Simultaneous Reinforcing and Toughening of Polyurethane via Grafting on the Surface of Microfibrillated Cellulose

Abstract

In the present work, a series of thermoplastic polyurethane (TPU)/microfibrillated cellulose (MFC) nanocomposites were successfully synthesized via in situ polymerization. TPU was covalently grafted onto the MFC by particular association with the hard segments, as evidenced by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and thermogravimetric analysis. The adequate dispersion and network structure of MFC in the TPU matrix and the strong interfacial interaction through covalent grafting and hydrogen bonding between MFC and TPU resulted in significantly improved mechanical properties and thermostability of the prepared nanocomposites. The tensile strength and elongation-at-break of the nanocomposite containing only 1 wt % MFC were increased by 4.5-fold and 1.8-fold compared with that of neat TPU, respectively. It was also very interesting to find that the glass transition temperature (Tg) of TPU was decreased significantly with the introduction of MFC, indicating potential for low-temperature resistance applications. Most importantly, compared with TPU nanocomposites reinforced with other nanofillers, the TPU/MFC nanocomposites prepared in this work exhibited excellent transparency and higher reinforcing efficiency.

Physical gelation and macromolecular mobility of sustainable polylactide during isothermal crystallization

“…The additional relaxation process with longer relaxation time is ascribed to the interfacial relaxation of suspended spherulites with immobilized chains in RAF. Similar double relaxation time distributions have been reported in branching polymers and polymer composites in which extra confinement effects to chain relaxation rather than entanglements exist as well. The relaxation spectra for crystallizing PLA samples reveal that the presence of spherulites, formation of the spherulite physical network, and interfacial interaction between the spherulites and matrix do not change the mobility of free PLA chains or segments in MAF as compared to neat melt.…”

“…The low relaxation time indicates that the PLA chains can relax rapidly at 165 °C. This rapid relaxation of the molecular chains, due to the sparse entanglement points, features the instinct viscoelastic property of PLA, which is responsible for the failure in foaming and blown filming process . The relaxation spectrum intensity enhances with the increase in crystallinity, while the short relaxation time remains unchanged before gelation and only gains a diminutive increase after gelation.…”

Thermal properties of nanocellulose‐reinforced composites: A review

“…Therefore, chemical treatments such as 2,2,6,6‐tetramethylpiperidine‐1‐oxyl radical (TEMPO) oxidation combined with mechanical and chemical treatments have recently been developed for the production of NFC to minimize the intensity of mechanical treatment . In addition to TEMPO oxidation, enzymatic hydrolysis combined with mechanical shearing and high‐pressure homogenization has also been introduced as a method for the production of NFC . Due to its high effectiveness and eco‐friendly nature, enzymatic hydrolysis has emerged as a new and efficient method for NFC preparation.…”

Waterborne polyurethane nanocomposites based on vegetable oil and microfibrillated cellulose

“…In general, CNs display good interfacial interaction with PUs due to strong hydrogen bonding, and this is also observed in WBPU, allowing for improved dispersion of the particles. Depending on the interfacial interactions and in some cases, on their effect on phase separation, the incorporation of these particles can result in noticeable changes in the glass transition temperature of the composites …”

“…Depending on the interfacial interactions and in some cases, on their effect on phase separation, the incorporation of these particles can result in noticeable changes in the glass transition temperature of the composites. [22][23][24] In this work, a single reaction step was used to prepare the PUs, and thus microphase mixing is to be expected. The use of WBPUs offers the opportunity of using the polymeric suspension as the matrix in the preparation of composites with the reinforcement dispersed in the same medium.…”