The effects of thermoplastic poly(olefin) (TPO) morphology on subsequent paintability and thermal shock performance

Adhesion to thermoplastic olefin (TPO) substrates is strongly influenced by the type and amount of solvent contained within paint applied. Morphological changes in the TPO substrate are accomplished in the presence of solvent from the topcoat and vary depending upon paint bake times and temperatures. These morphological changes at and near the surface of TPO affect not only the paint adhesion to the substrate but also the cohesive integrity of the painted plastic composite. This paper attempts to delineate the influence of paint and paint processes on the adhesion/cohesion and mechanical properties of coated TPO parts, in particular, the performance of 2K topcoated TPO substrates under thermal shock conditions. It was found that the most important attribute contributing to thermal shock resistance of painted TPO parts was the bake temperature of the topcoat. A temperature of 250 °F in either the adhesion promoter bake or the topcoat bake is necessary to afford acceptable thermal shock performance. It is postulated that the rearrangement of poly(propylene) crystallites at the uppermost surface of the TPO under a 250 °F bake accounts for the increased cohesive strength of the painted composite.     

Modification of the polarity and adhesive properties of polyolefins through blending with maleic anhydride grafted Fischer–Tropsch paraffin wax

The modification of the polarity and adhesive properties of linear low‐density polyethylene, low‐density polyethylene, and isotactic polypropylene through blending with paraffin wax (Fischer–Tropsch synthesis), grafted by maleic anhydride, was investigated. Maleic anhydride grafted paraffin wax significantly increased the polar component of the total surface free energy of polyolefins. Modified polyolefins also had significantly higher adhesion to the polar substrate, a crosslinked, epoxy‐based resin. The conservation of the good mechanical properties of the blends was observed up to 10 wt % wax, except for isotactic polypropylene blends, for which there was a reduction in the stress and strain at break at wax concentrations higher than 5%. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3069–3074, 2006     

Adhesion of flame-treated polyolefins to styrene butadiene rubber

Samples of polyethylene and polypropylene have been submitted to repeated short duration (75 ms) flame treatments, at optimum flaming conditions. Surface energies of untreated and flamed specimens were determined by liquid contact angle measurements. It appears that the surface energy of polyethylene increases much more than that of polypropylene after flame treatment. The flamed polymer surfaces were further examined by electron spectroscopy, Fourier Transform IR spectroscopy and secondary ions mass spectrometry. The adhesion properties of modified polymer surfaces were studied by testing in peel the bonded Styrene Butadiene Rubber/polyolefins assemblies. Scanning electron microscopy (SEM) and water contact angle measurements have been used to observe the locus of failure. Good correlations were obtained between surface energy and adhesion strength, the increase in adhesion strength being particularly important for flamed PE/SBR assemblies. In addition, the peeling in a liquid medium allowed the determination of the respective contribution to adhesion of chemical and physical interactions. It is shown that a major part of the adhesion strength increase is of chemical origin, particularly for the bonded flamed PE/SBR assemblies.     

2003 Roy W. Tess Award

Conclusions Mechanical interlocking of topcoat with the nonpolar TPO surface can be achieved through the use of an adhesion promoter, namely a chlorinated poly(olefin). The type of CPO used, in addition to the types of solvents and heat effects used, can substantially influence the degree of adhesion/cohesion obtained within the CPO.TPO system. Heat histories, TPO molding variations, CPO types, including solvent and resin variations, and topcoat (basecoat/clearcoat) chemistries were all found to influence the adhesion/cohesion of the painted TPO assembly. Surface damage resistance was found to mirror the effects of adhesion as described earlier. Control of the interphase formed between the TPO substrate and the subsequent topcoat layers becomes increasingly important if one wishes to maintain damage resistance within the painted composite. Testing methodology development, namely “gouge” chip, abrasion, and scratch resistance, is paramount in predicting performance under specified loads. Through interpretation of data received in the various testing methodologies, the mechanical properties of the topcoat/substrate combination may be varied to obtain the performance required in a variety of applications. The Roy W. Tess Award in Coatings is presented annually by the Division of Polymeric Materials: Science and Engineering (PMSE) in recognition of outstanding contributions to coatings science and technology. Funded by a grant to the Division by Dr. and Mrs. Roy W. Tess, the purpose of the award is to encourage interest and progress in coatings and recognize significant contributions to the field. Dr. Rose Ryntz, Manager and Staff Technical Fellow with Visteon Corporatiom, Dearborn, MI, received the award from Dr. Paul Valint, Jr., Chair of the PMSE Division in September 2003 during the 226th meeting of the American Chemical Society in New York, NY. Dr. Ryntz's award address followed the Award Symposium. The following papers were presented at that symposium.     

TPO／CPO形态、界面结构及粘结性能研究的最新进展

从介绍热塑性聚烯烃TPO及其在汽车工业中的应用出发,综述了近年来国内外在TPO组分的相容性、TPO的形态和性能、TPO／CPO（氯化聚烯烃）的界面形态和结构、TPO／CPO粘结性能和机理几个方面研究的最新进展,并提出了未来的发展趋势。     

The Adhesion Properties of an Ozone Modified Thermoplastic Olefin Elastomer

The adhesion properties of a thermoplastic olefin elastomer (TPO) after ozone exposure are studied with attenuated total reflection infrared spectroscopy (ATR), the lap shear test, and contact angle measurement. The ozone treatment is applied after the TPO is dip-coated with acrylic acid (AA) that is mixed with benzophenone, benzoyl peroxide (BPO), and azobisisobutyronitrile initiators. ATR spectra confirm the presence of grafted AA on TPO, the amount of which depends on the ozone exposure time and the type of initiator applied. The total surface energy, the polar component, and lap shear strength (LSS) of the grafted TPO increase with increasing ozone exposure time and also vary with the initiator. All AA-grafted TPOs have much greater LSS than the TPO without AA. The greatest LSS is obtained from the specimen grafted with AA and BPO. In addition, the small differences in surface energies and failure strains associated with the great changes in LSS obtained from various specimens implies that the nature of the grafted layer has a significant effect on the adhesion strength.     

Surface modification of calcium carbonates studied by inverse gas chromatography and the effect on mechanical properties of filled polypropylene

Inverse gas chromatography (IGC) has been used to characterize the surfaces of a pure calcitic calcium carbonate as well as samples that had been treated with sodium polyacrylate and/or stearic acid. The dispersive components of the surface free energy for the pure material agreed well with related literature data. Polar contributions to the surface interactions with a range of probes were determined. The results show that the surface treatments reduced the polarities of the surfaces and that modification with stearic acid produced a non-polar, low-energy surface. Some mechanical properties of the polypropylene composites containing the modified calcium carbonates were found to correlate well with the filler surface energies. Copyright © 2004 Society of Chemical Industry     

Comparison of polarity parameters for glass fibers obtained by inverse gas chromatography and solvatochromism

Glass fibers with different surface properties (differently sized and unsized) have been investigated by means of inverse gas chromatography (IGC) at infinite dilution as well as by UV/Vis spectroscopy of solvatochromic probe dye molecules. Surface acid–base parameters obtained from the specific energies of adsorption of polar probes using IGC were compared with empirical polarity parameters obtained from shifts in the UV/Vis absorption maxima of adsorbed solvatochromic probe dyes. Both methods give useful information on surface characteristics. Solvatochromism seems to be suitable for a quick sizing characterization and, therefore, this method may become a significant surface analytical tool in the field of adhesion compared with the established IGC methodology.     

Understanding the Affinity between Components of Wood–Plastic Composites from a Surface Energy Perspective

To evaluate surface compatibility in wood-plastic composites (WPCs), the dispersion and acid–base components of surface energy of various thermoplastic resins (matrices) and several wood-based reinforcing materials were determined using inverse gas chromatography (IGC). Polypropylene (PP), nylon 6, poly(ethylene terephthalate) (PET), poly(trimethyl terephthalate) (PTT), high impact polystyrene (HIPS), and styrene maleic anhydride (SMA) were used as thermoplastic resins, while wood flour (hot water extracted and un-extracted), microcrystalline cellulose (MCC) (50 μm and 90 μm), α-cellulose (60 μm), and silicified microcrystalline cellulose (SMCC) (60 μm) were used as reinforcing materials. All matrices and reinforcing components were exposed to low vapor concentrations of apolar (decane, heptane, nonane, octane) and polar (chloroform, ethyl acetate, dichloromethane, acetone, and tetrahydrofuran) probes. Methane and helium were employed as reference and carrier gases, respectively. IGC retention times were used to determine the acid–base component of surface energy of the analyzed materials. The corresponding surface energy, work of adhesion, and work of cohesionwere calculated based on the van Oss–Chaudhury–Good approach (acid–base and Lifshitz–van der Waals interactions). Composite performance was analyzed by measuring tensile and flexural strengths according to ASTM standards. The results indicated that for the same type of filler (assuming similar shape and dimensions), the mechanical properties of the composites increased when the ratio of the work of adhesion to the work of cohesion increased. A similar trend was observed when the thermoplastic resin employed to create the composite possessed an acid–base component of surface energy greater than zero.     

Theoretical analysis and experimental characterization of the TPO/adhesion promoter/paint interface of painted thermoplastic polyolefins (TPO)

Exterior and interior automotive applications of TPO (thermoplastic polyolefin) resins, which are, often, composed of a paint coating over an injection‐molded TPO, have increased interest in the surface chemistry and physics of TPOs. Specifically, the interface system composed of base‐coat paint/adhesion promoter/TPO is of primary importance in controlling the paint adhesion to the TPO. The major, active component in the adhesion promoter is a chlorinated polypropylene (CPO). A theoretical model based on phase thermodynamics and diffusion kinetics resulted in a prediction that the TPO/CPO interface should have a lower bound thickness of about 11 nm and an upper bound of about 400 nm. A battery of experimental strategies to characterize this interface system was discussed. Techniques used were transmission electron microscopy (TEM), atomic force microscopy (AFM) and scanning transmission X‐ray microscopy (STXM). The near‐surface morphology of both unpainted and painted, injection molded TPO plaques exhibited ethylenepropylene rubber particles close to the surface, i.e. within the first 0.1–0.8 micrometer of the TPO surface, and no “overlayer” of transcrystalline polypropylene at the surface of the TPO. Each of these microscopic methods showed that the adhesion promoter/TPO interface was very sharp. The thickness of this interface was measured with respect to the interdiffusion of the CPO and TPO by STXM. The STXM measurements yielded an apparent interface thickness between the adhesion promoter and TPO of 340 ± 80 nm. This was in good agreement with the theoretical predictions.     

A new technique for evaluating ink–cellulose interactions: initial studies of the influence of surface energy and surface roughness

Ink–cellulose interactions were evaluated using a new technique in which the adhesion properties between ink and cellulose were directly measured using a Micro-Adhesion Measurement Apparatus (MAMA). The adhesion properties determined with MAMA were used to estimate the total energy release upon separating ink from cellulose in water. The total energy release was calculated from interfacial energies determined via contact angle measurements and the Lifshitz–van der Waals/acid–base approach. Both methods indicated spontaneous ink release from model cellulose surfaces, although the absolute values differed because of differences in measuring techniques and different ways of evaluation. MAMA measured the dry adhesion between ink and cellulose, whereas the interfacial energies were determined for wet surfaces. The total energy release was linked to ink detachment from model cellulose surfaces, determined using the impinging jet cell. The influences of surface energy and surface roughness were also investigated. Increasing the surface roughness or decreasing the surface energy decreased the ink detachment due to differences in the molecular contact area and differences in the adhesiom properties.     

Fused Deposition Modeling of Polyolefins: Challenges and Opportunities

Polyolefins are the largest class of commercially available synthetic polymers that are extensively used in a variety of applications from commodities to engineering owing to their low cost of production, good physico-mechanical properties, light weight, good processability, and recyclability. Compared to conventional molding techniques, fused deposition modeling (FDM)-based 3D printing is a smart manufacturing technology for thermoplastics due to its low cost, ease of production of complex geometrical parts, rapid prototyping, and scalable customization. FDM 3D printing can be an ideal manufacturing technology for polyolefins to manufacture various complex parts. However, FDM 3D-printing of polyolefins is challenged bycritical printing problems like high warpage, dimensional inaccuracies, poor bed adhesion, and poor layer-to-layer adhesion. In this review, a fundamental understanding of polyolefins and their FDM 3D-printing process is established, and the recent progress of FDM 3D printing of polyolefins is summarized. Furthermore, strategies to overcome warpage and to improve mechanical strength of the 3D-printed polyolefins are provided. Finally, future prospectives of FDM 3D-printing of polyolefins are critically discussed to inspire prospective research in this field. It is believed that this review article can be tremendously useful for research work related to FDM of polyolefin-based materials.     

Friction and its effect on the mechanical- to-thermal energy conversion during extrusion of poly(vinylidene chloride)

Solid state friction reduction has been found to be an effective method for extrusion stabilization of a high coefficient of friction (COF) thermally sensitive polymer. A poly(vinylidenechloride) copolymer (PVDC) was studied alone and blended with various polyolefins to change its frictional behavior. COF of the polymer rubbing on a metal surface was measured under conditions typical of an extrusion process. These results correlated well with the measured mechanical energy consumed during extrusion. Of the polyolefins studied, high and low density polyethylene were found to be very effective for lowering friction and improving extrusion performance of the PVDC. Polypropylene was found to be much less effective. Interface temperature where melting occurs due to frictionally generated heat has been experimentally shown to be a function of COF and the bulk metal temperature.     

Chemical oxidation of high-density polyethylene: Surface energy,functionality, and adhesion to liquid epoxy

The application of polyolefins has increased significantly over the past few decades. However, their chemical inertness and low surface energy limits their application in many industries where high adhesion to polar materials is required, such as for composites and protective coatings. Herein, six different acids are used to create polar functional groups on High-Density Polyethylene's (HDPE) surface and to increase its adhesion to liquid epoxy (LE). Contact angle measurements, Fourier Transform Infrared Spectroscopy (FTIR), X-ray Photoelectron Spectroscopy (XPS), and pull-off strength measurements are used to analyze the surface energy and functionality of HDPE and to measure its adhesion to LE. The results show that each acid increases both the polar and disperse surface energies of HDPE to a different extent, but that this is not necessarily a function of acid strength. Chlorosulfonic acid and chromic acid increase the oxygen to carbon ratio by a factor of 8 and increase HDPE's adhesion to LE by more than 400%. Furthermore, a comparison between predicted work of adhesion values from the OWRK model and experimental results shows that the latter are significantly higher than what is predicted, especially with increasing surface polarity.     

The role of adhesion in the mechanical properties of filled polymer composites

Filled polymer composites have been prepared in which the energetics of the filler surfaces was systematically varied in order to investigate the dependence of the mechanical properties of the composite on the interfacial strength as predicted by the thermodynamic work of adhesion at the filler-matrix interface. A high-purity silica filler was used, treated with three different organofunctional silane coupling agents (two alkylsilanes and an aminosilane) to varying degrees from zero to complete coverage. The surface energetics of the modified fillers was characterized using both inverse gas chromatography (IGC) and dynamic contact angle analysis (DCA). While the surface energy assessments from IGC were higher than those obtained with wetting measurements, as expected, the trends with fractional coverage of silane were the same for each method, and were used to evaluate the thermodynamic work of adhesion. Highly filled polymer composites were prepared by dispersing the variously treated silica fillers into the amorphous thermoplastic matrix polymers: poly(methyl methacrylate) and poly(vinyl butyral). Specimens of the composites were tested mechanically to give the yield stress. The poly(methyl methacrylate) composites all failed cohesively in the matrix, unaffected by any of the filler surface treatments. The poly(vinyl butyral) composites, however, all displayed purely interfacial failure, with the yield stress strongly dependent on the type and extent of the filler surface treatment. While all three silanes were found to decrease the filler surface energy, and consequently the thermodynamic work of adhesion, with higher surface coverage, corresponding decreases in the yield stress were found only for the alkylsilanes. For the aminosilane, the measured yield stress was found to increase with surface coverage and therefore to decrease with the work of adhesion. The difference in behavior between the two types of coupling agent is explained in terms of acid-base effects.     

Characterization of adhesion performance of topcoats and adhesion promoters on TPO substrates

Adhesion of organic coatings to thermoplastic olefin (TPO) substrates in automotive applications has been an issue for makers of automotive parts since TPO was first used in exterior applications, primarily fascia. A widely used technique for assuring paint adhesion to TPO is the use of adhesion promoter primers based on chlorimated polypropylenes (CPO). Much research has been focused on understanding the forces involved at the interfaces of substrate, adhesion promoter, and topcoats resulting in the adhesion or the loss of adhesion in various environmental conditions. This study correlates the adhesion performance of CPO and nonchlorinated adhesion promoters (NCPO) as measured by peel strength with properties observed through microscopy techniques. Adhesion performance of CPOs, NCPOs, and blends are quantified through the use of 90° and 180° peel strength studies. Surface characteristics of adhesion promoters applied over a TPO substrate and cured at various temperatures are examined through the use of atomic force microscopy (AFM).     

Functional lignin-SiO2 hybrids as potential fillers for phenolic binders

Functional lignin-SiO₂ hybrid fillers were synthesized and characterized with a view to their potential application in binders for phenolic resins. The properties of these fillers and of composites obtained from them with phenolic resin were compared with those of systems with lignin or silica alone. The chemical structure of the materials was investigated by Fourier transform infrared spectroscopy. Surface properties of lignin-SiO₂ fillers were tested using inverse gas chromatography (IGC). IGC was used for determination of surface energy and surface heterogeneity of the studied fillers. IGC made it possible to assess the adhesion between the tested fillers and phenolic resins. Interactions of functional fillers with phenolic resins were also evaluated by IGC. The results indicated that lignin-SiO₂ interacted strongly with the phenolic resin, more strongly than pure lignin. This was proved by SEM observations: thanks to the stronger interactions of lignin-SiO₂ hybrid with phenolic resins, a more homogeneous composite was obtained. Thermo-mechanical properties of lignin–silica and resin systems were investigated by DMTA. DMTA results showed that phenolic binders with lignin-SiO₂ fillers have better thermo-mechanical properties than systems with lignin or silica alone: higher glass transition temperature and a smaller decrease in storage modulus. Lignin fillers can thus provide new, promising properties for a phenolic binder combining the good properties of lignin as a plasticizer and of silica as a filler improving mechanical properties.     

The Influence of Surface Energetics of Calcium Carbonate Minerals on Mineral-Polymer Interaction in Polyolefin Composites

Surface energetics of ground calcium carbonates (GCC), with or without stearic acid treatment, were determined by Inverse Gas Chromatography (IGC). The surface energy data were utilized as a predictive tool to explain the optimum coating level often needed on calcium carbonate minerals to obtain the desirable mechanical strength in filled polypropylene composites. The dispersive components of the surface energies for the uncoated carbonates were also correlated with the corresponding impact resistance data. The surface with the highest energy was found to be the least resistant while the least energetic mineral, on a comparative scale, was the most resistant to impact. It is suggested that understanding the surface energetics of finely-divided solids may be a key for the development of future mineral-filled polymer composites.     

The Influence of Surface Energetics of Calcium Carbonate Minerals on Mineral-Polymer Interaction in Polyolefin Composites

Surface energetics of ground calcium carbonates (GCC), with or without stearic acid treatment, were determined by Inverse Gas Chromatography (IGC). The surface energy data were utilized as a predictive tool to explain the optimum coating level often needed on calcium carbonate minerals to obtain the desirable mechanical strength in filled polypropylene composites. The dispersive components of the surface energies for the uncoated carbonates were also correlated with the corresponding impact resistance data. The surface with the highest energy was found to be the least resistant while the least energetic mineral, on a comparative scale, was the most resistant to impact. It is suggested that understanding the surface energetics of finely-divided solids may be a key for the development of future mineral-filled polymer composites.     

Examination of the surface properties of kaolinites by inverse gas chromatography: Dispersive properties

The application of inverse gas chromatography (IGC) for the examination of the surface properties of untreated kaolinite and kaolinites surface-treated with titanate coupling agents is discussed. This paper presents and discusses the dispersive properties expressed by γ_S^D, the dispersive component of the surface free energy, as determined at various temperatures. The γ_S^D values of all the samples were negatively correlated with the temperature of IGC measurement. At the same temperature of IGC measurement, the values of γ_S^D determined by IGC were significantly lower for the surface-treated kaolinites than for the untreated ones. The γ_S^D value of the kaolinite surface-treated with isopropyl triisostearoyl titanate (ITT) at 150°C exhibited a surface energy close to that (28.3 mJm^-2) of polyethylene with no surface polarity.