Shuihan Zhu

Interfacial characterization of compatibilized PVC/SBR blends by solid-state NMR and TEM

At ambient temperature, n.m.r. relaxation measurements of poly(vinyl chloride) (PVC)/styrene-butadiene rubber (SBR) blends, compatibilized by acrylonitrile-butadiene rubber (NBR), reveal two rotating-frame spin-lattice relaxation (TH1ρ) components for the methylene protons of rubbers (SBR+NBR). The short TH1ρ component may be interpreted as the contribution of the rubbers in the PVC/rubbers interface. The long TH1ρ component is attributed to the rubbers isolated from PVC. As sulfur concentration increases, the long TH1ρ decreases due to increasing restraints imposed on the rubber chains by crosslinking, but the fraction of rubbers with short TH1ρ increases, indicating that the rubber fraction at the interface increases. The TEM micrographs of stained and unstained samples show identical morphological information. For the unstained samples, the PVC and SBR regions appear as dark and light areas, respectively. The dehydrochlorination of PVC in the blends under an electron beam reduces the contrast between the dark and light areas, producing an inversion of contrast. However, when the blends are compatibilized by NBR, the deterioration rate of the contrast slows down significantly. As the dark PVC regions become lighter, dark boundaries are visible between the PVC and SBR phases. In particular, the dark boundaries remain visible upon extended exposures of electron beam irradiation. This is explained by the stabilizing effect of the higher rubber concentration in the interfacial regions between PVC and SBR. The TEM micrographs of the unstained samples for this system provide a unique method to show the segregation of rubbers at the interfacial regions between PVC and SBR for the compatibilized blends.

Miscibility and mechanical properties of sulfonated polystyrene–polyurethane blends

A sulfonated polystyrene (SPS) and a polyurethane containing a tertiary amine group (NPU) were blended in solution. The effect of blend composition was studied in the blend of SPS with 9.83 mol % of sulfonation (SPS-9.83) and NPU with 33 mol % of MDEA (NPU-33). As the SPS concentration increases, a significant improvement of miscibility is observed. The tensile strength of the blends is greater than either pure NPU or SPS. A maximum strength and a maximum density occur at 50 wt % SPS. The stress–strain curve shows a well-defined yield when the SPS concentration in the blend is 30 or 50 wt %. The yield is more dramatic in the blend with 50 wt % SPS than that of 30 wt % SPS. At a lower SPS concentration, the blend behaves like a rubber, while a higher SPS concentration in the blend results in a brittle failure before yield. An increase in the sulfonation level of SPS in the SPS–NPU-33 (30/70) blends leads to an improved miscibility. A significant enhancement of tensile strength is observed as the sulfonation increases. A clear yield point on the stress–strain curves occurs when the sulfonation of SPS in the blend is 4.79 mol % or greater. Increasing the MDEA content of NPU up to 8.3 mol % can lead to an enhancement of tensile strength. A further increase in the MDEA content has little influence on the tensile strength, but a clear yield on the stress–strain curve occurs.