
being chosen as the sufficient material for 3D printing of masks during the beginning of
the COVID-19 pandemic [3,9,10]. Srinivasan et al. [11] studied the mechanical propertiesof PETG. Their research noted that the tensile strength of the printed models is directly
proportional to infill density and inversely proportional to layer thickness. Additionally,
it is characterized by reverse relations in surface roughness. Durgashyam et al. [12] investigated PETG materials not only tensile but also flexural strength while considering
the specifications mentioned above. The main conclusion was that, among tested parameters, layer thickness had the highest contribution in affecting mechanical properties of
produced objects.
On the one hand, Hanon et al. [13], after evaluating the outcome of their analyses
deduced that PETG used in FFF technology demonstrates anisotropic properties, but on theother hand, Mercado-Colmenero et al. [14], after complex research proved that in numericalsimulations FFF manufactured PETG could be treated as an isotropic material.
Since the world is currently struggling with COVID19, AM has been exploited tothe boundaries of its possibilities. In medicine, it filled significant gaps where traditional
subtractive manufacturing is lacking, injection molding is not ready for mass production,or is economically unjustified. AM is a technology in which the product is constructed byadding material in cross-sectioned layers, this way of processing influences the fatigue
performance of the element.
The main reason for using PETG for the health protection during the beginningof the COVID19 pandemic is two-fold. The first is related to the material properties—
it is more resistant to temperature than the PLA—it can withstand temperatures up to75 ◦ C and its properties are not affected by the UV radiation. Also, it is characterized
by better chemical resistance than ABS and PLA and is less fragile than the PLA parts.
Such characteristics allow bettering disinfection using high temperature or alcohols which
made it better customized to medical solutions than the PLA and other commonly usedmaterials in ME-AM. On the other hand, the usage of the PETG at the beginning of the
COVID19 pandemic was related to low filament diameter tolerance increase after winding
increase (prusament.com) to allow the increase of manufactured material dedicated to
FFF technology.
Additionally, there are available in the market, materials dedicated for the ME-AM,
and usage in medical applications. The most popular are ABS-based filaments. Suchmaterials are mostly certified by basing on USP VI and ISO 10993-1 standards. Its usage
during the pandemic was marginalized due to its high cost and low availability.
Nowadays, many Universities and companies joined forces to produce better protection for the medical staff as they are the most endangered. AM has been used chiefly tocreate protection helmets as it is a fast way to build many specific parts [15] or connectorsfor HEPA filters. This equipment needs to be disinfected regularly to avoid introducing
pathogens, which are the cause of the illness. Low-level disinfection (LLD) is based on
exposing the surface to a liquid for at least 1 min. The substance used is a fluid that contains
70–90% of alcohol [16]. The aftermath of its effect should be the annihilation of viruses,
vegetative bacteria, and some fungi. Going further, high-level disinfection (HLD) results indestroying all microorganisms except some bacterial spores with heat treatment performedby subjecting the material to 65 to 75 ◦ C for half an hour [16].
Based on Huang et al. work [17] the main categories of chemical cleaning agents canbe listed as follows: acids, alkalis, disinfectants (including alcohols), surfactants, metalchelating agents, and enzymes. The authors of the mentioned work [17] discussed somemost important cases of disinfection mechanisms:
1.

2.2-Dibromo-3-nitrilopropionamide inhibits respiration and inactivates proteins containing nucleophilic partial amino acids such as methionine and cysteine.

Materials 2021, 14, 4823

3 of 21

2.

3.
4.
5.
6.
7.
8.

Isothiazolones quickly inhibit the physiological functions of microorganisms, including growth, respiration, energy production (such as adenosine triphosphate synthesis),and destroy thiol-containing proteins.
Glutaraldehyde reacts with biomolecules like protein, RNA, and DNA, which containamino, amide, and carboxyl groups.
Tributyl tetradecyl phosphonium chloride inactivates bacteria by destroying anddecomposing the negatively charged membrane of bacteria.
Dichloroisocyanurate releases hypochlorous acid and isocyanuric acid in water toinactivate bacteria.
Copper and silver ions interfere with enzymes involved in cell respiration and bind to
DNA at specific sites.
Ethyl lauroyl arginate inactivates microorganisms by changing their cell membrane
structure and interfering with their membrane potential.
Chlorhexidine gluconate acts as a biguanide and cation-active compound with significant antibacterial activity and inhibits microorganism adherence and prevents
biofilm formation.

To render more stringent the case of polymers chemical disinfection, Roman et al. [18],analyzed different types of disinfection that could be used for AM parts. The authors
revealed five different methods which could be used for such parts:

•
•
•
•
•

ultraviolet (UV) sterilization using a germicidal fluorescent bulb,
autoclave sterilization,
submersion in a glutaraldehyde solution,hydrogen peroxide sterilization,
alcohol disinfection.

Based on mentioned research [18], hydrogen peroxide sterilization is the best alternative to avoid the deformation of PLA and PETG AM objects. It is also preferable to steam
sterilization for PLA and PETG, as it causes only submillimeter morphological distortions,instead of dynamically damaging the materials in consequence of high temperature (121 ◦ C
for 5 min) [19].
Electron beam and gamma radiation are also a practice in the mentioned above field
and are safely used for PLA and PETG. However, ethylene oxide cannot be implemented
for PLA and PETG, as it inflicts the polymeric structures, causing weight loss and creatinga risk of inducing toxic deposits on the surface of the element [19]. On the other hand, UV
and gamma radiation does not impact the alignment of the fibers, therefore are suitablefor PLA sterilization [20]. ABS disinfection is not an often mentioned topic in studies buthydrogen peroxide works very well with it, not altering the morphology of the filament [21].
The abovementioned methods were not available in smaller facilities that struggled withthe effects of the COVID19 pandemic. Despite many available methods, the most available
disinfection medium for most medical aid centers and social welfare facilities was alcohol.
Additionally, the usage of disinfection liquid allows better penetration of the whole volumeof each part. It is especially important in AM parts which are often characterized bygeometrical complexity.
As shown, in most of the cited studies conducted over the past two years, the mechanical properties of PETG are still being investigated. Still, none of them has included LLD
or HLD influence on mechanical properties of FFF manufactured PETG models such as
face shields widely used by rescue teams and hospital staff during the pandemic. Usageof the PETG in FFF technology seems to be a good alternative in some solutions wheremuch more expensive AM technologies are unnecessary. This statement results from ourprevious research, connected with other material also dedicated for medical solutions–316L
steel obtained during selective laser melting (SLM) process [17–21].

Materials 2021, 14, 4823

4 of 21

2. Materials and Methods
The FFF method produced the test specimens using AM technology. The main reason
for selecting the FFF technology was using that kind of device during the 3D print of manydifferent parts dedicated to increasing protection against COVID19. The principle of the
FFF process is very similar to fused deposition modeling (FDM) technology, where theplastic wire (named as 3D printing filament) is being pushed by extruder mechanism tothe heated nozzle. After that, the material is being plasticized and put into the substrate
plate. A fully automated movement algorithm of the printing nozzle and substrate plateallows for different (often very complex) shapes creation. Regarding the additive characterof the process, the parts are built layer-by-layer until the final geometry creation.
For the research PETG filament (Rosa 3D, Hipolitów, Poland) was used. That kind of
material is prevalent for manufacturing parts dedicated to protection against COVID19. It
was also commonplace for using different colors of the material during many supporting
actions. Hence, two types of PETG were tested: with color pigment and without any
additions. All parts were manufactured using the Prusa Original MK3s device (Prusa
Research, Prague, Czech Republic), the manufacturing processes were prepared using
PrusaSlicer Software (version 2.1.0) using the default parameters for the Prusa device for
PETG materials:

•
•
•
•
•
•
•
•

Hotend temperature (for both materials): 240 ◦ C,
Heatbed temperature: 90 ◦ C,
Layer thickness: 0.2 mm,
Infill: 100%,
Part cooling intensity: 40%,
Printing speed: 60 mm/s,
Nozzle diameter: 0.4 mm,
Number of the contour lines: 5

Additionally, an ABS Medical (SmartMaterials 3D, Jaén, Spain) filament was used forresults compared with the PETG results. That kind of material is certified by basing on
USP VI and ISO 10993-1 standard, which assures its biocompatibility. The properties ofused materials are shown in Table 1.
Table 1. Properties of used materials: PETG and ABS medical provided by producers’ data sheets.
Material

PETG

ABS

Material density (g/cm3 )

1.27
2100
69
70
85

1.05
2600
75
98
101

Flexural modulus (MPa)
Flexural strength (MPa)
Thermal deflection temperature (◦ C)
Vicat softening temperature (◦ C)

A manufacturing process with the usage of the ABS Medical was prepared in the same
software and manufactured on the same device as PETG parts. Process parameters–default
for the Prusa device for the ABS material were as follows:

•
•
•
•
•
•
•
•

Hotend temperature: 255 ◦ C,
Heatbed temperature: 110 ◦ C,
Layer thickness: 0.2 mm,
Infill: 100%,
Part cooling intensity: 25%,
Printing speed: 60 mm/s,
Nozzle diameter: 0.4 mm,
Number of the contour lines: 5

Based on “ASTM D638: Standard Test Method for Tensile Properties of Plastics” dogbone-shaped parts were made to determine the mechanical properties. For each test, fivesame samples were prepared to keep mechanical properties results reliable.

Materials 2021, 14, 4823

5 of 21For structural analysis, Keyence VHX 7000 optical microscope (Keyence International,
Mechelen, Belgium) was used. All parts were observed using an additional scattered lightfrom the bottom side of the elements.
Axial tensile strength tests were carried out using the Instron 8802 (Instron, Norwood,
MA, USA) hydraulic pulsator using an extensometer with a measuring base of 50 mm.
During tensile testing, a digital image correlation (DIC) (non-contact, optical method) wasused to measure three-dimensional (3D) deformations from Dantec Dynamics (Dantec,
Ulm, Germany).
All manufactured parts were divided into four different groups for the HLD process,each group was characterized by different disinfection times. There were four groups:

•
•
•
•

0.5 h disinfection,
12 h disinfection,
24 h disinfection,
48 h disinfection.

To reach desirable results, a Gigasept Instru AF (Schülke & Mayr GmbH, Norderstedt,
Germany) disinfection liquid was used. Parts were put into two disinfection can–with 4%
liquid solution with water and 100% liquid. After the process, all elements were drained
into the laboratory dryer at a temperature of 45 ◦ C for one hour. Such temperature wasselected to be at the safe level below the glass temperature of the PETG (which is 70 ◦ C).
All samples were held at the same temperature. Additionally, to allow better analysis, alldisinfected parts were compared to non-disinfected reference samples. All combinations
with sample type descriptions are shown in Table 2.
Table 2. All configurations of samples prepared for the research.
Material

PETG without
pigment

PETG with color
pigment

Solution
Concentration

Disinfection Time

Samples’Description

0%

None

P0

4%

0.5 h
12 h
24 h
48 h

P4_05
P4_12
P4_24
P4_48

100%

0.5 h
12 h
24 h
48 h

P100_05
P100_12
P100_24
P100_48

0%

None

PC0

4%

0.5 h
12 h
24 h
48 h

PC4_05
PC4_12
PC4_24PC4_48

100%

0.5 h
12 h
24 h
48 h

PC100_05
PC100_12
PC100_24
PC100_48

0%

None

A0

4%

0.5 h
12 h
24 h
48 h

A4_05
A4_12
A4_24
A4_48

100%

0.5 h
12 h
24 h
48 h

A100_05
A100_12
A100_24
A100_48

ABS Medical

Materials 2021, 14, 4823

6 of 21

3. Microscopical Investigation—Results and Discussion
To properly describe the microstructural phenomena during HLD all registered images
for each sample were compared in Tables 3 and 4. There is a visible effect of disinfection
with two different substance concentrations: 4% and 100%. Also, a comparison withnondisinfected samples (0%) was made. Investigating samples under a light microscope has
shown no significant impact (like melting or rinsing of the material) on samples’ structure.
Table 3. Microscopic images registered for samples kept in 4% solution.
Microscope Images

A0

A4_0.5

A4_24
A4_12

A4_24
A4_24

A4_48
A4_48

P0
P0
P0

P4_0.5
P4_0.5

P4_12
P4_12

P4_24
P4_24

P4_48
P4_48

PC0
PC0

PC4_0.5
PC4_0.5

PC4_12
PC4_12

PC4_24PC4_24PC4_48
PC4_48Materials 2021, 14, 4823

7 of 21

Table 4. Microscopic images registered for samples kept in 100% solution.
Microscope Images

A0
A0

A100_0.5
A100_0.5
A100_0.5

A100_12
A100_12

A100_24
A100_24

A100_48
A100_48

P0
P0

P100_0.5
P100_0.5

P100_12
P100_12

P100_24
P100_24
P100_24

P100_48
P100_48

PC0
PC0PC100_0.5
PC100_0.5

PC100_12
PC100_12

PC100_24
PC100_24

PC100_48
PC100_48

In the case of PETG samples held in 4% solution (Table 4), there is an outer contour
and the infill visible, between these two parts of geometry there are visible some brighter
areas—especially in samples after 12-, 24-, and 48-h during disinfection. This can be seen
as intense flashes in the picture. Materials used in this study like most materials being
used in FDM printing are known for their porous structure. This leads to the conclusionthat during the disinfection process the liquid is penetrating the structure of the sample
and does not evaporate during the drying process, as a result, it may stay inside longer. In
the case of the ABS material, the effect of penetrated water inside the object is much lessnoticeable. It could be due to better filling of materials or, basically, its hygroscopicity.

Materials 2021, 14, 4823

8 of 21

At 100% concentration (Table 4) brighter areas in PETG are more visible than at
4% concentration. Such phenomenon is connected to the lower dilution of used liquid.
Perhaps it may be caused by the high viscosity of not diluted concentrate. This leads to theconclusion that during the disinfection process the liquid is penetrating the structure of thesample and in cases of lower water content in used formulas, the liquid does not evaporate
during the drying process, as a result, it may stay inside longer. Also, in the case of 100%solution, samples made of the ABS material has no visible liquid inside their volume.
Accumulating high concentrations of disinfection liquids in structures of FDM/FFF
based face shields may ensure protection from some microorganisms but on the other
hand, it may also lead to aggregation of dirt or in worse cases, raising of bacterial biofilm,by creating a good habitat for pathogens, or else come into reaction with the component,
which might be harmful to the user, this may indicate using different materials in the
production of medical helmets or additional covers (for example resin-based).
4. Tensile Testing and DIC Analysis—Results and Discussion
To better understand the influence of HLD on AM parts, tensile tests were made. All
samples have been additionally analyzed by using DIC. A representative course of samples
from each group is shown to allow a more straightforward interpretation of the test results.
Strain–stress curves of PETG without pigment in three conditions: 4% liquid solution withwater, 100% liquid, and without any disinfection (P0) are shown in Figure 1.

(a)

(b)

Figure 1. Strain-stress curves of noncolored PETG material after 4% water solution (a) and 100% concentrate (b) incomparison to material without disinfection.

All types of HLD in 4% negatively affect tensile properties, especially in the case ofsamples that were kept in disinfection solution for 48 h–where tensile strength decreased
from 53.98 MPa to 45.11 MPa, which is about 20%. More significant differences wereregistered for samples subjected to HLD in 100% concentrate. The most significant decrease
was reported for samples kept in the disinfection for 12 h and 48 h, and the value wasabout 25%. Results of the obtained DIC analysis are shown in Table 5.

ɸMaterials 2021, 14, 4823

9 of 21

Table 5. DIC results for without pigment PETG samples in the condition without HLD, in 4% water solution HLD and 100%concentrate HLD.
P0
Initial Condition
Strain X
StrainX

Strain YY
StrainRp0.2
Strain X
StrainX

Strain Y
StrainY

RmStrain X
StrainX

Breaking Point
Strain Y
StrainY
StrainY

Strain X
StrainX

Fracture

Scale

Strain Y
Strain
Y

ε (%)
10
8
6
4
2
0
P4_05
Initial Condition
Strain X
StrainX

Strain Y
StrainY
StrainY
X

Rp0.2
Strain XX
StrainStrain Y
StrainY
StrainY

Rm

Breaking Point

Fracture

Scale

StrainStrainStrainX
StrainY
Strainrain
rain
XXStrainStrainYY
StrainStrainXX
StrainStrainYY
rainXXX StrainStrainY
Y StrainStrainX StrainStrainYΉΉΉΉ (%)
10
ΉΉΉΉΉ
8
6
4
2
0
P4_
P4_12
P4_12
Initial C Initial C
Initial Condition
R
Rm
Strain X p0.2 Strain Y
Strain X
Strain X
StrainX
StrainYY
StrainStrainY
StrainStrain Y
StrainStrainStrainStrainSt
X
StrainY
StrainStrainXXXX Strain
StrainY
StrainXXX Strain
StrainYYYY StStrainrainXXX StrainStrainY
StrainStrainY
Y StrainStrainX
StrainStrainBreaking Point
Strain X
StrainX
StrainStrainX

Fracture

Strain Y
StrainY
StrainStrain
Y

Scale

ɸɸɸɸ
ɸɸɸɸɸε (%)
10
8

6
4
2
0
Initial C Initial C
Strain X
Strain X
StrainY Strain X
Strain Y Strain X

P4_24
P4_
Fracture

Strain Y
Strain X

Strain Y

Scale

Strain Y

ɸɸɸɸ
ɸɸɸɸɸ

Materials 2021, 14, 4823

10 of 21

Table 5. Cont.
P4_24
Initial Condition
Strain X
StrainY

Strain Y
Y
StrainStrainStrainY
Y
StrainY

Rp0.2
StrainXX
StrainStrainX
Y
StrainStrainX
X

Strain Y
StrainY

RmStrainX
StrainStrainX
StrainXX

StrainYY
StrainY
StrainStrainY

Breaking Point
Strain X
StrainX

Fracture

Scale

Strain Y
StrainYY
Strain

10

ε (%)

8
6
4
2
0
P4_48
Initial Condition

Rp0.2

Rm

StrainXXXXX Strain
StrainYYYY Strain
StrainStrainStrainrain
Strain
X
YY
XXX
YYYY
StrainStrainStrainStrainSt
StrainStrainStrainStrainYY St
St
StrainStrainStrainStrainStrainrain
rainXXXX
StrainStrainStrainXXX Strain
StrainSt

StrainStrainStrainStrainYYY
Y

Breaking Point
StrainXX
StrainStrainStrainXX

Fracture

Scale

StrainY
StrainStrainStrainYYY

ɸɸɸɸ(%)
ɸɸɸ
10 ɸɸɸɸɸɸɸ
8
6
4
2
0
P100_05
P100_05
Initial Condition
StrainX
StrainStrainStrainXX Strain
StrainStrainYYYYStrainStrainXXXStrainYY
StrainStrainRp0.2
StrainStrainStrainXX
StrainStrainXXXStrainX

StrainYY
StrainStrainY
StrainStrainYYY
StrainRm
Strain
rain
XX
rain
rain
St
St
St
StrainXX
St

StrainStrainYYY
StrainY
StrainBreaking Point
StrainXX
StrainXX
StrainStrainStrainYYY
StrainY
StrainStrainFracture

Scaleɸɸɸɸɸɸɸ
ɸɸɸɸɸɸɸ(%)
10
8
6
4
2
0

P100_12ɸɸɸɸɸɸɸ
ɸɸɸɸɸɸɸ

Materials 2021, 14, 4823

11 of 21

Table 5. Cont.
P100_12
Initial Condition
Strain X
X
StrainStrain Y
StrainY

Rp0.2
Strain X
X
StrainRm
StrainStrain Y
Y

Strain X
StrainX

Breaking Point
StrainStrain Y
Y

Strain X
X
StrainFracture

Scale

StrainStrain Y
Y

ε (%)
10
8

6
4
2
0
P100_24
Initial Condition
Strain X
X
StrainStrainStrain Y
Y

Rp0.2
StrainStrain X
X

Rm
StrainStrain Y
Y

Strain X
StrainX

Breaking Point
StrainStrain Y
Y

Strain X
X
StrainFracture

Scale

StrainStrain Y
Y

ε (%)
10
8
6
4
2
0
P100_48
P100_48
InitialStrainX Condition

Strain XRp0.2 Strain Y

Strain X Rm Strain Y

Strain X
X
StrainStrain X
StrainX

Strain X
X
StrainStrainStrain Y
Y

Strain Y
StrainY

StrainStrain Y
Y

Breaking
Breaking Point
Strain X
X
StrainFracture
Fracture
Fracture

Scale
Scale

StrainStrain Y
Y

ε (%)
10
8
6
4
2
0

The material without any HLD is characterized by increased strain areas and morethan one spot of fracture initiation. In most samples subjected to different types of HLD,
there is only one spot of fracture initiation. Additionally, in some HLD cases, there is novisible strain increase along X-axis. That phenomenon could relate to a negative influenceMaterials 2021, 14, 4823

12 of 21of the disinfection liquid, which came into the material volume between the infill andoutline perimeter shell.
The same type of analysis was conducted for colored PETG material. Stress–strain
curves for all tested samples, including reference material without any disinfection, areshown in Figure 2.

(a)

(b)

Figure 2. Strain–stress curves of colored PETG material after 4% water solution (a) and 100% concentrate (b) in comparison
to material without disinfection.

In the case of colored PETG, there is also visible a slight decrease in tensile strength ofsamples subjected to HLD, but it is lower than 5% compared to non-disinfected samples. A
base for the pigment addition could increase the material’s chemical resistance and lower
the influence of a disinfection liquid. That hypothesis could be proven by the DIC analysis
shown in Table 6.
Table 6. DIC results for colored PETG samples in the condition without HLD, in 4% water solution HLD and 100%concentrate HLD.
PC0
Initial Condition

Rp0.2

StrainX
StrainYY
Strain X
StrainXXXStrainStrainStrainStrainY
X
StrainXXX Strain
StrainYYY Strain
StrainStrainStrainStrainStrainYY
StrainStrainYYY
StrainRm
Strain X
StrainX

Breaking Point
StrainStrainY
StrainYYY
StrainStrain X
StrainX

Fracture

Scale

Strain Y
StrainStrain
Y

ε (%)
12
10
8
6
4
2

0
PC4_05Initial C ondition
R
R
Breaking
StrainXXXStrainStrainStrainStrainX
StrainYYYY Strain
StrainXXXX Strain
StrainYYYY Strain
StrainXXX Strain
StrainYY
Y
StrainStrainStrainStrainStrainStrainXXX Strain
StrainYYY Strain
StrainXXX Strain
StrainYY
StrainStrainStrainStrainStrainStrainStrainFracture

Materials 2021, 14, 4823

13 of 21

Table 6. Cont.
PC4_05Initial Condition

Rp0.2

Rm

Breaking Point

StrainX
StrainYYY
StrainXX
StrainYYYXX
StrainYYYY
StrainXXXStrainStrainStrainXXXXXStrainStrainStrainStrainStrainStrain
XStrain
Strain
YStrain
StrainX StrainStrainY StrainStrainX StrainStrainY StrainStrainX
StrainStrainStrainStrainStrainX
XX
StrainStrainStrainStrainYYY
YYStrainStrainStrainStrainXX
X
XX
StrainStrainStrainY
YYStrainStrainStrainX
XX
StrainStrainStrainFracture

Scale

StrainStrainYY
Y
Strain

ε (%)
12
10
8
6
4

2
0
PC4_12
PC4_12
PC4_12Fracture
Initial C ondition
R
oint
R
Breaking
Fracture
InitialCondition
R
R
Breaking
Point
Fracturem
p0.2
StrainX
StrainY
StrainX
StrainY
StrainX
StrainX
StrainStrainStrainStrainXXXXXXStrain
StrainStrainStrain
YStrain
StrainStrainXXX
X StrainStrainStrainY StrainStrainX
X StrainStrainYY
Y StrainStrainX
Strain Y
StrainYYYY
StrainStrainStrainStrainX
XX
StrainStrainStrainStrainY
YYStrainStrainStrainStrainX
XX
StrainStrainStrainYYY
YYStrainStrainStrainX
XX
StrainStrainYY
StrainStrainXX
Strain
XXXXX
YYYY
XXX
YY
StrainStrain XX
StrainStrainStrainStrainStrainStrainStrainXX Strain
StrainStrainYY Strain
StrainStrainXX Strain
StrainStrainYY Strain
StrainStrainStrainStrainStrainStrainStrainStrainXXX Strain
StrainYYY Strain
StrainStrainYY

Scale
Scale

ε (%)
12
10
8
6
4

2
0
PC4_24
Initial Condition

Rp0.2

Rm

StrainX
StrainYYY
StrainXYYXXXStrainXXXStrainStrainStrainStrainStrainStrainStrainStrainStrainStrainStrainXX Strain
StrainYY Strain
StrainXX
XX Strain
StrainYY Strain
StrainBreaking Point
StrainStrainYYY
StrainStrainStrainX
StrainXX

Fracture

Scale

Strain Y
Strain
Y

12

ε (%)

10
8
6
4
2
0
PC100_05
Initial C
Strain X

StrainYYYY
StrainStrainStrainX XX
Strain Y Strain
StrainStrainFracture
Breaking oint
Fracture
Strain X Strain Y

Scale

Materials 2021, 14, 4823

14 of 21

Table 6. Cont.
PC100_05
Initial Condition
StrainStrainStrainStrainYY
StrainXX Strain
StrainYYYYStrainRp0.2
StrainStrainXX

RmStrainStrainStrainX
StrainXXXX
StrainStrainYY Strain

Breaking Point
StrainStrainYY

StrainStrainXX

Fracture

Scale

StrainStrainYY

ε (%)

12
10
8
6
4
2
0
Initial Condition
ondition
Initial Condition
StrainX StrainStrainYY
Strain XX Strain
StrainStrainStrainStrainStrainYYYYY

PC100_12
PC100_12
PC100_12
RR
Rp0.2
StrainStrain X
StrainXXRmStrainXX
X
StrainStrain Y Strain
StrainStrainStrainStrainXX Strain
StrainStrainYY
StrainXX
StrainYY Strain
StrainX XX

Fracture
Fracture

Breaking
Breaking Point
Strain XX
StrainScale

Fracture

Scale

StrainStrainYY

ε (%)

12
10
8
6
4
2
0
Fracture
Fracture

PC100_24
Initial Condition
Strain Y
Strain XX
StrainStrainStrainYY

Rp0.2
StrainStrainXX

Strain XRmStrainStrainYY

Strain X
StrainX
StrainStrainX

Breaking Point
Strain YY
StrainStrain XX
Strain

Scale
Scale

Fracture

Scale

StrainStrainStrainYYY

ε (%)
12
10
8

6
4
2
0
Initial C
Strain X

Strain Y
Strain Y

R
Strain X
Strain Y

PC100_48
Strain X R
Breaking oint
StrainStrainY
Strain Y
Y
Strain X Strain
StrainY Y Strain X

Fracture
Fracture

Scale

Materials 2021, 14, 4823

15 of 21

Table 6. Cont.
PC100_48
Initial Condition
StrainStrainXX

StrainStrainYY

Rp0.2
StrainStrainXX

RmStrainStrainYY

StrainStrainXX

Breaking Point
StrainStrainYY
Y
StrainStrainStrainXX

Fracture

Scale

StrainStrainYY

ε (%)
12
10
8
6
4
2
0

Regarding obtained DIC results, there is a visible a different behavior of the material
after HLD in 4% water solution and 100% concentrate. After disinfection in 4% water
solution, there was an equal strain distribution, which cannot be concluded in samples thatwere sunk in 100% concentrate. Also, those samples have a visible increase in strain acrossthe X-axis (especially in the breaking point) in comparison to samples held in a 4% water
solution. It could be related to the significant concentration of the disinfection liquid, which
did not affect that kind of phenomenon in 4% water solution. It is worth mentioning thatafter HLD in all cases, there was not any discoloration of samples and liquid after eachdisinfection period. Hence, it could be stated that color pigment does not affect material
properties after different types of HLD. The only one phenomenon of that kind of additionis the positive influence of chemical resistance.
The last type of sample was AM using the ABS medical. Strain–stress curves after
tensile testing of that kind of material are shown in Figure 3.

(a)

(b)

Figure 3. Strain–stress curves of colored PETG material after 4% water solution (a) and 100% concentrate (b) in comparison
to material without any disinfection.

ABS medical is characterized by a lack of significant influence of used HLD. The only
one registered phenomenon is a slight decrease in the ultimate tensile strength (UTS) of
samples held in 4% water solution, which could be connected with a hygroscopicity of theABS. Similar insights were spotted in the DIC results shown in Table 7.

Materials 2021, 14, 4823

16 of 21

Table 7. DIC results for ABS medical samples in the condition without HLD, in 4% water solution HLD and 100%concentrate HLD.
A0
Initial Condition

Rp0.2

Rm

StrainX
StrainY
StrainXX
StrainY
StrainStrainXXXX Strain
StrainYYYY Strain
StrainXXXX Strain
StrainYYYY Strain
XXXX
StrainStrainStrainStrainStrainX
StrainStrainStrainXXXX
StrainStrainY
StrainStrainX
StrainY
StrainStrainStrainStrainStrainStrainYY
StrainStrainStrainBreaking Point
StrainStrainYYYY
StrainStrainStrainStrainXXXStrainFracture

Scale

Strain Y
StrainStrain
Y

ε (%)
10
8
6
4
2
0
A4_05
A4_05
FractureR
Fracture
Initial C ondition
Breaking
R
Initial X
Condition
R Strain Y
Breaking Point
Fracture
StrainStrainYYYY Strain
StrainStrainStrainYYYY Strain
StrainXXXXRmStrain
StrainYYYY Strain
Strain Y
StrainStrainStrainXXXXXXX Strain
StrainStrainY
StrainStrainX
XXp0.2Strain
StrainStrainStrainX
StrainStrainStrainStrainStrainYY
StrainStrainStrainStrainXXXStrainYY
Strain X
StrainY
StrainStrainStrain X
Strain Y
StrainStrainStrainStrainStrainStrainStrainStrainXXX Strain
YY Strain
X
StrainX
StrainY
X
StrainStrainStrainXXXX Strain
StrainStrainYYYY Strain
StrainStrainYYYY Strain
StrainX
StrainY
Strain
Y

Scale

ε (%)
10
8
6
4
2

0
A4_12
Initial Condition

Rp0.2

Rm

StrainXXXXXX
StrainY
StrainX
StrainY
StrainStrainStrainStrainY StrainStrainStrainStrainXX
StrainStrainYY
StrainXX Strain
StrainYYYYY Strain
StrainStrainStrainY
StrainXX
StrainStrainX X Strain
StrainBreaking Point
Strain Y
StrainYY
StrainStrainStrainXXXStrainFracture

Scale

Strain Y
Strain
Y

ε (%)
10
8
6

4
2
0
A4_24
R
StrainStrainStrainStrainYY Strain
StrainStrainStrainStrainStrainXX Strain
StrainYYYY
StrainX
StrainY
StrainYY
StrainStrainStrainStrainStrainXXXXX Strain
StrainXXXXXRBreaking
StrainXXX Strain
StrainY
StrainYY
StrainStrainYY Strain X
StrainY
StrainStrainFracture

Scale

Materials 2021, 14, 4823

17 of 21

Table 7. Cont.
A4_24
Initial Condition

Rp0.2

StrainXX
StrainY
StrainX
Strain Y
StrainStrainXXXXStrainStrainStrainStrainX StrainStrainStrainStrainY StrainStrainStrainStrainX StrainY
StrainStrainStrainStrain
XXXXX
YYYYY

Rm
StrainStrainStrainXXXX
StrainBreaking Point
Strain Y
StrainY
StrainY

Strain X
StrainX

Fracture

Scale

Strain Y
Strain
Y

ε (%)

10
8
6
4
2
0
A4_48
A4_48
Breaking oint
R
Initial C ondition
Fracture
Fracture
Initial Condition
Rp0.2
Rm
Breaking
Point
Fracture
StrainStrainStrainXX
StrainStrainStrainStrainXXXXXXXX StrainStrainStrainStrainYYY
Y StrainStrainStrainStrainXXX
X StrainStrainStrainStrainYYYY
Y StrainStrainStrainXXXX
StrainYY
Y StrainStrainYY
StrainStrainStrainStrainStrainStrainStrainStrainStrainStrainXX Strain
StrainYYY
StrainX
StrainYY
StrainX
StrainY
StrainX
StrainStrainStrainStrainStrainStrainX
StrainStrainY
StrainX
StrainStrainStrainStrainXXXXXX Strain
StrainStrainYYYYYY Strain
StrainStrainXXXXXX Strain
StrainYYYYYY Strain
XXXXX Strain
StrainStrainStrainStrainStrainStrainStrainStrainStrainStrainStrainStrainStrainYYYYY Strain
StrainXXXX Strain
StrainYYY
StrainXX
StrainStrainStrainStrainStrainStrain

Scale
Scale

ε (%)
10
8
6
4
2
0
A100_05
Initial Condition
Strain X
StrainX

Strain Y
StrainY

Rp0.2
Strain X
StrainX

Strain Y
StrainY

RmStrain X
StrainX

Breaking Point
StrainStrainStrainStrainYYY
StrainYY

StrainStrainStrainXXXStrainX

Fracture

Scale

StrainStrainStrainYYY

ε (%)
10
8
6
4
2
0
A100_12R
Initial C
Breaking P
StrainX
StrainX
StrainY
StrainX
StrainY
StrainStrainXX Strain Y Strain
StrainStrainXXXX
StrainStrainStrainStrainStrainStrainStrainStrainStrainStrainStrainStrainXXX X Strain Y
StrainXXXX Strain
StrainYYYY Strain
StrainXXXX Strain
StrainYYYY Strain
StrainFracture
Fracture
Fracture

Materials 2021, 14, 4823

18 of 21

Table 7. Cont.
A100_12
Initial Condition
StrainX
Strain Y
StrainStrainXX
StrainStrainXX Strain
StrainStrainStrainStrainX
XXXXYStrainRp0.2

Rm

StrainX
StrainY
StrainXX
StrainYY
StrainXX
StrainYY
StrainXX
StrainStrainXXXXX Strain
StrainYY Strain
StrainXX
StrainStrainStrainStrainStrainStrainStrainStrainBreaking Point
StrainStrainStrainYY
StrainStrainYYY

StrainStrainXX
StrainStrainXX

Fracture

Scale

Strain Y
Strain
Y

ε [%]
10
8

6
4
2
0
A100_24
A100_24
R
Initial C ondition
InitialR
Rm Strain
p0.2Strain
StrainX StrainStrainY StrainStrainX
StrainY StrainStrainXX
StrainYY
Y
StrainStrainStrainYY
StrainXX
StrainYY
StrainXX
StrainYY
StrainXX
StrainStrainX
StrainStrainY
StrainXXXX
StrainY
StrainX
StrainY
StrainStrainStrainStrainX
XXXCondition
X
StrainStrainYYYY
StrainStrainStrainStrainStrainStrainStrainX
StrainY
StrainX
StrainY
StrainX
StrainY
StrainX
StrainY
StrainX
StrainY
StrainX
StrainStrainStrainStrainXX
StrainStrainStrainYY
StrainStrainXXX
XX
StrainStrainYY
StrainStrainXX
StrainStrainStrainStrainStrainX StrainStrainY StrainStrainX StrainStrainYY
Y StrainStrainX
X StrainStrainYY
YY
StrainStrainStrainXXXXXStrainYYYY
StrainStrainBreaking oint
Breaking
Point
StrainX StrainStrainX
Y
StrainX
StrainX
StrainY
StrainX
StrainStrain X
X Strain Y

Fracture

Scale

Fracture

Scale

ε [%]
10
8
6
4
2
0
A100_48
Initial Condition

Rp0.2

Rm

StrainX
StrainY
StrainX
StrainY
StrainX
StrainStrainStrainStrainStrainStrainStrainYYYYY
StrainXXXStrainYY
StrainStrainStrainStrainStrainStrainStrainStrainStrainXXXXXX Strain
StrainStrainStrainYYYYYY Strain
StrainStrainXXXXXXX Strain
StrainYYYYYY Strain
XXXXX Strain
StrainStrainStrainStrainStrainStrainStrainStrainStrainStrainStrainBreaking Point
StrainStrainX
StrainStrainXXXFracture

Scale

StrainStrainY
Strain
YY

ε [%]
10
8
6

4
2
0

ABS medical material is characterized by a lack of any changes between samples
before and after HLD in all used conditions. A fracture mechanism of all samples was
similar–equal strain distribution in the UTS point and one, clearly visible fracture spot.
Hence, that kind of material seems to be the most suitable for parts production which will

Materials 2021, 14, 4823

19 of 21be subjected to additional HLD to allow further usage from the tensile properties pointof view.
Comparing all tested materials: PETG, colored PETG, and ABS medical, there arevisible typical phenomena for those materials: ABS is characterized by 30% lower UTS than
PETG with similar total strain values. In the case of comparison between colored PETG
and noncolored there is visible a positive influence of pigment which make the material
more resistant to disinfection but also lowered its UTS. Also, there are visible different
phenomena registered during DIC where the PETG strain mechanism is strictly affected by
the direction of material line distribution. At the same time in the ABS such behavior is
local and the highest strain values are present in the necking area.
5. Summary and Conclusions
Based on obtained research results it could be stated that there is visible a slightinfluence of HLD on the material’s structure, its tensile properties, and strain mechanism.
Regarding that kind of analysis, there were some changes registered that negatively affected
PETG material. It has been proven that filament pigmentation does not affect material
properties after HLD and does not cause any discoloration of the parts. Such phenomenon
was observed during a longer analysis made by Buozi Moffa et al. [22] where there wasalso no discoloration registered. Using other types of disinfection for polymers such as
photodynamic treatment [23] or microwaves [24] would negatively affect the mechanicalproperties of obtained parts by extending glass temperature or even plasticizing temperature which causes material degradation [25–27]. Such phenomena affect the material
structure and also decrease its fatigue properties [28–30].
Regarding conducted research, the authors could form the following conclusions:
1.

2.
3.
4.

AM technologies could be used to produce human life and health protection partsfor sudden, unexpected cases. However, the layered structure of the obtained parts
during the AM and some tiny pores between the infill and outline lines connection
increases the possibility of penetration of that kind of imperfections by some fluids orbacteria strains. Form two types of tested materials, ABS medical seems to be a better
candidate to produce such parts using AM.
Pure PETG material is exposed to an even 20% decrease in tensile strength after HLD.
Addition of color pigment in PETG material does not affect parts discoloration or decrease in tensile properties. It even slightly increases the material’s chemical resistance.
Registered phenomenon with tensile strength decreasing observed in PETG samples
could be related to the different alcohol diffusivity and solubility in these two materials.
Additionally, the presence of the alcohol between extruded material lines could affectthe joint volume between those lines. Another important issue is the fact that usedin the research ABS material was dedicated for medical solutions—so its chemical
resistance was increased to allow proper disinfection. PETG was a typical material
available in the market which was not adopted for such a solution, but during the
pandemic, it was the most popular material used in AM of tools dedicated for a fightagainst COVID19.

The next step in our research would be to investigate how long the liquid will stayinside the sample. If it would be a few hours, it would not impact drastically the usage
daily. This is also an important question of whether the disinfectant reacts with the material.
Further examination is required.
To reduce the presence of revealed voids in the structure of the parts a kind of heat
treatment with an additional vacuum (like hot isostatic pressing in AM metals) could
be used, which make it possible to fit that kind of technology for medical solutions andbroader usage in that kind of application which could be another topic for further research.

Materials 2021, 14, 4823

20 of 21

Author Contributions: Conceptualization, J.K., K.G., J.P., J.Ł. (Julia Łaszcz) and P.M.; Methodology,
K.G., J.K. and J.Ł. (Jakub Łuszczek); Tensile testing, J.T.; DIC analysis, I.S. and R.S.; Formal analysis,
J.T. and K.G.; Microstructural investigation J.Ł. (Jakub Łuszczek), J.P. and P.M., Writing—originaldraft preparation, J.Ł. (Julia Łaszcz), J.P., P.M. and J.K.; Writing—review and editing, J.K. andJ.T.; Visualization, J.Ł. (Jakub Łuszczek) and R.S.; Supervision, K.G.; Project administration, K.G.
and J.K.; Funding acquisition, K.G. All authors have read and agreed to the published version of
the manuscript.
Funding: This research was funded by the Military University of Technology, grant number 22 889;
and partially supported by the Student Affairs Department from the Military University of Technology.
Institutional Review Board Statement: Not applicable.
Informed Consent Statement: Not applicable.
Data Availability Statement: The study did not report any data.
Acknowledgments: Authors would like to thank Vice-Rector for Student Affairs—Monika Szyłkowska,
former Vice-Rector for Student Affairs—Marzena Tykarska and Dean of Mechanical Engineering
Department—Jerzy Małachowski for their support during our fight against COVID19 pandemic
by additive manufacturing of face-shields, HEPA masks connectors, and their support during thisresearch activities.
Conflicts of Interest: The authors declare no conflict of interest.

References
1.
2.
3.

4.
5.
6.

7.
8.
9.

10.
11.
12.
13.
14.

15.
16.

Nagarajan, V.; Mohanty, A.K.; Misra, M. Perspective on Polylactic Acid (PLA) based Sustainable Materials for Durable Applications: Focus on Toughness and Heat Resistance. ACS Sustain. Chem. Eng. 2016, 4, 2899–2916. [CrossRef]
Tino, R.; Moore, R.; Antoline, S.; Ravi, P.; Wake, N.; Ionita, C.N.; Morris, J.M.; Decker, S.J.; Sheikh, A.; Rybicki, F.J.; et al. COVID-19
and the role of 3D printing in medicine. 3D Print. Med. 2020, 6, 11. [CrossRef] [PubMed]
Perez-Mañanes, R.; García de San José, S.; Desco-Menéndez, M.; Vaquero-Martín, J.; Pascau González-Garzón, J.; Trapero-Moreno,
D.; Antonio Calvo-Haro, J. Application of 3D printing and distributed manufacturing during the rst-wave of COVID-19 pandemic.
Our experience at a third-level university hospital. 3D Print. Med. 2021, 7, 7. [CrossRef] [PubMed]
Yang, M.; Hu, J.; Xiong, N.; Xu, B.; Weng, Y.; Liu, Y. Preparation and properties of PLA/PHBV/PBAT blends 3D printing filament.
Mater. Res. Express 2019, 6, 065401. [CrossRef]
Małek, M.; Łasica, W.; Kadela, M.; Kluczyński, J.; Dudek, D. Physical and mechanical properties of polypropylene fibre-reinforced
cement–glass composite. Materials 2021, 14, 637. [CrossRef] [PubMed]
Kluczyński, J.; Śnieżek, L.; Kravcov, A.; Grzelak, K.; Svoboda, P.; Szachogłuchowicz, I.; Franek, O.; Morozov, N.; Torzewski,
J.; Kubeček, P. The Examination of Restrained Joints Created in the Process of Multi-Material FFF Additive Manufacturing
Technology. Materials 2020, 13, 903. [CrossRef] [PubMed]
Soares, J.B.; Finamor, J.; Silva, F.P.; Roldo, L.; Cândido, L.H. Analysis of the influence of polylactic acid (PLA) colour on FDM 3Dprinting temperature and part finishing. Rapid Prototyp. J. 2018, 24, 1305–1316. [CrossRef]
Szykiedans, K.; Credo, W.; Osiński, D. Selected Mechanical Properties of PETG 3-D Prints. Procedia Eng. 2017, 177, 455–461.
[CrossRef]
O’Connor, Z.; Huellewig, D.; Sithiyopasakul, P.; Morris, J.A.; Gan, C.; Ballard, D.H. 3D printed mask extenders as a supplement
to isolation masks to relieve posterior auricular discomfort: An innovative 3D printing response to the COVID-19 pandemic. 3DPrint. Med. 2020, 6, 27. [CrossRef]
Aydin, A.; Demirtas, Z.; Ok, M.; Erkus, H.; Cebi, G.; Uysal, E.; Gunduz, O.; Ustundag, C.B. 3D printing in the battle against
COVID-19. Emergent Mater. 2021, 4, 363–386. [CrossRef]
Srinivasan, R.; Ruban, W.; Deepanraj, A.; Bhuvanesh, R.; Bhuvanesh, T. Effect on infill density on mechanical properties of PETG
part fabricated by fused deposition modelling. Mater. Today Proc. 2020, 27, 1838–1842. [CrossRef]
Durgashyam, K.; Indra Reddy, M.; Balakrishna, A.; Satyanarayana, K. Experimental investigation on mechanical properties of
PETG material processed by fused deposition modeling method. Mater. Today Proc. 2019, 18, 2052–2059. [CrossRef]
Hanon, M.M.; Marczis, R.; Zsidai, L. Anisotropy evaluation of different raster directions, spatial orientations, and fill percentageof 3d printed petg tensile test specimens. Key Eng. Mater. 2019, 821, 167–173. [CrossRef]
Mercado-Colmenero, J.M.; Dolores La Rubia, M.; Mata-Garcia, E.; Rodriguez-Santiago, M.; Martin-Doñate, C. Experimental andnumerical analysis for the mechanical characterization of petg polymers manufactured with fdm technology under pure uniaxial
compression stress states for architectural applications. Polymers 2020, 12, 2202. [CrossRef] [PubMed]
Wesemann, C.; Pieralli, S.; Fretwurst, T.; Nold, J.; Nelson, K.; Schmelzeisen, R.; Hellwig, E.; Spies, B.C. 3-D printed protective
equipment during COVID-19 pandemic. Materials 2020, 13, 1997. [CrossRef]
Rutala, W.A.; Weber, D.J. Disinfection and sterilization: An overview. Am. J. Infect. Control 2013, 41, S2–S5. [CrossRef]

Materials 2021, 14, 4823

17.
18.
19.

20.
21.

22.
23.

24.
25.
26.
27.

28.
29.
30.

21 of 21Huang, J.; Luo, J.; Chen, X.; Feng, S.; Wan, Y. How Do Chemical Cleaning Agents Act on Polyamide Nanofiltration Membrane
and Fouling Layer? Ind. Eng. Chem. Res. 2020, 59, 17653–17670. [CrossRef]
Roman, N.; Cojocaru, D.; Coman, C.; Repanovici, A.; Bou, S.F.; Miclaus, R.S. Materials for respiratory masks in the context of
COVID 19 pandemic. Mater. Plast. 2021, 57, 236–247. [CrossRef]
Oth, O.; Dauchot, C.; Orellana, M.; Glineur, R. How to Sterilize 3D Printed Objects for Surgical Use? An Evaluation of theVolumetric Deformation of 3D-Printed Genioplasty Guide in PLA and PETG after Sterilization by Low-Temperature Hydrogen
Peroxide Gas Plasma. Open Dent. J. 2019, 13, 410–417. [CrossRef]
Valente, T.A.M.; Silva, D.M.; Gomes, P.S.; Fernandes, M.H.; Santos, J.D.; Sencadas, V. Effect of sterilization methods on electrospunpoly(lactic acid) (PLA) fiber alignment for biomedical applications. ACS Appl. Mater. Interfaces 2016, 8, 3241–3249. [CrossRef]
Bosc, R.; Tortolano, L.; Hersant, B.; Oudjhani, M.; Leplay, C.; Woerther, P.L.; Aguilar, P.; Leguen, R.; Meningaud, J.P. Bacteriologicaland mechanical impact of the Sterrad sterilization method on personalized 3D printed guides for mandibular reconstruction. Sci.
Rep. 2021, 11, 1–10. [CrossRef] [PubMed]
Moffa, E.B.; Giampaolo, E.T.; Izumida, F.E.; Pavarina, A.C.; MacHado, A.L.; Vergani, C.E. Colour stability of relined dentures
after chemical disinfection. A randomised clinical trial. J. Dent. 2011, 39, e65–e71. [CrossRef] [PubMed]
Eldwakhly, E.; Saadaldin, S.; Aldegheishem, A.; Mostafa, M.S.; Soliman, M. Antimicrobial capacity and surface alterations using
photodynamic therapy and light activated disinfection on polymer-infiltrated ceramic material contaminated with periodontal
bacteria. Pharmaceuticals 2020, 13, 350. [CrossRef]
Basso, M.F.M.; Giampaolo, E.T.; Vergani, C.E.; Machado, A.L.; Pavarina, A.C.; Ribeiro, R.C. Influence of Microwave Disinfection
on the Dimensional Stability of Denture Reline Polymers. J. Prosthodont. 2010, 19, 364–368. [CrossRef]
Latko-Durałek, P.; Dydek, K.; Boczkowska, A. Thermal, Rheological and Mechanical Properties of PETG/rPETG Blends. J. Polym.
Environ. 2019, 27, 2600–2606. [CrossRef]
Belloncle, B.; Bunel, C.; Menu-Bouaouiche, L.; Lesouhaitier, O.; Burel, F. Study of the Degradation of Poly(ethyl glyoxylate):
Biodegradation, Toxicity and Ecotoxicity Assays. J. Polym. Environ. 2012, 20, 726–731. [CrossRef]
Moreno Nieto, D.; Alonso-García, M.; Pardo-Vicente, M.A.; Rodríguez-Parada, L. Product design by additive manufacturing
for water environments: Study of degradation and absorption behavior of pla and petg. Polymers 2021, 13, 1036. [CrossRef][PubMed]Moskala, E.J. Fatigue resistance of impact-modified thermoplastic copolyesters. J. Mater. Sci. 1996, 31, 507–511. [CrossRef]
Dolzyk, G.; Jung, S. Tensile and Fatigue Analysis of 3D-Printed Polyethylene Terephthalate Glycol. J. Fail. Anal. Prev. 2019, 19,
511–518. [CrossRef]
Bárány, T.; Ronkay, F.; Karger-Kocsis, J.; Czigány, T. In-plane and out-of-plane fracture toughness of physically aged polyesters asassessed by the essential work of fracture (EWF) method. Int. J. Fract. 2005, 135, 251–265. [CrossRef]