Recent developments in the fire retardancy of polymeric materials

The widespread applications of polymeric materials require the use of conventional flame retardants based on halogen and phosphorous compounds to satisfy fire safety regulatory standards. However, these compounds, particularly halogen-based examples, are persistent organic pollutants of global concern and generate corrosive/toxic combustion products. To account for eco-friendliness, ultimate mechanical/physical properties and processing difficulties, the window of options has become too narrow. Although the incorporation of non-toxic nanofillers in polymers shows positive potential towards flame retardancy, many obstacles remain. Moreover, most of the literature on these materials is qualitative, and often points to conflicting/misleading suggestions from the perspectives of short-term and long-term fire exposure tests. Hence, there is a renewed need to fundamentally understand the fire response of such materials, and complement experimental results with theoretical modelling and/or numerical simulation.     

Effect of pigmentation on organic coating characteristics

The paper reviews the effects of pigmentation, i.e. type of pigment and pigment volume concentration, on organic coating characteristics, such as curing and film formation, mechanical properties, thermal expansion coefficient, glass transition temperature, stress development, physical ageing and water transport. The main families of pigments used in the fabrication of organic coatings and the effect of nanopigments incorporation in binders are also discussed.     

Preparation and characterization of waterborne polyurethane/silica hybrid dispersions from castor oil polyols obtained by glycolysis poly(ethylene terephthalate) waste

Castor oil polyols (COLs) have been synthesized from glycolyzed oligoester polyol in order to produce waterborne polyurethane (WPU)/silica hybrid dispersions. Soft drinks poly(ethylene terephthalate) (PET) bottles were depolymerized by glycolysis with different molar ratio of poly(ethylene glycol) ( PEG 400), in the presence of zinc acetate as catalyst. The obtained glycolyzed products were reacted with castor oil (CO) to attain castor oil polyols by the process of transesterification. Five castor oil polyols were used with hydroxyl values of 255, 275, 326, 366 and 426 mg KOH g⁻¹. Several castor oil-based, polyurethane/silica hybrid dispersions having soft segment content of 39.6% to 28.2% and two concentrations of SiO₂ nanoparticles (0.5 and 1.0) have been prepared.The incorporation effect of SiO₂ nanoparticles into the PU matrix and the hydroxyl functionality of the COLs on the thermal and mechanical properties of resulting polyurethane films has been examined by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), thermal gravimetric analysis (TG) and measurement of the mechanical properties. The degree of phase separation (DPS) between oxide nanoparticles and hard segment, and particle size in the polyurethane, depends to some extent on nanosilica content and the hydroxyl functionality of the polyols employed in the polyurethane preparation process.Thermal stability of obtained hybrid materials depends on the hydroxyl functionality of the COLs and nanosilica content. The T_10% and T_50% (the temperature where 10 and 50% weight loss occurred) of WPU films decreased with the rise of OH functionality of castor oil polyols, caused by the increase of hard segment content. Glass transition temperature increased with increasing OH functionality and SiO₂ content. The hardness, adhesion and gloss quality of the polyurethane films were also determined with a view to assessing the effect of mole ratios of PET to glycol in glycolyzed products, the hydroxyl functionality and the SiO₂ content.     

Nanocomposites for food packaging applications

Most materials currently used for food packaging are non-degradable, generating environmental problems. Several biopolymers have been exploited to develop materials for eco-friendly food packaging. However, the use of biopolymers has been limited because of their usually poor mechanical and barrier properties, which may be improved by adding reinforcing compounds (fillers), forming composites. Most reinforced materials present poor matrix–filler interactions, which tend to improve with decreasing filler dimensions. The use of fillers with at least one nanoscale dimension (nanoparticles) produces nanocomposites. Nanoparticles have proportionally larger surface area than their microscale counterparts, which favors the filler–matrix interactions and the performance of the resulting material. Besides nanoreinforcements, nanoparticles can have other functions when added to a polymer, such as antimicrobial activity, enzyme immobilization, biosensing, etc. The main kinds of nanoparticles which have been studied for use in food packaging systems are overviewed, as well as their effects and applications.     

Water Absorption of Poly(lactic acid) Nanocomposites: Effects of Nanofillers and Maleated Rubbers

Injection-molded poly(lactic acid)/organo-montmorillonite (PLA/OMMT) and poly(lactic acid)/ nano-precipitated calcium carbonate (PLA/NPCC) were exposed to a water absorption test at 30°C for 70 days. The analysis was focused on the water diffusion kinetics and impact strength changes induced by the hydrolysis. The diffusion exponent (n) values of all the PLA samples are less than 0.5, indicating the Fickian diffusion model (case I) is obeyed. Adding nanofillers and maleated rubbers (SEBS-g-MAH or EPR-g-MAH) increased equilibrium moisture content but decreased diffusion coefficient values of PLA. The recoverability and retention-ability of the maleated rubbers toughened PLA/OMMT and PLA/NPCC after water absorption are excellent.     

Effect of carbon nanofillers on anticorrosive and physico-mechanical properties of hyperbranched urethane alkyd coatings

Effects of three geometrically different carbon nanofillers (CNs) namely carbon black, multiwall carbon nanotubes and graphene on the anticorrosive and physico-mechanical properties of hyperbranched alkyd resin (HBA) based coatings were investigated. Hyperbranched urethane alkyd coatings (HBUA) were made by curing the synthesized resin with hexamethylene diisocyanate trimer. All the carbon fillers are treated with a surfactant (Nonidate-P40) to achieve a uniform dispersion. The addition of surfactant treated CNs to HBUA resulted in a significant improvement in the corrosion resistance and mechanical properties in comparison with the neat HBUA coating. Among the HBUA/CN composites, the improvement in corrosion resistance was found to be superior in the case of HBUA/graphene composite. Transmission electron microscope (TEM) clearly indicated the uniform dispersion of carbon nanofillers in the resin. The uniform dispersion of CNs is believed to originate from an interaction of π electron clouds of CNs with the delocalized π electrons of Nonidet-P40 and H-bonding interaction between Nonidet-P40 and the HBA. This type of interaction does not disturb the π electron clouds of MWCNTs as opposed to chemical functionalization strategy.     

Recent advances in fiber/matrix interphase engineering for polymer composites

This review summarizes the recent (from year 2000) advancements in the interphase tailoring of fiber-reinforced polymer composites. The scientific and technological achievements are classified on the basis of the selected strategies distinguishing between (i) interphase tailoring via sizing/coating on fibers, (ii) creation of hierarchical fibers by nanostructures, (iii) fiber surface modifications by polymer deposition and (iv) potential effects of matrix modifications on the interphase formation. Special attention was paid to report on efforts dedicated to the creation of (multi)functional interphase in polymer composites. This review is round up by listing current trends in the characterization and modelling of the interphase. In the final outlook, future opportunities and challenges in the engineering of fiber/matrix interphase are summarized.     

Influence of a wollastonite microfiller and a halloysite nanofiller on properties of thermally curable pressure-sensitive structural adhesives

A thermally curable pressure-sensitive structural tape (SAT-0) was prepared using an epoxy acrylate copolymer and an epoxy resin and modified with a wollastonite microfiller (SAT-W) and a halloysite nanofiller (SAT-H). Influence of the minerals on self-adhesive features and curing behavior of the tapes as well as on shear strength of aluminum/SAT/aluminum joints has been investigated. Thermally uncured SATs containing the fillers exhibited higher T_g (+5 °C for SAT-H), adhesion (+64% for SAT-H) and tack (+10% for SAT-W) while their cohesion was lower (−22% for SAT-W and −86% for SAT-H) in relation to SAT-0. Moreover, filler addition reduced the shear strength of the Al/SAT/Al overlap joints (−6% for Al/SAT-H/Al and −22% for Al/SAT-W/Al), however, the microfiller-based systems exhibited better crack and fatigue resistance, and higher shear strength after ageing tests than SAT-0 and SAT-H (+100% after thermal ageing, +85% after exposure in a climatic chamber, and +27% after immersion in a fuel).     

Physical and morphological properties of nanoclay in low molecular weight phenol formaldehyde resin by ultrasonication

The aim of the present study was to examine the characteristics and physical properties of a low molecular weight phenol formaldehyde resin (LmwPF, mw approximately 600) and modified nanoclay admixture. LmwPF resins (45% w/v) were combined separately with 0.5%, 1.0% and 1.5% w/w montmorillonite nanoclay nanomer (based on solid PF). Each of the solutions was ultrasonicated in a sonifier. The dispersion of nanoclay in LmwPF was examined using X-ray diffraction (XRD), and Transmission Electron Microscopy (TEM). It was found that ultrasonication in a sonifier at 50 kHz for 60 min was able to disperse modified nanoclay up to 1.5% into the resin. XRD and TEM analyses showed that the nanoclay dispersion in the resin were either intercalated or exfoliated. The results also showed that the presence of nanoclay in the admixture significantly increased non-volatile content and reduced gelation time and pH values.     

Effect of nanoscale SiO2 and ZrO2 as the fillers on the microstructure of LLDPE nanocomposites synthesized via in situ polymerization with zirconocene

In the present study, the nanoSiO₂ and nanoZrO₂ were used as the fillers for linear low-density polyethylene (LLDPE) nanocomposites. In fact, the LLDPE nanocomposites were synthesized via the in situ polymerization of ethylene/1-octene with a zirconocene/MAO catalyst in the presence of the fillers. The LLDPE-nanocomposites were further characterized by means of TEM, DSC, ¹³C NMR and XPS. It was found that productivity increased more when the nanoZrO₂ filler was applied. The similar distribution for both fillers was observed by TEM. Based on the ¹³C NMR results, it appeared that the LLDPE nanocomposites obtained from both fillers were random copolymer. In particular, the resulted binding energy and elemental concentration at surface obtained from XPS measurement were further discussed in more details.