Shuhao Qin

Effect of migration of layered nanoparticles during melt blending on the phase morphology of poly (ethylene terephthalate)/polyamide 6/montmorillonite ternary nanocomposites

To study the effect of migration and selective localization of layered nanoparticles during melt compounding on the phase morphology of polymer blends, poly (ethylene terephthalate) (PET)/polyamide 6 (PA6)/organic montmorillonite (OMMT) ternary nanocomposites were prepared. Three different blending sequences were adopted either by pre-compounding OMMT into PET or into PA6 or by mixing all three components together. The morphology and tensile properties of PET/PA6/OMMT nanocomposites were investigated. TEM observation showed that OMMT platelets exclusively localized within the PA6 phase independent of the blending sequences, suggesting OMMT platelets migrated from PET into the PA6 phase during both the one-step and two-step compounding processes with pre-mixed PET/OMMT, and this migration was attributed to interfacial effects. SEM results revealed that the migration and selective localization of OMMT platelets had great influence on the size of the dispersed phase due to the conjunct action of the migration cutting effect and viscosity effect. The morphology determines the final properties of the nanocomposites as indicated by tensile test. It is believed that this work provides a way to tune the morphology and performance of immiscible blends.

Effect of fiber length and dispersion on properties of long glass fiber reinforced thermoplastic composites based on poly(butylene terephthalate)

Long glass fiber reinforced poly(butylene terephthalate) (LGF/PBT) composites with different original glass fiber lengths were prepared using a impregnation device designed by the authors. The influence of fiber length and fiber distribution on the properties of the LGF/PBT composites were studied. The results showed that the length of the residual glass fibers increased with the original glass fiber length increase of LGF/PBT composites. Scanning electron microscopy results indicated that the glass fibers of LGF/PBT composites (16xa0nm and 20 mm) were unevenly dispersed and this is a phenomenon of their reunion in the resin matrix. Various rheological plots including viscosity curve, storage modulus, loss modulus, and loss angle, were used to characterization the rheological properties of the pristine matrix and the LGF/PBT composites. Dynamic mechanical thermal analysis results indicated that the storage and loss modulus of the LGF/PBT composites firstly increase and then decrease with original glass fiber length. The storage and loss modulus, glass transition temperatures of the pristine matrix and LGF/PBT composites increase with test frequencies increase. The activation energies of glass transition relaxation for the activation energies for loss tangent (tanu2006δ) and loss modulus (E′′) peaks were calculated. Furthermore, the glass transition relaxation determined from the tanu2006δ peaks were more reliable than using the E′′ criterion. Differential scanning calorimetry analysis indicated that the crystallization temperature (Tc), percentage crystallinity (Xc) and melting point of the LGF/PBT composites firstly increased and then slightly decreased with the increase of the original glass fiber length. Thermogravimetry (TG) and differential thermal gravimetric analysis curves of the LGF/thermoplastic polyurethane (TPU)/PBT/polyethylene-butylacrylate-glycidyl methacrylate (PTW) composites were shifted to higher temperatures with the increase of the LGF content. Thermogravimetric analysis results showed that the TG curves of the LGF/TPU/PBT/PTW composites firstly shifted to higher temperatures and then shifted to lower temperatures as the original glass fiber length increased. The limiting oxygen values of the pristine matrix and LGF/PBT composites showed little change, which indicated that the effect of the original glass fiber length on the combustion behavior of LGF/PBT composites was not obvious. The tensile strength, notched Izod impact strength, flexural strength and modulus of the LGF/PBT composites firstly increase and then decrease with the original glass fiber length. When the original glass fiber length was 12 mm, the mechanical properties of LGF/PBT composites were optimal.

EFFECT OF INTERCALATION METHOD AND INTERCALATING AGENT TYPE ON THE STRUCTURE OF SILANE-GRAFTED MONTMORILLONITE

Supercritical carbon dioxide (scCO2) processing has been proven as a method for preparing polymer/montmorillonite (MMT) nanocomposites with improved platelet dispersion. The influence of scCO2 processing on the shape and size of the MMT tactoid/platelet, which is of great importance to the final platelet dispersion in the polymer matrix, is scarcely reported in the literature. In the present study, the pristine MMT was first surface modified with 3-glycidoxypropyltrimethoxysilane (the grafted MMT is labeled as GMMT), and then intercalated using three kinds of intercalating agents, myristyltrimethyl-ammonium bromide (MTAB), tetradecyltrihexylphosphonium chloride (TDTHP), and ethoxyltriphenyl-phosphonium chloride (ETPC), in water or scCO2, to study the effect of intercalating agent type and intercalation method on the morphology and thermal properties of GMMT, as a part of a program devoted to the synthesis of polymer/MMT nanocomposites. The structure of intercalated GMMT was characterized by thermogravimetric analysis, X-ray powder diffraction, and scanning electron microscopy (SEM). The optimum intercalation conditions in scCO2 were established by trying a range of reaction times and pressures. The structures of intercalated GMMT obtained under optimum scCO2 conditions and water were compared. The basal spacing of GMMT intercalated in scCO2 was almost the same as that in water, and both were obviously larger than that of GMMT. The GMMT exhibited a compact spherical morphology (examined using SEM), and the surface structures (including surface morphology, surface roughness, and surface compactness) of samples intercalated in water became ‘less compact’ and the degree of the ‘compactness’ of samples intercalated in scCO2 decreased further. Whether in water or scCO2, samples intercalated with TDTHP exhibited a larger basal spacing and the extent of disorder increased compared to that for samples intercalated with MTAB. The pristine MMT was also intercalated for comparison and silane grafting was proven to contribute to the increased basal spacing and ‘less compact’ surface structure.

Effects of annealing stress field on the structure and properties of polypropylene hollow fiber membranes made by stretching

By adopting three types of annealing stress fields, this work focused on investigating their effects on the microstructural evolution of polypropylene (PP) hollow fiber precursors obtained by the melt spinning process. PP hollow fiber membranes were then prepared by stretching the precursors at designed stretching ratios. The microstructure and properties of the precursors and membranes were characterized by differential scanning calorimetry (DSC), two-dimensional small-angle X-ray scattering (2D-SAXS), scanning electron microscopy (SEM), optical microscopy, pure water permeability, solute rejection, etc. In terms of the results, the effects of the stress on the development of crystal structure and rigid amorphous fraction (RAF) in the precursors were further discussed. Their roles in controlling the structure of the membranes were also studied in detail. It was indicated that stress acting on the precursors influenced the development of shish-kebab crystal structure and RAF during the annealing process. Fine crystalline lamellae structures in the RAF of the precursors were obtained when no stress was applied. Corresponding membranes made by stretching had better structure and properties, which mainly depended on the development of crystalline lamellae in the transition zone. Thus this study might provide a new insight for controlling the structure of membranes.

The effect of hybrid nanoparticle with silica sol as the supporter on the crystallization behavior and mechanical properties of isotactic polypropylene

Abstract Colloidal dispersions of hybrid nanoparticles with silica sol as the supporter (PKSol) were prepared by supporting aromatic phosphate on silica sol via a chemical action with γ-aminopropyltrimethylsilane (KH550) as a linker in wet process for the first time. Dynamic light scattering (DLS) demonstrated that hybrid nanoparticles with an average size of about 200 nm were formed and transmission electron microscopy (TEM) confirmed the presence of the ultrafine silica sols within the hybrid particles, which exhibited “currant-bun” particle morphologies, rather than typical “core-shell” structures for most polymer-encapsulated silica particles. Compared to aromatic phosphate alone and silane-modified silica sol, the effect of PKSol on the crystallization behavior and mechanical properties of isotactic polypropylene (iPP) was investigated using a polarized optical microscope (POM) and differential scanning calorimetry (DSC). The results demonstrated that PKSol showed superior nucleating ability on iPP than the other two. After adding 0.2 wt% PKSol, the crystallization peak temperature of iPP increased from 116.35°C to 120.81°C and the crystallinity increased from 39.6% to 50%. Correspondingly, the haze decreased from 37.6% to 23.3% and mechanical properties were improved.

Flame-retardant effect of a phenethyl-bridged DOPO derivative and layered double hydroxides for epoxy resin

Flame-retardant epoxy resin (EP) composites were prepared by the incorporation of a phenethyl-bridged DOPO derivative (DiDOPO) and modified layered double hydroxide (OLDH). In addition, the flame-retardant behaviour, thermal stability, synergism between DiDOPO and OLDH, and mechanical properties of the flame-retardant EP composites were examined. The introduction of a specific amount of OLDH in the intumescent flame-retardant EP led to considerable enhancement in flame retardancy, thermal stability, and mechanical properties. Furthermore, the effects of DiDOPO and OLDH on the flame-retardant properties of the EP composites were characterised by the limiting oxygen index (LOI) as well as the UL-94 vertical burning and cone calorimeter tests (CCT). The LOI of the EP/DiDOPO5/OLDH5 composites increased from 21.8% to 31.5%, and the composites exhibited the V-0 rating in the UL-94 vertical burning test. Moreover, the EP/DiDOPO5/OLDH5 composite exhibited the highest tensile strength and a low peak heat release rate and the total heat release values. In addition, scanning electron microscopy observation revealed a considerably more continuous, compact char residue for the EP/DiDOPO/OLDH composite. Thermogravimetric analysis and CCT revealed that DiDOPO and OLDHs exert gas- and condensed-phase flame-retardant effects. Overall, different flame retardant performance is related to the characteristics of each composite; dispersion state in the EP matrix; and structural changes during burning.

Influence of Thermo-Oxidative Ageing on the Thermal and Dynamical Mechanical Properties of Long Glass Fibre-Reinforced Poly(Butylene Terephthalate) Composites Filled with DOPO

In this work, the long glass fibre-reinforced poly(butylene terephthalate) (PBT) composites filled with 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) were prepared by melt blending, and the influence of thermo-oxidative ageing on the static and dynamic mechanical properties, thermal behaviours and morphology of composites with different ageing time at 120 °C were investigated and analysed. The results showed that the mechanical properties decreased in the primary stage of ageing, while embrittlement occurs in the later period, and the crystallinity of PBT decreases first, and then recovers to some extent. The scanning electron microscopy (SEM) photos of the samples indicated that the obvious crack appeared on the sample surface and a deeper, broader crack occurred with a longer ageing time. The results of energy dispersive X-ray analysis (EDAX) proved the DOPO filler diffused to the sample surface by measuring the content of phosphorus. Thermal gravimetric analysis (TGA) curves showed that the thermal stabilities of composites increased with longer ageing time, as did the values of the limited oxygen index (LOI). Meanwhile, the results of dynamic mechanical analysis (DMA) indicated that the glass transition temperature shifted to a higher temperature after ageing due to the effect of crosslinking, and both the crosslinking and degradation of PBT molecular chains act as the main factors in the whole process of thermo-oxidative ageing.

Nucleation ability of nonmetallic organophosphate derivatives in isotactic polypropylene

Nonmetallic organophosphate derivatives of ammonium (An), triethylammonium (CAn), and quaternary phosphonium (SP) salts of 2,2′-methylene-bis-(4,6-di-tert-butylphenyl) phosphate were synthesized and characterized. Their nucleation effects on isotactic poly(propylene) (iPP) were investigated in detail. The melting temperature of An, CAn, and SP was 262, 208, and 271xa0°C, respectively, which was near to the processing temperature of iPP (220xa0°C). Their particle morphologies revealed a great difference. An with a glossy rod-like structure can be uniformly dispersed in iPP matrix, while the bulk-like and layer structures of CAn and SP cannot play the same role. Moreover, with the incorporation of these derivatives at the same mass (0.15xa0mass%), iPP/An possesses an increased crystallization peak temperature of 15xa0°C and significant enhanced optical property as compared to neat iPP, but iPP/CAn and iPP/SP do not showed an overall enhanced property. Furthermore, nucleation effects of the compound nucleating agent consisting of these derivatives and sodium laurate (SNa) (a conventional compounded composition) on iPP were examined to clarify the role of particle morphology on the dispersibility in iPP. The results demonstrated that SP-SNa presented the most uniform dispersion in iPP, and the haze value of iPP/SP-SNa (concentration of 0.15xa0mass% of SP-SNa) was decreased to 11.8xa0%, showing the best synergistic effect of layer shape of SP with SNa.

Structure and Properties Study of PA6 Nanocomposites Flame Retarded by Aluminium Salt of Diisobutylphosphinic Acid and Different Organic Montmorillonites

Two different types of organic montmorillonite, namely quaternary ammonium salt intercalated MMT (CMMT) and quaternary phosphonium salt intercalated MMT (PMMT) were used as fillers in the flame-retardant polyamide (PA6) based on aluminium salts of diisobutylphosphinic acid (ABPA). The influence of different types of organic montmorillonite (OMMT) on the structure and properties of flame-retardant PA6 nanocomposites were systematically investigated. The X-ray diffraction and transmission electron microscopy results suggested that the introduction of OMMT improved the dispersion of the flame retardant particles independently of the type of OMMT. The derivative thermogravimetry (DTG) curve transformed to one peak from two peaks (representing the degradation of ABPA and PA6, respectively) after incorporation of the OMMT, which further confirmed better ABPA dispersion. Viscoelastic measurements demonstrated that a mechanically stable network structure was formed with the introduction of OMMT or ABPA and OMMT, while PA6/ABPA/PMMT presented the highest storage modulus and viscosity, suggesting a more efficient network structure. From UL-94 and limited oxygen index (LOI) tests, PA6/ABPA/PMMT presented the best flame performance, with a UL-94 of V-0 and a LOI of 33%. In addition, the PA6/ABPA/PMMT presented the lowest peak heat release rate (pHRR) among the investigated samples. Combined with the char layer analysis, it can be deduced that the introduction of PMMT improved the dispersion of ABPA, and promoted the formation of more efficient network structure, before promoting more compact char structures, which finally resulted in improved flame retardancy.

Mechanical, Heat-resistant, Crystallographic and Dynamical Mechanical Properties of Nylon 6/ P(N-phenylmaleimide-alt-styrene) Blends

In this work, nylon 6/ P(N-phenylmaleimide-alt-styrene) blends were prepared by melt blending, and the mechanical, heat-resistant, crystallographic and dynamical mechanical properties of nylon 6/ P(N-phenylmaleimide-alt-styrene) blends with different contents were investigated and analyzed. The results showed that the mechanical properties decreased with increasing PNS, while the heat deflection temperature (HDT), relative crystallinity (Xn), and storage modulus (G’) increased with increasing PNS. The results of differential Scanning Calorimetry (DSC) proved the PNS played the positive role of nucleating PA6. And the results of dynamic mechanical analysis (DMA) proved the PNS could improve the rigidity of PA6/PNS blends. From the SEM, these PNS domains were between 0.2 and 4 μm in diameter. The experimental results indicated that the addition of PNS improved the rigidity of PA6/PNS blends, and then improved the heat-resistant property.