The preparation of nanofibrillar composite (NFC) materials using single‐polymer nanofibrils as starting materials is described. Such a possibility is offered by (i) the concept of polymer/polymer NFCs, which have recently been manufactured and represent a further development in the field of microfibril‐reinforced composites, and (ii) the opportunity to isolate neat nanofibrils through selective dissolving of the second blend component. The resulting nanofibrillar single‐polymer composites are characterized by superior mechanical properties (the tensile modulus and strength are improved up to 350%), competing with glass‐fiber‐reinforced PET.
A blend composition of poly(3‐hydroxybutyrate‐co‐valerate) and polylactide is used as a bioplastic matrix and reinforced with soy hull to engineer novel green composites. A comparative study with soy‐hull‐reinforced polypropylene composite system is performed. A compatibilizer is used to engineer the novel class of green composites with a balanced stiffness and toughness performance with the target to substitute PP‐based composites. The flexural and impact strength along with hydrophobicity of compatibilized composites are improved significantly over the noncompatibilized counterpart. The fiber/matrix interaction is investigated by SEM. These green composites have the potential to substitute PP‐based composites in some applications.
A novel technique is described that uses stretching‐controlled thermal micromolding with etched metal surfaces as templates for the mass‐production of superhydrophobic polymer films. First, the metal surface is etched and then used as a template to thermally replica‐mold the polymer (e.g., polyethylene). The resulting film surfaces exhibited stable superhydrophobicity with water contact angles >150° and sliding angles ≈7°. SEM imaging demonstrates that the microstructure on the superhydrophobic surface is formed by stretching from the microholes of the template during separation. This technique can be easily combined with melt‐flow casting for manufacturing superhydrophobic polymer surfaces on a large scale.
Supercritical CO2 has been used as a blowing agent to foam poly(styrene‐co‐acrylonitrile)‐based materials in a single screw extruder specially adapted to allow fluid injection. The cellular morphology depends on foaming temperature, more regular cells being obtained with decreasing extrusion temperature. In a second step, a natural and an organomodified nanoclay have been added for the purpose of imparting some flame resistance to the foamed material. The filler efficiency in reducing sample combustion rate appeared to be dependent on its delamination level inside the matrix and better results were obtained when the organomodified clay was first delaminated in the polymer in an efficient twin screw extruder using water assistance, prior to foaming in the single screw extruder.
Poly(lactic acid) (PLA) and soy protein concentrate (SPC) were compounded using poly(2‐ethyl‐2‐oxazoline) as compatibilizer by twin‐screw extrusion, and the resulting blends were foamed by a chemical blowing agent (CBA) using the same extruder. Effects of foaming temperature and CBA content on cell density and foam density were investigated. Polymeric methylene diphenyl diisocyanate (pMDI) as a co‐compatibilizer was added prior to foaming extrusion and its effects on foam morphology and properties were also studied. The results showed that cell density and foam density were greatly influenced by foaming temperature and CBA content. Using the strong interfacial modifier pMDI in PLA/SPC blends resulted in high‐cell density and low‐foam density when CBA concentration was low.
Silane coatings with different thicknesses were synthesized on CNFs for reinforcement of polyethylene composites. The thickness of the silane coating was adjusted by using a basic catalyst to increase the overall reactivity of the silane groups, resulting in a thick coating of ≈46 nm (ca. 90% increase in fiber diameter). DMA performed on the polyethylene composites showed a substantial increase in storage modulus from 1.68 to 2.34 GPa (40%) at low temperatures in the composite with the thick silane coating (≈46 nm) at a low loading of 0.4 wt.‐%. We believe that the silane‐treated nanofillers with thick coatings are very promising for high‐performance nanocomposites with non‐polar polymer matrices.
PLA biodegradable composites reinforced with various silk fibroin powder contents (0, 1, 3, 5 and 7 wt.‐%) were prepared by solution processing technique using CH2Cl2 as solvent. After that the composites and virgin PLA were foamed by using supercritical CO2. The influence of silk contents on PLA/silk fibroin powder composite foams were investigated by using SEM, XRD and DSC. Compared with PLA foam, the composite foams exhibited a reduction in cell size and increase in cell density at high silk content. With an increase in saturation temperature and pressure, the cell size was increasing and both the cell density and foam density were decreased simultaneously.
A new completely biodegradable shape‐memory elastomer consisting of PLLCA reinforced by in situ PGA fibrillation is described. The manufacturing processes and shape‐memory effects of the composites are discussed. DMA results reveal a strong interface interaction between in situ PGA fibrillation and PLLCA. Compared with the SMP‐based composites that are commonly used, the shape‐memory test shows that in situ PGA fibrillation can improve the recovery properties of PLLCA; in fact, the shape‐recovery rate increases from 80.5 to 93.2%.
A method of manufacturing free‐standing, micrometer‐scale honeycomb polyetherimide films is reported for the first time. Films are manufactured with a dip‐coating technique under water‐assisted self‐assembly. It is shown that the addition of poly(organosilane/siloxane)s and poly(ethylene glycol) allows the formation of regular honeycomb patterns. The films demonstrated the high thermal stability inherent for polyetherimide. The wetting properties of films are reported. The presence of nanopores was revealed with SEM imaging of the films. The makeup of the films allows their use as asymmetric membranes for reverse osmosis and ultrafiltration.
Factorial design analyses and numerical optimization are performed to establish material compositions (wood flour content, particle size, and impact modifier content) and mechanical property relationships for PLA/wood flour composites. Numerical optimization produces two scenarios based on materials compositions to manufacture composites with similar mechanical properties as unfilled PLA. High wood flour and impact modifier contents are required for composites made with fine wood flour particles, whereas the formulation requires low wood flour content and excludes impact modifiers for composites with coarse wood flour particles. These optimization solutions are validated experimentally.
CNT/NR composites were fabricated based on a CNT treatment using an acid bath followed by ball‐milling with HRH bonding systems. Thermal properties, vulcanization characteristics and mechanical properties of the CNT/NR composites were characterized. Compared to CB, the incorporation of CNTs into NR was faster and the energy consumption was less. The over‐curing reversion of CNT/NR composites was alleviated. After acid treatment and ball‐milling, the dispersion of CNTs in the rubber matrix and the interaction between CNTs and the matrix was improved. The performance of the CNT/reinforced NR composites was enhanced by the incorporation of the treated CNTs as compared to neat NR and CB/NR composites.
Curaua fibers were treated with ionized air to improve the fiber/phenolic matrix adhesion. The treatment with ionized air did not change the thermal stability of the fibers. The impact strength increased with increase in the fiber treatment time. SEM micrographs of the fibers showed that the ionized air treatment led to separation of the fiber bundles. Treatment for 12 h also caused a partial degradation of the fibers, which prompted the matrix to transfer the load to a poorer reinforcing agent during impact, thereby decreasing the impact strength of the related composite. The composites reinforced with fibers treated with ionized air absorbed less water than those reinforced with untreated fibers.
A new flame retardant based on an ammonium phosphonate is studied with respect to its thermal decomposition and its mode of action in wood‐plastic composites (WPCs). The measurements are carried out by means of fire tests (cone calorimeter) and pyrolysis investigations (thermogravimetry, infrared spectroscopy). The flame retardant acts mainly in the condensed phase by increasing the amount of residue formed by the wood part in the WPC. Additional flame dilution is achieved by the release of water, ammonia and carbon dioxide during the decomposition of the flame retardant.
In this study, the use of PLA‐g‐MA is investigated as a potential method for improving interfacial adhesion between agricultural residues and PLA, with the goal of enhancing mechanical properties. Compatibilization was achieved by using PLA‐g‐MA prepared via reactive extrusion. Green renewable and compatibilized PLA/wheat straw composites were extruded and injection‐molded. Addition of 3 and 5 phr PLA‐g‐MA to the composites resulted in significant improvements in tensile strength (20%) and flexural strength (14%) of the composites, matching that of the neat polymer. The observed improvement in strength was attributed to the good interfacial adhesion between the fiber and matrix.
Near‐monodisperse, size‐controllable, poly(methyl methacrylate)‐pigment nanoparticle composites were produced using electrohydrodynamic atomization (EHDA). The geometric mean diameters of the composite particles were in the 0.91 to 1.90 µm‐diameter range with geometric standard deviations of approximately 1.05 to 1.12. Increasing the polymer volume fraction and liquid flow‐rate resulted in an increase in the diameter of the composite particles, which agreed well with droplet scaling relations for EHDA. The results here demonstrate that EHDA can be used for polymer‐nanoparticle‐composite production and as an alternative to conventional inkjet printing.
A reactive organic montmorillonite clay (VMMT), modified with (4‐vinylbenzyl) triethylammonium cations, has been prepared and used as a nanofiller to reinforce a corn‐oil‐based polymer resin. The polymer resin was prepared by the cationic polymerization of conjugated corn oil, styrene and divinylbenzene, using boron trifluoride diethyl etherate modified with Norway fish oil as the initiator. The results indicate that the VMMT is intercalated in the corn‐oil‐based polymer resins. When compared with the pure polymers, these novel nanocomposites reinforced with 2 to 3 wt.‐% VMMT exhibit significant improvements in modulus, strength, strain and toughness. Furthermore, incorporating VMMT into the corn‐oil‐based polymer matrix also leads to improved thermal stability of the nanocomposites over the pure resins of up to 400 °C.
The surface functionalization of wood fiber was performed by chemical modification with bi‐functional organo‐silane 7‐octenyldimethylchlorosilane (7‐ODMCS) and mono‐functional organo‐silane n‐octyldimethylchlorosilane (n‐ODMCS). The chloro functionality of organo‐silane modifiers was utilized to functionalize wood fiber. The resulting modified fiber was characterized for thermal stability (thermal gravimetric analysis), presence of organic groups on the surface (Fourier‐transform IR), for particle size (microscopy) and for its hydrophobicity by dispersing in toluene. The modified fiber was used for in situ polymerization of propylene to obtain a wood fiber–polypropylene hybrid. The terminal olefin functionality of 7‐ODMCS was utilized for co‐polymerization of propylene during in situ polymerization. The wood fiber–polypropylene hybrid samples were characterized for thermal analysis. In order to confirm the co‐polymerization of propylene in 7‐ODMCS modified fiber during in situ polymerization, n‐ODMCS modified fiber having no olefin functionality was also used in in situ polymerization.
Novel silver/polymer composites based on thiol‐ene chemistry are prepared by an in situ bottom‐up approach. The in situ synthesis of silver particles inside the polymer matrix is achieved in one pot by photoreduction reaction in presence of a silver precursor and the concurrent crosslinking reaction. XPS analysis confirms the formation of silver particles; TEM morphological investigation shows a very good dispersion and distribution of the nanometric silver particles within the thiol‐ene network. Antimicrobial properties of the photocured hybrids are also evaluated.
We study the effect of the gap size on the molecular orientation and crystalline structure of uniaxially well‐aligned nylon‐6 nanofibers produced in the gap between negatively charged metal plates. The relative intensities of several absorbance bands are found to be different in the parallel‐ and perpendicularly polarized FTIR spectra. X‐ray analysis indicates that the metastable γ‐form is predominant in as‐spun nylon‐6 nanofibers, and is transformed into the thermodynamically stable α‐form by increasing the gap size. The polymer chains are thought to be oriented perpendicular to the fiber direction, and the molecular orientation to the fiber axis is enhanced on increasing the gap size.
A new technique to provide melt elasticity using flexible fine fibers prepared from a polymer with high melting point is demonstrated. A polymer composite of poly(propylene) with a small amount of fine fibers of poly(butylene terephthalate) shows marked strain‐hardening behavior in elongational viscosity, i.e., a rapid increase in the transient elongational viscosity with time or strain. The blend also shows prominent normal stress difference at steady shear. These elastic properties have not been observed for polymer composites with rigid fibers and can be applicable to the modification of rheological properties and thus the improvement of processability.
