The effects of ultrasound on the chemical structure of polypropylene (PP) and its composites with different MWCNT content were investigated. The PP composites with 0

Epoxy blends of diglycidyl ether of bisphenol A (DGEBA) and 2-[2-(dimethylamino) ethoxy] ethanol (DMAEE) were prepared. The effect of DMAEE concentration on the rheological properties of the epoxy blends were investigated through oscillatory rheometry under isothermal conditions. A novel technique was developed to study the rheological behavior of the epoxy blends by using a Rubber Process Analyzer (RPA). The rheological study enabled analyzing the variations in the storage modulus (G'), loss modulus (G'') and torque during the progress of the curing reaction. Additionally, the theoretical cross-linking density (nu e) and the degree of conversi & oacute;n of the curing reaction (alpha). The gel time (tgel) was determined at different temperatures, and the activation energy (Ea) was calculated by using Arrhenius-type equation based on the gel time results. The activation energy values found are 24.79 kJ/mol and 23.01 kJ/mol. The results obtained are consistent with the values described in the literature. It was demonstrated that the proposed methodology is valid and, the use of the tertiary amine DMAEE curing agent for epoxy resins was confirmed. An effective methodology for the preparation of epoxy resin samples was developed, which allows rheological measurements using an oscillating rheometer type RPA. The methodology proved to be efficient for determining the curing kinetics of the epoxy system DGEBA with DMAEE initiator. Parameters such as elastic modulus (G '), gelation time (tgel) and activation energy (Ea) were determined. image

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.

The food waste and single-use packaging problems require efforts to develop active, sustainable packaging to extend the shelf life of perishable products. Therefore, the (3-Cyclodextrin-Clove essential oil inclusion complexes (IC) obtained by ultrasound (IC-U) and kneading (IC-K) methods were incorporated into a PBAT matrix. The effect of the IC on the structural, functional, and biodegradability features of the PBAT matrix was assessed. The results show that the IC exhibited high thermal stability and adequate dispersion in the PBAT matrix during the extrusion process. The PBAT-IC films, as prototypes of packaging bags, improved the shelf life of perishable foods (blueberries), reducing their weight loss by 20 % and 8 % after 28 days at room and refrigerated temperatures, preserving the diameter of the blueberries and inhibiting fungal growth, corroborating an improvement in functional properties. Moreover, IC-U and IC-K incorporation did not affect Young's modulus (85 N/mm2), tensile strength (19 N/mm2), elongation at break (553 %), and disintegration degree (90 %) of the films, making them alternative food preservation packaging for the food industry.

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.

The combination of keratin fibers (KF), obtained from poultry feathers, with chitosan (Ch) are employed in polypropylene (PP) composites to enhance the flame-retardant (FR) properties. The combined effect of each additive and the use of functionalized PP with ammonium polyphosphate (PP-gAPP) as a compatibilizer, compared with PP-gMA, on composite FR properties was analyzed. This compatibilizer was prepared by melt reaction of maleic anhydride grafted PP (PP-gMA) with ammonium polyphosphate (APP). The grafting of APP was characterized by FTIR, XRD, and NMR. PP/KF/Ch composites using PP-gAPP as compatibilizer were characterized by TGA, mechanical properties, and fire-retardant tests such as UL-94 (HB), limiting oxygen index (LOI), and cone calorimeter evaluations. These tests demonstrated the enhancement in fire-retardant characteristics obtained by using PP-gAPP as a compatibilizer agent compared with PP-gMA. The combination of the additives (KF and Ch) with PP-gAPP as compatibilizer in PP, increases the modulus and tensile strength and significantly improves the LOI and reduces the peak heat release rate during cone calorimetry tests with better thermal stability and a noticeable reduction in horizontal burning rate. Most important, the results indicated that the combination of these additives produce similar flame retardancy than a reference sample with high magnesium hydroxide loading. These composites are a promising way to meet the growing demand for high-performance materials with FR characteristics using bio-fire retardant additives such as KF and Ch, in sustainable and environmentally friendly composites.

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.

ABSTRACT Thermal and flammability properties of ethylene vinyl acetate/starch/organoclay (EVA/S/C20A) nanocomposites are shown in this work. Wide-angle X-ray diffraction (WAXD) patterns and micrographs obtained by field emission scanning electron microscopy (FE-SEM) show the formation of nanostructured systems. The organoclay layers were preferably intercalated-exfoliated with the EVA polymer. Even so, the vinyl acetate group in EVA interacted with both the C20A clay and the starch macromolecules, achieving compatibility between the three components. The intercalated layers of clay provided protection against thermal degradation of the EVA. However, based on the kinetic study, the Ea of the nanocomposite degradation was lower than that of pure EVA. The flammability tests demonstrated the absence of dripping during burning and the self-extinguishing capacity of the flame (HB in the UL-94 test) in the EVA/C20A and EVA/S/C20A nanocomposites. The results are related to the nanointercalation of the clay and the compatibility between the three components with different properties. Thus, the flame self-extinguishing potential of ternary nanocomposites, previously studied as biodegradable, is demonstrated. GRAPHICAL ABSTRACT

Poly(lactic acid) (PLA) can be functionalized with maleic anhydride (MA) to obtain MA-grafted PLA (PLA-g-MA), which in turn, can be functionalized with ammonium polyphosphate (APP) to obtain PLA-g-APP. This functionalization should facilitate the obtaining of compounds with flame-retardant properties through intumescence and also could function as a compatibilizer for the addition of bio-fillers. To achieve this, the PLA was first functionalized with MA using dicumyl peroxide (DCP) as free radical former, at varying peroxide and maleic anhydride concentrations. FTIR and NMR confirmed the functionalization. In addition, it was found that at certain DCP and MA concentrations, the attained grafting values were close to 1% MA into PLA. Thereafter, APP was grafted onto PLA-g-MA, in order to obtain PLA-g-MA/APP. XPS analyzes showed the effective functionalization of PLA with MA and subsequently, the grafting of APP. The SEM images showed that the “new” material (PLA-g-APP) does not show a brittle fracture as that of pure PLA, although a tough fracture and an interfacial adhesion between PLA and APP is improved revealing its compatibilization effect. This compatibilization allowed an improvement in tensile strength, impact resistance and a slight increase in HDT of the PLA. Finally, it was observed that the use of PLA-g-APP in a pure PLA matrix has a positive effect on its mechanical properties. The flame retardancy was tested by cone calorimeter which showed that pHRR and THR are reduced at 30% and 35%, respectively. In addition, the better flame retardancy was obtained when using PLA-g-APP with 15% (by weight) of grafted APP. This functionalized PLA (PLA-g-APP) is a new and good option to prepare bio-fire retardant composites with enhanced flame-retardant properties, in sustainable and environmentally friendly applications.

Packaging systems are facing a paradigm shift where challenges like recycling issues, non-biodegradable nature, and the migration of harmful chemical substances into food need to be solved. As a response, active packaging from sustainable materials has gained attention. Considering this, the extrusion process was employed to elaborate active mono-material films and elucidate the internal interactions between different content (0, 2.5, 5, and 7.5

Post-consumer PET (rPET) has become a worldwide concern due to the huge waste accumulation. Therefore, it is necessary to explore processing methods to recycle or reuse rPET to save resources and contribute to solving environment-related issues. Furthermore, the addition of inclusion complexes in the rPET matrix increases its application in terms of the release of active compounds that improve the added value of the polymer. Thus, active rPET films with thyme and orange essential oils were prepared by compression molding or extrusion. The effect of the different processing methods, as well as reprocessing, on the structural, mechanical, and antifungal properties of the active films was assessed. The results show that compression molding is not a suitable method to produce active films since their operation conditions, such as residence time and temperature, triggered the decomposition of the inclusion complex (IC), negatively affecting the appearance and mechanical properties (brittle and fragile) of films. Conversely, the extrusion process allowed preserving the IC and dispersing them adequately within the rPET matrix, maintaining the mechanical integrity of the films and resulting in a high antifungal activity against the growth of Penicillium funiculosum hyphae. This behavior was also observed after the re-extrusion process, corroborating that extrusion is a suitable method to process the active rPET films more than once without the detriment of their mechanical and antifungal properties.

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 CuC and Cu-C, respectively. This "wet" mechanical milling methodology represents a good option to prepare graphene/metal (hybrid) fillers.

PGA and PGA-GO hybrids with relatively low graphene oxide (GO) concentrations (0.5–2.5 wt%) were mass synthesized. In the preparation of GO, a modified Hummer’s method was used, and both PGA and PGA-GO followed similar synthesis routes. After forming PGA-GO hybrids, it was demonstrated that the reaction products rendered higher molecular weights as the GO concentration increased. The calorimetric traces showed heterogeneous nucleation and dual crystallization and melting mechanisms, the PGA-GO hybrids having higher melting points than neat PGA. There were no changes in crystal habits in these products, although crystal perfection and crystal thickening depended on the GO concentration. Both effects were associated with the higher melting points of the PGA-GO hybrids. Thermo-gravimetric measurements showed increases in thermal stabilities up to 20% depending on the GO concentration. Isothermal mass crystallization indicated enhancement of crystallization rates and crystal geometry changes from spherical to cylindrical depending on the GO concentration. There were also small clusters and other entities involved in the crystallization process.

Green synthesis may be a useful approach to achieve selective cytotoxicity of silver nanoparticles on cancer cells and healthy cells. In this study, the concomitant biosynthesis of silver (Ag)/silver chloride (AgCl) nanoparticles from pineapple peel extracts and their behavior on the breast cancer cell line MCF-7 is shown. Bioreactions were monitored at different temperatures. Fourier-transform infrared spectroscopy (FTIR), ultraviolet–visible spectroscopy (UV–vis), thermogravimetric analysis (TGA), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX), and transmission electron microscopy (TEM) techniques were used to characterize nanoparticle development. The breast cancer cell line MCF-7 was used as a test model to study the cytotoxic behavior of Ag/AgCl nanoparticles and, as a counterpart, the nanoparticles were also tested on mononuclear cells. Ag/AgCl nanoparticles with spherical and triangular morphology were obtained. The size of the nanoparticles (10–70 nm) and the size distribution depended on the reaction temperature. A dose close to 20 µg/mL of Ag/AgCl nanoparticles considerably decreased the cell viability of the MCF-7 line. The best cytotoxicity effects on cancer cells were obtained with nanoparticles at 60 and 80 °C where cell viability was reduced up to 80% at a concentration of 50 µg/mL. A significant preference was observed in the cytotoxic effect of Ag/AgCl nanoparticles against cancer cells in comparison to monocytes.

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.

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.