ABSTRACT
The creation and application of PET nanofibrils for PP composite reinforcement were studied. PET nanofibrils were fibrillated within a PP matrix using a spunbond process and then injection molded to test for the end-use properties. The nanofibril reinforcement helped to provide higher tensile and flexural performance in solid (unfoamed) injection molded parts. With foam injection molding, the nanofibrils also helped to improve and refine the microcellular morphology, which led to improved performance. Easily and effectively increasing the strength of a polymeric composite is a goal for many research endeavors. By creating nanoscale fibrils within the matrix itself, effective bonding and dispersion have already been achieved, overcoming the common pitfalls of fiber reinforcement. As blends of PP and PET are drawn in a spunbond system, the PET domains are stretched into nanoscale fibrils. By adapting the spunbonded blends for use in injection molding, both solid and foamed nanocomposites are created. The injection molded nanocomposites achieved increased in both tensile and flexural strength. The solid and foamed tensile strength increased by 50 and 100%, respectively. In addition, both the solid and foamed flexural strength increased by 100%. These increases in strength are attributed to effective PET nanofibril reinforcement.
ABSTRACT
Double-layered absorption-dominated electromagnetic interference (EMI) shielding composites are highly desirable to prevent secondary electromagnetic wave pollution. However, it is a tremendous challenge to optimize the shielding performance via the trial-and-error method due to the low efficiency. Herein, a novel approach of computation-aided experimental design is proposed to efficiently optimize the reflectivity of the double-layered composites. A normalized input impedance (NII) method is presented to calculate the electromagnetic wave reflectivity of multilayered EMI shielding composites. The calculated results are a good match with the experimental results. Then, the NII method is utilized to design polyvinylidene difluoride/MXene/carbon nanotube (PVDF/MXene/CNT) composites. According to the optimization of the NII method, the prepared PVDF/MXene/CNT composite has an ultralow reflectivity of 0.000057, which outperforms that reported in current work and satisfies the requirement of electromagnetic wave absorbing material. Additionally, its average EMI shielding effectiveness is 30 dB, demonstrating that PVDF/MXene/CNT composite simultaneously achieves shielding and absorption. The ultralow reflection mechanism can be ascribed to the ideal impedance match. Both the PVDF/MXene and the PVDF/CNT layers can attenuate electromagnetic energy, which subverts the traditional cognition of double-layered absorption-dominated EMI shielding composites. The NII method opens a way for the practical fabrication of double-layered absorption-dominated EMI shielding composites.
ABSTRACT
Background: The study aimed to conduct a systematic review and meta-analysis comparing the efficacy of teprenone with control or other drugs for reducing the incidence of gastrointestinal (GI) adverse events in patients receiving long-term non-steroidal anti-inflammatory drugs (NSAIDs). Methods: Databases of PubMed, Embase, BioMed Central, CENTRAL, and Google Scholar were searched up to November 10th, 2020 for randomized controlled trials (RCTs) comparing teprenone with control or other drugs. A random-effects model was used for the meta-analysis. Grading of Recommendations Assessment, Development, and Evaluation (GRADE) tool was used for assessing the certainty of evidence. Results: Seven RCTs were included. Six compared teprenone with control and one with famotidine. Meta-analysis indicated a statistically significant reduced risk of GI ulcers in patients receiving teprenone as compared to control after 12 weeks/3months (RR 0.37 95% CI 0.17, 0.18 I 2 = 0% p = 0.01). Pooled data of three open-label studies indicated statistically significant reduction of GI symptoms in patients on teprenone as compared to control at 6 months and 12 months, but not at 3 months. Comparing teprenone with control, our analysis indicated non-significant but a tendency of better reduction in Modified Lanza Score (MLS) with teprenone. The RCT comparing teprenone to famotidine demonstrated better reduction of MLS with famotidine. The certainty of evidence-based on GRADE was deemed to be low. Conclusion: Low-quality evidence indicates a beneficial role of teprenone in preventing GI injuries in patients receiving long-term NSAIDs. Further high-quality RCTs comparing teprenone with placebo as well as other gastroprotective drugs are needed to strengthen current evidence.
ABSTRACT
We characterized the morphological features of an organic resorcinol-formaldehyde (RF) aerogel and correlated each feature to the thermal insulation properties. Several RF aerogels were synthesized with different morphological features and structural assemblies. This was done by changing the catalyst percentages and the dilution ratios at the polymerization stage. Then, each morphological feature was assessed and categorized using two scales: the macro scale and the micro scale. We found that the macro-features were independent of the catalyst percentages and depended only on the dilution ratios. By contrast, the micro-features were highly sensitive to any changes during the polymerization process. These changes altered the samples' three main micro-structural factors: (i) the structural assembly, (ii) the porous structure, and (iii) the fractal parameters. Thus, we characterized and quantified each component within these areas. Then, we assessed the structure's heat transfer modes and classified them as follows: (i) solid conductivity through the solid particles, (ii) gas conductivity through the gas molecules, and (iii) thermal radiation. We identified the morphological features in our RF samples and correlated them to each mode of the heat transfer. For example, the samples' solid conductivity was highly dependent on the fractal parameters of our structure; that is, the particles' roughness, the structural complexity, and the structural homogeneity. For those samples with extremely rough particles and a complex structure, the solid conductivity reached the lowest possible point. We also found that the total thermal conductivity was mainly controlled by the micro-morphological features, and that the solid conductivity was the most dominant heat transfer mode.
ABSTRACT
In this study, we fabricated conductive poly(vinylidene fluoride) (PVDF)/carbon composites simply by dispersing multiwalled carbon nanotubes (MWCNTs) and graphene nanoplatelets into a PVDF solution. The electrical conductivity and the electromagnetic interference (EMI) shielding of the PVDF/carbon composites were increased by increasing the conductive carbon filler amounts. Moreover, we also found that the EMI shielding properties of the PVDF/CNT/graphene composites were higher than those of PVDF/CNT and PVDF/graphene composites. The mean EMI shielding values of PVDF/5 wt %-CNT, PVDF/10 wt %-graphene, and PVDF/CNT/graphene composite films with a thickness of 0.1 mm were 22.41, 18.70, and 27.58 dB, respectively. An analysis of the shielding mechanism showed that the main contribution to the EMI shielding came from the absorption mechanism, and that the EMI shielding could be tuned by controlling the films' thickness. The total shielding of the PVDF/CNT/graphene films increased from 21.90 to 36.46 dB as the thickness was increased from 0.06 mm to 0.25 mm. In particular, the PVDF/carbon composite films, with a thickness of 0.1 mm, achieved the highest specific shielding values of 1â¯310 dB cm2/g for the PVDF/5 wt %-CNT composite and 1â¯557 dB cm2/g for the PVDF/CNT/graphene composite, respectively. This was due to the ultrathin thickness. Our study provides the groundwork for an effective way to design flexible, ultrathin conductive polymer composite film for application in miniaturized electronic devices.
