Influences of hyperbranched polyethylenimine on the reactive compatibilization of polycarbonate/polyamide blends

The influences of hyperbranched polyethylenimine(h PEI), which possesses many reactive amino end-groups, on the blending properties of bisphenol-A polycarbonate(PC) and amorphous polyamide(a PA) were systematically investigated. Scanning electron microscopy(SEM) and differential scanning calorimetry(DSC) were used to observe the effect of h PEI on morphologies of PC and a PA phases in bulk blends. While the interfacial fracture toughness between planar PC and a PA layers with and without h PEI was studied by using augmented double cantilever beam(ADCB) method. Results show that the compatibility in PC/a PA blends can be significantly improved by adding a small amount of h PEI, mainly due to the interchange reactions between the polymers leading to the formation of block copolymers, cross-linked polymers and molecules with other constitutions. The augmented double cantilever beam experiments showed that the reactive process drastically reinforced the interfacial adhesion between planar layers of PC and a PA. However, degradation takes place during annealing at 180 °C, which was responsible for the production of small molar mass species of PC.     

The effect of impurities on the viscoelastic response of polycarbonate reinforced with short glass fibers

Observations are reported in oscillatory torsion tests at room temperature on unfilled and fiber-reinforced polycarbonates melt-blended with impurities (acronitrile–butadiene–styrene, high-impact polystyrene, low-density polyethylene, poly(ethylene terephthalate) and Nylon 6,6). Constitutive equations are derived for the viscoelastic behavior of glassy polymers. With reference to the theory of cooperative relaxation, a polymer is treated as an ensemble of meso-regions with arbitrary shapes and sizes. The time-dependent response of the ensemble is attributed to rearrangement of meso-domains. The rearrangement events occur at random times, when meso-regions are excited by thermal fluctuations. Stress–strain relations are derived by using the laws of thermodynamics. The governing equations are determined by four adjustable parameters that are found by fitting the experimental data. Fair agreement is demonstrated between the observations and the results of numerical simulation. The study focuses on the effects of the concentration of impurities and glass fibers on material parameters.     

Chemoselective Polymerization Control: From Mixed‐Monomer Feedstock to Copolymers

A novel chemoselective polymerization control yields predictable (co)polymer compositions from a mixture of monomers. Using a dizinc catalyst and a mixture of caprolactone, cyclohexene oxide, and carbon dioxide enables the selective preparation of either polyesters or polycarbonates or copoly(ester‐carbonates). The selectivity depends on the nature of the zinc–oxygen functionality at the growing polymer chain end, and can be controlled by the addition of exogeneous switch reagents.     

Plasma Treatment of Polymers

Abstract

Plasma treatment of polymers encompasses a variety of plasma technologies and polymeric materials for a wide range of applications and dates back to at least the 1960s. In this article we provide a brief review of the United States patent literature on plasma surface modification technologies and a brief review of the scientific literature on investigations of the effects of plasma treatment, the nature of the plasma environment, and the mechanisms that drive the plasma–surface interaction. We then discuss low‐radio‐frequency capacitively coupled nitrogen plasmas and their characteristics, suggesting that they provide significant plasma densities and populations of reactive species for effective plasma treatments on a variety of materials, particularly when placing the sample surface in the cathode sheath region. We further discuss surface chemical characterization of treated polymers, including some results on polyesters treated in capacitively coupled nitrogen plasmas driven at 40 kHz. Finally, we connect plasma characterization with surface chemical analysis by applying a surface sites model to nitrogen uptake of poly(ethylene terephthalate) (PET) and poly(ethylene naphthalate) (PEN) treated in a 40 kHz nitrogen plasma. This example serves to suggest an interesting practical approach to comparisons of plasma treatments. In addition, it suggests an approach to defining the investigations required to conclusively identify the underlying treatment mechanisms.     

A novel efficient halogen-free flame retardant system for polycarbonate

A novel silicon- and phosphorus-containing flame retardant, poly (9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide siloxane), P(DOPO-VTES) was synthesized from 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide(DOPO) and vinyltriethoxy silane(VTES). Its chemical structure was confirmed by FTIR. The thermal gravimetrical analysis (TGA) showed that P(DOPO-VTES) had good thermal stability and a high of char yield (86.31%) at 700 °C in nitrogen atmosphere. Its XRD patterns showed that this compound had a certain ordered structure. P(DOPO-VTES) was blended with polycarbonate (PC) together with montmorillonite(MMT) to prepare a series of organic-inorganic hybrids of flame retardant (PC)/P(DOPO-VTES)/MMT via melt blending. The thermal degradation behavior and flame retardancy of those hybrids were investigated with TGA, limiting oxygen index (LOI), vertical burning test (UL-94), and cone calorimeter. The LOI value of the flame-retardant PC systems could reach a maximal value of 32.8 when the content of P(DOPO-VTES) was 5 wt%. When 2 wt% MMT was added into the PC/5%P(DOPO-VTES) system, the UL-94 rating reached V-0. The possible flame retardant mode of MMT was studied via the dynamic rheological properties of the systems and the morphology of the chars remaining after the LOI test and the cone calorimeter test.     

Novel polycarbonate-based polyurethane elastomers: Composition–property relationship

Novel all-aliphatic polycarbonate-based polyurethane (PC-PU) elastomers, as well as PC-PU nanocomposites filled with organic-modified clays were synthesized, characterized and studied. It was found that they have very attractive mechanical properties (e.g., elongation at break between 600% and 800%). The prepared PC-PUs possess a distinctly segmented structure, which is the key prerequisite for their behavior as strong physical rubbery networks. All synthesized materials melt at elevated temperatures (between 110 and 200 °C) and hence can be processed like normal thermoplastics. The dispersion of the clay nanofiller was achieved by its one day swelling in the alcohol and a brief successive stirring. This procedure is very successful and leads to a partial exfoliation of the clay (documented by X-ray diffraction and TEM). The best nanocomposites with very good tensile properties, particularly with significantly increased moduli were obtained using the bentonite nanofiller. The study shows that the nanofiller interacts strongly with the hard domains and influences their melting temperature (DMTA and DSC), but it does not affect the glass transition temperature of soft domains. While Cloisite 15A was found to interact preferentially with the hard domains, the organic modified bentonite shows a strong interaction with both soft and hard segments, behaving as a blending agent. Hard domains in neat matrices, formed by hydrogen bonding of hard segments, were practically invisible by X-ray or TEM, but were successfully detected by AFM. Besides excellent mechanical properties, the prepared elastomers and their nanocomposites showed an interesting phase behavior (which was studied by combining DMTA and modulated DSC).     

Toughening of polycarbonate through reactive melt blending: Effect of hydroxyl content and viscosity of hydroxyl-terminated polydimethysiloxane

In this study, four hydroxyl-terminated polydimethylsiloxanes(PDMSOH) with different viscosities and hydroxyl contents were used to improve the toughness of polycarbonate(PC) through reactive melt blending. A largely improved toughness of PC has been achieved, and the low temperature toughness of PC/PDMSOH blends could overtake that of PC homopolymer in much higher temperatures(e.g.-10 °C versus 23 °C). Moreover, it was found that the more the hydroxyl content, the less the PDMSOH was needed to reach the highest toughness, suggesting that equivalent molar ratio between the carbonyl group content of PC and the hydroxyl group content of PDMSOH was required for the toughening of PC. Ultraviolet spectrophotometry was used to analyze the possible reaction between PC and PDMSOH. Contact angle was measured to assess the change of interfacial interaction between PC and PDMSOH as change of viscosity and hydroxyl content. The formation of PC-co-PDMSOH copolymer was believed to be the key for the toughening effect. This work gives a profound recommendation of the optimum kind and dosage of PDMSOH which should be used to improve the toughness of PC and will find immediate industrial applications.     

The effect of different impact modifiers in halogen-free flame retarded polycarbonate blends - II. Fire behaviour

In this second of a series of two papers, the fire behaviour of halogen-free flame retarded polycarbonate (PC) blends with different impact modifiers was studied. The impact modifiers were acrylonitrile-butadiene-styrene (ABS), a poly(n-butyl acrylate) rubber (PBA) with a poly(methyl methacrylate) (PMMA) shell and two silicone-acrylate rubbers consisting of PBA with different amounts of polydimethylsiloxane (PDMS) and different shell materials (PMMA and styrene-acrylonitrile, SAN). The flame retardant was bisphenol A bis(diphenyl phosphate) (BDP). Flammability was determined by LOI and UL 94. The burning behaviour under forced flaming conditions was studied by cone calorimeter under different external irradiations and by pyrolysis combustion flow calorimeter measurements. The exchange of ABS with the pure acrylate rubber worsened flammability, while similar results were obtained in cone calorimeter measurements. The exchange of ABS with the silicone-acrylate rubbers is promising, particularly with higher amounts of PDMS. In flammability tests strongly enhanced LOI values were obtained and therefore silicone-acrylate rubbers look like promising alternatives for ABS.     

Sample temperatures during outdoor and laboratory weathering exposures

Effective exposure temperatures (T_eff) in Arizona were calculated from hourly or 10-min parsed irradiation data along with ambient, black panel, and sample temperatures. The T_eff represents a constant temperature that creates the same amount of photodegradation as the naturally varying temperature and provides a benchmark temperature for making lifetime predictions from accelerated laboratory exposures. The annual ambient and black panel T_eff at a Wittmann, Arizona site were 30 °C and 42 °C, respectively, assuming that the photodegradation has an activation energy (E_a) of 21 kJ/mol (5 kcal/mol). T_eff was only weakly dependent on E_a over the range of 10-40 kJ/mol (3-10 kcal/mol). Samples exposed as van sunroofs were found to have T_eff that were offset from the black panel temperatures by a constant amount for the entire year. Thus, measurements of sample and black panel need to be made for only a few weeks to determine the offset and give the annual sample T_eff if the annual black panel T_eff is known. Light-colored samples probably are better compared with the ambient temperatures. Sample temperatures in xenon arc exposures usually are higher than the outdoor T_eff, so Arrhenius temperature corrections need to be carried out to relate accelerated to outdoor exposures. Temperatures in xenon arc exposure tests often correspond more closely to maximum temperatures that samples might encounter for only a few hours per year.     

Polycarbonate nanoparticles spray coated on silicon substrate using micro-electromechanical-systems-based high-frequency ultrasonic nozzle

Mono-disperse polycarbonate (PC) nanoparticles 20 nm in diameter was spray coated on silicon substrate using a novel high-frequency ultrasonic nozzle. Specifically, Bisphenol-A polycarbonate with a molecular weight (M_w) of approximately 6.4 × 10⁴ g/mol was first dissolved in pyridine. The resulting solution was sprayed into surfactant-containing de-ionized (DI) water using a 300 kHz silicon-based multiple-Fourier horn nozzle (MFHN). As pyridine was extracted into the water, PC nanoparticles formed but remained dispersed. This suspension of PC nanoparticles was then sprayed onto a silicon substrate using a 500 kHz 3-Fourier horn nozzle. Scanning electron microscopy (SEM) of the dried substrate revealed that PC nanoparticles were spread uniformly with no aggregation.