Review of Polydimethylsiloxane (PDMS) …
267
Additive manufacturing (AM) is the latest way to make products layer by layer.
Using these processes, one can create a product with complex geometries. The developments in processes of AM have quickly occurred in the last few years. Based on
the type of material, i.e. liquid, solid, powder, the processes are classified. In stereolithography (SLA) liquid polymer is used, and in selective laser sintering (SLS)
powdered material is used, whereas a solid filament or solid wire is used in fused
deposition modelling (FDM). The above-listed processes have a unique method of
converting the raw material into the solid part and the different characteristics that
help to distinguish each of the processes. In addition to this, all processes have similarities in the layer by layer manufacturing concept to make the solid model. In SLA,
the liquid resin is available as a monomer, which is exposed to the UV light in a
controlled manner. In this process of polymerization due to the incident light on
the liquid resin surface, the spot gets polymerized. The solidification of the resin
typically shows the polymerization. Although the resin is solidified, it is not having
sufficient strength. Therefore, after the photo-polymerization, the solid part is kept
in a UV chamber where the crosslinking of the polymeric chains occurs resulting
in the strength of the solid. Usually, in the SLA process, the polymer used is of
thermosetting type.
In contrast, FDM converts a thermoplastic polymer filament to make a solid part.
A Polymer wire passes through a heated nozzle converting it into a sticky solid of
reduced cross-section. The semisolid wire coming out of the extruder is deposited on
a horizontal surface with the help of Computerized Numerical Contro (CNC) control.
Within a few seconds, the wire gets converted back to solid. The sticky polymer gets
adhered to the already laid wire. In SLS, the conversion to the solid part happens
under laser incident on the powder spread on a horizontal surface. Wherever the laser
spot incident, powder grain gets converted to the semisolid state. In that state, it fuses
with the adjacent powder grain. As soon as the laser spot moves ahead, the fused
powder grains get converted to solid. In this process, the manufacturing of the solid
part results from the controlled incidence of the laser. With the help of the controlled
incidence of laser, the solid part is manufactured.
The challenges faced in application and use of PDMS in AM are classified into
two categories; the first includes the process of printing and the second is about
enhancing the properties of PDMS.
Prior involves process, SLA with which, printing PDMS having high viscosity
isn’t possible. ˙ In FDM printing the challenge is printing PDMS without support
materials and with more resolution. ˙ In addition, there is always problem clogging
nozzle. ˙ It is possible to print PDMS by increasing its yield stress. The later uses
PDMS having low Young’s modulus. ˙ It should be able to increase Young’s Modulus
more than 2 MPa.
Even at levels significantly higher than those seen in the field sampling, experiments with both aquatical and terrestrial species demonstrated no adverse effects.
Therefore, the environmental risk of PDMS is not expected [11].
267
Additive manufacturing (AM) is the latest way to make products layer by layer.
Using these processes, one can create a product with complex geometries. The developments in processes of AM have quickly occurred in the last few years. Based on
the type of material, i.e. liquid, solid, powder, the processes are classified. In stereolithography (SLA) liquid polymer is used, and in selective laser sintering (SLS)
powdered material is used, whereas a solid filament or solid wire is used in fused
deposition modelling (FDM). The above-listed processes have a unique method of
converting the raw material into the solid part and the different characteristics that
help to distinguish each of the processes. In addition to this, all processes have similarities in the layer by layer manufacturing concept to make the solid model. In SLA,
the liquid resin is available as a monomer, which is exposed to the UV light in a
controlled manner. In this process of polymerization due to the incident light on
the liquid resin surface, the spot gets polymerized. The solidification of the resin
typically shows the polymerization. Although the resin is solidified, it is not having
sufficient strength. Therefore, after the photo-polymerization, the solid part is kept
in a UV chamber where the crosslinking of the polymeric chains occurs resulting
in the strength of the solid. Usually, in the SLA process, the polymer used is of
thermosetting type.
In contrast, FDM converts a thermoplastic polymer filament to make a solid part.
A Polymer wire passes through a heated nozzle converting it into a sticky solid of
reduced cross-section. The semisolid wire coming out of the extruder is deposited on
a horizontal surface with the help of Computerized Numerical Contro (CNC) control.
Within a few seconds, the wire gets converted back to solid. The sticky polymer gets
adhered to the already laid wire. In SLS, the conversion to the solid part happens
under laser incident on the powder spread on a horizontal surface. Wherever the laser
spot incident, powder grain gets converted to the semisolid state. In that state, it fuses
with the adjacent powder grain. As soon as the laser spot moves ahead, the fused
powder grains get converted to solid. In this process, the manufacturing of the solid
part results from the controlled incidence of the laser. With the help of the controlled
incidence of laser, the solid part is manufactured.
The challenges faced in application and use of PDMS in AM are classified into
two categories; the first includes the process of printing and the second is about
enhancing the properties of PDMS.
Prior involves process, SLA with which, printing PDMS having high viscosity
isn’t possible. ˙ In FDM printing the challenge is printing PDMS without support
materials and with more resolution. ˙ In addition, there is always problem clogging
nozzle. ˙ It is possible to print PDMS by increasing its yield stress. The later uses
PDMS having low Young’s modulus. ˙ It should be able to increase Young’s Modulus
more than 2 MPa.
Even at levels significantly higher than those seen in the field sampling, experiments with both aquatical and terrestrial species demonstrated no adverse effects.
Therefore, the environmental risk of PDMS is not expected [11].