Michel F. Champagne

Interfacial tension coefficient from the retraction of ellipsoidal drops

Keywords: interfacial tension ; polymer blends ; ellipsoid retraction Reference LTC-ARTICLE-1997-011 URL: http://www3.interscience.wiley.com/cgi-bin/jhome/36698 Record created on 2006-06-26, modified on 2016-08-08

Parameters regulating interfacial and mechanical properties of short glass fiber reinforced polypropylene

The performance of thermoplastic composites is known to depend on the intrinsic properties of the two composite components, the quality of the fiber-matrix interface, and the crystalline properties of their matrix. The objective of this work is to characterize the effect of the addition of modified polypropylene (PP) and silane coupling agent on the mechanical and interfacial properties of short fiber reinforced PP composites. Differential scanning calorimetry (DSC), single fiber composite fragmentation tests (SFC), and mechanical testing are used to understand the different parameters regulating the interfacial properties of composites. No influence of the modified PP on the level of crystallinity is observed. Some differences in the size of the spherulites are observed for acrylic acid grafted PP (PP-g-AA). Those samples also show lower mechanical properties in spite of good interfacial interactions. Maleic anhydride grafted PP (PP-g-MAh) leads to better mechanical performances than PP-g-AA. A high MAh content PP-g-MAh grade with low viscosity is the best polymeric additive used in the present work.

Foaming Polystyrene with a Mixture of CO2 and Ethanol

Use of mixtures of blowing agents in thermoplastic foam extrusion has been an industrial practice for a long time. However, it has gained renewed interest in the past few years due to the introduction of difficult-to-process alternative gases, targeted as potential replacement for the banned ozone-depleting blowing agents. Reasons for blending physical foaming agents (PFA) are numerous. The incentives may be economical, environmental, or technical. With respect to that latter factor, blending suitable PFAs is often regarded as providing a better control of processing conditions. For example, a specific PFA could be selected for its inflation performance and blended with other co-blowing agents chosen for their stabilizing role. Although a considerable amount of work has been done in that area, very little information has been disclosed in open literature. Carbon dioxide (CO2) has been reported as an interesting candidate for low-density polystyrene (PS) foaming, although the required concentrations are associated with high processing pressures due to the low solubility of the gas. Thus, stable processing conditions are difficult to achieve. This work studies the effect of blending CO2 with ethanol (EtOH) as a co-blowing agent for PS foaming. Extrusion foaming performance of this mixture is discussed, with respect to its solubility (i.e., degassing conditions) and rheological behavior. The function of each blowing agent during the process is analyzed with respect to the plasticization, nucleation, expansion, and stabilization phases. Attention is also paid to the interaction involving the two PFA components.

Autoclave Foaming of Poly(ε-Caprolactone) Using Carbon Dioxide: Impact of Crystallization on Cell Structure

The purpose of this study is to develop a better understanding of the main mechanisms controlling the foaming of poly(ε-caprolactone) (PCL), a semi-crystalline biodegradable polymer, using batch processing and CO 2 as the physical blowing agent. A detailed study of the dissolution of CO2 is conducted in order to establish its impact on the transition temperatures of PCL. In a following step, particular attention is paid to the effects of crystallization on cell structure. This foam structure is subsequently linked to the processing window, expressed in terms of the processing temperature with respect to the shifted crystallization temperature and modified crystallization kinetics of PCL. The effects of talc addition on PCL crystallization and foam structure are also investigated, as talc is expected to modify the nucleation rate of crystallites and cells.

Extrusion Foaming of Poly(Lactic acid) Blown with CO2: Toward 100% Green Material

This paper presents a thorough investigation of the continuous extrusion foaming of amorphous poly(lactic acid) (PLA) using carbon dioxide (CO2) as the blowing agent. Detailed results describing the plasticization induced by CO2 dissolution as measured from two different methods, on-line rheometry and in-line ultrasonic technique, are given. Characteristics of the foams obtained from extrusion performed under various processing conditions are also reported. Extrusion of PLA foams in the 20–25 kg/m3 density range was achieved. However, the associated processing window was very narrow: CO2 content lower than ca. 7 wt% did not lead to significant foam expansion while foams blown at CO2 contents larger than 8.3 wt% showed severe shrinkage upon ageing.

Impact-Compression-Morphology Relationship in Polyolefin Foams*

The relationship between the morphology and the mechanical properties of polyethylene (PE) foams has been studied. Experiments have been made on closed cell low density foams at low testing speed as well as in impact conditions. A careful characterization of the cell size distribution and anisotropy was performed and related to the foams mechanical response. The results indicate that the mechanical response of the foams is anisotropic and can be expressed as a function of the foam morphology, using a unique morphological parameter taking into account the cell size in the appropriate direction and foam density. Previously developed for polystyrene foams, the use of this parameter is thus successfully extended to PE-based foams.

Effect of Physical Foaming Agents on the Viscosity of Various Polyolefin Resins

The effect of temperature and type of physical foaming agent (HCFC-142b, n-pentane, and carbon dioxide) on the shear viscosity have been investigated for various types of polyolefin resins (PP, LLDPE, and HDPE). The viscosity changes have been monitored using a commercial on-line process control rheometer mounted on a twin-screw extruder. A plasticization index, based on the respective molecular weights of the foaming agent and the repeat unit of the polymer, is proposed. Comparison with an amorphous polymer, namely polystyrene, is also made for mixtures using the same physical foaming agents.

Foam Extrusion of PS Blown with a Mixture of HFC-134a and Isopropanol

Use of mixtures of blowing agents in foam extrusion has gained interest in the past few years. Reasons for blending physical foaming agents (PFA) are numerous. The incentives may be economical, environmental or technical. With respect to that latter factor, blending suitable PFAs is often regarded as providing a better control of processing conditions. For example, a specific PFA could be selected for its inflation performance and blended with other co-blowing agents chosen for their stabilizing role. Although considerable amount of work has been done in that area, very little information has been disclosed in open literature. 1,1,1,2-tetrafluoroethane (HFC-134a) has been reported as an interesting candidate for polystyrene (PS) foaming, although low densities cannot be easily obtained and stable processing conditions are difficult to achieve. This work studies the effect of blending HFC-134a with isopropanol as a co-blowing agent for PS. Off-line solubility data, on-line rheology measurements and extrusion foaming performance of this mixture will be discussed. The function of each blowing agent during the process will be analyzed with respect to the plasticization, nucleation, expansion and stabilization phases. Attention will also be paid to interaction involving the two PFA components.

Supercritical fluids in thermoplastics foaming : Facts or fallacies?

The past two decades have seen extensive interests and efforts for developing processes based on supercritical fluids (SCF). Microcellular foaming is one of these processes that take advantage of the unique properties of supercritical fluids when they are used as physical foaming agents (PFA). In this technology, the emphasis has been mostly focused on inert gases such as carbon dioxide and nitrogen that both inherently provides very high cell densities and very small cell sizes. Incidentally the benign carbon dioxide is frequently considered as the panacea of PFA, in response notably to the environmental pressures related to the destruction of the ozone layer. Hydrofluorocarbons (HFCs) have also been identified as potential alternative agents for extruded polystyrene foam. Unfortunately, HFCs remain difficult to process at the high concentrations required to yield low-density foams. Surprisingly, the processing difficulties occur when the pressures required for dissolving high HFCs concentrations reach the range located immediately above the critical pressure of the PFA used. PS/HFC systems have been well documented in terms of abnormal behaviors occurring as the foaming agent gets into the supercritical conditions, and similar observations have also been made for other SCF used for thermoplastic foaming. These observations are reported here, and attempts are made to link the supercritical nature of the fluid to the PFA heterogeneities suspected under these conditions.

Foam Extrusion of PP–EMA Reactive Blends

The foaming of PP–EMA thermoplastic elastomers with CO2 during dynamic cross-linking has been investigated. The cross-linking of the ethylene and methyl acrylate (EMA) phase was obtained through an alcoholysis reaction with 1,5-pentanediol. The influence of chemical composition and processing parameters on cross-linking extent was determined. PP–EMA foams were then obtained under different conditions, and analyses were carried out to assess their gel content and density, as well as cell and blend morphology. These properties were found to be closely related: the gel content determines the blend morphology, which in turn greatly influences the foam morphology and the final density.