Volume 37, Issue 8

Skeletal defects reconstruction, using custom-made substitutes, represents a valid solution to replacing lost and damaged anatomical bone structures, renew their original function, and at the same time, restore the original aesthetic aspect. Rapid prototyping (RP) techniques allow the construction of complex physical models based on 3D clinical images. However, RP machines usually work with synthetic polymers; therefore, producing custom-made scaffolds using a biocompatible material directly by RP is an exciting challenge. The aim of the present work is to investigate the potentiality of 3D printing as a manufacturing method to produce an osteogenic hydroxyapatite-polylactic acid bone graft substitute.

The blends of poly (butylene terephthalate) (PBT) and 4,4′-dihydroxyphenyl (DHP) were prepared by melt blending, and the effects of DHP on the crystallization and melting behaviors of PBT were investigated by differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), and polarized optical microscopy (POM). The results showed that crystallization temperature and crystallinity of PBT apparently decreased with the addition of DHP. A remarkably decline in crystallization rate of PBT was achieved, and the blends had higher σ e and q values than that of pure PBT as analyzed based on the Avrami equation and Lauritzen-Hoffman equation. The crystal structure of PBT did not change by the addition of DHP, while the spherulite size of PBT decreased.

The gelation process of poly(vinyl chloride) (PVC) plastisol is very important to ensure the quality of the product and is affected by the type of resins, plasticizers, and other additives. In this study, the gelation process of the as-prepared PVC plastisol was characterized by measuring the evolution of vibrational viscosity with temperature or time using a vibrational viscometer. Furthermore, the effect of some commercial resins with different particulate morphologies on the gelation process was investigated by synchronously combining scanning election microscopy and laser particle size analyses. The results of this study proved that the particle size distribution and the aggregation degree of the secondary particles of a resin are the key factors affecting the gelation process. For the resin with bimodal particle size distribution, the closer the aggregation of the secondary particles, the slower the gel speed; however, an opposite behavior was observed for the resins with unimodal particle size distribution.

In this study, blends of low-density polyethylene (LDPE)/aluminum nitride (AlN) ceramic nanocomposites have been prepared through melt blending technique. Increased loading of AIN leads to reduction in tensile properties but improvement in rheological property (storage modulus). The rheological behavior tends to become unique at higher frequencies (≥10 rad/s). Differential scanning calorimetry (DSC) results show that the total crystallinity has decreased with the increase in AlN loading in the composites. It is seen that there is an improvement in electrical conductivity, dielectric constant, and flammability properties with the addition of AlN in the nanocomposites. The experimental data of tensile modulus, electrical conductivity, and dielectric constant have been fitted with some available theoretical models to check the models’ applicability for the present composite systems. Results show that only Nicolais-Nicodemo model, McCullough model, and Rahaman-Khastgir model are applicable for predicting the tensile modulus, electrical conductivity, and dielectric constant of the composites, respectively.

In the present work, β-cyclodextrin was grafted to the surface of ZSM-5 via 2,3-epoxypropyl trimethylammonium chloride (ETMAC) and epichlorohydrin (EPI) as the bridging agent by ion exchange and sequential grafting. The mixed matrix membranes were prepared using polyurethane (PU) and ZSM-5 before and after modification. Modified ZSM-5 and corresponding MMM were characterized by Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), and scanning electron microscope (SEM). These membranes were applied for the removal of phenol from aqueous solution in pervaporation process. The results showed that modified ZSM-5 dispersed homogeneously in polymer. The flux and pervaporation separation index of PU increased greatly with a limited decrease in selectivity by the addition of modified ZSM-5. The increased feed temperature enhanced both the flux and separation factor of PU and modified PU membranes.

The effects of hybridization of multi-walled carbon nanotubes (MWCNTs) with carbon black (CB) and the structure-property relationships of nanocomposites based on hydrogenated nitrile-butadiene rubber/hydrogenated carboxylated nitrile-butadiene rubber blends were extensively studied. MWCNTs used in this work were modified through acid treatment to improve the dispersion of MWCNTs in the rubber matrix and the surface interaction between MWCNTs and matrix. Synergistic interaction between CB and MWCNTs increased the tensile modulus and tear strength of nanocomposites. The effect of MWCNTs on the transport properties invoked an increment in the thermal conductivity of the nanocomposites. A combination of 10 phr (parts per hundred rubber) MWCNTs with 40 phr CB dramatically increased the modulus at 100% elongation, tear strength, and thermal conductivity of the nanocomposite by 66%, 28%, and 36%, respectively, compared with those of nanocomposite filled with 40 phr CB.

The morphological distribution of carbon nanotubes (CNTs) in polymer matrix has a crucial impact on the performance of CNT-filled polymer composites. A novel microlayer extrusion technology used in the dispersion and orientation of CNTs was proposed, and polypropylene (PP)/multiwalled CNT (MWCNT) composites with different numbers of layers were prepared with it. The MWCNT dispersion was investigated by scanning electron microscopy and Raman mapping method, and the MWCNT orientation was quantified by Raman spectroscopy. The influences of the dispersion and orientation of MWCNTs on the electrical conductivity and crystallization behavior of the composites were investigated. The results showed that the anisotropic conducting properties of the multilayered composites varied distinguishably with the increase of layer numbers and rotation speed. Furthermore, the degree of crystallinity of PP increased when the layer number increased from 1 to 729. All of these results suggest that with the increase of the layer numbers and the rotation speed, the dispersion and orientation of MWCNTs in PP matrix improve greatly. Overall, we provide an efficient and practical approach to control the dispersion and orientation of CNT in polymer matrix, which has a promising application prospect in the field of plastic processing.

Mechanical and electromagnetic interference shielding composites containing Ag-plating micro-nano cellulose fibers (ANCFs) were prepared as multifunctional materials. ANCFs, as electromagnetic wave reflection filler containing micro-nano cellulose fibers (NCFs) used as the structural component to reinforce the mechanical strength and Ag enhancing electromagnetic shielding effectiveness, were prepared by electroless Ag-plating technology on NCFs surfaces. Ag coating had a thickness of 60 µm without the oxide phase detected. The incorporation of 5 wt % ANCFs into epoxy (EP) substrate yielded impact strength and flexural strength of 1.84 kJ/m 2 and 41.6 MPa, which is approximately 2.4 times and 1.41 times higher than EP. The ANCFs-EP composite performed an electromagnetic shielding effectiveness of 34–25 dB at a frequency of 90 kHz in the electromagnetic wave; the EMI shielding effectiveness was improved obviously up to 34 dB, which can meet the requirement of general places.

This paper deals with the study of screw configuration for dispersing nanofillers in thermoset polymers using an intermesh co-rotating twin screw extruder. The influence of kneading elements on the dispersion of nanoclay in epoxy was examined using 10 different screw configurations. Nanoclay was dispersed in epoxy at a barrel temperature of 5°C and a screw speed of 100 rpm. The combination of right hand kneading block and three/four lobed kneading blocks resulted in uniform dispersion of nanofiller. Positive staggered angle with right hand kneading elements yielded uniform dispersion of the nanofiller. Mechanical properties of epoxy nanocomposites processed with these configurations were better than those of neat epoxy. Excessive shear was associated with four lobed kneading block (4KB)/4KB configuration and hence degradation of polymers leading to shorter chains, whereas inadequate shearing in neutral kneading block (NKB)/NKB configuration led to agglomerations. These observations were evidenced by scanning electron microscopy (SEM) and X-ray diffraction (XRD).

A thorough study was carried out to investigate the priority of a novel co-rotating non-twin screw extruder (NTSE) over a traditional twin screw extruder (TSE) in the mixing process of halogen-free intumescent flame-retardant acrylonitrile-butadiene-styrene (ABS) composites. The homogeneity of the flame-retardant additives of the composites processed by NTSE and TSE under the same operating conditions was characterized by using mechanical performance properties, limiting oxygen index values, UL-94 tests, and thermogravimetric analysis. All the results suggested that NTSE could achieve better mixing of the flame-retardant additives in the polymer matrix than TSE, which was further clarified by the scanning electron microscope pictures.

The main criterion in the design of extrusion dies is to ensure a uniform velocity distribution of the plastics melt at the die outlet. In the case of spiral mandrel dies, the flow balance can be influenced negatively by thermal effects which are especially dominant in the pre-distributor. In previous works, it was shown that thermal inhomogeneity in a 2 n -pre-distributor leads to an uneven melt distribution at the end of the pre-distributor. In the present study, the temperature influence on the melt distribution in a star-pre-distributor is investigated for three different polyethylenes with the help of flow simulations in Polyflow (Ansys). The simulation model depicts the whole pre-distributor and takes both the shear heating in the melt and the heat conduction in the pre-distributor into account. The simulative analysis shows that the dissipative shear heating leads to an uneven throughput distribution in the star-pre-distributor. In order to compensate this effect, in the next step of the simulations, heating cartridges are applied to the pre-distributor. In this way a significant homogenization of the pre-distribution can be achieved.