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Conference Proceedings

Effects of Montmorillonite Layered Silicates on the Crystallization Properties of Polylactic Acid
Timmy Chan, May 2006

Recently, polylactic Acid (PLA) has been increasingly considered for many applications due to its origin from renewable resources and its biodegradability. Separately, there has been interest in montmorillonite layered silicates (MLS), because of their remarkable ability to improve polymer properties. Strength and barrier properties are particular improvements to PLA that are considered critical. We examine the influence of MLS and processing on the crystallinity of PLA nanocomposites. Screw speed and feed rate of an extruder connected to a blown film die were systematically varied. The materials were supplied by the Naticak Army Research Laboratory and developed by Ratto and Thellen.Increasing screw speed during manufacturing decreases the residence time and is associated with the generation of smaller crystallites. Feed rate is another variable that is considered.Permeability and non isothermal Differential Scanning Calorimetry (DSC) at a single heating rate was reported recently. Here we report on the Avrami parameters of the PLA and corresponding nanocomposites.

Strategies to Balance the Flow in Profile Extrusion Dies
J.M. Nóbrega, O.S. Carneiro, May 2006

There are two strategies commonly adopted to balance the flow in an extrusion die for profiles: those involving and those not involving modifications of the die land cross section. In this work, a numerical code, which is being developed by the authors to perform the automatic optimization of profile extrusion dies, is used to illustrate the main issues concerning the die design strategies and to show the consequences of their application. It was concluded that the design strategies based on adjustments of the die land cross section generate dies more stable to variations of the processing conditions, but produce profiles with lower dimensional stability. On the other hand, strategies based on modifications of the die land length may be difficult to apply to profiles having significant differences in flow restriction, fact that can be overcame by the use of flow separators. However, this approach affects negatively the sensitivity of the tool and may hinder the mechanical resistance of the produced profiles.

Beam Shaping with Diffractive Optics for Laser Micro-Machining of Plastics with a Femtosecond Laser
Kittichai Sojiphan, Miranda Marcus, Hae Woon Choi, Chunmeng Lu, Avraham Benatar, Dave F. Farson, L. James Lee, May 2006

Microfluidic devices and micro-electro-mechanical systems (MEMS) have become one of the most interesting and important applications in biotechnology, biomedical, pharmaceutical, life sciences, and agriculture. Research in manufacturing technologies used to fabricate these devices is important for improved quality as well as for time and cost savings during mass productions. A new approach for the fabrication of these MEMS devices is the laser ablation using diffractive optics elements (DOE) for beam shaping. In results described in this report, a 775 nm-wavelength high power femtosecond laser was used to ablate circular channels on polystyrene specimens. This approach to creating channels in the polystyrene was found to be promising even though the DOE used was not optimized for the femtosecond laser wavelength.

The Effect of Polyethylene Catalyst Type and Pigment Concentration on Crystal Growth during Rotomoulding
P.R. Hanna, G.M. McNally, J. Kissick, M. Kearns, W.R. Murphy, May 2006

This work studied the effect of catalyst type and pigment concentration on the impact properties, crystallinity and morphology of rotationally moulded polyethylene (PE) parts. Microscopy, shrinkage and differential scanning calorimetry analysis techniques were used. It was observed that the base PE catalyst had an effect on the extent of crystallinity but that the level of pigmentation had only limited effect on the extent of crystallinity. The reduction in impact performance for turboblended pigmented samples was due to the relatively poor distributive and dispersive mixing of the pigment within the polymer matrix.

Structural and Thermal Aspects of the Performance of Hybrid Moulds with SLS
P.G. Martinho, P.J. Bartolo, A.J. Pontes, A.S. Pouzada, May 2006

Hybrid moulds with molding blocks obtained by rapid tooling techniques are used for production of small batches. The mechanical and thermal performance of the inserts is particularly important at the design stage. This paper describes the use of Selective Laser Sintering (SLS) inserts for hybridmoulds. These inserts were experimentally study and the feasibility of this technology for the fabrication of hybrid-moulds investigated. Computer simulations using commercial software were also carried out. The obtained results show a good agreement between simulation and experimental data.

Analysis of Powder and Pellet Melting during Extrusion with a Perturbation Method
Mark D. Wetzel, Donald A. Denelsbeck, Susan L. Latimer, May 2006

It was reported previously that the melting of a polymer during twin screw extrusion can be quantified using dynamic, on-line monitoring of a perturbation technique. Preliminary results suggested significant differences between the progression of melting of Polypropylene (PP) feed pellets and powders. This paper reports additional data on PP and Polyethylene (HDPE) feeds in the form of pellets, powder and pellet/powder mixtures. In addition to a delay of melting in the case of the powder feed, reductions in power intensity of the melting peak were also observed with the pulse perturbation technique. Unexpected behaviors in the melting of powder/pellet blends are described. The perturbation method is further examined by comparing the pulse energy input profiles with the residence time distribution and steady state power consumption over a range of throughput/screw speed (Q/N) operating conditions.

Measuring the Depth of Penetration of the Laser Beam in the Absorbing Material for Through-Transmission Welding Processes
Dan Watt, Yingping Huang, Bobbye Baylis, Inna Severina, Elena Maeva, May 2006

The numerical modeling of various TTLW processes has the potential to be very useful for predicting laser welding results. However these models must assume either an absorption coefficient, or a depth of penetration in which the beam is absorbed. Accurately measuring the coefficient is not generally convenient, and is sensitive to small changes in carbon black concentration from batch to batch. A simpler test procedure for estimating the depth of penetration in the absorbing layer is described in this paper.

Characteristics of PP/PS/Clay Nanocomposite Produced by High-Intensity Ultrasonic Process
Kyung Yl Kim, Hyung Su Kim, Jae Wook Lee, May 2006

Polymer-clay nanocomposites of various concentrations were prepared by ultrasonically assisted melt blend process. The ultrasonic blend process using high intensity ultrasonic wave was employed to enhance nano-scale dispersion during melt mixing of polymer blend and organically modified clay. The materials studied were linear polypropylene and polystyrene reinforced with organophilic montmorillonite clay (nanoclay) at 3-5 wt% loadings. The effectiveness of the proposed ultrasonic processing technique on polypropylene matrix nanocomposites was evaluated by XRD, rheological measurements and thermal properties. We expected enhanced breakup of layered silicate bundle and further reduction in the size of dispersed phase with better homogeneity compared to the different immiscible blend pairs.Also, it was expected that generation of macroradicals in polymer mixture can lead to in-situ copolymer formation by their mutual combination, which should be an efficient path to compatibilize immiscible polymer blends and stabilize their phase morphology in the absence of other chemical agents.

A Numerical Study of Scanning Through-Transmission Laser Welding
Yingping Huang, Alfred Yu, Dan Watt, Bobbye Baylis, May 2006

A numerical model has been developed to simulate the heat conduction during the through-transmission laser welding (TTLW) process. The simulations were performed using the SIMPLER (Semi Implicit Method for Pressure Linked Equations Revised) software. The model was used to calculate the changes in the temperatures at points throughout the heated areas of the parts during the entire welding time. The temperature distributions and peak temperatures generated in the faying surface of welds at same line energy (LE) but different powers and speeds have been predicted and examined. Large temperature differences obtained when keeping LE constant, but doubling both power and speed were calculated and interpreted using this model.

Characterization of the Twin Screw Extrusion Process
Mark D. Wetzel, Donald A. Denelsbeck, Susan L. Latimer, May 2006

In contrast to the well developed field of polymer characterization, the advances of extrusion process characterization lagged far behind. Engineers have to deal with problems such as process scale-up and product quality control primarily by empirical means. Practically no quantitative expressions exist between the operating conditions and the important process parameters such as degree of mixing, intensity of mixing and melting, the nature of polymer melting or plasticization, or energy consumption. We propose along with new supporting data that the parameters introduced previously, ?P/?Q and ?P/?N, that is, energy per unit of additional mass and energy per unit of screw revolution could be used to characterize the melting behavior of a polymer in an intermeshing, co-rotating twin screw extrusion process. The parameters appeared to be independent upon the extrusion rate (Q) and screw speed (N) in the ranges examined (4.5 to 36kg/hr and 100 to 500RPM). We further propose that additional parameters, such as those defining the kinetics of melting, average residence time (for melting and the over all) and residence time distribution obtainable by the pulse perturbation technique may be required in order to sufficiently define a given extrusion process.One can also predict with excellent agreement the observed specific mechanical energy input of extrusion, defined by extrusion power/throughput (P/Q), with simple linear expressions (Eqs. 1 and 2). The parameters c1 (?P/?Q), c2 (?P/?N), and a constant c3, can be determined directly by steady state extrusion experiments without employing pulse or step perturbation methods.

Ultrasonic Plunge Welding of Polypropylene Nonwovens
Hakan Ozaltun, Avraham Benatar, Satinder K. Nayar, May 2006

Polypropylene blown micro fibers with spun bonded cover web made from Polypropylene and polyester fibers were used for the experimental study of the ultrasonic plunge welding of nonwovens. A face centered central composite design of experiment (DOE) with 3 process variables and 3 levels was used to evaluate the effects of vibration amplitude, weld time and weld pressure. In addition to those settings, three different welding profiles were used resulting in forty-five different welding conditions with five specimens welded for each condition. Increasing the welding time generally improved the weld strength until it leveled off. For high welding pressures physical damage was observed around the welding area. Finally increasing the amplitude of vibration resulted in making the welding seam tougher with higher breaking forces.

Constructing Unique Micelle Structures of Charged Block Copolymers via Co-Assembly with Organic Counterions
Honggang Cui, Zhiyun Chen, Kelly Hales, Kai Qi, Zhibin Li, Karen L. Wooley, Darrin J. Pochan, May 2006

A variety of fascinating micelle structures have been achieved by the assembly of charged triblock copolymers through the interaction with organic counterions in mixed THF/water solution. Essentially, the formation of toroidal micelles was observed in specific conditions of polymer chain constitution, the chain length of each block, the ratio of THF to water and mixing procedures. Our results showed that final assembled structures can be easily tuned by either varying the chain structure of organic counteirons or changing the ratios of THF to water.

Flash Prevention Due to Skin Solidification
Kalan Shah, Mihir Patel, Sonny Nguyen, May 2006

The purpose of this paper is to investigate the role of skin solidification in preventing flash during injection molding of amorphous and semi-crystalline resins. In conventional injection molding, polymer melt is injected into a comparatively cold mold, resulting in the development of a solidified layer. A null hypothesis of this paper is that the development of a solidified layer reduces the exerted clamp tonnage on the machine and may even prevent the formation of flash under high pressures resulting in improved part quality. A set of Design of Experiments was implemented with control factors including barrel temperature, mold coolant temperature, pack pressure and delay time; the characterized responses included part weight, part thickness, and flash length. The results indicated that the addition of a delay time between the injection and packing stages eliminated flashing in this application.

Study of Ultrasonic Welding of HDPE-Based Nanoclay Composites
Sean Flowers, Seth Humphrys, James Thomas, Abbass Mokhtarzadeh, Avraham Benatar, May 2006

Clay-based nanocomposites have high modulus, high specific strength, and low permeability. They have become popular in many industries because these material properties can be achieved by the addition of small volume fractions of inexpensive clay particles. Ultrasonic welding of four high density polyethylene nanocomposites with 0 wt%, 3 wt%, 6 wt% and 9 wt% nanoclay was investigated. The effects of weld force, amplitude of vibration, and weld time for energy director joints or weld collapse for shear joints on weld strength were evaluated. Three parameter, three level design of experiments (DOE) were utilized to find near-optimum welding parameters. For the best welding conditions for both energy director and shear joints, increasing the nanoclay content resulted in significantly decreasing weld strength. For energy director joints the decrease in strength with increasing nanoclay content was greater than for the shear joints.

Biomimetic Surface Microstructures and Their Replication to Polymeric Materials
Pratapkumar Nagarajan, Katherine Woo, Donggang Yao, May 2006

Biomimetic surface structures such as anti-reflective protrusions on the moth eye and self cleaning pillars on the Lotus leaf have a profound influence in the development of technologically important engineering devices and systems. In this study, we prepared microstructured polymer surfaces that mimic the surface patterns on the pronotum and the wing of dung beetles (Phanaeus vindex) using micromolding techniques. The patterned embossing master was fabricated by electroforming the surface of the dung beetle. The electroformed nickel replica was then used to hot emboss on ABS substrates. The replicated polymer surface patterns were found to be comparable with the original surface patterns on the dung beetle.

In-Situ Synthesis of Nanocomposite Systems by Interfacial Polycondensation
Zehra Sibel Kalkan, Lloyd A. Goettler, May 2006

In this work, layered silicate- and silica-polyamide 66 nanocomposites are synthesized in-situ by interfacial polycondensation to produce highly dispersed nanocomposite products. The two routes involve either incorporating a highly exfoliated silicate structure from a suspension of silicate platelets in one of the monomer phases or generating a silica hybrid through sol-gel chemistry. Two different approaches in the latter route allow the tetraethoxysilane (TEOS) condensation to occur either simultaneously with or sequentially to the nylon polymerization. Transmission electron and x-ray dispersive scanning microscopy, along with TGA, DSC and FT-IR measurements, are used to monitor and characterize the well dispersed structures produced, which are expected to manifest in enhanced thermo-mechanical properties of the nylon.

Effects of Metallization Coating on Ultrasonic Welding of Abs
Abbass Mokhtarzadeh, Avraham Benatar, Chung-Yuan Wu, May 2006

Thin metal coating of plastic parts for increased optical reflectivity, improved EMI/RFI shielding, decreased permeability, or for decoration has gained more importance in recent years in automotive, electronics, medical and toy industries. This coating is often found in the weld area and there are concerns regarding its effect on weldability. Therefore, in this work ultrasonic welding of ABS components with metallic coatings was studied to evaluate their effect on weld strength. Two types of coatings were studied: an aluminium coating with hexamethyldisiloxane (HMDSO) as its topcoat and a stainless steel coating. The coated ABS was ultrasonically welded to uncoated ABS. Three factors, weld time, weld pressure, and amplitude of vibration were varied to find near optimum welding conditions. It was found that the aluminum or stainless steel coating had a very small effect on the ultrasonic weld strength for ABS. The maximum weld strength obtained was 28.5 MPa, 28.2 MPa and 26.9 MPa for uncoated, and for aluminum, and stainless steel coated ABS, respectively.

Ultrasonic Assisted Extrusion of HDPE/Clay Nanocomposites
Sarat K. Swain, Avraam I. Isayev, May 2006

High density polyethylene (HDPE) /clay (Cloisite-20-A) nanocomposites were prepared by using single screw compounding extruder with continuous treatment of ultrasound at different amplitude up to 10?m. The die pressure and power consumption due to ultrasound were measured at different feed rates of materials of various clay concentrations up to 10 wt%. Rheological, mechanical and thermal properties of ultrasonically treated and untreated nanocomposites were studied. X-ray diffraction (XRD) and transmitted electron microscope (TEM) were used to investigate the dispersion of clay and nanocrostructure of composites. The experimental results showed that sonication enhanced the dispersion during melt mixing of HDPE and clay.

Thermal Transitions and Rheology of Propylene-Ethylene-Based Terpolymers
Abdelhadi Sahnoune, César García-Franco, Sudhin Datta, May 2006

We report on the thermal and the flow characteristics of newly developed propylene-ethylenediene terpolymers. These propylene-rich products were made using single site metallocene catalyst Exxpol™ technology and cover a broad range of chemical composition. The thermal transitions were determined using thermal scanning calorimetry (DSC). The glass transition temperature decreased from about -18 to -28 °C as the ethylene content was increased from 8 to 16 wt%. The crystallinity and the crystallization rate were also strongly affected by the composition. The linear viscoelastic behavior of the different polymers was measured with small amplitude oscillatory shear at various temperatures. The modulus and the viscosity are characteristic of linear polymers and are, for similar molecular weight, independent of chemical composition. The incorporation of un-saturation makes these polymers easily cross-linkable using various chemical or radiation techniques. The crosslinking helps extend their end-use application to elevated temperatures, much higher than their uncrosslinked copolymer counterparts, as demonstrated by dynamic mechanical thermal analysis measurements.

Synthesis of Needle-Like Polyanilines
Woo-Hyuk Jung, Dong-Young Kim, Young-Moo Lee, Stephen P. McCarthy, May 2006

Needle-like polyanilines (PANi) were prepared in aqueous media by chemical oxidation. P-toluenesulfonic acid (pTSA) used to protonate aniline formed good conditions to make anilinium complexes. By slow addition of ammonium peroxydisulfate (APS), polyanilines were prepared in the micelles and grew to be needle-like aggregates potentially useful as conductive fillers for electromagnetic interference and radar absorbing materials. The needle-like aggregates prepared at 15°C showed conductivity up to 3 S/cm and a maximum aspect ratio of 26 L/D, and were observed to partially peel off into fibrils after washing by means of optical microscopy and scanning electron microscopy (SEM). The needle-like polyaniline-pTSA complexes prepared with 0.5 M aniline concentration showed good thermal stability up to 200°C. The high conductivity of the needle-like aggregates was ascribed to their well developed crystalline structures compared with those of spherical particles.

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