It is particularly important to investigate the mechanical performance of carbon fiber (CF) reinforced polyamide 6 (PA6) composites used for automotive and aerospace applications, where diffused ...moisture of the environment may potentially weaken the material over time. In this work, CF/PA6 composites were subjected to two different types of conditioning: distilled water at a temperature of 80 ºC and saline solution for 12 weeks. The volumetric fraction of CF, PA6 matrix, and the voids of the CF/PA6 composites were determined by acid digestion analysis. At the end of the environmental conditionings, the moisture absorption content and the diffusion coefficient (D) were determined. The mechanical performance of CF/PA6 composites unconditioned and conditioned was evaluated through tensile and interlaminar shear strength (ILSS) tests, and morphological characteristics of the fracture surface after the mechanical tensile test. CF/PA6 composites conditioned in saline solution showed a decrease of 53% (tensile sample) and 72% (ILSS sample) in the diffusion coefficient (D) and insignificant losses of mechanical properties when compared to CF/PA6 composites conditioned in distilled water at 80 ºC. This behavior is attributed to the salt molecules blocking the pores and consequently reducing the migration of water into the samples, maintaining the internal integrity of the specimens.
The present study carried out the characterization of carbon nanotubes (CNT) recovered from the biodegradation process of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV)/CNT nanocomposites and ...the use of this recovered CNT (CNT-rec) in the production of new PHBV nanocomposites. The results obtained by characterization of CNT-rec were very similar to the CNT. Therefore, it was possible to state that CNT properties were preserved during the biodegradation process; however, CNT-rec contained impurities such as proteins and residual PHBV. Regarding the performance as nanofillers, although both CNT and CNT-rec decreased the thermal stability of nanocomposites compared to neat PHBV, this effect was less intense in the CNT-rec nanocomposites. It is expected that both nanofillers acted as nucleating agents in the PHBV matrix crystallization process but with different effectiveness. There was no significant difference between the electrical conductivity comparing PHBV/CNT 2% and PHBV/CNT-rec 2% nanocomposites. Therefore, the recovery and use of CNT-rec is a feasible process.
The use of high contents of carbon fillers in polymeric composites may decrease the mechanical properties of the polymeric matrices, as well as reduce their processability and increase the production ...costs of antistatic packaging used in the electronic industry. Therefore, it is of great technological interest the research on alternative approaches to produce polymer composites with low electrical percolation threshold. In this way, this review article focuses on the discussion of the main factors that interfere in the electrical percolation threshold of electrically conductive polymer composites, such as the aspect ratio of the carbon fillers and its particle size, the compatibility between the composite phases, the crystallinity degree of the polymeric matrix, the processing route and the location of fillers in multi‐phase polymer blends. Additionally, the review article reports the latest studies related to the obtainment of polymer composites with low percolation threshold contents and produced with different types of carbon fillers.
Many factors interfere in the percolation threshold content of polymer composites for antistatic applications, such as the aspect ratio of the fillers and their particle size, the compatibility between the composite phases, the crystallinity degree of the polymeric matrix, the processing route and the location of fillers in multi‐phase polymer blends.
In this study, chitosan hydrogels were produced with 0, 2, 4 and 6 wt% of cellulose nanocrystals (CNC) using hexahydrate zinc nitrate (Zn(NO3)2.6H2O) as a catalyst for chitosan crosslinking reaction. ...CNC´s size was estimated by dynamic light scattering (DLS) and surface charge by zeta potential. Hydrogels were characterized by rotational rheometer, swelling test, uniaxial compression test, in vitro degradation, scanning electron microscopy (SEM) and microtomography. Results showed that zinc nitrate and CNC addition did not influence mechanical properties, degradation, and morphology of the hydrogels. However, zinc nitrate decreased 36.54% of the gel time and 41.37% of the swelling degree, and increased the crosslinking degree of the chitosan hydrogels, proving not only its catalytic effect but also its participation in the crosslinking reaction. Porosity was slightly reduced after addition of zinc nitrate and incorporation of CNC. In the mechanism of crosslinking reaction, a competition between CNC and zinc nitrate was observed.
In this work, the surfaces of silver nanowires (AgNWs) were modified by silanization process to improve the mechanical and antibiofilm properties of polymethylmethacrylate (PMMA) dental resins. A ...two‐route methodology was used to silanize the AgNWs: first, a surface treatment using tetraethyl orthosilicate (TEOS) was performed to act as interface agent; and then, γ‐methacryloxypropyltrimethoxysilane (MPS) was used to insert functional groups compatible to the acrylic resin. PMMA/AgNWs composites were obtained using pristine (AgNWP) and modified AgNWs (AgNWM) at concentrations of 0.5 and 1.0 wt%. The mechanical (flexural and impact strength) and antibiofilm properties against Candida albicans was investigated. AgNWM showed an enhancement in the dispersion and adhesion within the PMMA matrix, which were responsible for improvements in the mechanical properties. Results of flexural strength showed significant improvements for the sample with incorporation of 0.5 wt% of AgNWM and no significative changes for the sample with AgNWP. In addition, a reduction of about 50% in the biofilm formation by C. albicans was observed for the samples with 0.5 and 1.0 wt% of AgNWM. The incorporation of silanized‐AgNWs into PMMA dental resins can combine improvements in antimicrobial activity and in the flexural strength, being a potential antimicrobial biomaterial for dental applications.
A thin film of acrylic groups was produced on the silver nanowires surfaces, increasing the dispersion and interaction with PMMA matrix. Flexural strength values and antibiofilm activity against C. albicans were improved after the incorporation of silanized silver nanowires.
Blends of ultra-high molecular weight polyethylene (UHMWPE) and different contents (0, 10, 20 and 30 wt%) of linear low-density polyethylene (LLDPE) with and without maleic anhydride-grafted LLDPE ...(LLDPE-g-MA) were prepared by melt blending and aging resistance, thermal and mechanical properties were evaluated. The degree of crystallinity increases with the content of LLDPE in the blends. On the other hand, the addition of compatibilizer agent modifies the crystallinity and the crystallite size. Non-compatibilized blends have excellent impact resistance properties and the addition of LLDPE-g-MA aids processing but decrease the impact resistance of the blends. Thermal and mechanical properties were greatly affected by thermal and water aging. The thermal aging leads to an increase in the degree of crystallinity and consequent a decrease in impact resistance.
Carbon nanotubes (CNT)-reinforced polymeric composites are being studied as promising materials due to their enhanced properties. However, understanding the behavior of polymers during non-isothermal ...crystallization is important once the degree of crystallinity and crystallization processes are affected when nanoparticles are added to matrices. Usually, crystallization kinetics studies are performed using a model-fitting method, though the isoconversional method allows to obtain the kinetics parameter without assuming a crystallization model. Therefore, in this work, CNTs were oxidized (CNT-Ox) and functionalized with gamma-aminobutyric acid (GABA) (CNT-GB) and incorporated into a poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) matrix. The influence of the addition and functionalization of CNT in the crystallization kinetics of PHBV was evaluated using the isoconversional method with differential scanning calorimetry (DSC), and by polarized light optical microscopy (PLOM) and Shore D hardness. The incorporation and functionalization of CNT into PHBV matrix did not change the Šesták and Berggren crystallization model; however, the lowest activation energy was obtained for the composite produced with CNT-GB, suggesting a better dispersion into the PHBV matrix. PLOM and Shore D hardness confirmed the results obtained in the kinetics study, showing the smallest crystallite size for CNT-containing nanocomposites and the highest hardness value for the composite produced with CNT-GB.
The influence of different contents, 0.25, 0.50, and 1.00 wt%, of graphite nanosheets (GNS) on the properties of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) nanocomposites obtained by ...solution casting method has been studied. GNS were prepared by three steps: intercalation (chemical exfoliation), expansion (thermal treatment), and the GNS obtainment (physical treatment by ultrasonic exfoliation). X-ray diffraction (XRD), Raman spectroscopy, and field emission gun-scanning electron microscopy (FE-SEM) showed that the physical, chemical, and thermal treatments preserved the graphite sheets structure. XRD and Raman results also showed that GNS were dispersed in the PHBV matrix. The degree of crystallinity (Xc) of the nanocomposites did not change when the graphite nanosheets were added. However, the GNS acted as nucleation agent for crystallization; that is, in the second heating the samples containing GNS showed two melting peaks. The addition the GNS did not change the thermal stability of the PHBV.
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