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In this study, microcellular injection molding with the combination of the precision mold opening and rapid heat cycle mold technology is conducted to fabricate the 30% glass fiber reinforced polypropylene (PP/GF30) foam. By optimizing supercritical fluid, mold temperature, mold opening distance, and other process conditions, the injection‐molded PP/GF30 foam with a super high expansion ratio, density of 0.32 g cm−3, and porosity of 75%, is fabricated. The crystallization and rheological properties of the PP/GF30 samples are tested to determine the suitable injection molding parameters. The results show that glass fiber promotes the crystallization of polypropylene (PP) while improving its storage modulus and complex viscosity. The fiber distribution and orientation as well as the cellular structure are investigated by scanning electronic microscopy (SEM) and X‐ray computed tomography. Due to the high mold temperature, the shear effect and melt cavity filling are greatly changed. The oriented fibers in the core layer are randomly moved by the cell growth and presented as a scaffold to support the cell wall structure. The glass fiber increases the PP melt stiffness and avoids cell collapse so that the cellular structure with small cell size and even cell distribution is fabricated. The compression properties, surface roughness, and thermal conductivity are examined. [ABSTRACT FROM AUTHOR]

Surface treatment on multiwalled carbon nanotubes (MWCNTs) by covalent H2O2 and non‐covalent Triton X‐100 for the dispersion of carbon nanotubes in long carbon fiber reinforced polypropylene matrix was proposed to fabricate the electrically conductive long fiber reinforced polypropylene composites by melt mixing. Their mechanical, thermal, rheological properties, as while as their morphology and electrical conductivity, were systematically investigated. The combination of micro‐scale long carbon fibers and nano‐scale carbon nanotubes are co‐existed in the polypropylene matrix. A multiscale conductive network is formed which great favor of the electrical conductivity of the composites. The results showed that the volume and surface resistivity of the sample with 4 wt.% MWCNTs addition is only 26.97 kΩ cm‑1 and 4.82 kΩ, respectively. The surface treatment showed positive effects on the mechanical, thermal, dynamic mechanical, and rheological properties. Compared to Triton X‐100, covalent H2O2 treated MWCNTs exhibited more significant improvement on the structure and properties of the long carbon fiber reinforced polypropylene. [ABSTRACT FROM AUTHOR]

• Nano PTFE Fibrils well dispersed in PP matrix improved melt strength and crystallization behavior pronouncedly. • Nano PTFE fibrils decreased the cell size while increased the cell density effectively. • Injection molded PP/PTFE foams had an unprecedentedly increased impact strength up to 250.4% compared with PP foams. • This work made foam injection molding a promising future, to fabricate injection molded lightweight and strong polymer foams. Polypropylene (PP) shows wide applications in many industries, especially for automotive. To save resources and energy, lightweight is an essential pursuit for industrial products. Foam injection molding (FIM) is a cost-effective method to manufacture lightweight plastic products, but it is still challenging to fabricate high-performance PP microcellular products for structural applications. Herein, a facile way was reported to produce lightweight and strong foamed PP/polytetrafluoroethylene (PTFE) components. First, in-situ fibrillated PP/PTFE composites were prepared using a co-rotating twin-screw compounder. SEM analysis showed nanoscale reticular PTFE fibrils uniformly dispersed in PP matrix. DSC combined with online optical microscopy observation, and rheological analysis demonstrated PTFE fibrils pronouncedly improved crystallization and viscoelasticity, respectively. Thus, PP/PTFE foam showed obviously refined cell structure compared with PP foam. Thanks to the promoted crystallization and refined cellular morphology, PP/PTFE foam exhibited superior mechanical properties, particularly in Gardner impact strength. The higher the PTFE content, the higher the impact strength. With a PTFE content of 5 wt%, the impact strength was increased by more than 250%. Furthermore, PTFE fibrils also facilitated to improve PP foam's tensile strength and modulus. Therefore, lightweight and strong PP/PTFE foam, achieved by the flexible, efficient, and scale-up FIM technology, exhibits a promising prospect in applications. [ABSTRACT FROM AUTHOR]

Abstract Lightweight is of great significance for reducing material and energy consumptions. Microcellular injection molding is an advanced technology for fabricating lightweight plastic structural components, but the deteriorated mechanical performance is a big challenge. In this study, we reported a facile and scalable way to fabricate the lightweight and strong microcellular polypropylene/talcum (PP/talc) component. Both PP/talc microcomposite and PP/talc nanocomposite were prepared by the twin-screw compounding, and the SEM images show a uniform dispersion of talc. The DSC analysis results demonstrate that either the micro or nano talc is very effective in promoting the crystallization of PP. The rheological tests show that both the micro talc and the nano talc lead to obviously enhanced viscoelastic properties of the PP melt, while the effect of the nano talc is much more pronounced than that of the micro talc. Thanks to the enhanced crystallization and improved viscoelastic behavior, both the microcomposite foam and the nanocomposite foam shows much refined cellular structure than the pure PP foam. The PP/talc microcomposite foam shows significantly improved strength but seriously deteriorated toughness, compared with the pure PP foam. In contrast, the PP/talc nanocomposite foam shows simultaneously improved strength, rigidity and toughness. Notably, the tensile toughness and the Gardner impact toughness of the PP/talc nanocomposite foam are dramatically enhanced by 226.1% and 166.2%, respectively. Taking into account the flexible and scalable features of the processing methodology, the lightweight and strong PP/talc nanocomposite foam shows a promising future to replace the solid structural components in many industrial applications such as automotive and consumer electronics. [ABSTRACT FROM AUTHOR]

Lightweight plastic materials are important for saving resources and energy, reducing environmental pollution, and achieving sustainable development. Foam injection molding is a promising technology for manufacturing lightweight plastic components. However, these plastic components present poor mechanical properties and imperfect surface appearances. Herein, we reported a novel strategy to prepare lightweight and tough polypropylene (PP)/polytetrafluoroethylene (PTFE) nanocomposite parts with defect-free surfaces by combining in situ fibrillation and nanocellular injection molding technologies. The nano-fibrillary PP/PTFE nanocomposite was firstly prepared using an in situ method based on twin-screw compounding. Scanning electron microscopy (SEM), rheological and differential scanning calorimetry (DSC) analysis, combined with online optical microscopy observation, demonstrated the network structure of PTFE nanofibrils and its positive effects on melt strength and promoting crystallization. Using nanofibrillary nanocomposites, we achieved nanocellular foaming, for the first time, using the foam injection molding process. The nanocellular PP/PTFE nanocomposite foam thus obtained significantly enhanced mechanical properties compared to the regular PP foam, and even superior strength and ductility compared to unfoamed PP. In particular, the impact strength of the nanocellular foam was 700% higher than that of the regular foam and 200% higher than that of the unfoamed product. Moreover, unlike regular foam, the nanocellular PP/PTFE nanocomposite foam showed outstanding surface appearance without any silver or swirl marks. More importantly, the whole process was facile, flexible, efficient, and easy to scale-up, and could be easily extended to other materials. The remarkable mechanical performance and surface appearance, combined with the flexible and extendable process, confers nanocellular PP/PTFE nanocomposite foams a promising future in many advanced applications where both lightweight and mechanical integrity are required. [ABSTRACT FROM AUTHOR]

Rapid heat cycle molding (RHCM) is a newly developed injection molding technology in recent years. In this article, a new electric heating RHCM mold is developed for rapid heating and cooling of the cavity surface. A data acquisition system is constructed to evaluate thermal response of the cavity surfaces of the electric heating RHCM mold. Thermal cycling experiments are implemented to investigate cavity surface temperature responses with different heating time and cooling time. According to the experimental results, a mathematical model is developed by regression analysis to predict the highest temperature and the lowest temperature of the cavity surface during thermal cycling of the electric heating RHCM mold. The verification experiments show that the proposed model is very effective for accurate control of the cavity surface temperature. For a more comprehensive analysis of the thermal response and temperature distribution of the cavity surfaces, the numerical-method-based finite element analysis (FEA) is used to simulate thermal response of the electric heating RHCM mold during thermal cycling process. The simulated cavity surface temperature response shows a good agreement with the experimental results. Based on simulations, the influence of the power density of the cartridge heaters and the temperature of the cooling water on thermal response of the cavity surface is obtained. Finally, the effect of RHCM process on surface appearance and tensile strength of the part is studied. The results show that the high-cavity surface temperature during filling stage in RHCM can significantly improve the surface appearance by greatly improving the surface gloss and completely eliminating the weld line and jetting mark. RHCM process can also eliminate the exposing fibers on the part surface for the fiber-reinforced plastics. For the high-gloss acrylonitrile butadiene styrene/polymethyl methacrylate (ABS/PMMA) alloy, RHCM process reduces the tensile strength of the part either with or without weld mark. For the fiber-reinforced plastics of polypropylene (PP) + 20% glass fiber, RHCM process reduces the tensile strength of the part without weld mark but slightly increases the tensile strength of the part with weld mark. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013 [ABSTRACT FROM AUTHOR]

Abstract: Rapid heat cycle molding (RHCM) is a recently developed injection molding technology to enhance surface esthetic of the parts. By rapid heating and cooling of mold cavity surfaces in molding process, it can greatly alleviate or even eliminate the surface defects such as flow mark, weld line, glass fiber rich surface, silver mark, jetting mark, and swirl mark, and also improve gloss finish and dimensional accuracy without prolonging the molding cycle. Besides surface esthetic, mechanical property is also a very import issue for the molded plastic part. The aim of this study is focusing on the effects of the cavity surface temperature just before filling, T cs, in RHCM on the mechanical strength of the specimen with and without weld line. Six kinds of typical plastics including polystyrene (PS), polypropylene (PP), acrylonitrile butadiene styrene (ABS), acrylonitrile butadiene styrene/polymethylmethacrylate (ABS/PMMA), ABS/PMMA/nano-CaCO3 and glass fiber reinforced polypropylene (FRPP) are used in experiments. The specimens with and without a weld line are produced with the different T cs on the developed electric-heating RHCM system. Tensile tests and notched Izod impact tests are conducted to characterize the mechanical strength of the specimens molded with different cavity surface temperatures. Simulations, differential scanning calorimetry (DSC), scanning electron microscope (SEM) and optical microscope are implemented to explain the impact mechanism of T cs on mechanical properties. [Copyright &y& Elsevier]

[Display omitted] • Polytetrafluoroethylene (PTFE) nanofibrils and talc enhanced rheological and thermal properties of polypropylene (PP). • Lightweight PP/Talc/PTFE foams were fabricated by foam injection molding. • PP/Talc/PTFE foams exhibited surprisingly mechanical properties. • Enhanced flame-retardant PP/Talc/PTFE foams were prepared. With the ever-increasing demand for plastic structural components, the development of lightweight plastics is critical for environmental protection and reduced material consumption. Foam injection molding exhibits promise for manufacturing lightweight products, and hence, could be explored for the fabrication of foamed polypropylene (PP) parts. However, it is challenging to fabricate high-performance foam-injection-molded polypropylene (FIM-PP) foams due to the low melt strength of PP. Herein, we have proposed a novel method to prepare lightweight and strong ternary-blended PP foams with enhanced flame retardancy by incorporating in situ-fibrillated polytetrafluoroethylene (PTFE) and talc. The PTFE nanofibrils and talc effectively improved the melt viscoelasticity and crystallization of PP; hence, both, regular and mold-opening foam-injection-molded (MOFIM) ternary-blended PP foams, exhibited refined cellular structures. Furthermore, the MOFIM-PP/Talc/PTFE foam exhibited remarkable mechanical performance, including a 341% increase in the tensile toughness, 408% increase in the notched impact strength, and 121% increase in the flexural strength, which were attributed to the enhanced brittle-to-plastic transition by PTFE nanofibrils and the refined cellular structure. These advantages, combined with the enhanced flame retardancy of the MOFIM-PP/Talc/PTFE foam, make this method cost-efficient, scalable, and green to manufacture lightweight and strong PP foams, thereby broadening the application scope of PP in structural components. [ABSTRACT FROM AUTHOR]

The global energy crisis has been widely concerned by the public due to the massive energy requirement caused by rapid-developing economy and society. Ultra-lightweight, super-insulating, and strong polymer foams exhibit a promising prospect, in terms of saving materials and resources, and reducing energy consumption. However, there exists a great challenge to achieve highly expanded microcellular polymer with satisfactory thermal insulation performance. Herein, polypropylene (PP) with carbon nanotubes (CNTs) was used to prepare multifunctional foams by using batch foaming process with carbon dioxide. This cost-efficient and facile process endowed PP/CNT composite a variety of unprecedented advantages, including over 50-fold expansion ratio, a rather low thermal conductivity of 28.69 mW/m·K, and remarkably improved compressive strength. Acting as both crystal and cell nucleating agents, CNTs contributed to the fabrication of such ultralight foams with refined cell structure, which led to significantly reduced solid thermal conduction and enhanced mechanical properties. Moreover, thanks to CNTs' outstanding infrared radiation shielding capacity, the thermal radiation through the ultra-lightweight PP/CNT foam was significantly suppressed. Thus, ultra-lightweight, super thermal-insulation, and strong PP/CNT composite foams were achieved by using microcellular foaming technology, paving a way for designing and synthesizing multifunctional polymer-based composite foams for high-performance thermally insulating applications. Image 1 [ABSTRACT FROM AUTHOR]

Lightweight plastic foams are of great significance for saving resources and reducing energy consumption. Foam injection molding (FIM) shows a promising future to provide lightweight and shape‐complex plastic components. However, it is still challenging to produce lightweight and strong polypropylene (PP) foams by FIM due to PP's poor foaming ability. Herein, rubber and talc are employed to improve PP's foaming ability, and hence to enhance PP foam's mechanical properties. Due to the significantly enhanced rheological properties, injection molded PP composite foam exhibits greatly refined and homogenized cellular structure compared with pure PP foam. Thanks to rubber toughening effect and improved cellular morphology, PP/rubber foam shows much higher ductility than pure PP foam. Moreover, talc particles lead to remarkably enhanced rigidity of PP/rubber foams. Thus, lightweight and strong PP/rubber/talc composite foam is achieved with tensile toughness increased by 82.58% and impact strength increased by 106.21%, and they show broad industrial application prospects. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Crystal melting behavior of polypropylene under different CO 2 pressures was in-situ studied. • The semi-molten state of linear polypropylene was suitable for batch foaming. • Linear polypropylene foam with an ultra-high expansion ratio of 45 was fabricated. • The fabricated high expansion foam had a low thermal conductivity of 37.2 mW m−1 K−1. Abstract To prepare high expansion foams, the crystal melting behavior of linear polypropylene (LPP) under different CO 2 pressures was studied using an in-situ visualization method. It was found that with increasing temperature, the crystal boundaries were gradually melted. However, the melting window of the crystals was narrow. In this narrow window, we thought the high expansion LPP foams could be prepared by batch foaming. To verify this, foaming experiments were carried out. The results showed that at the temperature when crystals were nearly melted, the foam had an ultra-high expansion ratio of 45. This demonstrated that the semi-molten state was an important factor for preparing high expansion foams. The thermal insulation and compression performance of the foams were also studied. The lowest thermal conductivity was 37.2 mW m−1 K−1. The compression tests showed that the collapse stress decreased with an increasing expansion ratio and increased with a decreasing cell size. [ABSTRACT FROM AUTHOR]

This paper presented a new core-back chemical foam injection molding (CFIM) method. Different from the conventional method, the new method has a unique secondary filling stage right after core-back operation. By combining core-back and secondary filling, a closed shell composed of dense polymer skins can be created right before melt filling. This closed shell can prevent the gas loss from the melt flow front, and act as the gas counter pressure to reduce cell coalescence and collapse, thus leading to significant improvement of cell structure. The mechanical testing results show that the new technology can produce plastic foam with simultaneously enhanced tensile strength, elastic modulus, and notch impact strength. Moreover, this technology can also improve the surface appearance of the foamed sample. Thus, it shows a promising future in offering lightweight structural components with improved mechanical strength and enhanced surface appearance. [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract The preparation of high-expansion open-cell foam for oil spill clean-ups is important, but still challenging with linear isotactic polypropylene (PP). Therefore, a cooling batch foaming method was designed to fabricate the high-expansion PP foams using supercritical CO 2 as a blowing agent. To investigate the relation between the crystallization and foaming of PP, an in-situ visualization system was employed. It is found that the CO 2 dissolved in polymer melt depresses the crystallization temperature and nucleation of PP. When the foaming is triggered before the crystallization, high-expansion foams can be prepared. Moreover, foaming occurring before crystallization helps to produce an open-cell structure owing to a structural inhomogeneity induced by the PP crystallization. According to the hydrophobicity and oil absorption capacity tests, the open-cell foam prepared at 20 MPa and 135 °C exhibits a large water contact angle of 151.5° and a high adsorption capacity of 48.9 g/g for carbon tetrachloride. Further, it exhibits an excellent reusability for oil recovery in the cyclic adsorption and squeezing process. Therefore, the fabricated high-expansion open-cell foam shows good application prospects in oil spill clean-up fields. [ABSTRACT FROM AUTHOR]

Polymer foam has become an important thermal insulation material due to its outstanding features, while its fabrication is still very challenging by foaming injection molding technology. Herein, we reported the successful fabrication of low-density branched polypropylene (BPP) foam with an expansion ratio of up to 25-fold and fine cellular structures using mold-opening foam injection molding (MOFIM) technology. To improve foaming ability, polytetrafluoroethylene (PTFE) nanofiber reinforced BPP composite was prepared in an in-situ way through a simple twin-screw blending technology. The DSC results show that PTFE nanofibers can promote crystallization of BPP effectively, while the rheological measurements demonstrate that PTFE fibers can improve the viscoelastic behavior of BPP. Furthermore, the MOFIM experimental results show that the cell size is reduced by one order of magnitude while the cell density is increased by four orders of magnitude. Interestingly, PTFE nanofibers endow BPP/PTFE foams a unique cell wall structure with plenty of micro-holes and micro/nano fibrils. Moreover, BPP/PTFE foams show markedly improved thermal insulation and compressive mechanical performance with a thermal conductivity of as low as 32.4 mW·m −1 ·K −1 . Thus, this unique low-density BPP/PTFE foam shows a promising future in high-performance thermal insulation applications, particularly considering the used scalable, versatile, facile and cost-saving processing technology. [ABSTRACT FROM AUTHOR]

Polypropylene (PP) foams with a thermal conductivity of as low as 36.5 mW m − 1 K − 1 are fabricated by high-pressure foam injection molding followed by mold-opening with CO 2 as a blowing agent. Regular PPs are not suitable for foaming due to their poor melt strength. To improve melt strength, the in-situ fibrillated blends of PP/polytetrafluoroethylene (PTFE) are prepared using a regular co-rotating twin-screw extruder. The micromorphology characterized by SEM shows that fibrillated nanoscale PTFE fibers disperse very well in PP matrix. The DSC, dynamic shear rheology, and extensional rheology measurements demonstrate that the in-situ fibrillated PTFE fibers can significantly improve crystallization, visco-elastic performance, and strain-hardening behaviors, respectively. All these factors confirm that PTFE fibers are very effective to improve melt strength and thus foaming ability of PP. The foam injection molding results show that the PP foam's cell size reduces by nearly one order of magnitude while its expansion ratio increases by approximately three times in presence of PTFE fibers. Compared to PP foams, PP/PTFE foams show significantly improved thermal insulation performance due to the increased expansion ratio, as well as unique cell wall structures with micro-holes and/or nano-fibrils. Moreover, it demonstrates that smaller cell size leads to improved compressive strength. [ABSTRACT FROM AUTHOR]

[Display omitted] • An approach to control morphology of PTFE in PP was proposed. • Fibrosis mechanism of PP/PTFE microfibril reinforced composites was elucidated. • Crystallization of PP/PTFE composites with different morphology was studied. • PP/PTFE microfibril reinforced composites showed superior mechanical properties. In-situ fibrillary PTFE was usually developed by melt blending to enhance the melt strength and processability of PP. However, the fibrosis mechanism and the morphology evolution of PTFE during in-situ fibrillation process is still unclear. In this study, both in-situ PP/fibril-PTFE and PP/spherical-PTFE composites were prepared by one-step extrusion process. DSC, XRD, SEM, AFM, as well as O-PTIR analysis were conducted to elucidate the fibrosis mechanism of PTFE. The main reason for the in-situ fibrillation of PTFE-3800 could be ascribed to the chain-extended crystal structure. Furthermore, the acrylate layer of PTFE-3800 can also help PTFE to develop into fibrils. Shear rate was the key parameter in affecting the morphology evolution of PTFE, while processing time could also affect the morphology of PTFE to a certain extent. Interestingly, the SEM analysis showed that reticular crystals are generated in the presence of PTFE fibrils, while spherulites were generated in the presence of PTFE particles. Simultaneous enhancements in the strength, modulus and rigidity were achieved for in-situ fibrillary PTFE reinforced PP composites. [ABSTRACT FROM AUTHOR]