Band 38, Heft 6

Improving the applicability of polyethylene terephthalate (PET) by carbon fiber/glass fiber reinforcement is of great interest. Glass fiber (GF)/carbon fiber (CF)/PET hybrid composites were fabricated by direct fiber feeding injection molding (DFFIM) process. The aim of DFFIM is to obtain longer fibers in composites in order to improve their mechanical properties. In this study, the mechanical properties of GF/PET composites fabricated by conventional injection molding and hybrid GF/CF/PET composites fabricated by DFFIM process were investigated. The influence of GF and CF volume fractions on fiber distribution, fiber orientation, and fiber length is discussed. Fiber distribution status was quantitatively measured by the fiber distribution index. Fiber agglomeration problem was observed by scanning electron microscopy. The results indicate that incorporating CF in GF/CF/PET hybrid composites by the DFFIM process greatly enhances mechanical performance even when only a small amount of CF is added. Too high GF content leads to less effective CF hybridization because it causes poor fiber distribution and poor fiber orientation and intensifies fiber attrition. The ideal volume fractions of GF and CF for fabricating GF/CF/PET hybrid composites by using DFFIM are provided.

Vascular grafts provide promising scaffolds for patients recuperating from cardiovascular diseases. Since it is necessary to mimic the native vessel in order to overcome the limitations of currently employed synthetic prostheses, researchers are tending to focus on the design of electrospun biodegradable multi-layer scaffolds which involves varying either the polymer type or constructional properties in each layer which, in turn, reveals the importance of layer interactions and their composite effect on the final multi-layer graft. This study describes the fabrication of biodegradable single-layer tubular scaffolds from polycaprolactone and poly(L-lactide)caprolactone polymers composed of either randomly distributed or, preferably, radially oriented fibers. Subsequently, bi-layer scaffolds were fabricated with a randomly distributed inner layer and a radially oriented outer layer from various polymer couple variations. The study focuses on vascular graft production technology including its morphology and mechanical properties. The post-morphologies of single-layer and bi-layer tubular scaffolds designed for vascular grafts were investigated as a continuation of a previously performed analysis of their mechanical properties. The results indicate that the mechanical properties of the final bi-layer grafts were principally influenced by the radially oriented outer layers acting as the tunica media of the native vessels when the appropriate polymer couples were chosen for the sub-layers.

Surface covalent functionalization of multiwalled carbon nanotubes (MWCNTs) is carried out by coupling of isocyanate-decorated MWCNTs with hydroxyl-terminated polydimethylsiloxane (HTPS), resulting in the formation of functionalized MWCNTs. Thermogravimetry analysis (TGA) of functionalized MWCNTs-1,2,3 exhibits the similar peaks in the temperature range of 200–500°C, which all correspond to the degradation of chemically grafted polyurethane on the nanotube surface. Field emission scanning electron microscopy (FE-SEM) reveals that as the polyurethane grafted onto the surface of MWCNTs loading ratio increased, the surface roughness of the MWCNTs is reduced. The chemical interaction of HTPS with isocyanate-decorated nanotube surface using the grafting-to strategy in a one-step process is confirmed by Fourier transform infrared spectroscopy (FT-IR). The surface contact angle of MWCNTs-3 with the largest content of polyurethane reached 171°, indicating that the surface covered with low surface energy polyurethane shows a super-hydrophobic property. The good dispersion of polyurethane-functionalized MWCNT-3, particularly at high content in the NR nanocomposites, is evidenced from transmission electron microscopy (TEM).

In this study, hybrid composites based on carbon fiber (CF) and polypropylene (PP) were fabricated by melt mixing techniques. The composite with optimum fiber length (8 mm) was chosen as a reference material, and to it, CF of various lengths (6 mm, 100 μm, 60 μm and 100 nm) were added as secondary filler. To understand the synergism effect of these fibers, electrical, rheological, thermal and morphological properties of composites were studied. The surface resistivity of the neat PP is in the order of 10 17 ohm/square. It is observed that surface resistivity of a single fiber filled composite is in the range of 10 4 ohm/square, while it further decreased by three-fold (10 1 ohm/square) in the case of secondary fiber filled composites, indicating that the electrical network remains intact. Thermal analysis shows variation in crystallization of hybrid composites that can correlate to the lengths of secondary fibers. The rheological analysis shows that the frequency dependence of storage modulus (G′) and loss modulus (G″) in the lower frequency region indicates an elastic solid like behavior of these composites. The morphological behavior showed that the CFs are well dispersed and form a good adhesion with the polymer matrix.

In a study of antistatic transparent plastic for optical communication purposes, we previously prepared cyclo olefin polymer (COP)/BN105 composite material and confirmed the improvement of dust resistance as well as good antistatic property on the surface of the molded product. In this study, BN105 composite material using fluorene-based polymer (FBP) as base polymer was newly prepared and the injection molded product was evaluated. In the results, the surface electric resistivity of the molded product was reduced to 6.69×10 11 Ω/sq and good dust resistance similar to that of COP/BN105 was shown. In addition, the dispersion state of additive molecules inside the BN105 composite molded product was observed by transmission electron microscope, and molecule weight distribution measurement was also conducted for the molded product.

Inorganic-organic hybrid modifiers have attracted attention of scholars worldwide because they combine the advantages of both different components and provide a way for modifying the structure and properties of polymeric materials. The article describes and investigates a positive effect of reduced flammability of thermoset resins resulting from the use of nanocomposites containing new inorganic-organic hybrid flame retardants (FRs) that combine conventional phosphorous/nitrogen modifiers interacting with nanofillers. The impact of these inhibitors on the level of flammability of thermoset resin compositions was defined by determining the value of limiting oxygen index, thermogravimetric and cone calorimeter analysis of thermal destruction processes. Morphology of composites was assessed using a scanning microscope and an analysis of actual scanning electron micrographic images. The analysis of thermal decomposition of the materials under examination confirmed flammability reducing properties of the inorganic-organic hybrid FR used, and a synergist to generate integrated flame retarding effect was observed between conventional modifiers and nanofillers, in particular carbon nanofillers: expandable graphite, graphene and graphene oxide. The inorganic-organic hybrid FR will provide a new solution to efficient FR polymeric materials.

Selective laser sintering (SLS) of polymers is on the edge from a pure prototyping technique to a small-scale production. For this transition, characteristic values such as long-term properties, and thus the degradation mechanism, are crucial factors for enabling a series application. Due to the specific characteristics of SLS parts like porosity and rough surfaces, a direct transfer of known mechanisms and models for injection molded (IM) parts is not or just to a limited extent possible. This leads to the aim of this paper, which is to investigate and compare the degradation behavior of polyamide 12 parts produced by SLS and IM.

The combined deep drawing and back-moulding process shows great potential to reduce manufacturing costs of plastic/metal hybrids for structural components. To achieve this, a new mould technology with the components of both forming technologies is developed. By closing the mould, the inserted metal sheet is first deep drawn, and when the mould is fully closed, it is further formed by melt pressure. It can be shown that the forming quality of the second forming step mainly depends on the packing pressure. For a controlled flow of the metal, a downholder is necessary. By adjusting the downholder, force on the thinning of the metal through forming can be controlled.

In plastic pipe extrusion, hot molten extrudate emerges from an annular. This highly viscous liquid is then cooled and solidified, called quenching , in a quench tank. In this paper, we focus on the external cooling system. We use an adiabatic inner wall and differing outer wall boundary conditions: isothermal and convection. The solid-liquid interface, at the solidification temperature, moves inward with deceleration. We adimensionalize the energy balance and solve for the interface speed in terms of the solidifcation coefficient, λ . We arrive at the exact solutions for the evolving solidified thickness. Finally, we use the residual stress model developed by Jansen [ Int. Polym. Proc . 1994, 9, 82–89]. to predict the compressive residual stress at the outer pipe surface. Our new exact solution for the solidification time agrees well with the data from the plastic pipe industry. The goals of this paper are to help plastics engineers calculate the solidification time, to design the cooling chamber and to predict the residual quenching stress.

The evaluation method for a biaxially oriented film was developed using in-situ measurement during the stretching process. It can obtain basic data such as stress-strain curves, birefringence, light scattering, three dimensional refractive indexes and birefringence distribution. Stress and strain as functions of stretching speed and stretching temperature, as well as the deformation of spherulite of semi-crystalline polymer can be obtained by measuring the birefringence and light scattering during the biaxial stretching process with a small piece of polymer sample. The experimental results show the stress, retardation and three dimensional molecular orientations behavior during the simultaneous biaxial stretching and the sequential biaxial stretching process. Stretchability, thickness uniformity and spherulite size can be obtained simultaneously. In this paper, advantages and details of the newly developed system will be discussed with some experimental data.