Volume 22, Issue 2

The grafting reaction of ricinol-2-oxazoline methyl maleate onto molten low density polyethylene was investigated in a twin-screw extruder. The influence of peroxide content, added ricinol-2-oxazoline methyl maleate and process variables such as residence time, screw speed and reaction temperature were considered. The rate and level of grafting were quantitatively measured by FTIR technique. Maximum level of grafting at constant peroxide content was obtained when concentration of ricinol-2-oxazoline methyl maleate reached 3%, above which it declined. The rate of grafting increased with increasing peroxide content. However crosslinking of polyethylene was found to have taken place as parallel competitive reaction which was intensified with increasing peroxide content. It was demonstrated that it is possible to make an optimization of the grafting reaction on the basis of experimental results. The considerable grafting yield with acceptable melt flow rate for the samples was achieved when initial ricinol-2-oxazoline methyl maleate and peroxide concentrations were 2 to 3% and 0.06 to 0.1 %, respectively.

The implicit finite difference and fourth order Runge-Kutta method are used both to solve the heat transfer problem in the pultrusion reaction and to calculate the temperature and conversion distributions within a thermoset composite profile. The aim of our work is to study the influence of a rubbery phase added to the epoxy matrix in production conditions. The results have shown that the rubber modified systems have a low exothermic temperature peak value, so that neither the amount of cured resin nor the final product properties are limited. First of all we will show that the phase transition (gelation and vitrification) zones within the die change as the amount of rubber varies in the resin. The relationship between the position and of these zones and the resin systems will be discussed. We calculate the residual thermal stresses for all the investigated fibre/resin systems, showing a reduction when the rubber amount increases in the epoxy blend.

Real-time diagnostics of ceramic powder injection molding using a commercial micromolding machine was performed using ultrasound. Miniature ultrasonic sensors were integrated onto the mold insert. Melt front, solidification, temperature variation and part detachment of the feedstock inside the mold cavity were observed. It has been demonstrated that ultrasonic velocity in feedstock inside the mold cavity, the ultrasonic contact duration during which the part and mold are in contact, and holding pressure can be used to assist with optimization of injection and cooling parameters to minimize energy consumption and maximize process efficiency.

Three S-G HEUR thickeners were synthesized by a step growth polymerization technique of poly (ethylene oxide) (PEO) and dicyclohexylmethane – 4,40-diisocyanate (H 12 MDI) and then end capped with two monofunctional aliphatic alcohols. These polymers were mixed together according to the hydrophilic and hydrophobic nature of their segments. Based on this, two sets of associating polymers were introduced. In one set, the samples had identical hydrophobic segments while in the other one, hydrophilic segments were similar. The steady shear viscosity profiles of aqueous solutions of all models were determined. In addition, aqueous binary mixtures with various ratios of the S-G HEUR models were studied using steady state and dynamic rheometry. It is suggested that combinations of associating polymers with different size of hydrophobic segments and similar hydrophilic segments produce an associative polymer-like behavior. However, the combination of those with similar long hydrophobic segments and different hydrophilic segments at similar weight ratio in solution falls short of displaying an associative polymer – like behavior.

In the use of corn raw materials to produce glycol (corn-EG) and 1,2-propanediol (PDO), the output of PDO is more than that of corn-EG and the latter also contains some PDO. In order to produce high-performance polyester fibers by low-cost corn-EG instead of petroleum-EG, the paper initially seeks for the highest percentage of PDO that can be added in the conventional copolymerization of corn-EG/PDO/nano-SiO 2 and terephthalic acid (PTA). The experiment shows that as the content of PDO in copolyester exceeds 12 %, the POY breaking strength quickly decreases. The DTY of copolyester fiber with 12% PDO and 0.1% nano-SiO 2 can be dyed in the condition of atmospheric pressure and boiling water.

In this study, we developed a novel transcription-molding process and experimentally discussed its validity for fabricating polymer products having the precise microstructure on the surface. The process was named “Melt-Transcription Process” which consists of two characteristic stages; coating and compression. In the coating stage, a molten polymer is coated on the surface of a metal mold having the precise microstructure by a coating device specially designed in this study. The thickness of the coated polymer melt is typically 100 μm or more. Immediately after coating, the coated polymer is compressed against the mold surface so as to make the polymer flow into the microstructure cavities engraved on the mold, and to fabricate the 3-dimensional structure of polymer products. The pressure required for compression is quite lower than that in conventional nano-imprinting process, because the molten polymer of high temperature is distributed in advance over the mold surface in the coating stage. The “Melt-Transcription Process” was applied to fabricate polymer products with the size of 150 mm in length, 150 mm in width and 1 mm in thickness, having the microstructure of tens micrometers on their surface. Cyclo-olefin polymer (COP) and Polymethyl methacrylate (PMMA) were used as the polymer materials, and the dimensions and transcription ratios (the ratio of the height of the transcribed microstructure to the depth of the microstructure on the mold) of the molded microstructure were experimentally evaluated. As a result, by the Melt-Transcription Process, the microstructure was sufficiently transcribed on a very thin substrate of large surface area with high transcription ratios, typically 95% or more, under relatively low compression pressure of less than 10 MPa. The process was also applied for fabricating products with a range of thicknesses and we could experimentally verify that products composed of a membrane of 80 μm thickness and a surrounding frame with 1.95 mm thickness were successfully molded. Furthermore, we fabricated a micro-lens array product by using film grade PMMA with relatively higher viscosity in a product having 125 μm in thickness and a size of 102 mm × 102 mm.

The influence of content and aspect ratio of whiskers, calcium carbonate and aluminum borate, on the morphology evolution of liquid crystalline polymer (LCP) was investigated in polysulfone (PSF) matrix. The study showed that the deformation of LCP droplets was significantly promoted by adding whiskers into PSF/LCP blends, and the longer whisker produced a more pronounced fibrillation effect. The analysis of flow field and elasticity of system showed that the addition of longer whiskers increased the elasticity of materials more efficiently and enhanced the vortex in the converging flow area at the entry of capillary, which resulted in an increase of the elongational stress and promoted the formation of longer LCP fibrils in PSF/whisker system.

Techniques developed for three-dimensional simulation of gas assisted injection molding of thermoplastics are here extended to a complex industrial application, a car door handle, providing uniquely detailed insights into the molding process. Handling of the three stages of the process – plastic filling, and primary and secondary gas penetration – is described in terms of the boundary and initial conditions applied. Predictions for plastic filling patterns are compared successfully with molding results, and provide detailed forewarning of potential problems due to weld surfaces and air-traps. Particular emphasis is placed on accurate modeling of secondary gas penetration, which is also validated against practical results. A further novel feature is the export of an STL model of the gas core, providing a CAD model of the finished molding for subsequent in-service analysis.

An analysis of the steady-state film blowing process based on a two-phase constitutive model that accounts for flow-enhanced crystallization is presented. The amorphous melt phase is represented by a multi-mode Giesekus constitutive equation with a transformation-dependent relaxation time and the semi-crystalline phase is represented by a rigid rod model. The relaxation times in the two constitutive equations are linked by an Avrami, temperature-dependent rate expression which contains a term in the Helmholtz free energy to account for flow-enhancement. Comparisons are made to experimental data for film blowing of linear low density (LLDPE) and low density (LDPE) polyethylenes. Excellent fits for the bubble radius, temperature, and crystallinity are shown. It is also shown that the ratio of amorphous stress to total stress at the “lock-in” point provides an excellent correlating variable for the elongation to break and yield strength properties of the as-blown film. Inclusion of multiple relaxation times in the Giesekus model offers insights on the controlling role of the maximum relaxation time in the stress profiles and locking-in behavior due to crystallization.

An analysis of the transient film blowing process is presented based on the two-phase Giesekus/rigid rod model for flow-enhanced crystallization described in Part 1 [1]. Linearized frequency analysis has been used to explore the effects of system disturbances on the process. Results show that perturbations related to heat transfer and inflation pressure are more significant than the effects of film thickness (die swell). In addition, crystallinity is shown to have a consistent stabilizing effect on the system, with more crystallinity dampening the perturbations. Stability diagrams for each material show relatively wide regions of convergence in the blow-up ratio (BUR) – draw ratio space, however, at higher BURs (≥ ~ 4) the system becomes unstable for all DRs.

A composite model of solids conveying, melting and melt flow in a closely intermeshing counter-rotating twin-screw extruder of modular design has been developed. This is based on combining melt conveying models with new melting and solids conveying models. Computations are made for axial fill factor, pressure, temperature and melting profiles. The results are compared with experiment.

Benefits of reduced vehicle weight can have an important environmental impact since there is a 6 to 8% improvement in fuel efficiency for every 10% in weight reduction. In this work, foaming technology is used to produce injection molded TPO parts (thermoplastic olefin compounds) for the automotive industry with a minimum of 20% weight reduction while retaining a glossy surface quality. It was found by Guo et al. (2006, 2007) that the best strategy to raise the surface quality was to decrease the shot size, the cycling time and the temperature of the injected melt. However, the targeted objective of a minimum of 20% weight reduction was not achieved in these preliminary experiments. Therefore, in this work a blend of TPO and maleic anhydride modified polypropylene (PP-g-MA) was used in order to promote TPO foamability and improve the surface quality of injected parts. Under these conditions, we managed to produce injected molded TPO samples with a 24% weight reduction and good surface quality. Moreover, we investigated the effect of PP-g-MA in the TPO system by performing rheological measurements and photoacoustic Fourier transform infrared (PA-FTIR) analysis to characterize the PP-g-MA physico-chemical interactions with TPO.