SPE Library

Long chain branching (LCB) has long been recognized as an important molecular parameter that significantly influences both processing and property performance of polymers. In this study, we report on the effects of LCB on the blown film processing and performance behavior of both narrow and broad molecular weight distribution (MWD), linear-low density polyethylene (LLDPE) resins. The LCB was introduced by peroxide addition and by varying the finishing stabilization additives. The results showed that while improvements in some processing characteristics were observed with LCB addition, this generally came at the expense of physical properties. Thus, in contrast to the general belief in the literature, we contend that LCB addition in LLDPE type film resins involves a trade-off in improved processing at the expense of film properties.

The aim of this work is to obtain composite films of polypropylene (PP) to substitute paper. The plastic component is PP from mineral water bottle (PPb) collected from municipal plastic waste (MPW) and the filler component is CaCO3. Composite films with weight ratio of PPb and CaCO3 (70:30) were prepared. These films were surface treated by corone discharge. Preliminary results have shown a good printability with pencil and pen ink on these films without treating and an improved printability with ink jet after surface treatment. These films were then compared to cellulose paper by physico-chemical characterizations.

In an extrusion process polymer is melted and conveyed through the extrusion die. In the die the form of the melt is converted from a cylindrical into a requested cross-section of the profile. The primary objective of the rheological design of extrusion dies in polymer processing is to obtain an even melt velocity distribution at the outlet of the die. For a given complex cross-section of a profile, yet no procedure is known to calculate or predict the die flow channel geometry with respect to an even velocity profile at the outlet. By designing a complex profile extrusion die an iterative process has to be performed to optimize the flow channel.In this paper a new calculation method is presented which uses a combination of the Finite-Element-Analysis (FEA) and the 'network-theory'. With the aid of this method it is possible to accelerate the iterative optimization process for the design of profile extrusion dies. Furthermore, this method is combined with an optimization scheme based on the evolution strategy. The result is an algorithm to optimize the flow channels in extrusion dies automatically.

We have used computer simulations to study the phenomena of crack formation and propagation in two-phase polymeric materials. The simulated materials are subjected to constant-force tensile stress resulting in deformation. We use computer graphics to create animations of the cracking phenomena.We are trying to answer the key question where the cracks form: inside the flexible matrix, inside the rigid phase, or at the interface. Computer simulations provide answers to this and other questions which cannot be answered by conducting experiments.The results obtained guide us in the creation of real materials with improved mechanical properties.

In the “mold development” designation it is comprehended a process composed by the (sub)processes of the mold specification, contracting, design, planning, manufacturing, “in-field” service, etc. By the Concurrent Engineering (CE) principle, all these processes are performed simultaneously (with higher or lower degree) which reduces the mold development time, through the minimization of changes in the mold subprocesses procedures.The CE principles imply application of teamwork. These teams are composed by experts from different functional areas (for specific mold development subprocesses).It is presented a CE model based upon mold development processes to fulfill the increasing needs of design and mold making industry.

Shape memory polymers are novel materials that can be easily formed into complex shapes, retaining memory of their original shape even after undergoing large deformations. In this paper, we develop constitutive equations to model the thermo-mechanical behavior of crystallizable shape memory polymers. This is done using a framework that was developed recently for studying crystallization in polymers ([1],[2]). The constitutive equations are formulated in a full thermodynamic framework using the notion of multiple natural configurations. Here, we outline the main components of such a model and investigate its response for a crystallizable shape memory polymer undergoing a typical thermo-mechanical cycle. The results of the model compare favorably with experimental observations.

The blow moulding industry has achieved a good understanding of the process, which has been in large scale operation since the 1960's. Consequently, control of machine settings such as heater band temperatures, die gap position, die and mould temperatures is quite advanced. However, to date, little work has been done to address the control of state parameters describing material behaviour during processing, such as parison weight and temperature distribution. Control of state parameters is essential as material property changes, environmental factors and machine operating drifts can significantly change the dynamic operating point of the machine.

Nothing is more frustrating to decorators and assemblers of plastic parts that attempting to perform these functions with parts that are warped and out of specification. Injection molding is the process used to produce the bulk of these parts. There are three principal causes of warpage in injection molded parts: differential shrinkage, internal stresses and distortion resulting from ejection of the part from mold. Often, two or three of these conditions exist simultaneously, thereby complicating the solution significantly. This paper discusses the causes of these conditions and the means to control them through design.

With the emergence of today’s new geography model, where the omnipresent electronic place coexists with the physical one, the challenge is now to take advantage of the available technology to build and coordinate efficient and innovative business relationships, in order to draw strengths from the diverse and worldwide distributed knowledge, experience, expertise and competencies.In July 1998, an international consortium was established between three SME’s, two research and development institutes and one governmental organization. Six organizations from four different countries (Portugal, Germany, Mexico and People’s Republic of China) united by a shared goal: the development of the project “Round the Clock – 24 Hours Collaborative Product Development Work”[1].The basic idea, behind the project conceptualization was to take advantage of the time gap between the several organizations located in different time zones, for the establishment of a continuous non-stop product development cycle at a planetary scale based on the suitable use of a communication platform and coherently supported by an efficient work methodology.

The diversity of possible structures in copolymers of ethylene and a wide variety of comonomers provides an interesting field for research.Low-density polyethylene exhibits special properties not yet surpassed by other polymers such as linear low-density polyethylene.In this work, a highly branched unsaturated comonomer (HBU) was synthesized and copolymerized with ethylene by using Et(Flu)2ZrCl2/MAO catalyst system. Reactions were performed in a 500ml autoclave equipped with mechanical stirrer. Toluene and MAO were added to the reactor under nitrogen atmosphere. Ethylene was introduced until constant pressure of 2 bar at 90°C. Catalyst activity and polyethylene characteristics were evaluated and compared to LDPE. The results showed that the catalyst activities for the copolymerization were surprisingly higher when compared to the homopolymerization of ethylene and in the same order of magnitude of the copolymerization with 1-octene.

Polyurethane foam is often molded directly in place as a thermal or vibration insulator, energy absorbing material, or core material for a sandwich structure. A smooth thin skin forms between the mold and the interior cellular structure of the foam. A non-uniform microstructure is often visible when foam cross-sections are examined, resulting in density variations throughout the foam. This paper investigates the effect of processing temperature on the average density, density gradient, compressive modulus, and compressive strength, for a free rise, water blown polyurethane foam system molded in aluminum cylinders. Resulting properties are also compared to reference samples that have a uniform density. It is shown that the processing temperature has a significant effect on the foam density and density gradient. This density gradient, as well as the presence of the skin, affect the compressive modulus but have minimal effect on the compressive strength.

Specifying realistic tolerances that insure form, fit or function is one of the most overlooked areas in product development. All too often, tolerance specifications are missing, vague, and unrealistic. This and the subsequent 'variances' can lead to higher than necessary manufacturing costs, poor market acceptance and product liability exposure.This paper will examine the cost, quality and time-to-market implications of injection molded part tolerances and how to improve the tolerance specification and implementation process. The primary focus will be on the obvious - dimensional tolerances, but we will also look at the impact of visual specification tolerances and mechanical requirement tolerances.

In recent years, the use of stackable spiral (pancake") dies in blown film extrusion has been continuously growing. One main disadvantage of this die design is the susceptibility to mechanical die deflections resulting from melt pressure which can lead to a poor melt distribution or leakage problems. In this paper a flow simulation model will be presented that is able to calculate the melt velocity and pressure distribution in the spiral section. Additionally a mechanical simulation model has been derived that can calculate the deflection of the die plates for a given pressure load. Because of the mutual influence of melt flow and die deflection the two models are coupled and iteratively solved. The impact of the die deflection on the melt distribution and experimental results will be shown."

Nonlinear creep in polypropylene has been previously explored. In the present work we examine the influence of montmorillonite on nonlinear creep. The issue is of paramount interest since long-term properties have never been explored in this nascent field. Creep-recovery measurements were done for nanocomposites containing 1, 2, 3 and 5 % of montmorillonite. Master curves and shift factors were determined based on horizontal and vertical shifts using Schapery's equation. The results show the influence of the reinforcement on the properties of polypropylene. Infrared images show differences in deformation mechanisms from one sample to another.

Poly(ether ketone ketone) (PEKK) is a relatively new engineering plastic with high temperature stability and excellent chemical and solvent resistance. The ratio of terephthaloyl (T) and isophthaloyl (I) moieties, see scheme 1, can be varied to control the crystallization rate and crystallinity of PEKK without substantially changing the end-use temperature [1,2].Sauer et al. [3,4] reported that PEKK and a thermoplastic polyimide (PI) synthesized from 4,4’-bis(3-aminophenoxy)-biphenyl and pyromellitic dianhydride were miscible in the amorphous phase. Both homopolymers are semi-crystalline, so the phase behavior of PEKK/PI blends can be complex. Crystallization of either or both components in the blends depends on the miscibility of the two polymers in the melt, the temperature history during cooling from the melt and the kinetics of crystallization of the two polymers. In this study, we investigated the effect of crystallization in PEKK/PI blends on the thermal transitions and crystalline structure using differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and wide-angle X-ray diffraction (WAXD).

Cyclic-olefinic copolymers (COC) are being used in flexible packaging as a blend component or as a discreet layer in multi-layer polyolefin films. They are typically used to enhance stiffness and heat resistance in food packaging. As a core layer in laminated or coextruded multilayer films, they provide high moisture barrier and exceptional clarity and stiffness.In place of commonly used organic slip additives, they can decrease film to film coefficient of friction (C.O.F.) to levels of commercial interest. Performance as a slip additive, however, is related to a number of variables, including viscosity of the matrix, type and add level of the COC and the film process melt temperature. Various microscopy techniques investigated support the findings.

The strength of Polypropylene is influenced by the thermal history of the material and oxidation experienced during molding. As the material gains more thermal exposures and subject to more shear stress, the tensile strength of the material is going to be influenced. In this work, five trials of reground polypropylene will be compared to determine the effect of multiple processing on the strength of the material. The relationship between the elongation and tensile strength of the part will be compared.Five different trials will be compared in this paper with each gaining another cycle through the machine. What affect the thermal and physical processing parameters have on the material after five runs will be examined. All of the material being used has gone through the same number of cycles, and has been processed at the same parameters throughout the experiment.

Co-rotating twin screws are the prime choice of machinery in the field of polymer compounding. Additional applications beyond that are the mixing, blending and homogenizing of viscous materials in the chemical industry where a self-wiping and thus self-cleaning profile is of the utmost interest for best performance.A great number of these processes e.g. filling with high loading of fillers, does not require extremely high powered twin screws since energy input for these materials and processing tasks is relatively low when comparing it to polymer compounding tasks such as alloying and reinforcing.It was therefore the challenge for design and process engineers to design a deep-flighted twin screw coping with these processes. The two key characteristic dimensions of a co-rotating twin screw diameter ratio" and "power-volume factor" were adapted such to meet the requirements of the low energy compounding tasks. At the same time mechanical constraints such as shaft and element interface shaft strength and gear box design had to be considered too."

Rubber compounds used in tires usually contain blends of more than one rubber to synergistically combine the properties of these rubbers. These include styrene-butadiene (SBR) and butadiene (BR) rubber or blends of natural rubber (NR) and butadiene rubber.In this study we investigated the true-stress true-strain birefringence behavior of blend of SBR and BR with a new real time spectral birefringence system and obtained the stress optical constant for the SBR/BR blends covering 10-40% BR concentration. The stress optical constants were found to decrease with the increase of BR concentration.

To exploit fully the available software tools for Finite Element stress analysis of engineering polymers, there is a need for constitutive models that capture the complexity of material behaviour. Recent work has led to the development of such a model for glassy polymers, where glass structure evolves during deformation, causing strain-softening after yield. The new anisostructural model is an extension of the physically-based 3D Glass-Rubber" constitutive model proposed earlier by Buckley and Jones. To test the model further an experimental study has been made of plastic deformation in compression of a range of glassy atactic polystyrenes with varying molecular masses. The model gave good agreement with measured strain-softening in these polymers but in its present form over-predicted the dependence of yield stress on molecular mass."