Abstract
Herein, lightweight nanocomposite foams with expansion ratios ranging from 2–10-fold were fabricated using an isotactic polypropylene (iPP) matrix and cellulose nanofiber (CNF) as the reinforcing agent via core-back foam injection molding (FIM). Both the native and modified CNFs, including the different degrees of substitution (DS) of 0.2 and 0.4, were melt-prepared and used for producing the polypropylene (PP)/CNF composites. Foaming results revealed that the addition of CNF greatly improved the foamability of PP, reaching 2–3 orders of magnitude increases in cell density, in comparison to those of the neat iPP foams. Moreover, tensile test results showed that the incorporation of CNF increased the tensile modulus and yield stress of both solid and 2-fold foamed PP, and a greater reinforcing effect was achieved in composites containing modified CNF. In the compression test, PP/CNF composite foams prepared with a DS of 0.4 exhibited dramatic improvements in mechanical performance for 10-fold foams, in comparison to iPP, with increases in the elastic modulus and collapse stress of PP foams of 486% and 468%, respectively. These results demonstrate that CNF is extraordinarily helpful in enhancing the foamability of PP and reinforcing PP foams, which has importance for the development of lightweight polymer composite foams containing a natural nanofiber.
Highlights
Polymeric foams have aroused great interest in a variety of fields, including construction, transportation, thermal and sound insulation, together with tissue engineering [1,2,3]
We recently proposed the use of cellulose nanofiber (CNF), which originates from the most abundant biopolymer on earth, as a cell nucleating agent to improve the foamability of isotactic polypropylene (iPP), and for the purpose of reinforcing the mechanical properties of PP foams [29,30,31]
It was observed that the injection-molded foam a hierarchical morphology and could be intodivided the solid layers and foamed exhibited a hierarchical morphology anddivided could be into the solid layers core foamed layer
Summary
Polymeric foams have aroused great interest in a variety of fields, including construction, transportation, thermal and sound insulation, together with tissue engineering [1,2,3]. Isotactic polypropylene (iPP) is a widely-used commercial polymeric material and has good overall performance, including easy processing, excellent chemical resistance, high thermal stability, and good mechanical properties [14]. It demonstrates greater strength than other polyolefins such as PE, as well as better impact strength with respect to PS. The incorporation of nanoparticles is a simple and viable approach, which improves the melt strength of iPP and promotes its crystallization property This would notably improve the cellular structures of iPP and enhance its foaming ability. The effect of native and modified CNF on the cellular structures, tensile properties and compressive properties of PP foams were studied
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