1,721,292 research outputs found
Validation of the FFF quality and recyclability of PETG parts at different printing temperatures and printing speeds
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Is the impact of degradation during processing of fused filament fabricated and injection moulded PETG different or not?
No full textDimensional and mechanical quality of ABS parts produced via FFF and injection moulding in a steel and an AM mould
No full textEffect of multiflow vibration injection molding on the filler dispersion and thermal conductivity of polyethylene composites
No full textThermoplastic composites are emerging as promising alternatives for thermal management application,
especially in the development of next-generation electronics and heat exchangers. These materials offer
several advantages over traditional metals, including lower cost, reduced weight, and superior corrosion
resistance. However, their utilization depends on the possibility to improve their thermal conductivity
(TC). Achieving high TC in thermoplastic composites involves careful design of the material, such as
selecting appropriate filler types and shapes, and optimizing processing parameters like dispersion
quality and mixing. Although much research has already been done on the thermal conductivity of
thermoplastic composites, the majority of it is focused on the less economically relevant compression
molding, while injection molding remain less researched. Injection molding is a versatile, non-continuous
processing technique used for making products of different shapes and sizes. During the processing,
molten polymer or composite is pushed into a mold cavity. The flow causes orientation of the fillers
present in the polymer matrix, resulting in a material with anisotropic properties. More specifically, a
skin-core structure will be visible in the product, where filler will be strongly aligned with the flow direction
near the mold walls, while the center will show more random filler alignment, or alignment resembling
the flow front. This anisotropic behavior influences thermal conductivity and should be considered when
designing the composite material.
The aim of this research is to analyse the effect of multiflow vibration injection molding (MFVIM) on the
filler dispersion and thermal conductivity of polyethylene composites containing multiple fillers. A highdensity polyethylene (HDPE) matrix is considered, doped with 1.0 m% carbon nanotubes (CNT) in
combination with three fillers of varying shapes and sizes, i.e., aluminum oxide (Al2O3; sphere-shaped),
graphite (G; platelet-shape) and expanded graphite (EG; platelet-shape). Conventional injection molding
(CIM) is compared to MFVIM in which three and five melt flows are introduced, each for three different
filler combinations. Scanning electron microscopy (SEM) is used to observe the orientation and
dispersion of the fillers in the produced parts and thermal conductivity measurements are done in the
in-plane (IP) and through-plane (TP) direction. SEM images of these injection-molded samples revealed
clear differences between the CIM and MFVIM with three and five melt flows. For the TC measurements,
the IP conductivity was much higher than the TP conductivity due to orienting of the fillers in the direction
of the flow during processing. Differences in TC could also be distinguished between the CIM and
MFVIM, as the IP TC showed an increase up to 37% when five melt flows were introduced during
vibration injection molding compared to conventional injection molding
A preliminary study on the flow-induced crystallization phenomenon in 3D printing of polyvinylidene fluoride
No full textFused Filament Fabrication (FFF) is a widely used additive manufacturing (AM) technique, renowned
for its versatility, affordability, and ease of use. It involves the layer-by-layer deposition of extruded
thermoplastic filaments to build three-dimensional objects. In the context of high-performance semicrystalline polymers, FFF, which is also known as 3D printing, presents both opportunities and
challenges due to the unique properties of these materials. A notable opportunity lies in the ability to
orient and align polymer chains. During the 3D printing process, both the shear flow within the nozzle
and the velocity gradients induced by deposition can significantly deform the polymer microstructure.
This deformation, termed flow-induced crystallization (FIC), mitigates kinetic barriers to crystallization
and directs the resultant morphology. This phenomenon of enhanced oriented crystallization could be
crucial for the production of piezoelectric devices of Polyvinylidene fluoride (PVDF). PVDF is a
thermoplastic semi-crystalline polymer distinguished by its polymorphism, with multiple crystalline
phases that significantly impact its properties and applications. The piezoelectric effect of PVDF is
closely linked to the β-phase content, morphology, and alignment, all of which are influenced by
processing conditions. This study aims to investigate the potential and limitations of flow-induced
crystallization for producing PVDF specimens with high β-phase content.
A Design of Experiments (DoE) methodology was employed to examine the effects of two factors,
printing speed and extrusion temperature, on various response variables. These response variables
were identified through comprehensive characterization analyses. Post-printing, measurements such as
the total crystallinity and the melting temperature were obtained via differential scanning calorimetry
(DSC), while the β-phase percentage was assessed using Fourier Transform Infrared Spectroscopy
(FTIR).
ANOVA analysis of the DSC results indicated that extrusion temperature is the critical parameter,
positively influencing total crystallinity. Conversely, the melting temperature was found to increase as
the extrusion temperature decreased. Furthermore, statistical analysis of the FTIR results reinforced the
significance of extrusion temperature on the crystallization phenomenon, revealing that the β-phase
content increased with decreasing extrusion temperature. From these findings, it can be inferred that
low extrusion temperatures could decrease system entropy due to the alignment of polymer chains
induced by the material flow. Additionally, a combination of increased extrusion temperature and low
printing speed promotes the nucleation and growth of crystals. However, this condition diminishes the
likelihood of achieving a microstructure characterized by a high β-phase percentag
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