This study systematically investigates the polymer–carbon nanotube (CNT) interaction when the interphase is tailored. Maleic anhydride‐grafted‐polypropylene (MA‐g‐PP) or polypropylene (PP) was noncovalently coated onto acid functionalized multiwall nanotube (f‐MWNT) through solution mixing. These coated f‐MWNTs were melt microcompounded with neat PP to form PP/f‐MWNT nanocomposites. The effects of functional groups and the thin layer of solution processed polymers, namely, MA‐g‐PP or PP, at the PP/f‐MWNT interface on crystallization and on melting behavior of matrix PP were investigated. The results were compared with a pristine MWNT (p‐MWNT) incorporated system. It was shown that PP coated CNTs can serve as a strong nucleating agent for templated polymer crystal growth. Unlike other PP nanocomposites in the literature, a relatively high shift of 7°C in melting peak maximum (Tp), along with a sharp melt endotherm was achieved with the addition of 0.3 wt% f‐MWNT via PP/f‐MWNT master batch. This indicates refinement of matrix PP crystalline region due to the tailored f‐MWNT surface chemistry. With a designed self‐seeding and templated crystal growth approach, columnar crystalline interphases were found surrounding MWNT which melted at 10.5°C higher temperature than neat PP crystallized without undergoing the same heat treatment protocol. POLYM. ENG. SCI., 59:1570–1584 2019. © 2019 Society of Plastics Engineers
Maleic anhydride grafted polypropylene (MA-g-PP) or polypropylene (PP) was noncovalently coated onto acid functionalized multiwall carbon nanotube (f-MWNT) through solution mixing. These coated f-MWNTs and pristine MWNT (p-MWNT) were melt microcompounded with neat PP to form PP/f-MWNT and PP/p-MWNT nanocomposites at 0.1-1 wt% MWNT concentration. Complex viscosity and tan δ (ratio of loss modulus to storage modulus) behavior of these systems were studied using dynamic frequency sweep test, while relaxation time, activation energy, and melt homogeneity were also calculated and compared. Among the three types of samples, PP/f-MWNT masterbatch-based nanocomposite demonstrated not only the presence of interphase but also good processability. As a consequence, increase of both the crystallization rate in the presence of shear and the melt elasticity during annealing were found only in the masterbatchbased samples but not in the PP/p-MWNT. The mechanism of such increased melt elasticity was attributed to the formation of the space-spanning network, which is consistent with the Cole-Cole plot showing similar behavior to the branched polymers in the literature. This has implications in polymer processing due to suggested changes in the balance between melt strength and polymer flow. Nanocomposite rheological behavior has also been correlated with the mechanical properties.
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