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High-heat crystal polystyrene (HHCPS) and high-impact polystyrene (HIPS) macroscale parts with microscale features were injection molded using a commercially available mold base with matching steel insert and microfeatured silicon wafer [...]

This study investigates the effects that dynamic melt manipulation based injection molding has on the locally induced molecular orientation and tensile strength of injection molded polystyrene. Melt manipulation refers to a process where the polymer melt is manipulated during molding beyond the extent normally encountered in conventional injection molding. The specific melt manipulation process investigated in this article is vibration assisted injection molding, where a conventional injection molding machine is augmented by oscillating the injection screw (in the axial direction) during the injection and packing phases of the molding cycle. The localized final molecular orientation and morphology that results dictates the resultant product response, and typically improved mechanical properties are observed. Specimens with molecular orientation distributed more uniformly along the gage length typically exhibited higher tensile strength than samples with a gradient of orientation along the gage length. Smaller test specimens machined along the gage length of larger molded specimens showed dramatic tensile strength increase in the regions of higher melt manipulation, further supporting the promise of this novel processing methodology. POLYM. ENG. SCI., 47:1912-1919, 2007. © 2007 Society of Plastics Engineers, INTRODUCTION Injection molding processing is one of the most common manufacturing techniques for polymer products. While there are many types of molded plastic products that affect our daily lives, the [...]

This study investigates the effects of melt manipulation on the development of molecular orientation during injection molding processing. Vibration-assisted injection molding (VAIM), a particular method of melt manipulation, is a variation of conventional injection molding in which oscillatory energy is imparted to the polymer melt by vibrating the injection screw axially during the injection and packing stages of the molding cycle. Previous studies have shown that this process positively affects the tensile strength of polystyrene parts, but that the magnitude of the increase is dependent upon the processing parameters. Observation of birefringence patterns in VAIM processed samples show a significant impact on molecular orientation. A specially designed mold and associated image capture system has been developed and is used in this study to record the birefringence patterns of the polymer melt within the cavity during processing. Observation of birefringence shows that orientation develops primarily during post-vibration packing of the part and not during the vibration phase as previously thought. The observed effects of process parameters such as melt temperature, packing pressure, and vibration duration are discussed. POLYM. ENG. SCI., 46:1691-1697, 2006. [c] 2006 Society of Plastics Engineers, INTRODUCTION Vibration-assisted injection molding (VAIM) is one of several processes that seek to enhance the properties of injection molded articles by manipulation of the polymer melt within the mold cavity. [...]

With society focusing more and more on environmental issues, the recycling of materials of all types has become an important concern. As a result of previous processing and usage, the properties of recycled materials are often significantly inferior when compared to their unrecycled counterparts. Recycled polymeric materials, for example, have lowered molecular weights caused by previous thermal and/or shear histories. Thus, the scope of application for recycled materials has traditionally been very limited. With the aid of a new processing concept known as vibration-assisted injection molding (VAIM), the mechanical properties of products containing recycled polymeric materials could be dramatically improved. The current paper presents the results of an initial experimental investigation into the application of VAIM for recycled polystyrene (Recycled-PS) products. A number of recycled/new material blends were studied, and in all cases significant product mechanical property enhancements were realized through the use of VAIM. It was concluded that VAIM molded products containing as much as 50% low-grade recycled material could be made stronger than products made using traditional molding with 100% new polymer Detailed results are presented in the paper, along with some insight into the likely fundamental mechanism underlying the utility of the VAIM technique. [DOI: 10.1115/1.1870012]

During wire drawing processes a critical parameter is the micro-hardness distribution imposed. The present numerical and experimental investigation focused on the effects of and interdependence between processing parameters such as die angle, bearing length, lubrication, and draw speed during wire drawing. The micro-hardness distribution imparted by the drawing process was selected as the focal product quality attribute. The goal of the study was to evaluate the ability to create desired hardness levels in a drawn wire product. The numerical component of the study was performed using DEFORM-2D[TM], a commercially available metal forming software package based on the finite element method. In addition, experimental verifications of the software predictions were completed wherever possible. Full factorial designs of the processing parameters were studied, and it was found that the final hardness distribution was primarily affected by the die angle. Interactions between the four processing parameters were negligible. Based upon this finding, it was concluded that strength and hardness variations inherent to stock wire could be detected and minimized during wire drawing through the appropriate science-based selection of die angle. This could dramatically enhance the consistency of the wide range of common metal products that are manufactured from wire stock. [DOI: 10.1115/1.1688380]

The current investigation focused on the development of intelligent injection molding processes by utilizing a neural network based control unit. In this study, the emphasis was on the control of flow front progression during injection molding processes. The progression of a flow front into a mold cavity is crucial since it dictates the locations of possible air voids and weld lines. It is desired that the flow front progresses towards the vent locations and that weld lines coincide with locations where their quality decreasing influence has a minimum impact on the overall part performance. The intelligent control scheme developed is based on a neural network that was trained with data obtained from a first-principles based process model rather than actual molding experimentation. The control strategy was developed such that one can specify a desired flow progression scheme and the controller will take corrective actions during the molding process to realize this scheme. This is done by controlling the inlet flow rate at various inlet gate locations. Experiments were conducted with a 2-D, complex shaped mold cavity to test the performance of the control unit during actual injection molding processes. The mold had two inlet gates and three different desired flow progression schemes were considered. In all cases, the first principles model/neural network based control unit was able to steer the flow front along the corresponding desired flow progression path.

Poly(glycerol-sebacate) (PGS) is a biodegradable elastomer that is of interest in biomedical applications. While a porous format is common for tissue engineering, PGS degradation has been primarily studied in its nonporous format. This work investigates porous PGS degradation at three cure temperatures, resulting in materials with different mechanical and chemical properties that further influence degradation. Specimens exhibit varied structural degradation, ranging from limited loss of structure to complete loss. The thermal behaviors and mechanical properties also change during degradation, depending upon cure temperature. These observations can inform the choice of polymer processing methods for porous PGS applications. [ABSTRACT FROM AUTHOR]

Objectives: Because gestational trophoblastic disease is rare, little evidence is available from randomized controlled trials on optimal treatment and follow-up. Treatment protocols vary within Europe, and even between different centers within countries. One of the goals of the European Organization for Treatment of Trophoblastic Diseases (EOTTD) is to harmonize treatment in Europe. To provide a basis for international standardization of definitions, treatment and follow-up protocols in gestational trophoblastic disease, we evaluated differences and similarities between protocols in EOTTD countries. Methods: Members from each EOTTD country were asked to complete an online structured questionnaire comprising multiple-choice and multiple-answer questions. The following themes were discussed: incidence of gestational trophoblastic disease and gestational trophoblastic neoplasia, definitions, guidelines, classification system, treatment, recurrence, and follow-up. Results: Forty-four respondents from 17 countries participated in this study. Guidelines were present in 80% of the countries and the FIGO (Fédération Internationale de Gynécologie et d'Obstétrique) staging and risk classification was often used to estimate risks. Agreement about when to start chemotherapy for post-molar gestational trophoblastic neoplasia was present among 66% of the respondents. Preferred first-line treatments in low- and high-risk gestational trophoblastic neoplasia were methotrexate (81%) and EMA-CO (etoposide, methotrexate, actinomycin D, cyclophosphamide, vincristine) (93%), respectively. The definition of human chorionic gonadotropin normalization after hydatidiform mole evacuation was two consecutive normal values for nine countries. The FIGO definition of post-molar gestational trophoblastic neoplasia based on human chorionic gonadotropin plateau or rise was agreed on by 69% of respondents, and only 69% and 74% defined low-risk and high-risk disease, respectively, using FIGO criteria. There were major differences in definitions of recurrence, chemotherapy resistance and follow-up protocols among countries, despite EOTTD consensus statements. Conclusions: This questionnaire provides a good overview of current clinical practices in different countries. Based on the survey results, it is clear that there are several gestationaltrophoblastic disease-related topics that need urgent attention within the EOTTD community to create more uniformity and to aid the development of uniform guidelines in Europe. [ABSTRACT FROM AUTHOR]