bluuebunny/crossref_metadata_2025_split huggingface dataset:
The effects of filler size on the properties of thermoplastic polyolefin blends
Authors: Wong Tony L. , Barry Carol M. F. , Orroth Stephen A. 
Published: April 2004

AbstractThe effects of filler size on the properties of a thermoplastic polyolefin (TPO) blend were examined by using wollastonite and talc with particle sizes ranging from 1.2 to 40 μm. While addition of filler produced significant changes in the mechanical properties of the blend, filler size affected only impact strength. However, filler size, filler coating, and injection speed had a major effect on the surface properties of the blend. Faster injection produced denser “shear zone layers” which exhibited better scratch resistance and poorer paint adhesion than those obtained with slower injection. Scartch resistance and paint adhesion also decreased with increasing filler particle size. Filler coatings altered the scratch and adhesion properties of the polypropylene (PP) blends.
Role of processing aids in the extrusion of molten polymers
Authors: Achilleos E. C. , Georgiou G. , Hatzikiriakos S. G. 
Published: April 2004

AbstractProduct quality and, in general, processing windows and rates of production in the extrusion of molten polymers are limited by various flow instabilities (mainly melt fracture) that are observed at high production rates. While there still are unresolved issues in comprehending these phenomena, industry demands for process optimization dictate the employment of processing aids (PAs) for product quality improvement and energy requirement reduction. In this review paper, most commercially used processing aids (PAs) are discussed, namely, fluoroelastomers, stearates, small amounts of polymers blended with the process polymer, and the newly discovered boron nitride as pure and in combination with other fluoroelastomers. This paper focuses on the appropriate and optimum usage of the various PAs as well as on the mechanism that underlies their action for flow enhancement and instability elimination. Finally, numerous experimental observations are discussed, and several examples are illustrated.
Influence of atmospheric pollutants on the natural and artificial aging of rigid poly(vinyl chloride)
Authors: Belhaneche‐Bensemra Naïma 
Published: April 2004

AbstractThe natural aging of rigid poly(vinyl chloride) (PVC) used in building and construction areas has been studied. Bars of PVC exposed in Algiers, where the concentrations of atmospheric pollutants (NOx, O3, hydrocarbons) are known, show a small drop in strain at break and stress at break, whereas hardness remains practically constant. Analysis by IR and UV‐visible spectroscopy shows the appearance of chemical structures due to polymer degradation (carbonyl groups, hydroperoxide groups, and polyenes) after the first months of exposure at three sites. It seems that O3 exerted the most deleterious effect, followed by hydrocarbons and then by NOx. An artificial aging test was carried out to investigate the effect of O3 on the degradation of PVC, and the results were compared to those from outdoor aging.
Phosphite ester compositions for PVC compounds
Authors: Stevenson Don R. , Harr Mark E. , Jakupca Michael R. 
Published: April 2004

AbstractThe activity of various structural classes of liquid organophosphite esters has been examined in flexible PVC applications. Blends of the most active phosphites have been developed as alternative heat stabilizers for PVC. These new phosphite mixtures eliminate the dependence of compounders upon mixed‐metal stabilizer systems based on heavy metals such as barium and cadmium. Static oven aging tests showed the superior performance of these blends compared to that of traditional mixed‐metal stabilizers.
Effect of boron nitride on melt fracture phenomena and processability of lldpe during extrusion
Authors: Lee Sang Myung , Kim Jung Gon , Lee Jae Wook 
Published: April 2004

AbstractMelt fractures related to processing instabilities limit processing rates in many commercially important polymer processing operations, such as fiber spinning, film blowing, extrusion, and various coating flows. Therefore, melt fracture is responsible for deteriorating the quality and the mechanical properties of final products for rates greater than a critical processing one at which melt fracture occurs. In this study, a commercial linear low‐density polyethylene (LLDPE) was modified by adding a small amount of boron nitride (BN) during extrusion in order to improve processability. Capillary rheometry was used to assess processability at various temperatures, levels of applied shear rate, and the length‐to‐diameter (L/D) ratio for both the pure resin and resins containing boron nitride. Also, parallel‐plate rheometry was used to evaluate the dynamic rheological properties of these resins. The relationship between the characteristic relaxation time and the critical shear rate for the onset of melt fracture and slip is discussed.
Melt blending preparation of PVC‐sodium clay nanocomposites
Authors: Wang Dongyan , Parlow Daniel , Yao Qiang , Wilkie Charles A. 
Published: April 2004

AbstractPoly(vinyl chloride) (PVC)–clay nanocomposites were prepared by melt blending using a sodium montmorillonite clay. The nanocomposites were characterized by X‐ray diffraction and transmission electron microscopy techniques. The best description of these materials is as mixed immiscible‐intercalated nanocomposites. Mechanical testing showed some improvement in the mechanical properties of the nanocomposites relative to those of the virgin polymer. Cone calorimetry showed that the presence of the clay had an advantageous effect on the fire and smoke properties of the polymer.
The effects of plasticizers on the properties of poly(vinyl chloride) foams
Authors: Veličković Sava J. , Stojkov Dejan , Popović Ivanka G. , Brankov Klara , Čvorkov Ljubomir 
Published: April 2004

AbstractThe effects of plasticizers on poly(vinyl chloride) (PVC) plastisol mixtures were investigated. The investigations were carried out by determining the density of the PVC foam obtained by gelling the plastisol, as well as its elasticity and degree of expansion. Two series of experiments using different types of PVC were performed, using eight plasticizers, individually or as mixtures. Two‐component plasticizer mixtures showed better properties than single‐component plasticizers, and mixtures of di‐iso‐heptyl phthalate (DiHP) and butyl benzyl phthalate (BBP) proved to be the most appropriate. The effect of plasticizer amount also was investigated, and of the three parameters studied, the foam density, which steadily increased with plasticizer amount, was the critical one. It was also shown that in order to obtain consistent results, the foam expansion had to be precisely timed and the temperature carefully chosen.
Advances in the stabilization of flexible PVC by using a liquid calcium‐zinc technology
Authors: Reddy James E. , Hackett Jeremy A. 
Published: April 2004

AbstractThe global market for liquid mixed‐metal stabilizers is migrating toward heavy‐metal‐free products, Historically, these systems have not been performance and cost competitive. High efficiency calcium‐zinc stabilizers have the potential to replace heavy‐metal‐based products. The intrinsic value of non‐phenolic lubricating calcium intermediates and calcium‐zinc stabilizers is discussed.
Study of PVC stabilization using capillary rheometry
Authors: Bacaloglu Radu , Fisch Michael H. , Stewen Ulrich , Bacaloglu Ilze , Krainer Edward 
Published: April 2004

AbstractCapillary rheometry allows monitoring of PVC thermal and shear stress degradations separately. Based on testing of PVC compounds with a capillary rheometer, stabilizers can be efficiently optimized to reduce both degradation processes. Capillary rheometry is an important tool for further improving productivity of PVC processing at high shear rates.
Co‐injection molding of PVC with other thermoplastics: Processing, properties, and applications
Authors: Parsons Mark , Toyoda Paul 
Published: April 2004

AbstractRigid poly(vinyl chloride) (PVC) was co‐injected with glass‐fiber‐reinforced PVC (GFR‐PVC), polypropylene (PP), acrylonitrile‐butadiene‐styrene copolymer (ABS), and polycarbonate (PC) by using the Mono‐sandwich co‐injection process. Up to three through‐thickness skin‐core morphologies were observed along the length of the sample. Near the gate, the core was always a single, continuous layer. In some cases, the core diverged into multiple or discontinuous layers. Farther from the gate, flow of the core ceased, leaving a skin‐only region. The skin and core layers were more uniformly distributed through the test plaque when injection speed was low. Adhesion between PVC and PP was poor. Skin and core layers delaminated, and mechanical properties were poor. The PVC adhered well to GFR‐PVC, ABS, and PC. No layer delamination occurred, and mechanical properties were intermediate between those of the skin and core components alone. Dropped dart impact energy was controlled more by the skin layer than the core. In rigid PVC/GFR‐PVC co‐injected samples, impact energy was 2.5 times greater when GFR‐PVC was the core than when GFR‐PVC was the skin.
Molecular weight distribution of commercial emulsion grade PVC
Authors: Pepperl G. 
Published: April 2004

AbstractAt first glance the molecular weight distributions (MWDs) of suspension and emulsion grade PVC are very similar. However, studying the MWDs for both polymerization technologies in more detail reveals systematic differences that can be explained by the differences in the polymerization processes. The MWD of continuous emulsion PVC is broader than that of batch emulsion PVC, which, in turn, is broader than that of suspension PVC. When correlating molecular weight data to K values, it has to be considered that K values from resins including polymerization additives are different from the K value of the pure polymer. The knowledge of the differences in MWD may be helpful for estimating differences in other properties of the products.
Preparation of PVC‐clay nanocomposites by solution blending
Authors: Wang Dongyan , Wilkie Charles A. 
Published: April 2004

AbstractPVC‐clay nanocomposites have been prepared by solution blending of the polymer with both sodium montmorillonite and an organically modified clay. The nanocomposites have been characterized by X‐ray diffraction and transmission electron microscopy; in all cases the materials are best described as mixed immiscible—intercalated nanocomposites, Thermogravimetric analysis shows that, in some cases, the onset temperature of the degradation is enhanced, and the fraction of nonvolatile residue is always decreased. This decrease in the amount of char indicates a significant change in the degradation pathway of the polymer, caused by the presence of the clay. For some preparations, the tensile strength and modulus are enhanced, in agreement with the formation of a partially intercalated structure.
Kinetics of fatigue and creep crack propagation in PVC pipe
Authors: Hu Y. , Summers J. , Hiltner A. , Baer E. 
Published: April 2004

AbstractThe kinetics of creep and fatigue crack growth in PVC pipe were studied in order to develop a methodology for predicting long‐term creep fracture from short‐term fatigue tests. Fatigue and creep crack propagation followed the conventional Paris law formulations with the same power 2.7: da/dt = AfΔK2.7I and da/dt = BK2.7I, respectively. The activation energy for creep crack propagation, obtained from the temperature dependence of the Paris law prefactor, allowed extrapolation of high temperature creep fracture to low temperature creep crack growth rates. The activation energy for fatigue crack propagation was much lower than that for creep. Therefore, fatigue and creep could not be directly correlated by using the prefactor in the covenentional Paris law formulations. Furthermore, a unique value of the Paris law prefactor did not describe frequency and R‐ratio (amplitude) effects in fatigue crack propagation. Nevertheless, conformity of crack growth rates measured under all conditions to the same Paris law power suggested that correlation should be sought in alternative formulations of the crack growth rate.
PVC/wood‐flour composites compatibilized with chlorinated polyethylene
Authors: Guffey Virginia O. , Sabbagh Amiel B. 
Published: April 2004

AbstractChlorinated polyethylene has been demonstrated to be an effective compatibilizer for dissimilar materials in various mixed‐polymer or recycled‐polymer systems. In this paper the use of chlorinated polyethylene to compatibilize polymer/natural‐fiber composites is discussed. Examples of applications in PVC/wood‐flour composites are given.
Manufacture of rigid PVC/wood‐flour composite foams using moisture contained in wood as foaming agent
Authors: Matuana Laurent M. , Mengeloglu Fatih 
Published: April 2004

AbstractRelatioships between the density of foamed rigid PVC/wood‐flour composites and the moisture content of the wood flour, the chemical foaming agent (CFA) content, the content of all‐acrylic foam modifier, and the extruder die temperature were determined by using a response surface model based on a four‐factor central composite design. The experimental results indicated that there is no synergistic effect between teh CFA content and the moisture content of the wood flour. Wood flour moisture could be used effectively as foaming agent in the production of rigid PVC/wood‐flour composite foams. Foam density as low as 0.4 g/cm3was produced without the use of chemical foaming agents. However, successful foaming of rigid PVC/wood‐flour composite with moisture contained in wood flour strongly depends upon the presence of all‐acrylic foam modifier in the formulation and the extrusion die temperature. The lowest densities were achieved when the all‐acrylic foam modifier concentration was between 7 phr and 10 phr and extruder die temperature was as low as 170°C.
Effect of calcium carbonate on the abrasive wear of melt processing equipment in filled systems
Authors: Mobley Gary , Boutelle Tonia , Garrett Susan , Joiner Laurie , Calhoun Allison 
Published: April 2004

AbstractCalcium‐carbonate‐loaded systems were tested for abrasive wear on extruder parts through a test that measures the weight of a bronze alloy screen placed in a supporting screen pack before and after 5500 g extrusion run. The effects of particle size and mineral identity were explored in this work as well as the effect of mineral loading level. It was found that the abrasiveness of calcium carbonate is, as expected, much lower than that of titanium dioxide and increases with increased loading levels. It was also shown that the larger the median of the particle size distribution (PSD), the greater the abrasive wear on the screen. Finally, it was shown that the degree of wear could be correlated with the level of impurities present in the natural mineral.
Direct and indirect effects of online learning on distance education
Authors: Shin Namin , Chan Jason K.Y. 
Published: April 2004

AbstractThis paper presents an exploratory study that investigates the effects of online learning on distance education students in an open university context. Two hypotheses are posited: (1) a direct relationship exists between students’ involvement in online learning and distance learning outcomes, and (2) an indirect relationship exists between these two domains via the mediating variable of an institutional Transactional Presence (TP), that is, a student's sense of the availability of and connectedness with an educational institution. Student learning achievement, satisfaction and intent‐to‐persist are used as indicators of outcomes of distance learning. The analysis of data garnered from 285 distance students reveals multifaceted relationships between students’ engagement in online learning, their perceptions of institutional TP and the three learning outcome variables. Besides the findings, the paper will discuss factors affecting students’ engagement in online learning in relation to different requirements, that is, optional or compulsory online use as well as the level of the course (undergraduate or postgraduate).
Improving the quality and effectiveness of computer‐mediated instruction through usability evaluations
Authors: Crowther Michael S. , Keller Chris C. , Waddoups Gregory L. 
Published: April 2004

AbstractBrigham Young University's Center for Instructional Design (CID) creates online courses and multimedia instructional applications for university faculty. This paper asserts that including usability testing as a part of evaluation improves the quality and effectiveness of computer‐mediated instruction. The paper describes the fundamental purpose and functions of usability testing, and also distinguishes between different forms of evaluation: accessibility, quality assurance (QA), usability and implementation. Through a detailed case study, we describe how usability testing improved the quality of a computer‐based chemistry course and facilitated a clearer analysis of the learning effectiveness of this course.
The failure of a virtual social space (VSS) designed to create a learning community: lessons learned
Authors: McPherson Maggie , Nunes Miguel Baptista 
Published: April 2004

AbstractThe disappearance of physical social spaces from today's society is seen by some to be a modern phenomenon, resulting in isolation and lack of socialisation. In fact, this is always the case in distance education, due to geographical dispersion and disparate time schedules of learners. Very often, peer‐to‐peer socialisation in distance education only occurs as part of formal learning activities, or is just left to the student's own initiative. This situation is compounded by the modularity of Virtual Learning Environments (VLEs), forcing students to jump from one module space to another as they progress through a course. All discussion threads, conversations or record of previous dialogues are then lost. This paper reports on the design, development and extensive evaluation of a Virtual Social Space (VSS) conceived to address these problems and to support the creation of a learning community for a Continuing Professional Distance Education (CPDE) Masters in IT Management. An action research approach was adopted to establish student needs, design and develop the site and to explore it with students. Initially received with enthusiasm and perceived as a good idea by the students, the VSS was not entirely successful. This paper discusses how characteristics of this cohort had an impact on students’ perception and usage of this social space to create a learning community.
Mental constructions and constructions of web sites: learner and teacher points of view
Authors: Hazzan Orit 
Published: April 2004

AbstractThis research focuses on knowledge and ways in which knowledge may be constructed in the learner's mind. Specifically, it addresses the Web as a cognitive supporter for learning, organising and constructing a new domain of knowledge. In particular, the research analyses student reflection on constructing web sites. The analysis is based on an ongoing reflection of 40 prospective and in‐service teachers who took a course on educational computational environments. The students were asked to choose a complex topic and to document the process of constructing a web site that would present their chosen topic. They were to reflect upon the process with regard to their decision making, difficulties encountered, ways of thinking, considerations and insights. Student reflection is analysed from two perspectives: the first perspective examines how the task of constructing a web site contributes to student learning of complex topics, the second perspective views the students as teachers who explore how constructing a web site contributes to their understanding of learning processes.
The impact of environmental noise on song amplitude in a territorial bird
Authors: Brumm Henrik 
Published: April 2004

Summary

The impact of environmental background noise on the performance of territorial songs was examined in free‐ranging nightingales (Luscinia megarhynchos Brehm). An analysis of sound pressure levels revealed that males at noisier locations sang with higher sound levels than birds in territories less affected by background sounds.
This is the first evidence of a noise‐dependent vocal amplitude regulation in the natural environment of an animal.
The results yielded demonstrate that the birds tried to mitigate the impairments on their communication caused by masking noise. This behaviour may help to maintain a given transmission distance of songs, which are used in territory defence and mate attraction. At the same time, birds forced to sing with higher amplitudes have to bear the increased costs of singing.
This suggests that in songbirds the level of environmental noise in a territory will contribute to its quality and thus considerably affect the behavioural ecology of singing males.
A trade‐off between two resource‐demanding functions: post‐nuptial moult and immunity during reproduction in male pied flycatchers
Authors: Sanz Juan José , Moreno Juan , Merino Santiago , Tomás Gustavo 
Published: April 2004

Summary

Costs of reproduction might be mediated by a resource‐allocation trade‐off between immunity and reproductive effort. Recent studies have suggested that the moult–breeding overlap observed mainly in males may affect this trade‐off. In order to test whether increased investment in immunity may affect the onset of moult or reproductive output in a species with moult–breeding overlap, we immunized breeding male pied flycatchers Ficedula hypoleuca (Pallas) with a non‐pathogenic antigen (sheep red blood cells) in the first week post‐hatching and compared their moult score, parental effort and reproductive success shortly before fledging with that of control males injected with sterile phosphate‐buffered saline.
Immunized males provisioning nestlings delayed the onset of post‐nuptial primary moult compared to control males. The experimental activation of the immune defence of males affected their stress levels (heterophile/lymphocyte ratio, heat‐shock proteins) on day 13 after chicks hatched. An activated immune response tended to depress reproductive output, although the experimental design was not efficient enough to find a significant effect because the manipulation was not performed early enough in the nestling period.
The results suggest that experimental activation of the males’ immune system decreased the resources necessary for initiating post‐nuptial moult. The trade‐off between immunity and moult onset may imply costs of delayed moult in cases of infection and may interact with reproductive immunosuppression in cases of moult–breeding overlap. Moult, immunity and reproduction are locked in a three‐way interaction which may markedly affect avian life histories.