Jihai Zhang

Hydrogen bond breaking of TPU upon heating: understanding from the viewpoints of molecular movements and enthalpy

Hydrogen bond breaking of TPU based on 4,4′-methylenediphenyl diisocyanate (MDI)/1,4-butanediol (BDO) upon heating was studied and elucidated from molecular movements and enthalpy. Two temperature regions of hydrogen bond breaking, region I (80–133 °C) and region II (133–169 °C), were determined via the combination of PCMW2D correlation with FTIR and DSC. The method of calculating the enthalpy of the hydrogen bond breaking was established via Vant Hoff plots. We also proposed a method of calculating the relative content of different hydrogen bonds. In region I, ΔHh = 58.8 ± 0.5 kJ mol−1 for N–H and CO, and ΔHh = 37.2 ± 0.4 kJ mol−1 for N–H and C–O–C groups. The content of hydrogen bonds generated by N–H and CO is 88.4%, and that of N–H and C–O–C is 11.6%. In region II, ΔHh = 65.0 ± 1.1 kJ mol−1 for N–H and CO, and ΔHh = 73.0 ± 3.9 kJ mol−1 for N–H and C–O–C groups. The contents of these two hydrogen bonds are 71.2% and 28.8%, respectively. The surprisingly high value of ΔHh = 73.0 ± 3.9 kJ mol−1 for N–H and C–O–C in region II is actually due to the stabilizing effect of the repulsion energy on hydrogen bonds at the interface. 2D correlation analysis was used to investigate the sequential order of the groups movement involved in hydrogen bond breaking. In region I, the breaking of a small amount of hydrogen bonds between N–H and C–O–C at the interface first occurs, and then the breaking of irregular hydrogen bonds between N–H and CO in the TPU hard blocks dominates, resulting in the melting of the imperfect crystallinity in the hard blocks. In region II, the breaking of regular hydrogen bonds between N–H and CO in the perfect crystalline of the hard blocks first occurs, and is then followed by hydrogen bond breaking of N–H and C–O–C enhanced by the repulsion energy at the interface, leading to the order–disorder transition (ODT) of TPU.

A Simple Way to Achieve Legible and Local Controllable Patterning for Polymers Based on a Near-Infrared Pulsed Laser

This study developed a simple way to achieve legible and local controllable patterning for polymers based on a near-infrared (NIR) pulsed laser. The polycarbonate-coated nano antimony-doped tin oxide (nano ATO) was designed as a core-shell structure that was tailored to be responsive to a 1064 nm NIR laser. The globular morphology of polycarbonate-coated nano ATO with a diameter of around 2-3 μm was observed by scanning electron microscopy and transmission electron microscopy. This core-shell structure combined the excellent photothermal conversion efficiency of nano ATO and the high char (carbon) residue of polycarbonate. The X-ray photoelectron spectroscopy results of a polymer-patterning plate after laser irradiation demonstrated that, through local controlled photochromism, the well-defined legible patterns can be fabricated on the polymer surfaces contribute to the synergistic effect consisting of polycarbonate carbonization and nano ATO photothermal conversion. Furthermore, polymers doped with a minimal content of polycarbonate-coated nano ATO can achieve a remarkable patterning effect. This novel laser-patterning approach will have wide promising applications in the field of polymer NIR pulsed-laser patterning.

New understanding on the reaction pathways of the polyacrylonitrile copolymer fiber pre-oxidation: online tracking by two-dimensional correlation FTIR spectroscopy

Polyacrylonitrile (PAN) copolymer fiber pre-oxidation has important influence on the final properties of carbon fibers. Understanding and tracking the reaction pathways of this pre-oxidation has great significance in guaranteeing the quality of the resulting carbon fibers. In this study, in situ FTIR spectroscopy in combination with scaling moving-window two-dimensional correlation spectroscopy (scaling-MW2D) and 2D correlation analysis was used to study the reaction pathways. In addition, DSC and 13C solid-state NMR were used to assist in the determination and verification of chemical structures. Scaling-MW2D revealed that pre-oxidation consists of an initial process (A, 69–223 °C) and a main process (B, 223–309 °C). From the sequential order of 2D correlation analysis, more detailed pathways were obtained. The induced reaction of comonomer units took place in process A (69–223 °C). In process B (223–309 °C), the initial cyclic structures were first generated from the induced structure formed in process A. Then, these initial cyclic structures underwent a series of oxidations and subsequent isomerization. Subsequently, a large number of AN units were immediately involved in the main cyclization reaction, and some β-amino nitriles were produced. One new understanding obtained is that the initial cyclic structures after oxidation and isomerization are the real induced “nucleus” of the main cyclization reaction, and therefore oxygen in the air plays a key role in the main cyclization of PAN. The final step is the dehydrogenation reaction on the polycyclic structures at a high temperature.

Polypropylene elastomer composite for the all-vanadium redox flow battery: current collector materials

In this study, a carbon-based polypropylene thermoplastic elastomer (PP-elastomer) composite for current collectors of an all-vanadium redox flow battery (VRB) was successfully prepared. The volume resistivity of the PP-elastomer composite was 0.47 Ω cm. Its tensile strength and elongation at break were 6.6 MPa and 250%, respectively. In addition, the good flow property in processing means this composite has potential for the mass industrial production of current collectors. The single cell and the cell stack of a VRB equipped with the composite current collectors were assembled for battery tests, including cyclic voltammetry, long-term performance, long-term stability, and oxidation corrosion. To evaluate the stability and the performance of the cell stack under a long-term operating condition, tests with more than 2300 charge–discharge cycles were carried out. The coulombic efficiency (CE) and voltage efficiency (VE) of the cell stack were maintained at around 93% and 80% during 2300 charge–discharge cycles, and energy efficiency (EE) held at around 75%. The results proved that a VRB equipped with composite current collectors has good stability and performance. Furthermore, long-term corrosion tests indicated that the PP-elastomer composite could endure the strong corrosion of pentavalent vanadium and concentrated sulfuric acid. The composite materials prepared in this study are more suitable than other materials for producing the current collectors. The corrosion resistance of composite materials is much better than that of the graphite, and the mechanism is also discussed.

Selective Metallization Induced by Laser Activation: Fabricating Metallized Patterns on Polymer via Metal Oxide Composite

Recently, metallization on polymer substrates has been given more attention due to its outstanding properties of both plastics and metals. In this study, the metal oxide composite of copper-chromium oxide (CuO·Cr2O3) was incorporated into the polymer matrix to design a good laser direct structuring (LDS) material, and the well-defined copper pattern (thickness =10 μm) was successfully fabricated through selective metallization based on 1064 nm near-infrared pulsed laser activation and electroless copper plating. We also prepared polymer composites incorporated with CuO and Cr2O3; however, these two polymer composites both had very poor capacity of selective metallization, which has no practical value for LDS technology. In our work, the key reasons causing the above results were systematically studied and elucidated using XPS, UV-vis-IR, optical microscopy, SEM, contact angle, ATR FTIR, and so on. The results showed that 54.0% Cu2+ in the polymer composite of CuO·Cr2O3 (the amount =5 wt %) is reduced to Cu0 (elemental copper) after laser activation (irradiation); however, this value is only 26.8% for the polymer composite of CuO (the amount =5 wt %). It was confirmed that to achieve a successful selective metallization after laser activation, not only was the new formed Cu0 (the catalytic seeds) the crucial factor, but the number of generated Cu0 catalytic seeds was also important. These two factors codetermined the final results of the selective metallization. The CuO·Cr2O3 is very suitable for applications of fabricating metallic patterns (e.g., metal decoration, circuit) on the inherent pure black or bright black polymer materials via LDS technology, which has a prospect of large-scale industrial applications.

Local Controllable Laser Patterning of Polymers Induced by Graphene Material

Graphene has been successfully applied to the field of polymer laser patterning. As an efficient 1064 nm near-infrared (NIR) pulsed laser absorber, only 0.005 wt % (50 ppm) of graphene prepared by mechanical exfoliation endowed polymer materials with very good NIR pulsed laser patterning. Optical microscopy observed that the generated black patterns came from the local discoloration of the polymer surface subjected to the laser irradiation, and the depth of the discolored layer was determined to be within 221-348 μm. The X-ray photoelectron spectroscopy confirmed that the polymer surface discoloration was contributed by the local carbonization of polymers caused by graphene due to its high photothermal conversion capacity. Raman depth imaging successfully detected that the generated carbon in the discolored layer was composed of amorphous carbon and complex sp/sp2-carbon compounds containing C≡C or conjugated C═C/C≡C structures. This study also provides a simple guideline to fabricate laser-patterning polymer materials based on graphene. We believe that graphene has broad application prospects in the field of polymer laser patterning. Importantly, this work opens up a valuable, feasible direction for the practical application of this new carbon material.