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Polypropylene (PP) was compounded with β-nucleating agent and injection-molded at 180 °C or 220 °C. The samples were subsequently treated by supercritical carbon dioxide (scCO 2 ) at different temperatures. Results show that processing temperature and scCO 2 treatment could strongly influence the tensile and impact properties of β-nucleated PP. In particular, the sample processed at 220 °C and treated at 120 °C exhibit much enhanced impact strength (4.8 times that of its untreated counterpart). FTIR, WAXD, SEM and DMA were performed to explore the effects of processing temperature and scCO 2 treatment on structure of the samples. Deformation-induced plastic flow and micro-voids were also evaluated to construct structure-property relations. It was found that the influence of processing temperature on mechanical properties is mainly associated with the β-form content and β-crystalline morphology, while the structural changes in the crystalline lamellar scale may be responsible for the toughening effect of scCO 2 treatment. [ABSTRACT FROM AUTHOR]

There are principally two mechanisms to improve the impact resistance of polymer-based composites, intrinsic toughening and extrinsic toughening. But the interplay between them is far from being well understood. Here, glass fiber was incorporated into polypropylene to promote extrinsic toughening mechanism, while addition of elastomer and annealing were adopted for intrinsic toughening. In this way, the interaction among glass fiber, elastomer and annealing could be discussed based on various characterizations, and their combined effect on mechanical properties of the composites could be determined. The results show that the intrinsic toughening mechanism of elastomer will be suppressed by glass fiber irrespective of the support of annealing, though annealing could work synergistically with glass fiber to toughen polypropylene. The possible structure-property relations are discussed. This work will provide deeper insight into the toughening behavior of polymer composites and practical guidance for the design of composites with excellent stiffness-toughness balance. [ABSTRACT FROM AUTHOR]

Highlights: [•] ScCO2-assisted annealing was adopted to toughen polypropylene for the first time. [•] Polypropylene with well-balanced mechanical properties was prepared. [•] Polypropylene random copolymer with superior toughness was prepared. [•] Toughening mechanism of scCO2-assisted annealing was proposed. [ABSTRACT FROM AUTHOR]

Abstract: In this study, by directly melt-blending with 10wt% poly(lactic acid) (PLA) and 1.5wt% multiwalled carbon nanotubes (CNTs), yield strength of a biodegradable poly(propylene carbonate) (PPC) was increased more than one order of magnitude, and its Young’s modulus was enhanced by 8 times. Meanwhile, the high elongation at break of PPC was maintained. This overall property reinforcement could not be observed by adding either PLA or CNTs separately. At room temperature, the obtained mechanical properties of the reinforced PPC are comparable to or even better than those of some traditional petroleum-based polymers such as low density polyethylene, high density polyethylene and polypropylene (PP). Together with good biodegradability and excellent conductivity, the PPC/PLA/CNT composites prepared in this work exhibit a potential to be used as a sustainable alternative to petroleum-based polymers such as PP around room temperature. [Copyright &y& Elsevier]

Abstract: Controlling the hierarchical structure of melt-processed polymers is vital to “structuring” processing and tailoring properties of the product. In this work, polypropylene (PP)/octene-ethylene copolymer (POE) blends were injection-molded using so-called dynamic packing injection technique, which imposed oscillatory shear on the gradually cooled melt during the packing solidification stage. In this way, samples with highly oriented PP matrix and elongated POE particles were obtained. Most interestingly, it was found for the first time that the elongated POE particles could not improve any impact toughness of oriented PP, which is completely different from that for the isotropic ones. Polarized optical microscope, scanning electron microscope, micro-Fourier transform infrared spectroscopy and differential scanning calorimetry were used to characterize the microstructures along sample thickness. The crack-initiation term, impact fractured surface and cross-section of the impact surface were inspected to understand the difference in impact behavior between the oriented PP/POE blends and their isotropic counterparts. The results show that massive crazing or plastic flow of the matrix could not be effectively initiated in the oriented blends. Our work provides a good example for better understanding structure–property relationship of polymers via well controlling their internal hierarchical structure. [Copyright &y& Elsevier]

As part of a continuous effort to develop high performance isotactic polypropylene (iPP) based on β-form crystalline and morphological change induced by rare earth nucleator (WBG), various WBG contents (from 0.025 to 1.0 wt%) were adopted to prepare β-nucleated iPP at a fixed final molten temperature (240°C) in this study. The crystallinity, polymorphic composition, and crystalline morphology were inspected in detail by a series of crystallographic characterizations, including calorimeter, X-ray diffraction, polarized light microscopy (PLM), and electron microscopy. Furthermore, the self-organization and re-crystallization behavior of β-nucleating agent occurred during cooling was characterized by rheometry. Finally, the dependence of mechanical properties, including tensile strength, elongation at break, and impact strength, on WBG content was discussed based on the variations in β-form content and crystalline morphology. Interestingly, it is found that while the WBG content is below 0.1 wt%, the toughness of β-nucleated iPP increases with increase in WBG content due to additional β-form content; as the WBG content is in range of 0.1-0.5 wt%, the toughness increases at a lower rate with increase in WBG content due to β-crystalline morphological change. However, a decrease in toughness is observed while nucleator content is above 0.5 wt% as WBG remains undissolved in iPP upon the adopted processing conditions. The result of this study provides valuable information for potential industrial applications. Copyright © 2010 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: Long fiber reinforcement is well known to offer thermoplastic materials with high performances. But little work has been done to systematically investigate the effect of shear on the structures and properties of long glass fiber reinforced thermoplastics. The purpose of this work is to investigate the effect of shear on fiber orientation, fiber breakage and matrix molecular orientation in long glass fiber reinforced polypropylene composites, and to construct the structure–property relations. A so-called dynamic packing injection molding (DPIM) technique, which imposed oscillatory shear (10s−1) on the gradually cooled melt during the packing solidification stage, was used to prepare the dynamic samples, and optical microscope (OM), scanning electron microscope (SEM), micro-Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC) were used to characterize the samples. The results show that despite the well-published enhanced fiber and matrix orientation, shear will cause a remarkable fiber breakage. Combined effect of fiber breakage and orientation on the mechanical properties of the composites was qualitatively investigated and tensile properties of the dynamic samples, the conventional injection molded samples and the short glass fiber reinforced samples were compared. It is demonstrated that shear will induce more severe fiber breakage in long glass fiber reinforced polypropylene than in short glass fiber reinforced polypropylene, and that compromising the decreased strength caused by the severe fiber breakage is very difficult. [Copyright &y& Elsevier]

Abstract: In this study, cellulose nanocrystals (CNCs) were incorporated into poly(propylene carbonate) (PPC), which is a biodegradable alternative copolymer of propylene oxide and carbon dioxide, CNCs were prepared by sulfuric treatment of cellulose filter. An effective approach to prepare PPC environment-friendly composites is shown. The obtained PPC/CNCs nanocomposites display orders of magnitude increase in mechanical properties by adding a small amount of CNCs, in particular, with only 0.1wt% of CNCs incorporated, a 10-fold increase in tensile strength and 7-fold increase in Young’s modulus were achieved. The thermal stability of the nanocomposites is significantly improved as measured by dynamic mechanical analysis and differential scanning calorimetry. This is due to a combination of CNCs reinforcement in the soft matrix and increased effective molecular weight of the nanocomposties. The present nanocomposites outperform PPC composites reinforced with other nano-sized stiff and anisotropic fillers. [Copyright &y& Elsevier]

Abstract: Poly(propylene carbonate) is a new amorphous, biodegradable and biocompatible aliphatic polyester. It has a potentially wide range of applications, such as packing materials and biomedical materials. However, the low glass transition temperatures (T g ) and poor mechanical property have limited its applications. In this paper, poly(propylene-carbonate)/graphene oxide nanocomposites with a 10°C increase in T g and a 50 times increase in storage modulus at 30°C were firstly fabricated, then the nanocomposites were foamed using supercritical CO2 to widen their applications, particularly in the area of tissue engineering. It was demonstrated that the nanocomposite foams had good dimension stability and the final pore features were depended on supercritical CO2 saturation conditions. In addition, cytotoxicity and in vitro cell culturing tests of selected foams showed that the fabricated porous materials were non-cytotoxic and able to support cellular adhesion within the 3D structure, suggesting that these are promising materials for tissue engineering applications. [Copyright &y& Elsevier]