Volume 33, Issue 5

Many processing operations of polymeric materials are dominated by extensional flow. In this paper the question is addressed in which way rheological data obtained from elongational laboratory experiments can be used to describe the material behavior in various processes. Particularly discussed is the uniformity of geometrical features of items with respect to the strain hardening of the polymeric materials, because uniformity is important for many end-use properties. Convincing correlations with extensional rheology could not be established for thermoforming experiments on polypropylene. However, for blown and drawn films it was found that the uniformity of thickness improved, if strain hardening was introduced. The bubble stability could be related to the melt strength of the sample. Furthermore, the influences of elasticity and strain hardening on the neck-in during drawing of films were elucidated. Moreover, it was shown in which way extensional rheology can be used to assess foaming.

All polymeric slurries that have a high concentration of filler are shear thinning. Shear thinning is an important characteristic of polymers, filled and unfilled, because it enables an increase in the throughput, shear rate in a die or an injection molding system without having to use substantially more power to increase the flow rate. Newtonian fluid-based slurries show an increase in shear thinning as the concentration of “filler” increases above the percolation threshold. As particle maximum packing concentration is approached the slurries begin to approach a perfect pseudoplastic fluid. In some cases, the shear thinning characteristics of a filled polymer do not increase substantially as the filler loading is increased. This is a quite different response than in Newtonian fluid-based slurry. Therefore, it is important to understand the materials engineering interactions that control shear thinning so that process flow models can better predict the performance of filled polymer systems. Highly filled polymers can have processing issues, including high screw shaft torque, energy consumption, die pressure and melt temperature rise. Previous theoretical developments and experimental evaluations of highly filled polymer melts showed that the rheology can be effectively described with a percolation model. In this work, capillary rheometer measurements using several low-density polyethylene resins, calcium carbonate and titanium dioxide fillers are reported using percolation theory concepts. The theoretical treatment of the rheology as a particulate percolating system with power-law behavior is used to analyze capillary rheometer data. The observed effects of resin molecular weight, filler type and size on rheology are described. Engineers that design and debottleneck polymer processes need to utilize the polymer viscosity at the minimum process shear rate to determine the smallest motor that will allow the process to run; in addition, the shear thinning characteristics of the polymer are used to indicate how much increased production may be possible with a given motor size. Thus, some examples of expected effects on melt processing are also presented.

Biodegradable spun-bonded non-woven fabric slices of poly lactic acid (PLA)/polypropylene (PP) were prepared by melt blending. The influence of the proportion of raw materials, blending temperature, blending time and rotation speed on the mechanical properties and melt flow properties of the slices were investigated, the influence of the proportion of PLA and PP composite slices on the thermal properties and microstructure was also researched. According to the research results of optimization conditions, the biodegradable spun-bonded non-woven fabric slice of PLA/PP was prepared and its biodegradable performance was evaluated. The results showed that when (m)PLA : (m)PP was 8 : 2, blending temperature was 185 °C, blending time was 4 min and rotation speed was 50 min −1 , the melt blending condition of PLA/PP composite slices was optimal. With the increase of PP mass fraction in slices, slices of melt flow rate (MFR) and glass transition temperature (T g ) were on the decline; T −50 % , T −95 % and T P were on the rise; the crystallinity of PLA/PP slices was increased; SEM results showed that the slices had “sea-island” structure. When (m)PLA: (m)PP was 8 : 2, microorganisms on the slices surface were second level of growth after 28 days which showed that the slices has a good biodegradable performance.

Using capillary dies having different diameters, D, and length-to-diameter L/D ratios, a full rheological characterization has been carried out for a polypropylene melt, and the experimental data have been fitted both with a viscous model (Cross) and a viscoelastic one (the Kaye – Bernstein, Kearsley, Zapas/Papanastasiou, Scriven, Macosko or K-BKZ/PSM model). Particular emphasis has been given on the pressure-dependence of viscosity. It was found that only the viscoelastic simulations were capable of reproducing the experimental data well, while any viscous modeling always underestimates the pressures, especially at the higher apparent shear rates and L/D ratios.

Thermoplastic injection molding is applied in a wide variety of products. It is known that volatile components generated when resin melts cause structural defects during the thermoplastic injection process. Not only that, the pre-injection preparation work including drying the material and maintaining the metal mold, have become standard procedures to prevent these defects, but these procedures deteriorate productivity. Vent-type injection molding involves the use of cylinders featuring a vent hole at the center of the plasticizing cylinder. Although it is a conventional molding method, there are many issues including resin leakage from a vent hole and difficulty of material replacements. These issues prevented it from widespread application. Moreover, the vent-type plasticization process has not been examined theoretically or systematically. In order to maximize and generalize functions of vent-type molding, it is necessary to clarify the flow behavior of resin in the vent cylinder. In this study, we verified the flow behavior of resin in the vent-type plasticization cylinder through experimentation and simulation. In the simulation, using the flow analysis method, the filling rate inside the screw was determined by the pressure distribution inside the screw. In the experiments, the molding condition that causes venting up was verified by changing the screw rotation rates and the supply amount of the resin, for determining the filling rate of resin inside the screw. The filling rates obtained through the simulation and the experiment are almost the same. The result suggests that this simulation is very effective for predicting the filling rate.

A 3D flow analysis package is used to simulate the flow phenomena in a short section of the metering zone of a single screw extruder. The assumption of stationary screw and rotating barrel is used. For sharp flight root corners, in addition to the primary flow field a secondary flow was determined in front of the root of the pushing flight and behind the root of the trailing flight, akin to what is known in the fluid mechanics literature as Moffatt eddies. Fluid particles caught in Moffatt eddy regions require travel times which are at least two orders of magnitude larger than the average residence time. This implies high probability of degradation and explains the deposits of thin carbonaceous films and gels, which have been discussed in several publications in the technical literature. The computer simulations show the existence of Moffatt eddies in the presence or absence of pressure gradients. When the screw roots have relatively wide angles no Moffatt eddies are predicted, in agreement with recommendations for good screw design practices.

The crystallization and melting behavior of biodegradable poly(3-hydroxybutyrate-co-4-hydroxybutyrate) [P(3HB-co-4HB)] with 11 % 4HB content was investigated by differential scanning calorimetry (DSC), small and wide angle X-ray scattering (SAXS and WAXS). The Avrami analysis was performed to obtain the kinetic parameters of crystallization. The results showed that the Avrami equation was suitable for describing the isothermal and nonisothermal crystallization processes of P(3HB-co-4HB). Based on the values of the equilibrium melting temperature and the half-time of crystallization, its nucleation constant of crystal growth kinetics was obtained by using the Lauritzen-Hoffman model, which was found to be 1.92 × 10 5 K 2 , lower than that for pure PHB. During the subsequent heating process, quite different multiple melting behaviors were observed for P(3HB-co-4HB) crystallized isothermally or nonisothermally. The origins of the multiple melting behaviors were discussed based on either the presence of dual lamellar thicknesses or the melt-recrystallization mechanism. In general, the crystallization and melting behaviors were elucidated by this work.

The particle size and shape are of momentous significance for the mechanical properties of plastic composites. However, natural fillers, like wood, are not consistent in these attributes. In order to investigate the shared traits between these characteristics, WPCs were produced using polypropylene, hardwood and softwood fillers with different particle sizes and a coupling agent. Afterwards, specimens were processed using an injection molding machine. The filler sizes and shapes were measured using dynamic image analysis. Furthermore, a shortening of coarser particles was detected. Mechanical tests were carried out to gain information about the tensile, flexural and Charpy impact properties. Neither very coarse nor very fine particles showed the best results. Instead, medium-sized particles proved to be the best option. The evaluation of the particle geometry verified a definite correlation between the shape and the mechanical properties, especially regarding the convexity, which can be a useful indicator of the quality of fiber-matrix interaction. The fiber orientation in the matrix was visualized with images taken by X-ray micro tomography.

In order to solve conflicting decision problems, multi-criteria decision making (MCDM) methods are used to make the best choice among many criteria. In this research, sixteen different samples of melt compounded polyamide 6 (PA6) and multi-walled carbon nanotubes (MWCNTs) were studied. The raw materials were compounded using a twin-screw extruder and the samples were chosen based on an L 16 orthogonal array of Taguchi approach. The alternatives of the problem were samples produced under different injection parameters including holding pressure, injection temperature, and with various weight percentages of MWCNTs. The chosen criteria were tensile strength, elastic modulus, Charpy impact strength, Rockwell hardness, and cost. Analytical hierarchy process (AHP) was used to weight the criteria and due to the results, tensile properties were the most important criteria with the weight of 0.319. In the next step, a technique for order preference by similarity to an ideal solution (TOPSIS) and the multi-objective optimization on the basis of ratio analysis (MOORA) were implemented to rank the alternatives. Based on the considered criteria the samples containing 1 wt% of MWCNTs was selected as the best alternatives.

This paper presents reduction of ZnO in EPDM formulations and its influence on efficiency of cable isolation by measuring cure behavior, electrical and mechanical properties before and after ageing. These experiments were performed on EPDM formulations by changing three key variables in formulation (concentration of ZnO, type of peroxide and content of ethylene in EPDM). The rheological characterization showed that replacing ZnO in EPDM with proper ethylene content (75 %) with the lower content of ZnO (5 phr) in the recipes, resulted in lower cure time and higher scorch time and higher crosslinking density, which was further supported by Fourier transform infrared spectroscopy (FTIR). Mechanical properties before aging (elongation at break, tensile strength, and hardness) are greater with smaller content of ZnO. The value of percentage change of the properties after aging at 135 °C for 7 days, indicates that recipe D (Perkadox 14/40 (Di (tert-butyl peroxy isopropyl) benzene (DTBPIB)) peroxide cured EPDM has the best performance at tensile strength, and elongation at break. What is more, recipe D, containing 5 phr of ZnO exhibits the desired electrical performance. The paper provides sufficient experimental background to indentify the key physical aspects associated with each of the instabilities that occur at higher amounts of ZnO in formulation, and this in turns provides insight into different occurrences of each instability and how they can be minimized by reduction of ZnO in EPDM mixture.

Regarding the necessity of lightweight construction, performance and design, composites are well established. At this moment, the joining of these composites still is often a major challenge. While suitable technologies like welding, sticking or riveting do exist, there are several drawbacks of these technologies such as damaging the fiber structure and low bonding strength. The combination of welding and sewing is a novel approach to improve the bonding of glass fibre-reinforced polypropylene and the influence of the processing parameters is not yet well understood. This study aims at analyzing the influence of parameters such as operating temperature, overlap length, needle temperature and thread material on the tensile strength of thermoplastic composites joined in the previously described hybrid approach. Furthermore, the interaction between thread and composite material is investigated by a microscopical analysis. The joint strength has been found to depend on the overlap length of the joint and the results suggest a contribution of the seam to the joint strength, especially for lower overlap lengths. Influences of the processing temperature, the thread material and needle temperature are also present, however, due to the complex interaction, no systematic conclusions could be drawn for these yet. The optical analysis confirms the findings of thermoset composites stitched before impregnation, where additional seams cause dislocations and local agglomeration of fibers. Additional investigations are necessary to determine the effect of the stitching on the joint and to further the understanding of the interaction between composite and thread material.

Controlling fiber orientation and fiber distribution in plastic injection of glass reinforced polymers is important due to the improvement of the properties of the material. Variation in shear layer thickness of fiber distribution affects the properties of the injection moldings. In this study, 30 % glass fiber reinforced polypropylene was injected under various injection molding conditions in order to increase the shear layer thickness in which fiber orientation was parallel to the flow direction. The experimental study was carried out according to the Taguchi L9 orthogonal array. The mold temperature, nozzle temperature and injection rate were chosen as input parameters and the thickness of the shear layer was taken as output. Analysis of variance was also applied to observe the effectiveness of the process parameters on shear layer thickness. The shear layer thickness was measured over the images obtained by scanning electron microscopy. In order to investigate the dynamic mechanical behavior of the material depending on fiber distribution, dynamical mechanical analysis was applied. Storage modulus, loss modulus and tan delta values were obtained. It has been observed that higher mold temperature and nozzle temperature values increased shear layer thickness in injection molding of glass fiber reinforced polypropylene. It has been seen that 65 % of increment in shear layer thickness induced approximately 50 % of increment in storage modulus and loss modulus.

Autonomous self-healing was achieved by synthesizing epoxy coatings which contain dual micro/nanocapsules; epoxy and amine. Epoxy micro/nanocapsules were prepared by an in situ polymerization process and amine microcapsules were fabricated by vacuum infiltration of diethylenetriamine into nanoporous hollow glass microspheres. Both types of capsules were embedded into epoxy matrix. When cracks were created and started to grow in the coating, the micro/nanocapsules near the crack were ruptured and released their contents. As a result of curing reaction between released curing agents (epoxy and amine), healing of the cracked sites was completed. In this work, some properties of epoxy/amine micro/nanocapsule based self-healing coatings such as morphology of micro/nanocapsule and coating, healing and corrosion properties were studied. Also thermal stability and adhesion properties of this kind of coating were evaluated comprehensively. It was found out that optimum mass ratio of epoxy/amine capsules ratio is 1 : 1 and the highest healing efficiency was achieved for a total micro/nanocapsule concentration of 15 wt.%. Regarding thermal and adhesion behavior of coatings, it was observed that adding micro/nanocapsules to epoxy matrix did not change these properties significantly which means self-healing characteristics were achievable without deteriorating other properties.

Molding is a key stage in the manufacturing process of a rubber tire. An unvulcanized tire consists of several layers of rubber compounds, some of which are reinforced with sets of fabric cords or wire cords. The final shape of the tire, including the tread patterns and markings, is obtained after insertion of the tire into a curing mold and inflation with an appropriate pressure. The relative orientation of reinforcements may change during the inflation phase. This relative orientation change is referred to as pantographing, and it will affect the properties of the finished tire. Predicting possible changes of orientation of reinforcements during inflation is therefore useful for subsequent technological assessment.