It is frequently emphasized that the action of interfacial adhesion is a critical parameter to improve the stiffness and toughness of polylactic acid/thermoplastic starch (PLA/TS) blends. In this ...work, the micromechanical behavior of PLA/TS blends with droplet morphology selected from literature is predicted and analyzed systematically by finite element analysis. A quantitative assessment of the effect of interface (perfect or imperfect) on the elastic behavior and craze initiation for toughening of PLA/TS blends is presented. For the elastic behavior, the PLA phase is the blend's load‐bearing component as the TS is more compliant than PLA, so an interface perfectly bonded reduces the blend's elastic modulus when compared to the modulus obtained if the interface is weakly bonded. Regarding the toughening behavior, as a compliant phase, the TS has the potential to nucleate stable crazes in the host PLA matrix independently of the degree of interfacial adhesion because the highly stressed region lies near the equator of the particle; nonetheless, the critical stress for craze initiation is very sensitive to the TS particle size. On the other hand, as the TS is less capable than PLA to develop large hydrostatic stresses, the TS has a low potential to dissipate energy by cavitation.
Micromechanical finite element analysis of PLA/TS blends.
In this work, the methodology to obtain high‐density polyethylene (HDPE) and graphene (G) nanocomposites using phenol‐modified graphene and phenol‐modified HDPE as compatibilizer obtained from the ...reaction of malleated polyethylene (HDPE‐g‐MA) with phenol, is described. Six different methods were used to obtain these composites, resulting from the combination of melt and solution mixing with three different procedures to functionalize either graphene or HDPE‐g‐MA with phenol. Nanocomposites were characterized by Fourier transform infrared (FTIR), scanning electron microscopy (SEM), wide angle X‐ray diffraction (WAXD), dynamic mechanic analysis (DMA) and tensile properties. The FTIR results evidenced the occurrence of an esterification reaction between HDPE‐g‐MA and phenol groups serving as compatibilizer. The SEM and WAXD results showed that the addition of this compatibilizer agent had a positive effect on graphene dispersion, which promoted greater stiffness in these composite materials, presenting higher storage modulus. In addition, a noticeable enhancement in dimensional stability at high temperatures was observed according to Tan Delta measurements. These results indicated a good interfacial adhesion between graphene and the polymer matrix by using this compatibilizer agent. It was observed that the composites obtained by solution mixing method showed better performance and stronger interfacial adhesions than the composites produced by melt mixing methods. The use of this phenol modified HDPE compatibilizer offers a new option to enhance the final performance of HDPE/graphene composites with better mechanical and thermal properties to be used in materials for various applications, such as automotive industry, electrical and electronics, construction, aerospace, and other engineering applications.
Interactions Between Graphene and Phenol‐Functionalized HDPE.
Thermal conductivity of epoxy resins was highly improved (up to 1.95 W/mK) with the addition of 7, 10, and 15 wt% of a hybrid filler composed of 70–30 wt% ratio of graphene and copper nanoparticles, ...respectively. Hybrid filler was obtained by high energy mechanical milling in two manners; just the two nanoparticles “dry milling” and with the addition of ethylene‐glycol “wet milling.” The crystalline structure was severely destroyed with dry milling but not with wet milling. Wet milling was thereafter used to obtain the hybrid filler that was later used in producing the epoxy nanocomposites. Raman spectrometry, X‐ray diffraction, X‐ray photoelectron spectroscopy (XPS), and electron microscopy were used to determine the interaction between both nanoparticles in the obtained hybrid graphene‐copper filler. XPS findings suggest that certain amount of copper is bonded to the graphene surface nanoparticles. This bonding could be carried out by the charge‐transfer interaction between graphene and copper or by physisorption of copper between the graphene nanosheets. The signals in 119.2 and 120.7 eV, observed in the deconvolution of Cu3s signal, correspond to copper carbon bonds Cu═C and CuC, respectively. This “wet” mechanical milling methodology represents a good option to prepare graphene/metal (hybrid) fillers.
X Rays Diffractograms of Wet Milling and Dry Milling of GNP for different times and TEM micrographs showing the destruction of crystalline structure of GNP subjected to DM.
This study aims to investigate changes in the structural properties of alkali/acid‐ultrasound modified Agave fibers and their performance immersed on a polyvinyl alcohol (PVA) matrix with plasticizer ...during melt mixing processing. Structural analysis revealed that ultrasound enhances the effectiveness of the conventional alkaline/acid treatments to modify fibers since the simultaneous treatment increased the partial removal of lignocellulosic components, water molecules, and amorphous regions which improved their processability on a PVA matrix. Specific energy consumption values indicated that during melt mixing the modified fibers required more energy to expose the chains of cellulose fraction to function as an interaction site for PVA chains. Once the mixture was homogenized, the fiber‐matrix interactions promoted high viscosity, friction, and mechanical stress in the chamber. Therefore, the modified fibers restricted the interaction between plasticizer and PVA in the obtained films, resulting in a highly structured, and reinforced network, increasing the storage modulus as dynamic mechanical analysis indicated. These findings highlight a feasible way to valorize Agave fibers and allow the understanding of the matrix‐fiber interactions during melt mixing processing, useful to predict the structural and mechanical properties of the films.
Hydrothermal (HMT) and water agitation (WA) treatments using plasma-activated water (PAW) were employed as sustainable methods to modify the molecular and functional performance of small (rice) and ...large (potato) starch granules. HMT-PAW and WA-PAW treatments resulted in etched and damaged granular surfaces that rearranged the long and short-range crystallinity of the modified starches. Both treatments seemed to predominantly occur in the amorphous region of the rice starch and the crystalline regions of the potato starch, changing the crystallinity values from 22.9 and 14.8 % to 31.8 and 10.4 %, respectively. Thus, the level of the arrangement of chains reached after PAW treatment decreased the ability of rice starch granules to swell (16 to 9 %) and leach out starch molecules from the granules (4.5 to 1.3 %), decreasing the viscosity and pasting profiles as indicated by n and k values. Opposite behavior was observed in the modified potato starches since starch components leached out to a higher extent (1.7 to 5.4 %). The results showed that HMT and WA treatments using PAW are feasible eco-friendly methods for modifying starch granules without chemical reagents. These modified starches could be suitable as functional ingredients or biopolymeric matrices for the food and packaging industry.
•Plasma-activated water and granule size determined the starch modification degree.•Water molecules reduction disturbed the helical order of starch molecules.•Amorphous regions of rice starch were disrupted by treatments with PAW.•Crystalline structures of potato starch were more susceptible to reactive species.•The treatments are suitable green technologies to obtain functional starches.
On a global scale, new policies and regulations are being proposed to reduce plastic pollution and adopt a new path toward sustainable development. Considering this, the design of composites using ...green treatments (ultrasound/plasma) and sustainable materials (starch and Agave fibers) was performed. Structural analysis indicated that dual treatment promoted the structural alteration of the superficial lignocellulosic components, hydroxyl groups, and amorphous regions of fibers without incorporating new elements from hexamethyldisiloxane (HMDSO) on their surface. Nevertheless, the treatments provide higher polarity on the fiber surface, promoting stronger secondary bonds between fibers and starch molecules, resulting in starch films with smooth surfaces and better mechanical interlocking as changes in roughness (612 to 499 nm), melting temperature (130 to 146 °C), loss (474 to 1688 MPa) and Young modulus (12 to 202 MPa) indicated. These findings highlight a feasible way to obtain an eco-sustainable reinforcing Agave fiber-filler, suitable to develop starch films for packaging applications.
Graphical Abstract
The effect of different carbon structures on the properties of low density polyethylene film and linear low density polyethylene blends (LDPE/LLDPE) subjected to artificial weathering, was studied. ...The carbon structures used were carbon black (CB), multi wall carbon nanotubes (MWCNT) and Graphene nanoparticles (GNP), at various loadings: 0.05, 0.1, 0.3, 0.5, 1.0, and 2 wt%. The PE‐Carbon structure composite films were characterized by optical microscopy (MOP), Haze, visible light transmission, UV–visible, thermogravimetric analysis (TGA), melt flow determinations (MFI) and tensile properties. Weathering measurements were evaluated in a QUV panel chamber with UV fluorescent lamps. The films degradation was analyzed following the change in carbonyl index of FTIR spectra, mechanical properties, and molecular weight. A noticeable better dispersion of CB and CNT particles in polyethylene matrix was observed compared with GNP. MWCNTs and CB produced high Haze and low visible light transmission. Thermal stability measured by TGA increased with the presence of GNP and CB. The crystallinity, melting, and crystallinity temperature (Tm and Tc) of the polymers increased with MWCNT and GNP. All the films with carbon structures presented an increase in the modulus of elasticity, with CB giving the highest elastic modulus. Artificial weathering of films with carbon structures showed that CB particles and CNT provided the highest UV protection to polyethylene, with a noticeable increase in low molecular weights and a retention in tensile strength and elongation at break which was reflected in maintaining their flexibility. Films with CNT showed the least significant changes in their properties, being more resistant to photo‐degradation.
Biodegradable PLLA/SBA-15 mixtures and PLLA/SBA-15-g-OLLA grafted composites were prepared by solution blending. The purpose was to determine the effect of the SBA-15 additives on the PLLA hydrolytic ...degradation and systematically characterize the degraded products. Before hydrolysis, all the composites were crystalline with defined crystal periodicity. In particular, there was a slight increase in the SBA-15 crystalline reflections with increasing SBA-15-g-OLLA concentration in PLLA/SBA-15-g-OLLA composites. Molecular contact (through C–O–C bonds) and miscibility enhancements were determined in proportion with the OLLA segment concentration in SBA-15-g-OLLA samples. The highest concentration of SBA-15-g-OLLA rendered the most hydrolysis and pH decrement. Specifically, hydrolytic degradation in buffer and body tempered conditions increased up to 13 wt % in the grafted PLLA/SBA-15-g-OLLA (10 wt%). Non-isothermal crystallization from the melt of the degraded products indicated heterogeneous nucleation using both SBA-15 and SBA-15-g-OLLA additives, and crystallization enhancement was observed using the degraded PLLA/SBA-15-g-OLLA (10 wt%). Depending on the SBA-15-g-OLLA concentration of the degraded samples, there was a gradual decrease in the intensity of the PLLA melt-recrystallization, which continued until the formation of a new melting endotherm. Two crystal habits and a morphological explanation were given to explain these results. Although unexpected, due to the lower molecular weight of the hydrolyzed products, isothermal crystallization experiments showed the enhancement of the first melting endotherm as a function of SBA-15-g-OLLA with 70 days degraded samples. This effect was demonstrated as related to the PLLA molecular weight. Isothermal bulk crystallization experiments of the hydrolyzed samples showed acceleration of the crystallization rate and changes in the crystal's geometry as a function of SBA-15-g-OLLA. The corresponding isothermal crystallization optical micrographs indicated highly nucleated patterns of such samples.
