Composite Films of HDPE with SiO2 and ZrO2 Nanoparticles: The Structure and Interfacial Effects

Herein, we investigated the influence of two types of nanoparticle fillers, i.e., amorphous SiO₂ and crystalline ZrO₂, on the structural properties of their nanocomposites with high-density polyethylene (HDPE). The composite films were prepared by melt-blending with a filler content that varied from 1% to 20% v/v. The composites were characterized by small- and wide-angle x-ray scattering (SAXS and WAXS), small-angle neutron scattering (SANS), Raman spectroscopy, differential scanning calorimetry (DSC), and scanning electron microscopy (SEM). For both fillers, the nanoaggregates were evenly distributed in the polymer matrix and their initial state in the powders determined their surface roughness and fractal character. In the case of the nano-ZrO₂ filler, the lamellar thickness and crystallinity degree remain unchanged over a broad range of filler concentrations. SANS and SEM investigation showed poor interfacial adhesion and the presence of voids in the interfacial region. Temperature-programmed SANS investigations showed that at elevated temperatures, these voids become filled due to the flipping motions of polymer chains. The effect was accompanied by a partial aggregation of the filler. For nano-SiO₂ filler, the lamellar thickness and the degree of crystallinity increased with increasing the filler loading. SAXS measurements show that the ordering of the lamellae is disrupted even at a filler content of only a few percent. SEM images confirmed good interfacial adhesion and integrity of the SiO₂/HDPE composite. This markedly different impact of both fillers on the composite structure is discussed in terms of nanoparticle surface properties and their affinity to the HDPE matrix.

Microbeam two-dimensional small-angle X-ray scattering investigating the effects of reduced graphene oxide on local microstructures of high-density polyethylene/reduced graphene oxide nanocomposite bars

It has been reported that the introduction of reduced graphene oxide (RGO) can enhance the crystallization and orientation of high-density polyethylene (HDPE) matrix and thus improve the mechanical properties of HDPE/RGO nanocomposites. In this study, the local microstructures and orientations in different regions of HDPE/RGO bars with varied RGO contents were further explored by two-dimensional small-angle X-ray scattering using a microbeam technique. It is unveiled that the orientation orderings of each position is intensified with increasing RGO amount, and of particular interest is the observation of the slight change of the ordering degrees in diverse zones of HDPE/RGO nanocomposite bars, indicating that RGO imposes a uniform enhancing effect upon HDPE matrix within different areas and consequently induces an effective increase of the mechanical properties of HDPE/RGO nanocomposites.

HDPE/UHMWPE hybrid nanocomposites with surface functionalized graphene oxide towards improved strength and cytocompatibility

High-density polyethylene (HDPE)-based and ultra-high molecular weight polyethylene (UHMWPE)-based composites with carbonaceous reinforcements are being widely investigated for biomedical applications. The enhancement of material properties critically depends on the nature, amount and compatibility of the reinforcement with the polymeric matrix. To this end, this study demonstrates the efficacy of a 'dual' hybrid approach of incorporating modified inorganic nanofiller into an optimized polyethylene blend. In particular, a unique synthesis strategy was adopted to design a covalently bonded maleated polyethylene (mPE) grafted modified graphene oxide (mGO) hybrid nanocomposite. In this scheme, polyethyleneimine (PEI) was initially attached onto GO to synthesize amine functionalized GO (GO-PEI). This is followed by mPE grafting, resulting in mGO. Melt-extrusion together with injection moulding of a polymer mix (60% HDPE-40% UHMWPE) with different proportions (less than or equal to 3 wt%) of surface functionalized GO was conducted to develop nanocomposites of different sizes and shapes. When compared with unreinforced PE blend, the nanocomposites with 1 wt% mGO exhibited an increase in ultimate tensile strength by 120% (up to 65 MPa) and elastic modulus by 40% (up to 908 MPa). The uniform dispersion of modified GO nanofillers, confirmed using X-ray micro-computed tomography and transmission electron microscopy, facilitated effective interfacial adhesion and compatibility with the hybrid polymer matrix. The variation in mechanical properties with GO/mGO addition to PE blend was critically discussed in reference to the structural modification of GO, crystallinity and nature of dispersion of fillers. Importantly, the nanocomposites support the attachment and proliferation of C2C12 murine myoblast cells over 3 days in culture in a statistically insignificant manner with respect to polymer blends without any nanofiller. Taken together, the experimental results suggest that HDPE/UHMWPE/mGO is a promising biomaterial for bone tissue engineering applications.

Mechanical and dielectric properties of crystalline poly(arylene ether nitrile) copolymers

Poly(arylene ether nitrile) (PEN) copolymers (HQ/RS-PEN) containing different proportions of hydroquinone (HQ-PEN) block and resorcinol (RS-PEN) block were synthesized, and their crystalline, mechanical, and dielectric properties were investigated. Three HQ/RS-PEN copolymers with 10%, 20%, and 30% of RS-PEN blocks were prepared via condensation polymerization of HQ and RS with 2,6-dichlorobenzonitrile. The PEN copolymers were characterized and confirmed by Fourier transform infrared spectroscopy, intrinsic viscosity, and thermal analyses. With the addition of RS-PEN block, the flexibility of PEN copolymers was increased. In addition, even though the high loading content of RS-PEN block was incorporated, the PEN copolymers still exhibited relatively high dielectric constant, whereas the dielectric loss decreased. Furthermore, to investigate the effect of treatment time and temperature on the physical properties of crystalline PEN copolymers, HQ/RS-PEN20 was isothermally treated at different temperatures (280°C, 300°C, 310°C, 320°C, and 330°C) for a constant time and at a constant time for different hours (1, 2, 3, 4, and 5 h). After the optimization of the crystallization of HQ/RS-PEN polymer, excellent mechanical and dielectric properties of copolymers were obtained. The results showed that when isothermally treated at 320°C for 2 h, the HQ/RS-PEN20 showed optimal properties of tensile strength of 117.6 MPa and dielectric constant of 4.07 at 1 kHz.

Effects of shear on epitaxial crystallization of poly(ε-caprolactone) on reduced graphene oxide

Epitaxial crystallization of poly(ε-caprolactone) (PCL) on reduced graphene oxide (RGO) was investigated by shearing at different shear rates of 3 s⁻¹ and 75 s⁻¹ and different shear temperatures of 65 °C, 70 °C and 75 °C, respectively. Two dimensional wide angle X-ray diffraction (2D WAXD) results show that the crystallinity and the orientation degrees of the (110) plane of PCL/RGO nanocomposites with shear are higher than those without shear, but the imposed shear field has no obvious effect on the crystal structure of the PCL matrix. Two dimensional small angle X-ray scattering (2D SAXS) results suggest that the imposed shear field makes PCL chains epitaxially crystallize on RGO surfaces to form thicker lamellae. Thereby the melt points of PCL/RGO nanocomposites with shear are higher than that without shear from the differential scanning calorimetry (DSC) results. These results indicate that the imposed shear field can enhance the orientation of the PCL matrix, and promote epitaxial crystallization of PCL chains on RGO surfaces. Higher shear temperature is the requirement for PCL chains to epitaxially crystallize well on RGO at low shear rate, although it is not required for the samples at high shear rate.

Epitaxial crystallization of poly(ε-caprolactone) (PCL) on reduced graphene oxide (RGO) was investigated by shearing at different shear rates of 3 s⁻¹ and 75 s⁻¹ and different shear temperatures of 65 °C, 70 °C and 75 °C, respectively.