A fused-deposition
modeling (FDM) 3D-printed polyethylene terephthalate
glycol (PETG)–sepiolite composite showed effective synergetic
mechanical reinforcement in tensile testing compared to an injection-molded
composite. The results showed that the addition of 3 phr sepiolite
improved the tensile strength of 3D-printed PETG samples by 35.4%,
while the tensile strength of injection-molded PETG samples was improved
by 7.2%. To confirm these phenomena, FDM PETG–sepiolite composites
were investigated by small-angle X-ray scattering to correlate the
nanostructures of the composites with their mechanical strengths.
The small-angle X-ray scattering data and transmission electron microscopy
observations demonstrated that needle-shaped sepiolite particles were
aligned in the printing direction. This fine oriented nanostructure
formed during 3D printing created a synergistic effect that improved
the material properties of the composite. These novel PETG–sepiolite
composites with enhanced mechanical properties can be promising materials
fabricated via FDM 3D printing.
For flexible displays, recovery and relaxation of acrylic pressure-sensitive adhesives (PSA) must be enhanced; however, only a few studies have focused on their optimization. High cross-linking density of the PSA leads to improved recovery but deteriorates the stress relaxation; thus, it is difficult to perform optimization by simply controlling the cross-linking density. Herein, it was determined that a UV-patterned PSA with both high and low cross-linking densities in a single layer enables the optimization of both recovery and relaxation. By introducing the UV-patterned PSA, the elasticity and recovery largely deteriorated but the stress relaxation was significantly improved, compared to that of the nonpatterned PSA, and this effect was enhanced with increases in the applied strain. Thereby, the recovery and relaxation were well-optimized with both values above 71% only at 300% strain. The recovery and relaxation of PSA had, respectively, a positive and negative correlation with the storage modulus.
Carbon fiber reinforced plastic (CFRP) is currently used as a lightweight material in various parts of automobiles. However, fiber reinforced plastic (FRP) material may be damaged at the time of joining via mechanical bonding; therefore, adhesion is important. When bonding is conducted without surface CFRP treatment, interfacial destruction occurs during which the adhesive falls off along with the CFRP. Mechanical strength and fracture shape were investigated depending on the surface treatment (pristine, plasma treatment times, and plasma treatment times plus epoxy modified primer coating). The plasma treatment effect was verified using the contact angle and X-ray photoelectron spectroscopy. The wettability of the epoxy modified primer (EMP) coating was confirmed through surface morphology analysis, followed by observation of mechanical properties and fracture shape. Based on test data collected from 10 instances of plasma treatment, the EMP coating showed 115% higher strength than that of pristine CFRP. The adhesive failure shape also changed from interfacial failure to mixed-mode failure. Thus, applying an EMP coating during the automotive parts stage enhances the effect of CFRP surface treatment.
Epoxy foam adhesives are widely used for weight reduction, watertight property, and mechanical reinforcement effects. However, epoxy foam adhesives have poor impact resistance at higher expansion ratios. Hence, we prepared an epoxy composite foam adhesive with core–shell rubber (CSR) particles to improve the impact resistance and applied it to automotive structural adhesives. The curing behavior and pore structure were characterized by differential scanning calorimetry (DSC) and X-ray computed tomography (CT), respectively, and impact wedge–peel tests were conducted to quantitatively evaluate the resistance to cleavage of the CSR/epoxy composite foam adhesives under impact. At 5 and 10 phr CSR contents, the pore size and expansion ratio increased sufficiently due to the decrease in curing rate. However, at 20 phr CSR content, the pore size decreased, which might be due to the steric hindrance effect of the CSR particles. Notably, at 0 and 0.1 phr foaming agent contents, the resistance to cleavage of the adhesives under the impact wedge–peel condition significantly improved with increasing CSR content. Thus, the CSR/epoxy composite foam adhesive containing 0.1 phr foaming agent and 20 phr CSR particles showed high impact resistance (EC = 34,000 mJ/cm2) and sufficient expansion ratio (~148%).
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