Hua-Dong Huang

Cellulose composite aerogel for highly efficient electromagnetic interference shielding

An ultra-light and highly conductive cellulose composite aerogel was fabricated by a simple, efficient and environmentally benign strategy. The scaffold structure was well designed from nanofibrillar networks to nanosheet networks by controlling the concentration of cellulose in the sodium hydroxide/urea solution. The obtained conductive aerogel was first reported as an electromagnetic interference shielding material; it exhibits an electromagnetic interference (EMI) shielding effectiveness of ∼20.8 dB and a corresponding specific EMI shielding effectiveness as high as ∼219 dB cm3 g−1 with microwave absorption as the dominant EMI shielding mechanism in the microwave frequency range of 8.2–12.4 GHz at a density of as low as 0.095 g cm−3. This result demonstrates that this type of green conductive aerogel has the potential to be used as lightweight shielding material against electromagnetic radiation, especially for aircraft and spacecraft applications.

Ultra-low gas permeability and efficient reinforcement of cellulose nanocomposite films by well-aligned graphene oxide nanosheets

Cellulose is often considered to be an ideal candidate for biodegradable packaging films, but its main weakness is its poor gas barrier performance. We used a simple, efficient, low cost, recyclable, non-toxic and environmentally friendly processing solvent (an aqueous solution of NaOH/urea) to fabricate graphene oxide nanosheet (GONS)/regenerated cellulose (RC) nanocomposite films with an ultra-low O2 permeability and high mechanical performance. Transmission electron microscopy and two-dimensional wide-angle X-ray diffraction measurements showed that the GONSs were fully exfoliated, homogeneously dispersed and highly aligned along the surface of the cellulose nanocomposite films. Rheological and Fourier transform infrared spectroscopy measurements demonstrated the existence of strong H-bonding interactions between the GONSs and the cellulose matrix. A significant improvement in the barrier properties of the regenerated cellulose nanocomposite films was achieved. The O2 permeability coefficient was reduced by about 1000 times relative to the pure regenerated cellulose film at a low GONS loading of 1.64 vol%. The tensile strength and Youngs modulus of the regenerated cellulose nanocomposite films were enhanced by about 67 and 68%, respectively, compared with the RC film. The theoretical simulation results of the Cussler and Halpin–Tsai models consistently confirmed that the GONSs tended to align parallel to the film surface; this was probably induced by gravitational forces and further consolidated by hot pressing. The work presented here indicates that this simple and environmentally friendly method is an effective strategy to design highly aligned nanofillers in polymer nanocomposite films. The cellulose nanocomposite films obtained have excellent potential as packaging materials for protecting perishable goods susceptible to O2 degradation.

Poly(L-lactic acid) crystallization in a confined space containing graphene oxide nanosheets.

The semicrystalline polymer incorporated with nanofillers frequently exhibits complicated crystallization behavior, which is probably attributed to the nanofiller-constructed complex crystalline circumstance, especially a confined space. In the present work, in order to have a thorough understanding of biodegradable poly(L-lactic acid) (PLLA) crystallization behavior on the dependence of graphene oxide nanosheet (GONS) loadings, in particular the relatively high GONS loading, a set of GONS/PLLA nanocomposites with different GONS loadings ranging from 0 to 4.0 wt % were investigated in terms of isothermal crystallization behavior by differential scanning calorimetry and time-resolved Fourier-transform infrared spectroscopy techniques. The results indicated that GONSs not only served as heterogeneous nucleating agents for PLLA crystallization but also restricted the mobility and diffusion of PLLA chains. At low GONS concentrations of 0.25 and 0.5 wt %, GONSs acted as a temple for PLLA chains to land on due to extremely high specific surface area, thus promoting the conformational ordering and reducing the nucleating barrier. The nucleation effect of GONSs was dominant to achieve accelerated overall crystallization kinetics. As the GONS concentration rose up to 1.0 wt %, the GONS network was formed in the PLLA matrix, which was verified by solid-like rheological behavior at low frequencies in rheological measurement. The nanofiller network significantly constrained the mobility and diffusion of PLLA chains and offset the nucleation effect of GONSs, giving rise to a turning point in crystallization rate from promotion to restriction. Furthermore, a severely confined space was constructed by the more crowded and denser GONS networks at a higher GONS concentration of 4.0 wt %, compelling PLLA lamellae to grow in a two-dimensional mode. The unusual crystallization behavior of PLLA from promotion to restriction was also understood by the four-region model, in which the semiquantitative description of crystalline circumstance was provided. These results pave an effective way to further reveal the crystallization behavior of polymer at a relatively high nanofiller loading.

Super-Robust Polylactide Barrier Films by Building Densely Oriented Lamellae Incorporated with Ductile in Situ Nanofibrils of Poly(butylene adipate-co-terephthalate)

Remarkable combination of excellent gas barrier performance, high strength, and toughness was realized in polylactide (PLA) composite films by constructing the supernetworks of oriented and pyknotic crystals with the assistance of ductile in situ nanofibrils of poly(butylene adipate-co-terephthalate) (PBAT). On the basis that the permeation of gas molecules through polymer materials with anisotropic structure would be more frustrated, we believe that oriented crystalline textures cooperating with inerratic amorphism can be favorable for the enhancement of gas barrier property. By taking full advantage of intensively elongational flow field, the dispersed phase of PBAT in situ forms into nanofibrils, and simultaneously sufficient row-nuclei for PLA are induced. After appropriate thermal treatment with the acceleration effect of PBAT on PLA crystallization, oriented lamellae of PLA tend to be more perfect in a preferential direction and constitute into a kind of network interconnecting with each other. At the same time, the molecular chains between lamellae tend to be more extended. This unique structure manifests superior ability in ameliorating the performance of PLA film. The oxygen permeability coefficient can be achieved as low as 2 × 10(-15) cm(3) cm cm(-2) s(-1) Pa(-1), combining with the high strength, modulus, and ductility (104.5 MPa, 3484 MPa, and 110.6%, respectively). The methodology proposed in this work presents an industrially scalable processing method to fabricate super-robust PLA barrier films. It would indeed push the usability of biopolymers forward, and certainly prompt wider application of biodegradable polymers in the fields of environmental protection such as food packaging, medical packaging, and biodegradable mulch.

Improved mechanical and barrier properties of low-density polyethylene nanocomposite films by incorporating hydrophobic graphene oxide nanosheets

The high hydrophilicity of graphene oxide nanosheets (GONSs), arising from their abundant oxygen-containing functional groups, gravely restricts their application in non-polar polymer nanocomposites. In the present study, alkylated GONSs were fabricated by facile refluxing of GONSs and octadecylamine (ODA), thus giving rise to the selective dispersion of ODA–GONSs in non-polar xylene rather than in polar water. Fourier-transform infrared spectroscopy, atomic force microscopy, and X-ray diffraction results demonstrated the occurrence of the nucleophilic substitution reaction between the primary amine groups of ODA and the epoxide groups of GONSs during the refluxing. In the low density polyethylene (LDPE) nanocomposites, ODA–GONSs were uniformly and randomly dispersed, exhibiting excellent compatibility with the LDPE matrix. As a result, when adding 4.0 wt% ODA–GONSs, the Youngs modulus was improved by 58.9%; O2 permeability was reduced by 37.0%; and initial decomposition temperature was elevated by 15.9 °C. Besides, the inclusion of ODA–GONSs could effectively block the transmission of UV light in the nanocomposite films and serve as heterogeneous nucleating agents for LDPE crystallization. These results confirm that such long alkane chain modification holds great value or potential to design and prepare LDPE nanocomposite films for packaging applications with excellent integrated performance.

Highly crystallized poly (lactic acid) under high pressure

Biodegradable poly (lactic acid) (PLA) usually has a crystallinity less than 10% due to its poor crystallization ability. In this work, we found high pressure could significantly facilitate formation of crystallites of PLA, resulting in a crystallinity high up to 66.3% at pressure and temperature of 300 MPa and 185 oC. High-pressure induced crystalline reorganization and lamellar thickening led to two melting temperatures in the highly crystallized PLA but without cold crystallization compared to the normal-pressure crystallized PLA. Temperature dependence of high-pressure crystallization of PLA suggested desirable crystallization temperatures for highly crystallized PLA products.

Resistivity Relaxation of Anisotropic Conductive Polymer Composites

The electrical properties of anisotropic carbon nanotubes (CNTs)/polycarbonate (PC)/ polyethylene (PE) (ACPC) strongly depended on the CNTs’ concentration. When the ACPC was subjected to isothermal treatment (IT), the resistivity variation in both the parallel and perpendicular directions had the characteristics of a relaxation as a function of temperature. During the IT the orientation of the PC microfibrils was gradually damaged and CNTs/PC microfibrils were deformed and changed to short fibers, leading to a transition from anisotropy to isotropy. The velocity of the conductive network reconstruction could be characterized by the relaxation time, and the resistivity of the composite during the IT process can be instantaneously predicted based on the relaxation equation. The relaxation time and the equilibrium resistivity of the composite during IT were determined by the IT temperature and CNT content.

A Conductive Carbon Nanotube-Polymer Composite Based on a Co-continuous Blend

A conductive carbon nanotube (CNT) based polymer composite was constructed in which the conductive network utilized the selective distribution of CNTs in a co-continuous phase polymer blend. CNTs were first uniformly coated on the surface of polyethylene (PE) fine particles through alcohol assisted dispersion under ultrasonication, and then the CNTs coated PE particles were melt compounded with polycarbonate (PC). The theoretical prediction from both thermodynamics and kinetics indicated the CNTs mainly stayed at the interface between PC and PE. Rheological measurements and scanning electron microscopy (SEM) and optical microscopy (OM) observations provided the evidences for the selective distribution of CNTs and revealed the transition from the dispersed/matrix phase structure to the co-continuous phase structure at 50 wt% of PC. As PE and PC formed co-continuous phases, the CNTs formed a perfect conductive network on the phase interfaces, which resulted in a percolation threshold between 0.3 and 0.5 vol%, a relatively low value for CNTs filled thermoplastic composites reported in the literature.