ABSTRACT:The rectorite (REC), a form of layered silicate, was facilely intercalated and even exfoliated in soy protein isolate (SPI) matrix. Furthermore, the reinforced biodegradable nanocomposite sheets were produced, in which the exfoliated REC lamellae plays a key role. After solution-mixing, XRD patterns showed that the REC lamellae were intercalated and even completely exfoliated for 4 wt % REC added, but the expanded gallery gradually became narrower with increasing REC content. FT-IR also verified the molecular-level associations between SPI molecules and REC lamellae by vibration variances of hydrogen bonding. The compression-molding further promoted intercalation and exfoliation, namely the 8 wt % REC can also be almost dispersed as exfoliated lamellae, while the interlayer of RECs also further separated for nanocomposites with higher REC content. TEM images visualized the transfer from exfoliation to intercalation and the decrease of interlayer distance with increasing REC content. The thicker and longer exfoliated REC lamellae resulted in high load and easy-to-yield of material. The maximum strength of nanocomposite sheets occurred at the addition of 12 wt % REC. Thereafter, the SPI chain can move more easily because of weak interaction between free negative-charge rich domain of SPI and REC surface in gallery, which did not favor enhancing mechanical performance.
ABSTRACT:The modified waterborne polyurethane (WPU) with enhanced mechanical properties has been prepared after introducing lignosulfonate calcium (LS). Meanwhile, the LS was associated with WPU component by chemical grafting and/or physical attraction and hence produced a star-like network with LS and its supramolecular complexes as center. Especially, when the LS content was 1.5 wt %, the strength and elongation of WPU/LS blends (WLS) simultaneously increased. At this time, the center of network was dominated by the single molecules of spherical LS. Thereafter, with the increase of LS content, the strength of WLS blends increased unceasingly up to 6.0-7.5 wt % of LS loading while the elongation gradually decreased. Because the LS tend to aggregate as supramolecular complexes spontaneously, the center of network was gradually replaced by the LS supramolecular complexes. The structural changes of WLS blends were characterized by FTIR, DSC, and DMA. The results suggested that the LS component was mostly fused with hard-segments of WPU component and hence induced the formation of physical interaction, importantly for hydrogen bonding, depending on the compulsive association of chemical grafting and the impulse of similar hydrophilicity between the hard-segment and LS.
ABSTRACT:We have reported that a star-like network structure with lignin as center in polyurethane resulted in the simultaneous enhancement in mechanical strength and elongation. In this study, we aimed to enhance the mechanical properties of waterborne polyurethane by adding nitro-lignin (NL) to form analogical star-like network. It was found that the resultant material has optimal mechanical performances when the NL content is 3.0 wt %, i.e., its apparent mechanical strength and elongation increased by about 80% at one time. Especially, its real mechanical strength reaches 71.3 MPa at this time, which is 3.6-fold over that of neat waterborne polyurethane material. The simultaneous enhancements in strength and elongation are attributed to the forming of star-like network in the composites. The stiffness of lignin improved the mechanical strength, while the entangling and crosslinking in polyurethane component increased the elongation. However, higher NL loading and lower grafting level induced the forming of supramolecular NL aggregates, and hence greatly inhibited star-like network, resulting in lower mechanical strength and elongation. However, the Young's modulus of the material is enhanced with an increase of rigid supramolecular aggregates.
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