Effects of clay orientation and aspect ratio on mechanical behavior of nylon-6 nanocomposite

Enhancement of the mechanical properties of organic-inorganic hybrid elastomers by introducing movable and reversible crosslinks

Organic-inorganic materials have been widely utilized in various fields as multifunctional materials. Poly(dimethyl siloxane) (PDMS), a typical inorganic polymer, has industrially appealing functions, such as transparency, biocompatibility, and gas permeability; however, it has poor mechanical properties. We incorporated organic-inorganic hybrid elastomers (PDMS-γCD-AAl⊃P(EA-HEMA) (x)) with movable crosslinks, and we utilized hydrogen bonds as reversible crosslinks. The organic polymer poly ethyl acrylate-r-hydroxy ethyl methacrylate (P(EA-HEMA)) penetrated the cavity of triacetylated γ-cyclodextrin (γCD), which was introduced into the side chains of PDMS, and it compounded with PDMS at the nanoscale. Structural studies involving visual and X-ray scattering measurements revealed that movable crosslinks improved the compatibility levels of PDMS and acrylate copolymers. However, macroscopic phase separation occurred when the number of reversible crosslinks increased. Furthermore, studies on the mobility levels of acrylate copolymers and movable crosslinks indicated that the relaxation behaviour of PDMS-γCD-AAl⊃P(EA-HEMA) (x) changed with changing numbers of reversible crosslinks. Introducing reversible crosslinks improved the Young's modulus and toughness values. The movable and reversible crosslinks between the organic and inorganic polymers contributed to the high elongation properties. The design of PDMS-γCD-AAl⊃P(EA-HEMA) (x) incorporated cooperatively movable and reversible crosslinks to achieve high compatibility of immiscible polymers and to control the mechanical properties.

Repurposing of waste PET by microbial biotransformation to functionalized materials for additive manufacturing

Plastic waste is an outstanding environmental thread. Poly(ethylene terephthalate) (PET) is one of the most abundantly produced single-use plastics worldwide, but its recycling rates are low. In parallel, additive manufacturing is a rapidly evolving technology with wide-ranging applications. Thus, there is a need for a broad spectrum of polymers to meet the demands of this growing industry and address post-use waste materials. This perspective article highlights the potential of designing microbial cell factories to upcycle PET into functionalized chemical building blocks for additive manufacturing. We present the leveraging of PET hydrolyzing enzymes and rewiring the bacterial C2 and aromatic catabolic pathways to obtain high-value chemicals and polymers. Since PET mechanical recycling back to original materials is cost-prohibitive, the biochemical technology is a viable alternative to upcycle PET into novel 3D printing materials, such as replacements for acrylonitrile butadiene styrene. The presented hybrid chemo-bio approaches potentially enable the manufacturing of environmentally friendly degradable or higher-value high-performance polymers and composites and their reuse for a circular economy.

ONE-SENTENCE SUMMARY

Biotransformation of waste PET to high-value platform chemicals for additive manufacturing.

Microstructure and Mechanical Properties of Severely Deformed Polypropylene in ECAE (Equal Channel Angular Extrusion) via Routes A and C

Equal channel angular extrusion (ECAE) is a solid-state extrusion process for modifying microstructures via severe plastic deformation without modifying the specimen cross section. In this study, changes in the microstructure and mechanical properties of polypropylene resulting from extrusion orientation route A (no rotation between extrusions) and extrusion orientation route C (a rotation of 180° between extrusions) are investigated using a 90° die-angle tooling outfitted with back pressure. Important differences are reported for the ECAE-induced deformation behavior between the two processing routes. A focus is made on the occurrence of heterogeneous plastic deformations (periodic shear banding and warping) for both routes and the control and inhibition of the plastic instabilities via regulated back pressure and ram velocity. Wide-angle X-ray scattering is carried out to characterize the structural evolution as a function of the processing conditions including route, extrusion velocity and BP application. The mechanical properties of the specimens machined from the ECAE pieces are examined under different loading paths including uniaxial tension/compression and simple shear. Full-field displacements converted to volumetric strains revealed the profound impacts of the processing route on the deformation mechanisms during tensile deformation.

Solid-state extrusion of polymers using simple shear deformation

The review considers the possibilities of new methods of solid-state extrusion of polymers based on the use of deformation schemes that include simple shear - equal-channel angular extrusion, equal-channel multi-angle extrusion and combined extrusion. Information on the evolution of the physico-mechanical properties of glassy, semi-crystalline polymers, polymer blends and composites is given.

Green Synthesis of Soy Protein Nanocomposites: Effects of Cross-Linking and Clay Nanoparticles on the Mechanical Performance

A green synthesis scheme was adopted for preparation of soy-protein-based clay nanocomposites, in which soy protein isolates (SPIs) were utilized as the biodegradable resin and clay nanoparticles (CNPs) were used as the nanoreinforcing phase. Cross-linking of the SPIs was realized through an aqueous reaction scheme with oxidized sugars (e.g., glucose and sucrose as the typical constituents of soy flours) as the cross-linkers. Toughening effects of the cross-linkers, process parameters, and CNPs on the mechanical properties (e.g., tensile strength, stiffness, strain at break, and toughness) of the resulting SPI-based clay nanocomposites were examined by micromechanical tensile testing. The cross-linking and toughening mechanisms of the SPI-based nanocomposites were evaluated by Fourier transform infrared spectroscopy, sol-gel and color characterization, scanning differential calorimetry, and transmission electron microscopy. Thermal stability of the cross-linked SPIs was evaluated by thermogravimetric analysis. Experimental results show that cross-linking can noticeably improve both the tensile strength and tensile modulus of the resulting SPI films, and a small quantity of CNPs can obviously alter the mechanical properties of the resulting clay nanocomposite films. The present study indicates that defatted soy flours can be directly utilized for developing low-cost, SPI-based nanocomposites without the need for external plasticizers, and the entire synthesis is completely green without involvement of any petroleum-based organic solvents, polymers, and metallic catalysts. Such biodegradable SPI-based green nanocomposites have the potential to substitute fossil-based plastics and polymer composites for use in various industrial products and house utilities.

Cohesive Zone Modeling of the Elastoplastic and Failure Behavior of Polymer Nanoclay Composites

Cohesive zone model (CZM) is commonly used to deal with the nonlinear zone ahead of crack tips in materials with elastoplastic deformation behavior. This model is capable of predicting the behavior of crack initiation and growth. In this paper, CZM-based finite element analysis (FEA) is performed to examine the effects of processing parameters (i.e., the clay nanoparticle volume fraction and aspect ratio) in the mechanical behaviors of a polymeric matrix reinforced with aligned clay nanoparticles. The polymeric matrix is treated as an ideal elastoplastic solid with isotropic hardening behavior, whereas the clay nanoparticles are simplified as stiff, linearly elastic platelets. Representative volume elements (RVEs) of the resulting polymer nanoclay composites (PNCs) are adopted for FEA with the clay nanoparticle distributions to follow both stack and stagger configurations, respectively. In the study, four volume fractions (Vf = 2.5%, 5%, 7.5% and 10%) and four aspect ratios (ρ = 5, 7.5, 10, and 20) of the clay nanoparticles in the PNCs are considered. Detailed computational results show that either increasing volume fraction or aspect ratio of the clay nanoparticles enhances the effective tensile strength and stiffness of the PNCs. The progressive debonding process of the clay nanoparticles in the polymeric resin was predicted, and the debonding was initiated in the linearly elastic loading range. The numerical results also show that PNCs with stagger nanoparticle configuration demonstrate slightly higher values of the engineering stress than those based on the stack nanoparticle configuration at both varying volume fractions and aspect ratios of the clay nanoparticles. In addition, CZM-based FEA predicts a slightly lower stress field around the clay particles in PNCs than that without integration of CZM. The present computational studies are applicable for processing PNCs with controllable mechanical properties, especially the control of the key processing parameters of PNCs, i.e., the volume fraction and aspect ratio of the clay nanoparticles.

Effect of the Compounding Conditions of Polyamide 6, Carbon Fiber, and Al2O3 on the Mechanical and Thermal Properties of the Composite Polymer

Among the composite manufacturing methods, injection molding has higher time efficiency and improved processability. The production of composites via injection molding requires a pre-process to mix and pelletize the matrix polymer and reinforcement material. Herein, we studied the effect of extrusion process conditions for making pellets on the mechanical and thermal properties provided by injection molding. Polyamide 6 (PA6) was used as the base, and composites were produced by blending carbon fibers and Al₂O₃ as the filler. To determine the optimum blending ratio, the mechanical properties, thermal conductivity, and melt flow index (MI) were measured at various blending ratios. With this optimum blending ratio, pellets were produced by changing the temperature and RPM conditions, which are major process variables during compounding. Samples were fabricated by applying the same injection conditions, and the mechanical strength, MI values, and thermal properties were measured. The mechanical strength increased slightly as the temperature and RPM increased, and the MI and thermal conductivity also increased. The results of this study can be used as a basis for specifying the conditions of the mixing and compounding process such that the desired mechanical and thermal properties are obtained.

Preparation of Montmorillonite Nanosheets through Freezing/Thawing and Ultrasonic Exfoliation

The exfoliation of layered montmorillonite (MMT) into mono- or few-layer sheets is of significance for both fundamental studies and potential applications. In this report, exfoliated MMT nanosheets with different aspect ratios have been prepared via a new freezing/thawing-ultrasonic exfoliation method. Freezing/thawing processing can exfoliate MMT tactoids with low efficiency while virtually retaining the original lateral size. The ultrasonic method has better exfoliation efficiency but tends to damage the nanosheets. By combining them and reasonably controlling the cycle index of freezing/thawing and ultrasonic power, the MMT nanosheets with different aspect ratios have been prepared efficiently. Such a unique exfoliation method has broad applicability for layered materials to produce monolayer nanosheets on a large scale.

Structure and properties of PA6-66/γ-aminopropyltriethoxysilane-modified clay nanocomposites prepared by in situ polymerization

In this study, PA6-66/γ-aminopropyltriethoxysilane-modified clay nanocomposites were prepared by in situ polymerization. It was found that the γ-aminopropyltriethoxysilane was chemically grafted onto clay successfully, and the covalent bond was formed between the clay and polymer chains. The transmission electron microscopy (TEM) and X-ray diffraction (XRD) results indicated that intercalated and exfoliated nanocomposites were obtained. The PA6-66 nanocomposites exhibited improved mechanical performance compared to that of neat PA6-66. Most importantly, the PA6-66 nanocomposites showed significantly improved toughness. In comparison with neat PA6-66, the rupture stress and elongation at the break of the nanocomposite with only 0.5 wt% clay increased 91.9% and 91.8%, respectively. The excellent toughness of PA6-66 nanocomposites should be mainly ascribed to the combined effects of strong polymer-clay interaction, the intercalated-exfoliated structures of clay, refined crystalline, formation of γ-form crystals, and decreased crystallinity of PA6-66.

Nanotechnology for Food Packaging and Food Quality Assessment

Nanotechnology has paved the way to innovative food packaging materials and analytical methods to provide the consumers with healthier food and to reduce the ecological footprint of the whole food chain. Combining antimicrobial and antifouling properties, thermal and mechanical protection, oxygen and moisture barrier, as well as to verify the actual quality of food, e.g., sensors to detect spoilage, bacterial growth, and to monitor incorrect storage conditions, or anticounterfeiting devices in food packages may extend the products shelf life and ensure higher quality of foods. Also the ecological footprint of food chain can be reduced by developing new completely recyclable and/or biodegradable packages from natural and eco-friendly resources. The contribution of nanotechnologies to these goals is reviewed in this chapter, together with a description of portable devices ("lab-on-chip," sensors, nanobalances, etc.) which can be used to assess the quality of food and an overview of regulations in force on food contact materials.

High-density polyethylene/needle-like sepiolite clay nanocomposites: effect of functionalized polymers on the dispersion of nanofiller, melt extensional and mechanical properties

Influence of molar mass and polarity of PE-g-MA on different properties [Morphological, Melt extensional, Mechanical and Thermal] of HDPE/sepiolite nanocomposites is reported.

Processing of Polypropylene-Organic Montmorillonite Nanocomposite by Equal Channel Multiangular Extrusion

By the example of polypropylene-organic montmorillonite composite (PP-OMMT), the abilities of the method of equal channel multiangular extrusion have been studied with respect to the modification of the structure and the properties of polymeric nanocomposites. With using X-ray structure analysis, TEM, DSC, and dilatometry, it has been demonstrated that this kind of processing provides an additional intercalation of the polymer into OMMT tactoids with the succeeding exfoliation and facilitates an increase in the aspect ratio, the degree of platelet orientation, the crystalline lamellar thickness, and a decrease in the dispersion of the crystallite thickness, as well as the formation of biaxial orientation of the OMMT and PP crystals. The observed structure rearrangements determine enhanced microhardness, ductility, and the heat distortion temperature of the PP-OMMT composite.

Improving the fracture toughness and the strength of epoxy using nanomaterials--a review of the current status

The incorporation of nanomaterials in the polymer matrix is considered to be a highly effective technique to improve the mechanical properties of resins. In this paper the effects of the addition of different nanoparticles such as single-walled CNT (SWCNT), double-walled CNT (DWCNT), multi-walled CNT (MWCNT), graphene, nanoclay and nanosilica on fracture toughness, strength and stiffness of the epoxy matrix have been reviewed. The Young's modulus (E), ultimate tensile strength (UTS), mode I (GIC) and mode II (GIIC) fracture toughness of the various nanocomposites at different nanoparticle loadings are compared. The review shows that, depending on the type of nanoparticles, the integration of the nanoparticles has a substantial effect on mode I and mode II fracture toughness, strength and stiffness. The critical factors such as maintaining a homogeneous dispersion and good adhesion between the matrix and the nanoparticles are highlighted. The effect of surface functionalization, its relevancy and toughening mechanism are also scrutinized and discussed. A large variety of data comprised of the mechanical properties of nanomaterial toughened composites reported to date has thus been compiled to facilitate the evolution of this emerging field, and the results are presented in maps showing the effect of nanoparticle loading on mode I fracture toughness, stiffness and strength.

Preparing copolyester–titanium dioxide nanocomposites with low melting point via in situ hydrolysis, catalysis and esterification process

Copolyester (CP)-titanium dioxide (TiO2) (CPT) nanocomposites with low melting point were synthesized by esterification of terephthalic acid, isophthalic acid, ethylene glycol and 1,4-butanediol monomers in the presence of tetrabutyl orthotitanate (TBOT). TBOT hydrolysis caused the TiO2 nanoparticles to act as catalysts for polymerization. Transmission electron micrographs showed that the TiO2 nanoparticles with the content ranging from 0.2 wt% to 0.4 wt% were well dispersed in the copolyester matrix. The thermal properties of the nanocomposites were assessed by differential scanning calorimetry. The melting point of CPT nanocomposite with 1.2 wt% TiO2 was 201.9°C, significantly lower than that of pure polyethylene terephthalate (above 260°C). Therefore, the obtained CPT nanocomposites with low melting point are potentially better for industrial applications than the commercial product.

In Situ Self Assembly of Nanocomposites: Competition of Chaotic Advection and Interfacial Effects as Observed by X-Ray Diffreaction

The effects of chaotic advection on the in situ assembly of a hierarchal nanocomposite of Poly Amide 6, (nylon 6 or PA6) and platelet shape nanoparticles (NPs) were studied. The assemblies were formed by chaotic advection, where melts of pristine PA6 and a mixture of PA6 with NPs were segregated into discrete layers and extruded into film in a continuous process. The process assembles the nanocomposite into alternating pristine-polymer and oriented NP/polymer layers. The structure of these hierarchal assemblies was probed by X-rays as a processing parameter, N, was varied. This parameter provides a measure of the extent of in situ structuring by chaotic advection. We found that all assemblies are semi-crystalline at room temperature. Increasing N impacts the ratio of α to γ crystalline forms. The effects of the chaotic advection vary with the concentration of the NPs. For nanocomposites with lower NP concentrations the amount of the γ crystalline form increased with N. However, at higher NP concentrations, interfacial effects of the NP play a significant role in determining the structure, where the NPs oriented along the melt flow direction and the polymer chains oriented perpendicular to the NP surfaces.

A Surlyn/magnesium oxide nanocomposite as an effective water vapor barrier for organic device encapsulation

A novel system of reactive polymer nanocomposites with MgO was developed, which exhibits superior performances as encapsulants for OPV devices.

Synthesis of silsesquioxane urethane hybrid materials by a modified sol–gel process

UV-curable molecular hybrids were prepared by a sol–gel process that could be adopted industrially. The stability was improved and additional functional groups introduced.

Mechanical reinforcement of epoxy with self-assembled synthetic clay in smectic order

Epoxy films containing self-assembled 2D colloidal α-zirconium phosphate nanoplatelets (ZrP) in smectic order were prepared using a simple, energy-efficient fabrication process suitable to industrial processing. The ZrP nanoplatelets form a chiral smectic mesophase with simultaneous lamellar order and helical arrangements in epoxy. The epoxy nanocomposite films are transparent and flexible and exhibit exceptionally high tensile modulus and strength. The findings have broad implications for development of multifunctional materials for engineering applications.