Research Article pubs.acs.org/journal/ascecg
Morphology Controlled PA11 Bio-Alloys with Excellent Impact Strength Jumpei Kawada,*,† Masayuki Kitou,‡ Makoto Mouri,† Takuya Mitsuoka,† Tohru Araki,†,§ Chi-Han Lee,‡ Toshiyuki Ario,‡ Osamu Kitou,‡ and Arimitsu Usuki† †
Toyota Central R&D Laboratories, Inc., 41-1 Yokomichi, Nagakute, Aichi 480-1192, Japan Toyota Boshoku Corporation, 88 Kanayama, Kamekubi, Toyota, Aichi 470-0395, Japan
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S Supporting Information *
ABSTRACT: Polyamide 11 (PA11), 100% biobased plastics, and polypropylene (PP) were mixed with a reactive compatibilizer, maleic anhydride modified ethylene−butene rubber copolymer (m-EBR), by a twin-screw extruder, and mechanical properties and morphology of resulting injection molded PP/PA11 bio-alloys were investigated by flexural tests, Charpy notched impact tests, 13C NMR, differential scanning calorimetry, X-ray diffraction, field-emission scanning electron microscopy, scanning transmission X-ray microscopy, transmission electron microscopy, and atomic force microscopy. We found that it possible to control the morphology of bioalloys. When the morphology of the bioalloy showed “salami” structure, it achieved superior impact-resistance with high flexural modulus, which are generally not accomplished at the same time. The mechanical properties of the bioalloy were better than those of PP which was used in the car industry. When the bioalloy had a “nano-salami” structure, the impact strength was surprisingly improved. The morphology observations revealed that the reactive compatibilizers were in the interphase between a matrix and a dispersed phase and were in a dispersed subdomain in the dispersed phase. The compatibilizers played a key role in improving impact strength. The bioally will be expected to apply in the car industry and other areas. KEYWORDS: Biobased plastics, Renewable materials, Green chemistry, Polymer alloy, Morphology control, Salami structure, Nanosalami structure, Morphology characterization
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INTRODUCTION
Synthetic polymers have a history comparing with biobased plastics, and polymer blends and alloys have been widely studied with the aim of improving the physical properties of polymers,10−13 such as “poly(phenylene ether)/poly(styrene) (PPE/PS)”,14,15 “high impact poly(styrene) (HIPS)”,16,17 and so on, which could add different characteristics to the original polymer. Numerous research works on PP/polyamide blends18−21 and on improving impact toughness of PP by an alloy’s technique22−29 have been reported, the latter, nowadays, led to understanding the polymer toughening mechanism including crazing, cavitation, and shear yielding by polymer research pioneers.11,30−40 Nevertheless, there are few biobased plastics in the car and electric device industries. Recently, biobased alloys were studied as green materials41−43 since the processing method, so-called “melt blending”, was organic solvent-free. This study focused on improving mechanical properties of a biobased plastic alloy with PP since
Biobased plastics, such as those derived from plant-based resources, are one of the most promising materials, and the development of nonpetrochemical sources is strongly required for a sustainable society or circular environment since fossil resources are limited.1−3 Lots of multinationals, not only polymer suppliers but also plastic users, are focused on biobased plastics or renewable resources. During the first decade in this century, the science and technology of biobased polymers underwent a tremendous rise in significance, such as that for poly(lactic acid) (PLA) 4,5 and poly(hydroxy alkanoate)s (PHAs)3,6−8 by biotechnological fermentation involving recombinant DNA technology. There are some applicable and advantageous biobased plastics. PLA and PHAs are already on the market and used as commodity items such as disposable cups, trays, plastic bags, and so on.3,6,9 However, biobased polymers have several drawbacks such as inferior mechanical properties, susceptibility to hydrolyze, and uncompetitive pricing in comparison to synthetic polymers, such as polyethylene and polypropylene (PP). © XXXX American Chemical Society
Received: December 2, 2015 Revised: February 24, 2016
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DOI: 10.1021/acssuschemeng.5b01615 ACS Sustainable Chem. Eng. XXXX, XXX, XXX−XXX
Research Article
ACS Sustainable Chemistry & Engineering Table 1. Sample Compositionsa
biobased plastics were insufficient by themselves and PP was the most abundant polymer in industrial application. Polyamide 11 (PA11), used in this study, is a completely biobased plastic made from the castor bean plant that can absorb CO2 during the cultivation; hence, PA11 has a benefit to reduce the amount of carbon dioxide emissions. In fact, the total energy consumption to produce PA11 is less than the ones to produce polyamide 6, polyamide 66, and polyamide 12. Castor beans are not edible since they contain highly toxic ricin and are cultivated solely for the extraction of castor oil, which can be processed to produce 11-aminoundecanoic acid, the PA11 monomer, via methyl ricinoleate. PA11 has several advantages, including, good mechanical properties and high chemical resistance. However, PA11 hardly replaces the synthetic plastics in terms of physical and economic reasons. In the case of PP, although it is possible to improve its impact resistance, it was difficult to achieve both flexural modulus and impact strength at the same time. Accordingly, a biobased alloy with PA11 and PP was a good candidate as a biobased plastic with components to compensate for each other. The PP/PA11 bioalloy was studied, and the research revealed that PA11 was not compatible with PP and the alloy did not have good mechanical properties.44,45 Consequently, our incentive for creating a competitive bioalloy is to improve the mechanical properties of PP/PA11 biobased plastics by morphology control in injection molding with a short cycle time. It is challenging to apply biobased plastics to the manufacturing of more complex items, such as an automobile cabins that require high modulus and high impact strength together with short molding time. There are still many frontiers to explore with regard to biobased polymers, and therefore, it is important to perform additional research in this field.
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proportion (wt %) compatibilizers sample
PP
PA11
EBR
m-EBR
1 2 3b 4 5 6 7 8 9
100 0 72 65 65 90 90 70 55
0 100 28 25 25 0 0 25 25
0 0 0 10 0 10 0 0 0
0 0 0 0 10 0 10 5 20
a
Injection molded test specimens of compatibilizers could not be obtained due to the low melting point of the polymer (
