Guozhang Wu

Facile fabrication of high-performance polyimide nanocomposites with in situ formed “impurity-free” dispersants

Polyimide/carbon black (PI/CB) nanocomposite films were fabricated via the direct ball-milling method with poly(amic acid) (PAA), the precursor of PI, as an in situ formed impurity-free dispersant. FTIR and Raman spectral results reveal that, besides physical adsorption, chemical grafting of PAA chains onto the CB surface occurs during the ball-milling process. Comparative studies show that introduction of various commercial dispersants improves the dispersion of CB. However, the mixtures exhibit poor reproducibility, unstable electrical properties, and decreased tensile strength; these issues may be attributed to interfacial pollution brought about by differences in the chemical structures of the dispersant and the matrix. The impurity-free dispersant is effective not only in ensuring the uniform dispersion of CB particles but also in enhancing filler-matrix interfacial adhesion. High-molecular weight PAA chains are effective reagents for impurity-free modification and can therefore be used to improve the electrical and mechanical properties of the resultant composite.

Thermoplastics Reinforced with Self-Welded Short Carbon Fibers: Nanoparticle-Promoted Structural Evolution

The large volume of currently available fiber-reinforced polymer composites critically limits the intrinsic versatility of fibers such as high mechanical strength, heat resistance, and excellent thermal/electrical conductivity. We proposed a facile and widely applicable strategy to promote self-organization of randomly dispersed short carbon fibers (CFs) into a three-dimensionally continuous scaffold. The morphological evolution and structural reinforcement of the self-welded CF-polyamide 6 (PA6) scaffold in polystyrene (PS) matrix were investigated, with carbon black (CB) or titanium dioxide (TiO2) nanoparticles (NPs) selectively localized in the PA6 domains. Surprisingly, all of the PA6 droplets once dispersed in the PS matrix can migrate and evenly encapsulate onto the CF surface when 5.8 wt % CB is incorporated, whereas in the TiO2-filled system, the PA6 droplets preferentially segregate at the junction point of CFs to fasten the self-welded CF structure. In addition, a remarkable increase in the interfacial adhesive work between PA6 and CF was observed only when TiO2 is added, and a loading of even less than 0.8 wt % can effectively abruptly strengthen the self-welded CF scaffold. We clarified that the structural evolution is promoted by the nature of self-agglomeration of NPs. CB is highly capable of self-networking in the PA6 domain, resulting in high encapsulation of PA6, although the capillary force for preferential segregation of PA6 at the junction point of CFs is reduced. By contrast, the TiO2 particles tend to form compact aggregates. Such an agglomeration pattern, together with enhanced interfacial affinity, must contribute to a strong capillary force for the preferential segregation of PA6.

ACM/Hindered Phenol Hybrids: A High Damping Material with Constrained-Layer Structure for Dynamic Mechanical Analysis and Simulation

Due to the strong hydrogen bonding interactions, hindered phenol 3,9-bis[1,1-dimethyl-2{ I² -(3-tert-butyl-4-hydroxy-5- methylphenyl)propionyloxy}ethyl]- 2,4,8,10-tetraoxaspiro[5,5]-undecane (AO-80) demonstrated a remarkable damping effect when it was hybridized with acrylic rubber (ACM). The loss factor of ACM could be largely increased and the position of loss peak could be regulated by controlling the content of the hindered phenol. This kind of high damping hybrids can be used as the laminated layer of sandwich beam for vibration control. Instead of the traditional method ASTM E756-98, a new method based on dynamic mechanical analyzer (DMA) was developed to characterize the damping behaviors of ACM/AO-80 laminated beam. Testing results demonstrated that DMA can reflect the variation of damping behaviors of sandwich beams with various factors effectively, and a theoretical model established here was used to explain the damping behaviors. Based on this model, by means of adjusting the content of AO-80, a high damping ability for the sandwich beam could be obtained at appointed temperature during a wide frequency range.