Plastic foam with nano‐/micro‐scale cellular structures was prepared from a poly(propylene) (PP)/propylene‐ethylene copolymer (PER) blend by controlling bubble nucleation sites and bubble growth in disperse PER domains. Batch foaming experiments using a CO2 pressure quench method were conducted at room temperature. The bubble size and location were highly controlled in disperse PER domains by exploiting the differences in CO2 solubility and viscoelasticity between the PER domains and the PP matrix. The average cell diameter of PP/PER blend foams can be controlled within 0.5–2 µm by the PP/PER ratio, depressurization rate, and foaming temperature.
By curing bisphenol A‐based benzoxazine in a thermoplastic polystyrene‐block‐poly (ethylene‐co‐1‐butene)‐block‐polystyrene (SEBS) block copolymer, nanospherical polybenzoxazines as small as 150 nm with narrow size distribution are obtained in high yield. This specific condition allows simple and direct formation of nano‐ or microspherical thermoset resins. A model of how the thermoplastic block copolymer chains act as a molecular pocket where the thermoset curing proceeds is presented. It is demonstrated that this mechanism requires (i) a particular block of thermoplastic copolymer which allows specific interaction with monomeric thermoset molecules, and (ii) the curing of thermosets in a molecular assembly structure to confine the phase separation of thermoset prepolymer during curing.
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.
Boehmite alumina nanoparticles are added to PP‐g‐MAH‐compatibilized blends of PA 12 and PP to study the effects of nanoparticle loading in the resulting composites. WAXD and SEM data suggest that the nanoparticles enhanced the coalescence of PP. DSC, DMA, and TGA reveal that the final properties such as crystallization temperature, flexural storage modulus, thermal degradation temperature, etc., improve with increasing nanoparticle loading for blend/based composites. FTIR results show that the nanoparticles interfere with the interfacial activity at 5 wt% nanoparticle loading. All results are compared between the neat polymers and the compatibilized blend and show that despite a slight increase in dispersed‐phase domain size, all other properties improve with the addition of AlO(OH).
Novel nanocomposites based on conductive Ag nanoparticles and a self‐assembled polystyrene‐block‐polybutadiene‐block‐polystyrene (SBS) block copolymer were investigated. Good confinement of the nanoparticles into polystyrene microphase was achieved by the addition of DT as surfactant. The polymeric matrix kept its hexagonal order packed cylindrical structure up to 7 wt.‐% content of Ag nanoparticles. An electrostatic force microscopy (EFM) analysis of well‐dispersed metal‐organic hybrid Ag/SBS films was used to characterize the electric behavior of the conductive nanocomposites.
The morphological, electrical resistivity (ER), and electromagnetic interference (EMI) shielding effectiveness (SE) properties of poly(propylene) (PP), polystyrene (PS), PP/PS, and PP/PS/styrene–butadiene–styrene (SBS) blends filled with 10 vol.‐% high structure carbon black (CB) were studied. For the CB/PP/PS blends, TEM and SEM observations indicated that CB is preferentially localized in the PS phase. ER and EMI SE of the CB/PP/PS and CB/PP/PS/SBS blends were bounded between those of the PS composite (lower bound) and the PP composite (upper bound). In the PP/PS volume ratio ranging from (75/25) to (25/75), ER and EMI SE of the CB‐filled blends were independent of the PP/PS volume ratio. The EMI SE obtained by the 2 mm thick plates made of 10 vol.‐% CB‐filled (100/0)–(10/90) PP/PS blends are adequate for computers shielding applications.
This paper reports the properties of highly oriented nanocomposite tapes based on isotactic PP and needle‐like sepiolite nanoclay, obtained by a solid state drawing process. The intrinsic 1D character of sepiolite allows its exploitation in 1D objects, such as oriented polymer fibres and tapes, where it can be uniaxially oriented upon drawing. A synergistic increase in mechanical properties is presented for highly drawn tapes (λ ≤ 20) and low filler loadings (≤2.5 wt.‐%), which can not be simply explained by micromechanical composite models. Instead, mechanical properties are intimately related to the dispersion state of the nanoclays in PP, the rheological properties of the nanocomposites and the polymer morphology.
This study explored the combined influence of shear flow and nucleating agents on isotactic polypropylene (iPP) crystallisation. The study showed that oriented α‐iPP crystals were not necessary to form β‐iPP crystals, contrary to the accepted view that the surface of oriented α‐iPP crystals provides nucleation sites for an α‐iPP to β‐iPP growth transition. Instead it was proposed that flow‐induced mesomorphic point‐like nuclei preferentially nucleates β‐iPP. The combined effect of shear flow and nucleant was found to promote γ‐iPP crystals. The surprising γ‐iPP nucleation effect was explained by the high density of flow‐induced and heterogeneous nuclei present at the start of crystallisation.
Porous cellulose acetate butyrate foams with a bimodal cell size distribution were produced using supercritical carbon dioxide as a blowing agent. It is demonstrated that the cell size distribution is tunable, due to the semi‐crystalline nature of the polymer. The resulting morphology will either be homogeneous or bimodal, depending on the depressurization rate. Mercury intrusion porosimetry shows that the produced cellulose acetate butyrate foams possess an open cellular structure.
In recent years TPS has attracted more and more research interest as a promising replacement for commodity polymers in some applications. In this paper, a novel manufacturing technology to produce PLA fiber reinforced biodegradable TPS composite, and the microstructure and tensile properties of the composite, were first reported. PLA micro/sub‐micro fibers were generated in situ by elongational flow during die extrusion and subsequent hot stretching. The addition of 10% PLA significantly increased the drawability of TPS. Compared to direct extrusion, hot stretching tripled the tensile strength of the composite to 34 MPa. Extensive PLA fibrillation was evident in the composite. The generated PLA fibers measured ca. 400 nm in diameter with a large L/D ratio.
The role of polymer/filler interactions on the mechanical and electrical properties of elastomer nanocomposites is analyzed using dielectric spectroscopy, cyclic stress/strain tests, and online dc‐conductivity measurements. Pristine and deactivated (graphitized) CBs are studied in different rubber matrices. Due to confinement effects, an interphase of strongly immobilized polymer is present between adjacent filler particles, representing stiff but flexible mechanical bonds of the filler network. Under deformation of the sample, these bonds bend and finally break. Cyclic stress/strain measurements are analyzed by fitting the data to a microstructure‐based material model that allows for the evaluation of microscopic parameters of the polymer and filler network.
Reproducible and controllable hydrophilic layers were grafted on macroporous PP membranes by surface initiated grafting. Two methods were adopted, i.e., through adsorption of or entrapping the photo‐initiator on the membrane surface. The latter method yielded longer grafted chains under otherwise identical conditions. Depending on monomer solution composition, brush layers or network‐like structures were grafted onto the entire membrane surface without significant loss of water flux. The influence of the structure of grafted layers on water permeation, protein adsorption, and protein microfiltration fluxes was investigated. It was found that membranes grafted with network‐like structures have the best performance.
Ordered nanowells with diameters of ca. 40 nm and depth of 1–2 nm were prepared on a poly(methyl methacrylate) (PMMA) spherical domain, which was exposed on the polystyrene‐block‐poly(methyl methacrylate) (PS‐b‐PMMA) copolymer thin film. The PS‐b‐PMMA film formed spherical PMMA domains after the film was annealed above the order–disorder transition temperature. CO2 was dissolved into the PS‐b‐PMMA thin film at 8.6 MPa and at a temperature of 20 °C. The release of CO2‐pressure at the same temperature created the nanowell on the PMMA domain. The temperature and pressure to create nanowells in the PMMA domain affected the possibility of nanowell's formation.
The effect of CO2‐induced crystallization on the mechanical properties, in particular the yield and the ultimate stresses, of polyolefins is studied. PP and SEBS copolymer blends are used as examples and foamed after sorption of CO2 at temperatures below Tm. CO2 sorption thickens the crystalline lamellae and consequently increases Tm from 160 to 178 °C for both pure PP and PP/SEBS blend systems. Foams with an average cell size smaller than 250 nm retain the ultimate stress at the level of the polymer before foaming, even without the effect of CO2‐induced crystallization. Including CO2‐induced crystallization, the yield and the ultimate stresses of the foam can be improved by 30 and 50% over solid PP and by 22 and 40%, for solid PP/SEBS blends, respectively.
Aminated poly(propylene) was prepared by reacting aliphatic primary diamines with maleic‐anhydride‐functionalized poly(propylene) by in situ melt reaction. Around 60–70% of the initial acid groups had reacted to form amide and imide groups as confirmed by the almost complete disappearance of the maleic anhydride peak in FT‐IR spectra. The molecular weight of the diamines had an influence on changes in molecular structure of the PP‐g‐NH2 as a result of secondary reactions such as chain extension and cross‐linking. PP‐g‐NH2 and polycarbonate were pressed into two‐layer films and their adhesion strength was measured. The results showed that PP‐g‐NH2 was a very effective adhesion promoter.
The effect of hydrophilic and hydrophobic nanosilica on the morphological, mechanical and thermal properties of polyamide 6 (PA) and poly(propylene) (PP) blends is investigated by extrusion compounding. Depending on the difference between the polymer/nanoparticle interfacial tensions, different morphologies are obtained as highlighted by TEM and SEM. Hydrophobic nanosilica migrates mainly at the PA/PP interface, which leads to a clear refinement of PP droplet size. The macroscopic properties of the hybrid blends are discussed and interpreted in relation with the blend morphology and melt‐mixing procedure. The control over coalescence allows a morphology refinement of the blends and improves mechanical properties.
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.
In this paper, a novel intumescent system including MP as well as PER/TPU which acts as composite charring agent, is adopted to flame‐retarded PP. The encapsulation of charring agent PER by TPU effectively avoids the reaction of PER with MP during the compounding with PP at high temperature and also prevents the leaching out of polar PER from nonpolar PP matrix, thus remarkably enhancing the stability and water‐resistance of the intumescent system. PER and TPU have different but complementary charring mechanisms. So flame‐retarded PP with MP/composite charring agent shows a much better charring performance and flame‐retardancy than MP/PER flame‐retarded PP. The experimental results show that the former can reach UL‐94 V‐0 rating at 1.6 mm thickness at 25 wt.‐% flame retardant loading.
A simple route for preparing robust polymer nanotubes by SI‐ATRP within porous anodic aluminum oxide membranes and subsequent removal of the templates is presented. The nanotubes are composed of a crosslinked poly(styrene‐co‐divinylbenzene) shell and an inwardly grafted functional P4VP or PGMA brush‐like internal surface. The crosslinked skin endows the nanotubes with stability against organic solvents while the inwardly grafted polymer brushes supply the nanotubes with reactivity and functionalities. The inward PGMA hairs are post‐modified with sodium azides to introduce azido groups along tubular internal surfaces which are further reacted with propargyl alcohol. Structure and properties of the nanotubes are studied by SEM, TEM, LSCM, and FT‐IR spectroscopy.
In situ PET microfibrils are created by drawing melt‐blended PP and PET. The drawn blend is used to prepare polymer/polymer MFCs, and isolated PET microfibrils are used for the manufacturing of MF‐SPCs. Samples are prepared with different fibril orientations to determine the effect of orientation on the mechanical properties of the two types of composites. The resulting composites show improvements in stiffness of 77% for uniaxial MFCs, and 125% for uniaxial MF‐SPCs, with the highest recorded modulus of 8.57 GPa for a uniaxial MF‐SPC sample. SEM observations confirm that the fibrillar structure and excellent alignment is maintained. The changes in the reinforcement effect with orientation are very similar to those predicted by the rule of mixtures for the crossply.
