Volume 31, Issue 1

No abstract available

No abstract available

A phenomenological model for the hydrodynamic dispersion of silica agglomerates modified with a thermoresponsive hydrogel (poly- N -isopropylacrylamide, PNIPAM) is presented. The model well describes experimental observations of the dependence of the dispersion behavior on the presence of additives (water and PNIPAM hydrogels) and applied hydrodynamic stress. Most importantly, the thermosensitivity of the dispersion process is captured by characterizing the agglomerate structure and cohesive force at two different temperatures (above and below the hydrogel transition temperature). The transition in dispersion mechanism between rupture-like and erosion-like regimes with system temperature can also be accommodated within the model.

In this investigation, poly(lactic) acid (PLA)/multi-walled carbon nanotubes (CNTs) hybrids were prepared using a melt blending process. To increase the compatibility between CNTs and PLA, the surfaces of the CNTs were firstly pretreated in acid solution (HNO 3 ) to functionalize them with carboxylic groups (-COOH). Then, stearyl alcohol was grafted onto carboxylic groups using a dehydrating agent, N,N′-dicyclohexylcarbodiimide. Chemically modified CNTs (CNT-C18) were thus obtained. Therefore, modified carbon nanotubes (CNT-C18) dispersed excellently in organic solvents. PLA/CNTs nanocomposites were prepared by the melt-blending method. Experimental results reveal that the PLA/CNT-C18 nanocomposites that consisted of well-dispersed nanotubes exhibited enhanced thermal and mechanical properties. Adding 4 wt% CNT-C18 to a nanocomposite increased the storage modulus ( E ′) at 40°C by 17.8%, and the loss modulus ( E″ ) at the glass transition temperature ( T g ) by 15.1%. Adding 3 wt% CNT-C18 also reduced the surface resistivity of the PLA nanocomposites from >10 16  Ω/cm 2 to 10 4  Ω/cm 2 . Such PLA/CNT-C18 nanocomposites are highly efficient in anti-static agents and can be exploited in the outer coverings of electronic devices.

Researchers have been using DNA for flow visualization studies owing to its ability to be tagged by a fluorescent dye. We used DNA to study the apparent slip phenomena encountered in the in-mold coating (IMC) flow through thin channels. IMC can be basically considered a carbon black suspension. IMC of sheet molding (SMC) compound is a well-established and environmentally friendly processing technique used by many industries to improve surface quality of parts to meet automotive standards. It is recently being evaluated for use with thermoplastic injection molded parts to obtain similar surface quality improvements and eliminate the need for priming and/or painting. The flow geometry gaps encountered during the coating process, are mostly at the micro-scale. Previous work in our group has shown that the flow can be represented using continuous mechanics approaches with the incorporation of slip at the wall. In this paper, we used DNA, as a model suspension, to make further insights into the nature of the slip flow phenomena encountered during the coating process.

There are two different stretching processes that produce the biaxially oriented film, namely the tenter process and double bubble tubular film process. Furthermore, there are two tenter processes, i.e., the sequential biaxial stretching process and simultaneous biaxial stretching process. There is no report describing the difference among film physical properties of the three different processes. The biaxially oriented polyamide film using the double bubble tubular process has good balanced physical property and high impact strength, thus it is used for proper applications utilizing their advantage properties. In this report, the influence of each biaxial stretching process on film physical properties of polyamide, which has hydrogen bond, was studied in detail. As a result, the tentering process film has anisotropic tensile properties between machine direction (MD) and transverse direction (TD). This result was influenced by a later stretching process, namely TD stretching. On the contrary, the double bubble tubular film has good balanced properties, especially thermal shrinkage and impact strength. Tentering simultaneous stretching film has much larger shrinkage in MD than in TD. The sequential stretching film has larger shrinkage in TD than in MD. The double bubble tubular film has high impact strength, because it corresponds to the balanced molecular orientation.

Star copolymers of acrylamide and N , N -dimethyl- N -vinyl­nonadecan-1-aminium chloride (C 18 DMAAC) were synthesized by photopolymerization in water. Solution behaviors of these star hydrophobically modified acrylamide copolymers (SHMPAMs) with different C 18 DMAAC contents and the linear hydrophobically modified acrylamide copolymers (LHMPAMs) were characterized. The increase in C 18 DMAAC content resulted in decreased intrinsic viscosity and increased the Huggins constant for SHMPAMs. Similar results were observed for LHMPAMs. With similar intrinsic viscosity and C 18 DMAAC content, the Huggins constant of SHMPAMs was much higher than that of LHMPAMs, which could be due to the fact that SHMPAMs had much stronger intramolecular interaction in dilute polymer solutions. In semi-dilute solutions, the apparent viscosity of SHMPAMs was increased with increasing C 18 DMAAC content, which was similar to that of LHMPAMs. However, SHMPAMs exhibited higher apparent viscosity than LHMPAMs because it had more arms and thus had more chances to form three-dimensional networks in semi-dilute solutions. In the flow-induced scission experiment, SHMPAMs exhibited superior shear stability in comparison with LHMPAMs. When the strain rate was ≈40,000 s-1, the reduction ratios of the apparent viscosities of the four SHMPAMs after the scission were approximately 80%. By contrast, when the strain rate was ≈20,000 s-1, the reduction ratio of the apparent viscosity of LHMPAM-0.40 had already reached around 80%.

Accurately monitoring and controlling melt temperature in the injection molding process can be a challenge. A barrel temperature model was achieved with the use of a system modeling method. Because of time variance, uncertainty and non-linearity of injection molding barrel temperature, a learning control method based on the use of a cerebellar model articulation controller (CMAC) neural network was proposed. Simulations and experimental results have demonstrated that this method elicits high response speed and excellent control accuracy of barrel melt temperature.

Using the finite elements method, numerical simulations of the flow field of a rubber melt in the mixing sections of a conventional full-flight single-screw extruder and a pin-barrel single-screw extruder were carried out. Particle tracking analysis was used to statistically analyze the mixing state of the rubber melt in the mixing section with pin and that without pin. The mixing performance of both types of mixing section was quantitatively evaluated. The results show that the pins partially disorganize the particle trajectories, change the particle moving directions, and enhance the mixing performance. The particle residence time is longer in the mixing section with pins than in the mixing section with no pin, leading to better mixing in the former. The distributive mixing of particles in both types of mixing section was statistically analyzed. The pins increase the efficiency of stretching and the time-averaged efficiency of stretching, and hence the mixing efficiency. However, further increase in the number of pins does not necessarily enhance the mixing performance.

Despite their outstanding properties, the use of composites is still limited. The absence of an appropriate and economic high volume production technology is the most important restriction for the use of composites. This paper presents results of the research on new high volume production chains for continuous fibre reinforced composites which are based on the separation and parallelisation of the process steps “impregnation” and “forming and curing”. Two new impregnation processes for polyurethane and epoxy resin as well as a new compression moulding technology are introduced. The production of high performance parts with a fibre volume content higher than 50% in a cycle time below 10 min is described and analyses of the impregnation quality and the mechanical properties of the parts are presented.