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Applied Rheology

SPE Library content related to rheology

ON-LINE SENSORING IN EXTRUSION-BASED PROCESSES: PAST, PRESENT AND FUTURE

João M. Maia, May 2012

The challenges materials processing and compounding face nowadays are related not only with the design and control of better and more efficient machines but, essentially, with the manipulation of the molecular structure of the materials, with a view to obtaining innovative high performing products. Extruders are a fundamental part of any extrusion process and intermeshing co-rotating twin-screw extruders, in particular, have special application niches, being the equipment of choice for blending and compounding operations, mainly because of their good distributive and dispersive mixing capabilities. In fact, they are used in most important modern polymer applications such as compounding of filled polymer systems and masterbatches, polymer melt homogenization, polymer modification and the polymer blending. Very often, the last two operations involve, apart from polymer processing, chemical reactions, classical examples of which are the peroxide induced degradation of polypropylene to prepare grades with controlled rheology, and the grafting of maleic anhydride onto polyolefins to improve their compatibility with other polymers. Although these are widespread value-added processes in the polymer industry, there is often a gap in the fundamental knowledge of the properties and physical and chemical composition of the materials being processed during the extrusion process because the extruders are “black boxes” in which the properties of the initial materials, as well as those of the final product, are known, but not the kinetics of the transformation process. This poses severe limitations to current operations because without this knowledge any optimization effort of material structure and/or properties is done by trial- and-error and, thus, is very time consuming and offers no guarantees that the final product is, in fact, optimal. In this work, we present a review of recent developments in on-line sensors that allow for the monitoring of the rheological, chemical and s

HYDROLYTIC DEPOLYMERIZATION OF PET DURING EXTRUSION

Tahereh Mousavand, Maryam Dini Pierre J. Carreau, Pascal Hubert, Musa R. Kamal, May 2012

Depolymerization of PET to high molecular weight oligomers could introduce opportunities to re-use PET waste via chemical recycling. Hydrolysis of PET in the presence of water/steam was carried out in a twin screw extruder, at barrel temperatures of 265°C and 300°C with screw speeds of 20, 60 and 200 rpm. The extruded products were characterized to determine intrinsic viscosity (IV) of samples as well as thermal properties (DSC) and rheological behavior. Proton nuclear magnetic resonance (HNMR) analysis was used to estimate carboxyl end group content. The results showed that the average molecular weight (Mw) of extruded polymer was reduced to less than 10,000 g/mol

THE EFFECT OF NANOCLAY ON THE RHEOLOGICAL PROPERTY AND MELT STRENGTH OF POLYPROPYLENE/POLYAMIDE-6 BLEND

Haibin Zhao, Binyi Chen, Yongqiang Lin, Jinwei Chen, Jichang Fan, Xiangfang Peng, May 2012

Polypropylene (PP) and polyamide-6 (PA6) blend and nanocomposite were prepared using melt intercalation technique by blending PP and PA6 by the incorporation of nanoclay. The melt intercalation of PP and PA6 blend was carried out in the presence of a compatibilizer maleic anhydride grafted polyolyaltha olfin. The rheological property, melt strength and the morphology of PP/PA6 blend and PP/PA6/CN nanocomposite were studied. It was found that the incorporation of nanoclay has positive influence on the rheological property and the melt strength of PP/PA6 blend.

TRANSIENT PARTICLE FLUX DURING INJECTION OF COMPOSITE POLYMER COMPOUNDS AND THE RELEVANCE OF SUBSEQUENT MANIFESTATIONS IN MULTI-CAVITY TOOLING

Tyler Skiba, John Coulter, Samarth Desai, May 2012

An experimental analysis of the degree of particle diffusion is conducted and analyzed, focusing on multi-cavity tooling. Highly reinforced composite resins are injected into multi-cavity tooling and subsequently analyzed by thermal and mechanical approaches to uncover the degree of shear-induced particle diffusion manifesting under varying injection velocities, mold temperatures, and primary runner aspect ratios. Results indicate that shear induced diffusion is occurring in the length and time scales employed, yet the imposed environments, favorable to particle diffusion, show relatively low influence on cavity-to-cavity gradients in particle concentrations with net migrations occurring opposite to theoretical notions under molding environments. A significant local migration is found to occur radially within the melt delivery. Mechanical properties exhibit a dependence on the rheological history of the polymer in.

EFFECTS OF COMPONENT VISCOSITIES AND DISPERSED PHASE VOLUME FRACTION ON RELAXATION BEHAVIOR FOR POLYMER BLENDS

Lin-Qiong Xu, Han-Xiong Huang, Zhao-Ke Chen, May 2012

The influences of the viscosities of the matrix and dispersed phase, and the volume fraction of the dispersed phase on the relaxation behavior reflected on the Cole-Cole plot and the imaginary part of complex viscosity curve are analyzed using the Maxwell and the Palierne models and experimental data. It is found that these three parameters have a great impact on the radii of the circular arcs of the Cole-Cole plot. Moreover, the total relaxation time of the deformed droplets increases with the increase of the viscosity and volume fraction of the dispersed phase, especially the increase of the viscosity of the matrix. In addition, it is important to found that the Cole-Cole plot is invalid to analyze the miscibility of the polymer blend when the droplets of the dispersed phase have not enough time to relax during dynamic frequency sweep test.

IN SITU GENERATED BICONTINUOUS REINFORCEMENTS

O. Sinan Yordem, Alan J. Lesser, May 2012

The principle subject discussed in the current study is a method to form bicontinuous reinforcement within a polyether ether ketone (PEEK) polymer matrix by using metal stearates as fillers. X-ray scattering, differential scanning calorimeter, dynamic mechanical analysis (DMA) and melt rheology were used to investigate the dynamics of the material and the structure of the components. Metal stearates affect the packing of PEEK molecules and reduce the total crystallinity by slightly changing the crystal growth of PEEK with no change in unit cell of PEEK. Melt rheology and DMA results suggest that PEEK is a dominant phase in the composites and the metal stearates form a secondary continuous phase in the polymer resin. The reinforcing effect of the metal stearates at low temperatures is maintained up to their softening temperature around 100°C beyond which PEEK begins to dominate the mechanical behavior. Effective moduli of metal stearates in composites suggest that the secondary metal stearate phase forms bicontinuous morphology.

DETECTING POLYMER LONG CHAIN BRANCHING STRUCTURES BY USING ANALYTICAL RHEOLOGY

Xue Chen, Ronald Larson, May 2012

Polymer rheology is a very sensitive indicator of polymer long chain branching, and therefore can be used as a tool to determine polymer structures. This paper is thus focused on the study of the relationship between polymer linear viscoelastic properties and polymer structures using both rheological experiments as well as theoretical modeling methods applied to both model polymers and commercial polymers. In this work, the “hierarchical model” was employed to predict their rheological behaviors as well as to identify the impurities in the materials using the “analytical rheology” concept. After validating the tube model theory successfully on the model polymer melts, we tried to access the validity of the modeling predictions for commercial polyolefins.

RHEOLOGY AND MELT FRACTURE OF POLY(LACTIDES)

Norhayani Othman, Bashar Jazrawi, Parisa Mehrkhodavandi, Savvas G. Hatzikiriakos,, May 2012

The wall slip and melt fracture behaviour of several commercial polylactides (PLAs) have been investigated. PLAs with molecular weights greater than a certain value were found to slip, with the slip velocity to increase with decrease of molecular weight. The onset of melt fracture for the high molecular weight PLAs was found to occur at around 0.2 to 0.3 MPa, depending on the geometrical characteristics of the dies. Addition of 0.5wt% of a poly(?- caprolactone) (PCL) into the PLA that exhibits melt fracture was found to be effective in eliminating and delaying the onset of melt fracture to higher shear rates.

Particle motion dynamics in rotating molds

Denis Rodrigue , Amara Ait Aissa, Carl Duchesne, March 2012

Simple image analysis techniques are used to follow free-flowing particle motion and detect phenomena such as mixing.

Characterization of metallocene polyethylenes for sealing layer applications

Farhad Sadeghi, Abdellah Ajji, March 2012

Molecular weight, molecular weight distribution, chain branching, and melting behavior of metallocene polyethylenes play a crucial role in the sealability and hot tack properties of their films.

Toward better treatment for clogged arteries

Yuan Yuan, Yaru Han, Suming Li , Zhongyong Fan, March 2012

Bioresorbable composites prepared for mechanical performance are promising candidates as cardiovascular stent material.

Achieving robust thermoplastic vibration welds: insights from numerical simulations

Peter H. Foss, Bhaskar Patham, February 2012

Accounting for resin flow behavior in a process model can offer important guidelines for maximizing weld strength by tailoring resin properties and optimizing welding conditions.

Hindering crack growth in natural rubber and nanocomposites

Liqun Zhang, Shaojian He, Jun Liu, Xiaohui Wu , Yiqing Wang, January 2012

Nanodispersed clay can greatly improve crack growth resistance by enhancing tensile strength under static conditions and improving flex-fatigue properties under dynamic conditions.

Biaxial deformation of PET in stretch blow molding

Gary Menary, January 2012

A series of experiments help to understand the effects of temperature, strain rate, and mode of deformation on the biaxial stress-strain behavior of a common industrial plastic.

Specific nonlinear viscoelasticity in reinforced natural rubber

Chuanhui Xu, Yukun Chen, January 2012

Natural rubber reinforced with zinc dimethacrylate shows specific nonlinear viscoelasticity behavior due to ionic cross-links.

Improved vacuum thermoforming of polyamide

Dietmar Drummer, Andreas Seefried, December 2011

Irradiating semicrystalline polyamide 12 film stiffens it by promoting crosslinking and broadens the forming temperature window.

Stronger and faster-flowing plastics for miniaturizing personal electronics

Jiasong He, December 2011

An innovative technique promises to minimize trade-offs between the processability and mechanical performance of engineering plastics.

New dual-functional liquid crystalline photocrosslinkable polymers

Angayan Ravikrishnan, Palaninathan Kannan , Posa Sudhakara, November 2011

Polymers are prepared from stilbene-based precursors for use in photolithography and optical data storage, among other applications.

SEQUENTIAL INJECTION MOLDING: DESIGN CONSIDERATIONS

Jorge Aisa | Javier Castany | Angel Fernández, November 2011

New injection processes have been developed last decades, improving the designer freedom in order to launch attractive functionalities. All these procedures should be carefully analysed before to decide their use, because it is necessary to understand their natural restrictions, cost and operation requirements and rheological implications in the tools construction. This contribution presents a wide study made in the T.I.I.P., research group from the University of Zaragoza, which gives simulation results and experimental values about sequential injection moulding, and some practical considerations for designers and toolmakers, in order to get successfully results.

REACTIVE EXTRUSION OF POLY(LACTIC ACID) WITH STYRENE-ACRYLICGLYCIDIL METHACRYLATE

O. Santana Pérez | J. Cailloux | E. Franco-Urquiza | J. Bou | F. Carrasco | J. Gámez-Pérez | M. Ll. Maspoch, November 2011

In this paper are discussed the rheological changes observed in PLA by one-step reactive extrusioncalandering (REX) using as a chain extender (CE) an oligomeric copolymer styrene-acrylic multifunctional expoxide. Dymamic rheological experiments and gel permeation chromatography tests were used to characterize the architectural modifications of two grades of PLA, with different D-enantiomer content. According to the results, an increase on D-enantiomer content seems to reduce the CE coupling reactions. At the extrusion conditions used high level of chain modification is obtained as could be revealed by the increase on low frequency complex viscosity as well as in the storage modulus (G’) (associated to the melt elasticity).