Shuyan Yang

New insight into PEO modified inner surface of HNTs and its nano-confinement within nanotube

In this study, we demonstrate the use of poly (ethylene oxide) (PEO) for in-situ modification of the inner surface of halloysite nanotubes (HNTs) with water molecules as the hydrogen bond forming medium, as well as the nano-confinement of PEO molecular chains within the nanotube. Before testing, the Soxhlet experiment of PEO/HNTs powder is applied in order to remove the physical adsorption of PEO molecules onto the outmost surface of HNTs. The crystal temperature of PEO changes sharply from 36.9xa0°C of neat PEO to −25xa0°C of PEO in the PEO/HNTs powder and the decomposed temperature of PEO in the PEO/HNTs powder is about 13.1xa0°C higher than that of neat PEO, which is mainly owing to the nano-confinement effect of PEO within the HNTs with a diameter of about 10xa0nm. From thermo-gravimetric (TG) analysis, about 7.71xa0% by weight of PEO has been chemically bonded to HNTs. The hydrogen bonds among PEO, HNTs, and water molecules are evidenced by FTIR and XPS performances. Meanwhile, the binding energy of Al2p in the innermost surface of HNTs shifts from 74.7xa0eV in the neat HNTs to 74.5xa0eV in the PEO/HNTs powder, while that of Si2p on the outmost surface of HNTs keeps almost constant, indicating that the hydrogen bonds only exists inner the nanotube and PEO molecular chains have been trapped in nano-scale within HNTs, which is in accordance with the DSC and TG observation.

Effect of molecular weight on conformational changes of PEO: an infrared spectroscopic analysis

Effect of molecular weight on conformation, helix structure (H structure) and trans planar structure (T structure), of Poly(ethylene oxide) (PEO) has been investigated in detail by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and differential scanning calorimeter. Two main diffraction peaks at about 2θxa0=xa019° and 23° are discovered, and XRD patterns reveal that the unit cell of crystalline PEO belongs to the monoclinic lattice. The crystallinity decreases from 93.82 to 59.62xa0%, and the deviation of crystalline temperature of PEO-0.5 is larger than those of the other three under four reheated cycles. From FTIR results, a red shift about 11xa0cm−1 is observed in the stretching vibration of –C–O–C– with increasing molecular weight, suggesting the presence of chain–chain interactions to restrict the stretching vibration of -C–O–C– in main chains. Meanwhile, the bending region of –C–C–O– at about 533xa0cm−1 sensitive to tension shifts to lower wavenumber, and a new peak at about 510xa0cm−1 emerges with increasing molecular weight, which is the indicator of internal tension/strain and orientation. Furthermore, the peak intensity ratios of H structure decrease with increasing molecular weight. In contrast, T structure increases dramatically. Consequently, with respect to molecular weight, the possible interactions, entanglements and tie molecules, of PEO molecular chains to explain the difference between H and T structure is proposed, which is in agreement with the experimental observations quite well.

Study on the compatibility and crystalline morphology of NBR/PEO binary blends

Compatibility property, as well as crystalline morphology, of NBR/PEO blends has been investigated by Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), X-ray diffraction (XRD), and polarized optical microscopy (POM) thoroughly. There is no apparent shift of nitrile or ether groups in the FTIR spectra of NBR/PEO blends. Based on the calculations from glass transition temperature, the maximum volume fraction of PEO dissolved in NBR phase is about 6.41xa0% in blend with 5xa0wt% PEO content (PEO-5), indicating a weak intermolecular interaction in the NBR/PEO blends. From the characteristic absorption bands in the FTIR spectra, XRD and POM graphs, the crystallinity ratio of NBR/PEO blends decreases as the NBR content increases, which is further proved by DSC measurement that the crystallinity ratio and crystal melting temperature of pure PEO are 82.6xa0%, 69.9xa0°C, and that of PEO-5 are 16.9xa0%, 59.5xa0°C. This illuminates that the weak intermolecular interaction will affect the crystallinity ratio and crystal melting temperature of the NBR/PEO blends.

Thermo-oxidative aging resistance and mechanism of a macromolecular hindered phenol antioxidant for natural rubber:

Macromolecular antioxidant due to its low physical loss, high thermal stability, and good compatibility has been considered to be a promising candidate to inhibit polymer aging. In this study, thermo-oxidative aging resistance and antioxidative mechanism of a macromolecular hindered phenol antioxidant, namely, polyhydroxylated polybutadiene containing thioether binding 2, 2′-thiobis (4-methyl-6-tert-butylphenol) (PHPBT-b-TPH) for natural rubber (NR) vulcanizate was studied in detail by oxidation induction time and accelerated thermal aging tests. The results showed that the antioxidative efficiency of PHPBT-b-TPH was very high. When the amount of PHPBT-b-TPH was only 1 phr, the NR vulcanizate could exhibit excellent thermo-oxidative aging resistance, obviously higher than that of NR vulcanizate with low-molecular-weight antioxidant TPH. After aged at 100°C for 168 h, the retentions of tensile strength and elongation at break of NR vulcanizate with PHPBT-b-TPH were 43.6% and 58.6%, respectively. However, those of NR vulcanizate with TPH were 35.6% and 54.5%. In addition, it was found that both thioether and urethane groups in PHPBT-b-TPH had antioxidative ability and had synergistic effect with hindered phenol. Through our findings, new strategy to design and synthesize the macromolecular antioxidant with multi-antioxidative groups for rubber materials and other polymer materials could be developed.