11 research outputs found
Degradation Behavior of Polypropylene during Reprocessing and Its Biocomposites: Thermal and Oxidative Degradation Kinetics
Non-isothermal thermogravimetric analysis (TGA) was employed to investigate the degradation of polypropylene (PP) during simulated product manufacturing in a secondary process and wood–plastic composites. Multiple batch mixing cycles were carried out to mimic the actual recycling. Kissinger–Akahira–Sunose (KAS), Ozawa–Flynn–Wall (OFW), Friedman, Kissinger and Augis models were employed to calculate the apparent activation energy (Ea). Experimental investigation using TGA indicated that the thermograms of PP recyclates shifted to lower temperatures, revealing the presence of an accelerated degradation process induced by the formation of radicals during chain scission. Reprocessing for five cycles led to roughly a 35% reduction in ultimate mixing torque, and a more than 400% increase in the melt flow rate of PP. Ea increased with the extent of degradation (α), and the dependency intensified with the reprocessing cycles. In biocomposites, despite the detectable degradation steps of wood and PP in thermal degradation, a partial coincidence of degradation was observed under air. Deconvolution was employed to separate the overlapped cellulose and PP peaks. Under nitrogen, OFW estimations for the deconvoluted PP exposed an upward shift of Ea at the whole range of α due to the high thermal absorbance of the wood chars. Under air, the Ea of deconvoluted PP showed an irregular rise in the initial steps, which could be related to the high volume of evolved volatiles from the wood reducing the oxygen diffusion
Preparation and characterization of silicone rubber/graphene nanosheets nanocomposites by in-situ loading of the coupling agent
Hybrid effect of nanoperlite and nanoclay on mechanical and rheological properties of low-density polyethylene
Vapor Phase Modification for Selective Enrichment of Grafted Styrene/Acrylonitrile onto Carbon Nanotubes Via ATRP
Nitric acid vapor phase oxidation of multi-walled carbon nanotubes (MWCNTs) was proposed as a promising technique to fabricate poly styrene-co-acrylonitrile (SAN)-grafted-CNTs via atom transfer radical polymerization (ATRP). The in-situ ATRP grafting approach was successfully employed to graft polystyrene (PS), SAN and polyacrylonitrile (PAN), onto the convex surfaces of pristine MWCNTs (PCNT) and acid-functionalized MWCNTs (FCNT). Fourier transform infrared spectroscopy (FTIR), proton nuclear magnetic resonance (1H-NMR), and thermogravimetric analysis (TGA) confirmed the effectiveness of the modification via the ATRP grafting approach. The molar composition of acrylonitrile in the synthesized copolymer on the surface of CNTs for an FCNTs was calculated to be about 80% and 67.5% by 1H-NMR and TGA respectively, whereas the value is lower for PCNTs. Morphological studies showed that SAN-grafted FCNTs exhibit rougher surface morphology compared to the SAN-grafted PCNTs. Moreover, the higher diameter of the FCNTs indicated the higher polymer content, which was coated onto CNTs functionalized by vapor-phase oxidation. Therefore, the vapor phase oxidation strategy employed in this study could be utilized as a general method to prepare CNTs which can serve as an ATRP macroinitiator for the fabrication of various polymer grafted CNTs
Experimental and Finite Element Simulation of Polyolefin Elastomer Foams Using Real 3D Structures: Effect of Foaming Agent Content
In this study, polyolefin elastomer (POE) foams were prepared without any curing agent using a single-step foaming technique. The effect of azodicarbonamide (ADC) content as a chemical foaming agent on the foamsâ morphology and mechanical properties was studied using scanning electron microscopy (SEM), mechanical properties (tension and compression) and hardness. The results showed that increasing the ADC content from 2 to 3, 4 and 5 phr (parts per hundred rubber) decreased the foam density from 0.75 to 0.71, 0.65 and 0.61 g/cm3, respectively. The morphological analysis revealed that increasing the ADC content from 2 to 4 phr produced smaller cell sizes from 153 to 109 ”m (29% lower), but a higher cell density from 103 to 591 cells/mm3 (470% higher). However, using 5 phr of ADC led to a larger cell size (148 ”m) and lower cell density (483 cells/mm3) due to cell coalescence. The tensile modulus, strength at break, elongation and hardness properties continuously decreased by 28%, 21%, 16% and 14%, respectively, with increasing ADC content (2 to 5 phr). On the other hand, the compressive properties, including elastic modulus and compressive strength, increased by 20% and 64%, respectively, with increasing ADC content (2 to 5 phr). The tensile and compression tests revealed that the former is more dependent on foam density (foaming ratio), while the latter is mainly controlled by the cellular structure (cell size, cell density and internal gas pressure). In addition, 2D SEM images were used to simulate the foamsâ real 3D structure, which was used in finite element methods (FEM) to simulate the stressâstrain behavior of the samples at two levels: micro-scale and macro-scale. Finally, the FEM results were compared to the experimental data. Based on the information obtained, a good agreement between the macro-scale stressâstrain behavior generated by the FEM simulations and experimental data was obtained. While the FEM results showed that the sample with 3 phr of ADC had the lowest micro-scale stress, the sample with 5 phr had the highest micro-scale stress due to smaller and larger cell sizes, respectively
Physical Hybrid of Nanographene/Carbon Nanotubes as Reinforcing Agents of NR-Based Rubber Foam
Natural rubber (NR) foams reinforced by a physical hybrid of nanographene/carbon nanotubes were fabricated using a two-roll mill and compression molding process. The effects of nanographene (GNS) and carbon nanotubes (CNT) were investigated on the curing behavior, foam morphology, and mechanical and thermal properties of the NR nanocomposite foams. Microscope investigations showed that the GNS/CNT hybrid fillers acted as nucleation agents and increased the cell density and decreased the cell size and wall thickness. Simultaneously, the cell size distribution became narrower, containing more uniform multiple closed-cell pores. The rheometric results showed that the GNS/CNT hybrids accelerated the curing process and decreased the scorch time from 6.81 to 5.08 min and the curing time from 14.3 to 11.12 min. Other results showed that the GNS/CNT hybrid improved the foamâs curing behavior. The degradation temperature of the nanocomposites at 5 wt.% and 50 wt.% weight loss increased from 407 °C to 414 °C and from 339 °C to 346 °C, respectively, and the residual ash increased from 5.7 wt.% to 12.23 wt.% with increasing hybrid nanofiller content. As the amount of the GNS/CNT hybrids increased in the rubber matrix, the modulus also increased, and the Tg increased slightly from â45.77 °C to â38.69 °C. The mechanical properties of the NR nanocomposite foams, including the hardness, resilience, and compression, were also improved by incorporating GNS/CNT hybrid fillers. Overall, the incorporation of the nano hybrid fillers elevated the desirable properties of the rubber foam
Nano Graphene-Reinforced Bio-nanocomposites Based on NR/PLA: The Morphological, Thermal and Rheological Perspective
Thermal and morphological properties of epoxy matrix with chemical and physical hybrid of CNTs and nanoclay
<p>Synergistic effects of nanoclay and CNTs as physical and chemical hybrid on properties of epoxy matrix were studied. Hightemperature decomposition of methane was utilized for synthesis of carbon nanotube (CNT) on nanoclay supports to form chemical hybrid of CNTclay (CNC). The organo-modification of montmorillonite (MMT) before catalyst insertion is proposed as a priori to increase CNT yield on nanoclay supports up to 100% obtained by thermogravimetric analysis (TGA). Formation of CNTs on nanoclay surface is confirmed by transmition electron<br>microscopy (TEM), scanning electron microscopy (SEM). The process followed by the incorporation of as-prepared CNCs into epoxy matrix to make Epoxy-CNC composites. Physical mixture of commercial CNTs and nanoclay as physical hybrid of CNT-clay (PNC) was introduced into epoxy matrix<br>in order to fabricate Epoxy-PNC composites. The performance of the epoxy composites filled with CNT-clay hybrids interlinked with the type of filler<br>is investigated.</p>
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Preparation and characterization of silicone rubber/graphene nanosheets nanocomposites by in-situ loading of the coupling agent
Assessing Individual Material Degradation toward Organic Solar Cells Using Accelerated Nanolayer Lifetime Protocols: Implications for Solar Cell Longevity
Organic
solar cells (OSCs) can be highly affected by environmental
stresses like heat, moisture, and sunlight during their service life
if they are not encapsulated or if the encapsulation leaks. A deep
understanding of how each individual organic layer changes/reacts
to various environmental factors is a crucial aspect in designing
an effective OSC architecture to ensure the longevity and stability
of the materials toward the deviceâs performance. While there
are numerous examples of encapsulated OSCs operating outdoors for
extended periods of time, there is an insufficiency of information
available about the individual stability of the materials involved.
The focus of this study is to provide a quantitative assessment of
the individual unencapsulated OSC layers when they are exposed to
combinations of heat, humidity, and light. Ideally, a similar process
can be applied to different organic nanolayers in the future, and
the results can be used as a reference. Throughout the accelerated
aging process, the most impactful environmental stressor was the presence
of strong light. Via UVâvis and fluorescence data acquisition,
the chloro-boron subphthalocyanine (Cl-BsubPc) layer was observed
to be altered by some combination of hydrolysis and nanostructural
change, from the strong incident light, which was not observed if
aged in the dark. We also observed significant nanolayer film crystallization
for other materials when exposed to humid heat and an increase in
film hydrophilicity during the aging process. The nanolayer film crystallization
could have also contributed to the loss of Ï-conjugation/color,
which may not have undergone complete photobleaching. Though there
were property changes throughout the accelerated aging process, we
feel that the relatively long time scale of most changes highlights
a characteristic material stability that would translate strongly
to standard operating conditions in encapsulated devices. Adopting
these methodologies can also be useful to guide further material development
broadly in particularly susceptible materials in the future