Relating scratch resistance to injection molding‐induced morphology of polypropylene

The relationship between the scratch resistance and the injection molding‐induced morphology of polypropylene (PP) was investigated. The crystal structure near the surface was controlled by the mold temperature and the doping of a nucleating agent (NA). Although α‐ and β‐NA were used to improve the scratch resistance of PP that was molded at a mold temperature of 40°C, both of the NAs only slightly affected the scratch resistance due to low crystallinity at the surface. When the mold temperature was increased, the skin layer became thin and a β‐form crystal formed. Plastic deformation under the scratch was limited in the frozen layer. Consequently, the thickness of the frozen layer (which had low crystallinity) had the predominant effect on the scratch resistance in comparison to the polymorphism differences. The crystal morphology was analyzed with synchrotron micro‐beam wide angle X‐ray diffraction and Fourier transform infrared spectroscopy. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

A comparative study on the effect of type of reinforcement on the scratch behavior of a polyacrylic-based nanocomposite coating

In this article the effects of type of reinforcement on the scratch behavior of nanocomposite coatings are studied. Such coatings can be used in the automotive industry as clear top paint coats. Three types of reinforcements were used, including detonation nanodiamond, nondetonation nanodiamond, and nano-alumina, with an average particle size of 4–6, 50–60, and ~50 nm, respectively. Nanocomposites containing 1.5 and 3 wt% of each filler type in polyacrylic as matrix were produced by sonication. The macrostructure, microstructure, and scratch behavior of coatings were investigated and compared with those of neat polyacrylic polymer. The scratch behavior was evaluated based on the ASTM G171 standard and also by common industrial tests such as the pencil hardness test. The results revealed that the nano-alumina coatings showed the best, and the nondetonation nanodiamond coatings the worst, scratch resistance—even less than that of the neat polyacrylic polymer.     

The influence of annealing on the crystallization and tribological behavior of MWNT/PEEK nanocomposites

In this study, annealing influence on crystallization and scratch behavior of neat and multi‐wall carbon nanotube (MWNT) reinforced poly(ether ether ketone) (PEEK) nanocomposites have been investigated. Crystallization behavior of normal and annealed samples was investigated by using differential scanning calorimeter (DSC). Scratch behavior of normal and annealed samples was investigated by using micro scratch tester. In DSC analysis, it was detected that, melting enthalpy of annealed neat PEEK was increased sharply when compared to neat PEEK. Melting enthalpies of annealed PEEK nanocomposites prepared with addition of up to 1 wt% MWNT were increased with a decreased trend. However, nanocomposites with higher contents of MWNTs (>1 wt%) were dramatically affected by annealing process and melting enthalpy decreased sharply. Friction coefficient values of “annealed MWNT reinforced PEEK composites” were found to be lower than “normal PEEK composites.” Annealing process affects scratch hardness of both annealed and MWNT reinforced PEEK. Annealed nanocomposites with various MWNT concentrations showed higher scratch hardness values than normal PEEK nanocomposites. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers     

Effect of polymer properties on the structure of injection-molded parts

In this study, the distributions of both molecular orientation and crystallinity along the flow direction as well as across the thickness direction of injection-molded specimens of poly(ethylene terephthalate) (PET) molded at different mold temperatures were investigated. The degree of molecular orientation at the surface of the specimens was compared with that of other injected materials (polystyrene, high density polyethylene, liquid crystal polymer) showing different thermal, rheological, and crystallization characteristics. It was found that the molecular orientation at the skin layer of the molding increases with the polymer relaxation time, the rigidity of the polymer molecules, and the crystallization rate of the polymer. Moreover, in the case of PET, it was found that the crystallinity at the skin layer and in the core of the molding depends on the mold temperature. For low mold temperatures, near the gate, the maximum of crystallinity was observed at the subskin layer because of the “shear-induced crystallization” generated during the filling stage. On increasing the mold temperature, the maximum of crystallinity was found to shift to the skin layer as a result of the decrease of the thickness of this layer. For low mold temperatures, the variation of the molecular orientation in the thickness direction was found to be much the same as for the crystallinity of the polymer. This result indicates that the shear-induced crystallization process improves the degree of molecular orientation in the flow direction since it inhibits the relaxation process of the polymer molecules.     

Structure-scratch properties relationships of acrylate photo-polymerizable protective coatings for thermoplastic substrates

The relationships between the composition and the scratch resistance of clear photo-polymerized protective coatings for thermoplastic substrates were studied in relation with their thermomechanical properties. For this purpose, dynamic mechanical analyses of free-standing films were compared to micro-scratch tests of thick or thin coatings deposited on polycarbonate. In these experiments, the depth indented by the tip, the elastic recovery of the material, the residual depth of the scratch, and the load at which the first crack appears, were analyzed. Different coatings close in formulation were studied. First, the proportion of a specific difunctional monomer featuring a hard structure was varied in order to change the crosslinking density of the polymer network. The thermomechanical properties were consequently modified at high temperature, but remained similar at 23 °C, whereas at this temperature, the scratch properties of the coating evolved with its composition. The addition of 5 wt% alumina or silica nanoparticles did not modify the thermomechanical properties or the scratch resistance of the coatings, even if a more concentrated filler layer was observed near the surface of the coating. Nevertheless, the consequent incorporation of a new diacrylate monomer in the polymer matrix delayed the ductile-brittle transition. Finally the substitution of petro-based monomers by slightly different bio-based compounds led to a change of the scratch behavior of the thickest coatings (150 μm-thick), and increased the critical load for the thinnest coatings (15 μm-thick). It comes out that micro-scratch tests allow a finer comparison of the samples.     

Mechanical properties of block poly(propylene carbonate‐cyclohexyl carbonate) investigated by nanoindentation and DMA methodologies

To extend the practical application of poly(propylene carbonate) (PPC), the chemical methods were used to improve its mechanical properties. In this connection, random copolymer poly(propylene‐cyclohexyl carbonate) (PPCHC) and di‐block copolymers poly(propylene carbonate‐cyclohexyl carbonate) (PPC‐PCHC) were synthesized. Dynamic mechanical analysis (DMA), nanoindentation and nanoscratch test were applied to evaluate their mechanical properties. The storage's modulus, Young's modulus (E) and hardness (H) obtained from DMA and nanoindentation tests showed that the introduction of the third monomer cyclohexene oxide (CHO) can greatly improve the mechanical properties of PPC, and that the block copolymer PPC‐PCHC hand better mechanical properties than the random copolymer PPCHC. The annealing treated PPC‐PCHCs exhibited deteriorated mechanical properties as compared with untreated PPC‐PCHC. From the results of scratch tests, the plastic deformation of PPC‐PCHC was smaller than those of PPC and PPCHC. Meanwhile, the plastic deformations of the heat‐treated PPC‐PCHCs were smaller than the untreated PPC‐PCHC because of the possible rearrangement of the molecular chains of PPC‐PCHC. The scratch hardness (H_s) of the block copolymer PPC‐PCHC is larger than random polymer PPCHC and PPC, but lower than the values of heat‐treated samples indicating that the surfaces' hardness of block polymers increase after heat treatment. These different measurement methodologies provide a more precise assessment and understanding for the synthesized block polymers. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Spray coating process variable and property analysis of UV-curable polyurethane acrylate coating on polycarbonate substrate

A series of spray coating experiments were conducted on an UV-curable, polyurethane-modified, acrylate-based coating formulation with the aim to control defects, coating thickness, and thickness variation. Statistical approaches including design of experiment, residual examination, analysis of variance, and t-test were used in designing the experiments and analyzing data. Viscosity of formulation, atomizing pressure, liquid feeding pressure, distance between nozzle and substrate, and travel speed of substrate were the process variables studied. The ranges of process variables that gave defect-free coating were identified and used in the subsequent experiments to determine process variables and interactions that had significant contribution to the changes in coating thickness and thickness variation. All process variables studied were found to have contribution to the change in coating thickness, but they showed no significant contribution to the variation of coating thickness. No interaction displayed significant contribution. Confirmation tests performed on extra samples prepared with varying coating thicknesses indicated a good agreement with the experimental results. Additional samples were tested for total transmittance, transmission haze, adhesion, surface roughness, hardness, scratch hardness, abrasion resistance, and durability to attack of car wash chemicals. Spray coated samples showed slight improvement in the total transmittance over the uncoated samples, while maintaining the transmission haze and exhibiting rougher surfaces. Only samples with thin coatings were found to possess sufficient adhesion to the substrate. These thin coatings gave improved hardness, scratch hardness, and durability to car wash attack to the level comparable to commercial coated polycarbonate headlamp lenses, whilst giving better abrasion resistance.     

Structure and properties of polyblends of a thermotropic liquid crystalline polymer with an alloy of polyamide-6 and ABS

The relationship between the microstructure and corresponding mechanical properties developed during injection molding of blends containing a liquid crystalline polymer (LCP) as the minor component and an engineering polymer system has been studied. A wholly aromatic copolyester LCP (Vectra A950) was melt blended at different compositions with a thermoplastic matrix consisting of a commercial compatibilized blend of polyamide-6 and ABS (Triax 1180). These blends were prepared under two different sets of injection molding conditions. In the first case, a higher melt temperature, higher barrel temperature, lower injection pressure, lower mold temperature, and shorter residence time in the mold were used during injection molding, as compared with the second case. The mechanical properties of the blends were superior to those of the base polymer. In the second case, the resulting injection-molded specimens had a distinct skin–core morphology where elongated fibrils of LCP constituted the skin layer. The mechanical properties of the blends processed under the second set of processing conditions were superior to those of the first, though the trends in both cases were the same. To study the effects of process variables the 15% LCP blend and the second set of processing conditions were taken as the base. Samples were injection-molded by varying one parameter at a time. It was seen that the properties of the blend were increased by maintaining a lower barrel temperature, greater injection pressure, lower injection speed, higher mold temperature, and a greater residence time in the heated mold. Thus it was found that the processing conditions played a vital role in determining the mechanical properties and morphology of the polyblends. © 1996 John Wiley & Sons, Inc.     

Influence of processing variables on scratch and shrinkage behaviors and translucency of dental zirconia

Scratch tests were performed on porous 3 mol% Y₂O₃-stabilized zirconia dental blocks to relate compaction processing and partial sintering temperature to shrinkage and machinability of the blocks and microstructures and transmittance after full sintering. Scratch hardness of the blocks varied with increasing loads, and the variation was related to the sequential events of densification, densification and cleaving, disruption of the densified region, and chipping and longitudinal cracking. The shrinkage during final sintering was inversely proportional to the compact pressure and temperature with compact pressure having a greater impact. In contrast, the transmittance of fully sintered blocks depended largely on the partial sintering temperature because it governed the number and size of pores after completion of the sintering. Based on the influence of the variable on scratch hardness, a scratch response measure that possibly reflects the machinability of porous CAD/CAM blocks was proposed.     

The effects of processing parameters on the tensile properties of weld lines in injection molded thermoplastics

Weld or knit lines result wherever two or more polymer flow fronts unite. This results in a region of a different level of molecular entanglements than the bulk material. Consequently, weld regions have been observed to have inferior mechanical properties compared to the bulk. Although this phenomenon occurs in almost all the commercially important polymer processes, there has been little systematic investigation. The effects of melt temperature, mold temperature, injection speed and injection pressure on the tensile properties of commercial grades of polystyrene (GPS), high impact polystyrene (HIPS) and polypropylene (PP) are examined. The most important processing parameters seemed to be melt and mold temperature; injection speed and pressure had little effect on the tensile properties of any of the samples. A higher melt temperature increased both the strain and stress at break considerably in GPS. In HIPS increased melt temperature increased only the elongation to break substantially. Increased mold temperature improved the stress and elongation to break in GPS but not as much as melt temperature. Polypropylene showed improved weld yield strength with increased mold temperature. Under the conditions examined, injection pressure and injection speed showed no effect on the tensile properties of any of the materials investigated.     

Effect of Adhesion, Film Thickness, and Substrate Hardness on the Scratch Behavior of Poly(carbonate) Films

The effect of adhesion, film thickness, and substrate hardness on the scratch behavior of poly(carbonate) (PC) films was investigated. Films of various thickness were prepared by spin-coating solutions of PC in chloroform onto glass, ferroplate, Al 1100, Al 6022, and Al 6111 substrates. Adhesion between the films and the substrates was controlled by pretreatment of the substrates and the thickness of the films was controlled by the concentration of the PC solutions. Adhesion of the films to the glass substrates was measured by a blister test. Scratch tests were performed using a custom-built, progressive-load scratch tester with interchangeable diamond indenters; the resulting scratches were observed by optical microscopy, atomic force microscopy (AFM), and environmental scanning electron microscopy (ESEM). The critical normal load (i.e., the smallest applied normal load for which delamination of the film from the substrate was observed) was used as a criterion to determine the scratch resistance of the films. It was found that better film/substrate adhesion resulted in a higher critical load for delamination. As film thickness increased, the critical load and, thus, scratch resistance also increased. Substrate hardness had a strong influence on the scratch behavior of the PC films. For a low-hardness substrate (i.e., Al 1100), the work from scratching was mainly consumed by deforming the substrate. In the case of substrates with intermediate hardness (i.e., Al 6022, Al 6111, and ferroplate), the substrates were more resistant to the stresses that were generated in the films; hence, the deformation of the substrates was less severe. A high-hardness substrate (i.e., glass) resisted the applied load and resulted in higher stress concentrations in the films and at the interface. Consequently, a rougher surface inside the scratch track was observed.     

The effect of crystallinity on the scratch hardness of poly(ether ether ketone)

Summary This paper describes a study of the surface properties of the poly(ether ether ketone) (PEEK) using a scratch hardness technique. A comparison of the hardness values determined for amorphous and crystalline PEEK shows that the crystalline polymer is harder. In addition, comparison of the scratch frictional behaviour indicates several friction mechanisms apply for this polymer.     

Macrostructure and environment-influenced surface layer in epoxy polymers

Several epoxy polymers were shown to be two-phase systems; roughly spherical floccules arranged in layers in an interstitial fluid resembling the starting materials. The size of the floccules was found to be dependent on the initial rate of cure of a given polymer. The density, hardness, glass transition temperature, etching rate, and dielectric strength were related to the floccule size. The surface layer in the epoxy polymers and in several thermoplastic polymers was found to be different from the bulk material. The properties of the surface layer are dependent on the surface energy of the mold material and on the atmospheric environment. A gradient in properties was found to extend from the polymer surface several hundred microns into the bulk.     

Polyetheretherketone (PEEK): Processing-structure and properties studies for a matrix in high performance composites

The processing, structure and properties of polyetheretherketone (PEEK) semicrystalline thermoplastic as matrix polymer for high performance composites has been investigated in this work. In processing PEEK samples with different crystallinities, a specially designed mold capable of cooling the polymer in excess of 115°C/s from its melt temperature was constructed. In addition, during processing studies, a reaction of PEEK in the presence of copper was discovered. Analysis of the samples in terms of their crystallinity values also provided a new method for measuring crystallinity of the matrix in the composite. Crystallization of low crystalline samples at room temperature in the presence of methylene chloride was also confirmed for the first time with polarized microscopy. However, at the same time, the excellent hygrothermal resistance of PEEK was also confirmed. Finally, dynamic mechanical and stress-strain experiments with samples of different crystallinities elucidated the dependence of these properties to crystallinity. However, this study also elucidated that under normal processing conditions for high performance composites, PEEK properties may not be strongly affected by different levels of crystallinity.     

一种适于热压印成型的新塑料--PETG

通过将聚合物加热到其玻璃化温度以上，然后施加压力将模具上的图案转移到聚合物上的热压印成型方法，尝试一种新型塑料——PETG。将PETG与其它材料的热压印进行了对比性研究，并测试了四种不同模具对PETG的压印，实验结果表明，其复制精度都较高，热成型较为理想。     

Effect of Adhesion,Film Thickness,and Substrate Hardness on the Scratch Behavior of Poly(carbonate) Films

The effect of adhesion, film thickness, and substrate hardness on the scratch behavior of poly(carbonate) (PC) films was investigated. Films of various thickness were prepared by spin-coating solutions of PC in chloroform onto glass, ferroplate, Al 1100, Al 6022, and Al 6111 substrates. Adhesion between the films and the substrates was controlled by pretreatment of the substrates and the thickness of the films was controlled by the concentration of the PC solutions. Adhesion of the films to the glass substrates was measured by a blister test. Scratch tests were performed using a custom-built, progressive-load scratch tester with interchangeable diamond indenters; the resulting scratches were observed by optical microscopy, atomic force microscopy (AFM), and environmental scanning electron microscopy (ESEM). The critical normal load (i.e., the smallest applied normal load for which delamination of the film from the substrate was observed) was used as a criterion to determine the scratch resistance of the films. It was found that better film/substrate adhesion resulted in a higher critical load for delamination. As film thickness increased, the critical load and, thus, scratch resistance also increased. Substrate hardness had a strong influence on the scratch behavior of the PC films. For a low-hardness substrate (i.e., Al 1100), the work from scratching was mainly consumed by deforming the substrate. In the case of substrates with intermediate hardness (i.e., Al 6022, Al 6111, and ferroplate), the substrates were more resistant to the stresses that were generated in the films; hence, the deformation of the substrates was less severe. A high-hardness substrate (i.e., glass) resisted the applied load and resulted in higher stress concentrations in the films and at the interface. Consequently, a rougher surface inside the scratch track was observed.     

Optical monitoring of polypropylene crystallization during injection molding

The nonisothermal crystallization of polypropylene resins, i‐PP, during injection molding, using an optical device inserted in the injection mold cavity was monitored. The device detected the change of optical properties which occurs in polymers during their crystallization process; thus the intensity of a laser beam after it passed through the crystallizing polymer was measured during an injection molding cycle. The collected light intensity after the end of the cycle was correlated with the morphologies and final crystallinity degree of the samples. The influence of nucleating agents and the change of the parameters of the injection molding process on the morphology and optical signals were also investigated. The morphologies were analyzed by polarized light optical microscopy, PLOM. The % of crystallinity of the samples was measured by wide angle X‐rays diffraction, WAXS. It was concluded that the optical device was sensible to different polymer crystallization kinetics, morphology type, and changes in the injection molding parameters. It was also found that the mold temperature and packing pressure and time were the factors that affected most the kinetics of crystallization of these polymers in this particular disk geometry. The WAXS results showed that the lower the final light intensity the higher the % of crystallinity in the samples. POLYM. ENG. SCI., 2008. © 2007 Society of Plastics Engineers     

Analysis of scratch characteristics of automotive clearcoats containing silane modified blocked isocyanates via carwash and nano-scratch tests

The aim of this study was to investigate the scratch characteristics of automotive clearcoats based on an acrylic polyol resin, with butylated melamine and silane modified blocked isocyanates, using car-wash and nano-scratch tests.To scrutinize the effect of silane modified blocked isocyanate on the chemical and mechanical properties of clearcoats, with respect to changes in the crosslinking networks inside the clearcoats due to the curing reaction, dynamic mechanical analysis (DMA) and FT-IR analysis were performed. The scratch behaviors were analyzed via Amtec–Kistler car-wash and nano-scratch tests, accompanied with scratch images simultaneously visualized using atomic force microscopy (AFM) and scanning electron microscopy (SEM). The basic properties of various automotive clearcoats such as impact resistance, pencil hardness, solvent resistance, and stone-chip resistance, were also compared. The results showed that a close correlation existed between the scratch resistance data obtained from the car-wash and nano-scratch tests for clearcoats made from acrylic polyol resin, with melamine and silane modified blocked isocyanates. Also, all the mechanical properties, including scratch resistance, noticeably improved due to the increased crosslinking networks via the formation of urethane bonds, when the portion of silane modified blocked isocyanates was increased. This was verified from the surface profiles and images of the scratched clearcoats captured using AFM and SEM.     

The Effect of Radiation Dosages and UV/EB Radiation on the Properties of Nanocomposite Coatings

The aim of this study was to compare the effects of ultraviolet (UV) and electron beam (EB) radiation on the properties of cured nanocomposite coatings. Surface hardness increased with increasing radiation dosages (number of passes) for all samples. This was due to the increase in crosslinking with increasing radiation dosages. Pendulum hardness, gel content, and thumb twist results were analyzed to choose the appropriate curing dosage for both curing techniques. The selected dosages were then used to cure coatings for scratch and abrasion resistance tests. It was found that the UV curing produced coatings with better abrasion resistance, whereas EB curing was more suitable for producing scratch-resistant coatings.