Natural Ageing of Automotive Polymer Components: Characterisation of New and Used Poly(propylene) based Car Bumpers

The chemical and morphological structure of new and post‐consumer ten years old poly(propylene) based car bumpers has been investigated and their mechanical properties have been correlated to the chemical and physical degradation of the material. Poly(propylene) matrix and a rubbery ethylene‐propylene phase were the constituents of the bumpers. A strong impairment of the mechanical properties has been found in old samples which showed also a distinctive phase separation. The modification of the chemical structure was much less evident: oxidation on the exposed surface involving the poly(propylene) phase has been highlighted in old bumpers, and possible crosslinking. These relatively small changes, however, are responsible for the pronounced physical ageing. A tentative explanation is a poor interfacial adhesion of rubber particles from which the crazes can propagate further to form cracks.     

Poly(propylene) composite with hybrid nanofiller: Dynamic properties

Mechanical, impact, and relaxation properties of in situ synthesized carbon nanotubes‐polyaniline (CNT‐PANi) hybrid nanoparticle‐filled poly(propylene) (PP) composites with or without an amphiphilic dispersing agent were investigated using tensile testing, notched Charpy impact testing, and dynamical mechanical testing methods. The reference material was MWCNT filled PP composite. Ethyl gallate (EG) was the dispersing agent which realizes high conductivity in PP composites with hybrid filler. Measured properties showed quite similar behavior of CNT‐PANi hybrid and neat CNT filled composites. Addition of 20% EG in PP did not cause essential differences compared to the neat PP. When the dispersing agent was added in filler containing PP composites, remarkable effects were observed, especially in PP‐hybrid composites. Mechanically, these materials had improved tensile properties, but they were brittle compared to the materials without dispersing agent. Dynamic mechanical analysis showed improvement in storage modulus, and in loss modulus the α transition was well observable. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Fabrication of Uniaxially Aligned Poly(propylene) Nanofibers via Handspinning

A straightforward method, which is termed novel handspinning, is reported for producing uniaxially aligned sPP nanofibers. As demonstrated by SEM analysis, the morphologies of handspun sPP nanofibers are strongly dependent upon the processing conditions such as spinning method and solvent system. Compared to the normal electrospun sPP nanofibers, the handspun sPP nanofibers show smoother morphologies. FT‐IR analysis demonstrates a significant difference in polymer chain conformation between the handspun and electrospun sPP nanofibers. Moreover, interestingly, the handspun sPP single nanofibers show higher Young's modulus and tensile strength than electrospun sPP single nanofibers.

     

Dynamic Mechanical Properties of Poly(propylene) Blends with Poly[ethylene‐co‐(methyl acrylate)]

Summary: Blends of poly(propylene) (PP) were prepared with poly[ethylene‐co‐(methyl acrylate)] (EMA) having 9.0 and 21.5% methyl acrylate comonomer. A similar series of blends were compatibilized by using maleic anhydride grafted PP. The morphology and mechanical properties of the blends were investigated using differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) in tensile mode. The DMA method and conditions were optimized for polymer film specimens and are discussed in the experimental section. The DSC results showed separate melting that is indicative of phase‐separated blends, analogous to other PP‐polyethylene blends but with the added polarity of methyl acrylate pendant side groups that may be beneficial for chemical resistance. Heterogeneous nucleation of PP was decreased in the blends because of migration of nuclei into the more polar EMA phase. The crystallinity and peak‐melting temperature did not vary significantly, although the width of the melting endotherm increased in the blends indicating a change had occurred to the crystals. DMA analysis showed the crystal‐crystal slip transition and glass transition (T_g) for PP as well as a T_g of the EMA copolymer occurring chronologically toward lower temperatures. The storage modulus of PP and the blends was generally greater with annealing at 150 °C compared with isothermal crystallization at 130 °C. The storage modulus of the blends for isothermally crystallized PP increased with 5% EMA, then decreased for higher amounts of EMA. Annealing caused a decrease with increasing copolymer content. The extent of the trend was greater for the compatibilized blends. The T_g of the blends varied over a small range, although this change was less for the compatibilized blends.

Storage modulus for PP and EMA9.0 blends annealed at 150 °C.     

Flow Instabilities in Linear and Branched Syndiotactic Poly(propylene)s

Extrusion flow experiments of linear and branched syndiotactic poly(propylene)s were carried out. The work was focused on flow instabilities. Ionized radiation was employed to induce long chain branching in linear samples. Sharkskin and melt fracture were postponed in the case of slightly long branched samples, which possess an enhanced melt elasticity compared to linear samples. For the most elastic samples the nature of the flow instability changed: sharkskin disappeared and melt fracture was observed instead. The correlation between sharkskin and melt strength results is discussed.

     

Isotactic Poly(propylene) Nanocomposites Based upon Boehmite Nanofillers

The influence of boehmite crystallite sizes, varied between 10 and 60 nm, was studied with respect to the morphology development, crystallization behavior and mechanical properties of the boehmite‐based iPP nanocomposites. The nanometer‐scaled boehmites were formed during twin‐screw melt extrusion of iPP at 200 °C. Even in the absence of polymer compatibilizers, the boehmites, obtained from Sasol's process, enabled very effective deagglomeration and in‐situ dispersion of nanoboehmites. With increase in boehmite crystallite size it was possible to improve simultaneously stiffness and impact strength of iPP. As evidenced by means of DSC, POM and WAXS measurements, the deagglomerated nanoboehmites nucleated crystallization of poly(propylene)'s α‐modification.

     

Influence of Different Woven Geometry in Poly(propylene) Woven Composites

Summary: The difference between the melting temperatures of poly(propylene) (PP) fibre and random poly(propylene‐co‐ethylene) (PPE) was exploited in order to establish processing conditions for an all PP composite. Under these conditions the matrix must be a liquid in order to ensure good wetting and impregnation at the fibres, though the temperature must not be too high to avoid melting the fibres. The high chemical compatibility of the two components allowed creation of strong physico‐chemical interactions, which favour strong interfacial adhesion. The static and dynamic mechanical properties and morphology of poly(propylene) woven fabric reinforced random PPE composites have been investigated with reference to the woven geometry that influenced the properties of the woven composites. Among the various cloth architectures that were used in the PP‐PPE composites, the satin weave imparted overall excellent mechanical properties due to the weave parameters, such as high float length and fibre count, low interlace point and crimp angle, etc. Morphology of the composite has been investigated by macro photography and scanning electron microscopy. Images from scanning electron microscopy provided confirmation of the above results by displaying the consolidation and good fibre‐matrix wetting of the composites.

Loss modulus of poly(propylene) woven‐matrix composites with different types of woven geometry.     

Poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) and Poly(propylene carbonate) Blends: an Efficient Method to Finely Adjust Properties of Functional Materials

Polyhydroxyalkanoate (PHA) and poly(propylene carbonate) (PPC) are blended in order to investigate their mutual contributions in terms of functional properties. A wide range of blend composition is processed through extrusion from dry blends. Droplet‐matrix morphology is observed for all samples. Thermal investigations reveal the PPC effect on the PHA crystallization process with a decrease and broadening of the crystallization temperature window and on the depression of its glass transition temperature. This investigation also confirms the as yet un‐reported non‐miscibility of this kind of blend. However, a slight phase interaction is expected since thermal behavior of PHA is impacted. The fragile behavior of PHA is balanced by the high ductility of PPC. The weak strain at break of PHA can thus be increased by up to 200% although a significant amount of PPC is needed to start modifying this property. Stress at break and modulus are linearly decreased from pure PHA to pure PPC values. PPC also acts as an impact modifier for PHA. In terms of barrier properties, PHA brings a large contribution even at low content to the initially high oxygen and water vapor permeability of PPC.

     

Lignocellulosic Flour from Cladodes of Opuntia ficus‐indica Reinforced Poly(propylene) Composites

Summary: A lignocellulosic flour was obtained by grinding dried cladodes of Opuntia ficus‐indica. It was used as low cost natural filler in PP and the effect of the treatment of the filler with MAPP was also investigated. The morphology and thermal properties of these composites were evaluated by SEM and DSC, respectively. MAPP coating resulted in a better adhesion between the filler and the matrix and higher homogeneity of the material. A decrease of the degree of crystallinity of the PP matrix in presence of the untreated filler was observed. Dynamic mechanical analysis and tensile properties were also studied. High‐strain tensile properties display enhanced mechanical properties for MAPP treated‐based composites only. When conditioned in highly moist atmosphere (98% RH), both the water uptake and water diffusion coefficient decrease when the filler was treated. These effects were ascribed to the promoting interfacial adhesion induced by the coating treatment. In liquid water, this increased adhesion between the filler and the matrix results in a higher weight loss of the material. It is due to the removal of the grafted polymer from the material during the dissolution of part of the filler.

SEMs of freshly fractured surface for a PP film filled with 10 wt.‐% of MAPP treated OFI cladode (top) and calcium oxalate crystallite within the PP matrix for a 3 wt.‐% filled composite (bottom).     

Thermal Behavior of Isotactic Poly(propylene)/Maleated Poly(propylene) Blends

This paper analyzes the thermal and thermo‐oxidative degradation behavior, phase separation, melting, and crystallization of blends consisting of isotactic poly(propylene) (IPP) and poly(propylene) grafted with maleic anhydride (PP‐g‐MA). It has been established that, depending on the blend composition and crystallization/preparation procedure, the blends of IPP and PP‐g‐MA can either co‐crystallize or evidence phase separation. This conclusion has been attained by comparing the DSC results of crystallization under dynamic and isothermal conditions with X‐ray diffraction results. On the basis of the obtained results, the optimum mixing ratios have been established as 95–85 wt.‐% IPP/5–15 wt.‐% PP‐g‐MA. Thermo‐oxidative behavior has been studied by thermogravimetry and differential thermal analysis.

     

Mechanical and Morphological Studies of Poly(propylene)‐Filled Eggshell Composites

Poly(propylene) (PP) composites were prepared by using eggshell (ES) as filler and their mechanical properties were compared with those using talc (TA) and calcium carbonate (CC) of different grain sizes (X₅₀). A decrease in impact strength and deformation at break with increase in filler content was observed. The PP composite with ES (X₅₀ = 8.4 µm) was stiffer than those with CC (X₅₀ = 0.7 µm). The hybrid composite PP‐ES‐TA showed a similar stiffness as the PP‐TA composites due to the similar morphology of TA (X₅₀ = 0.5 µm) and ES, when TA was replaced up to 75 wt.‐% by ES. SEM study revealed evidence of improved interfacial bonding between PP and ES in theirs composites.

     

Effect of Carbon‐Based Particles on the Mechanical Behavior of Isotactic Poly(propylene)s

Different carbon‐based fillers such as carbon nanotubes (CNTs), graphite, and thermally reduced graphene oxide (TrGO) are melt mixed with an isotactic poly(propylene) (iPP) and the mechanical properties of the resulting composites in the solid and melt state are analyzed. The Young's modulus of composites is increased around 25% relative to the neat iPP at concentrations above 10 wt% of CNTs or graphite whereas composites with TrGO are increased around 40% at similar concentrations. These results are compared with theoretical models showing that the filler agglomeration and surface area are key parameters. The rheological results of the composites under oscillatory shear conditions at the melt state show that the viscous raw polymer melt experiences a solid‐like transition at a threshold concentration that strongly depends on the filler used. This transition appears at 10 wt% for CNTs, 8 wt% for TrGO, and 40 wt% for graphite. The viscosity of iPP/TrGO composites is further increased by adding CNTs particles, although the Young's modulus does not increase.

     

Evaluation of Coupling Agents in Poly(propylene)/Fly Ash Composites: Effect on Processing and Mechanical Properties

Composites containing 50 wt.‐% fly ash in a PP homopolymer were prepared via batch mixing and compression moulding. The following coupling agents were evaluated: Lubrizol Solplus C800, N,N′‐(1,3‐phenylene)dimaleimide, γ‐methacryloxypropyltrimethoxysilane and maleic‐anhydride‐grafted PP. At the filler level investigated, C800 gave the best balance of composite strength and toughness. In the latter case filler‐matrix adhesion appeared weaker relative to γ‐MPS, BMI and m‐PP, all of which gave excessively strong filler‐matrix adhesion leading to a reduction in composite toughness. The unexpected weakness of the C800/fly ash interaction may be related to removal of surface calcium ions from the fly ash via reaction of a single calcium ion with two C800 molecules.

     

Effect of Nucleating Agents on Crystallization and Melting Behavior and Mechanical Properties of Nucleated Syndiotactic Poly(propylene)

Summary: The effects of various nucleating agents [e.g. 1,3:2,4‐dibenzylidene sorbitol (DBS), 1,3:2,4‐di‐p‐methyldibenzilidene sorbitol (MDBS), 1,3:2,4‐di‐m,p‐methylbenzylidene sorbitol (DMDBS), kaolin, talcum, marl, titanium dioxide (TiO₂) and silica (SiO₂)] on non‐isothermal melt crystallization and the subsequent melting behavior and mechanical properties of nucleated syndiotactic poly(propylene) (sPP) in comparison with those of the neat sample were investigated. Analysis of the non‐isothermal melt‐crystallization exotherms revealed that the ability of these fillers to nucleate sPP could be ranked from the best to the worst as follows: DBS > talcum > MDBS > kaolin > SiO₂ > DMDBS > marl > TiO₂. The subsequent melting endotherms for most of the sPP compounds exhibited double melting peaks, while that for the marl‐filled sPP exhibited triple melting peaks. Wide‐angle X‐ray diffraction analysis showed that addition of these fillers did not affect the crystal modification of the sPP matrix. Mechanical property measurements revealed that both the tensile strength and the percentage of elongation at yield for the sPP compounds investigated were not much different from those of the neat sPP. After natural weathering for 1 month, the tensile strength at yield for the sPP compounds investigated increased, at the expense of the percentage of elongation at yield, but, after natural weathering for 3 months, both the tensile strength and the percentage of elongation at yield were found to decrease.

Effects of various organic and inorganic nucleating agents on non‐isothermal melt‐crystallization of syndiotactic poly(propylene) (recorded at a cooling rate of 10 °C · min^?1).     

Controlled Degradation of Poly(propylene) in Industrial Extruders

Summary: The main objective of this work was to study the controlled degradation of PP in industrial extruders at different operating conditions. Firstly, the investigation of certain key polymer properties, such as the MI and the MWD, revealed that the changes undergone by the polymer resin during the reactive extrusion depend strongly on the operating conditions. In the absence of oxygen, the results indicated that spontaneous thermal and/or mechanical degradation were not very important. Therefore, resin properties were not expected to change during extrusion if no peroxide was fed into the extruder, in the absence of oxygen. On the other hand, in the presence of oxygen, MWD analysis showed that the MWD could be shifted towards higher or lower molecular weights, indicating that both chain growth and chain scission were possible during extrusion. Finally, simple expressions are presented here in order to allow for the monitoring and control of the important final properties of the extruded resin.

The molecular weight distribution of polymer powder and polymer pellets during extrusion.     

Electron Beam Crosslinking of Atactic Poly(propylene): Development of a Potential Novel Elastomer

Atactic amorphous poly(propylene) of various molecular weights has been modified with high energy electrons over an irradiation dose range of 0–200 kGy. Tri‐ and tetrafunctional monomers in varied concentrations have been used as crosslinking additives. A correlation between the original molecular weight and crosslinking behavior of the polymer was observed. A higher gel content is obtained with the tetrafunctional acrylate as compared to that with the trifunctional one, under the same treatment conditions. Electron irradiation treatment at elevated temperature gives rise to an increased gel content over that at room temperature. Similarly, the mechanical properties also enhance with gel content. Moreover, the stress‐strain behavior of the electron modified systems indicates a more pronounced elastomeric nature.

     

热固化聚富马酸丙二醇酯/丙烯酸羟乙酯材料的制备与性能

以富马酸二乙酯和1,2-丙二醇为原料，通过两步反应成功合成聚富马酸丙二醇酯（PPF），并以PPF、丙烯酸羟乙酯为单体，热固化构筑体系材料。利用FTIR）与1HNMR等手段对聚合物进行了表征，并测试了材料的热稳定性能、润湿性能、力学强度、体外细胞毒性及降解性能。结果表明，体系材料具有较好的热稳定性能，其中当PPF和丙烯酸羟乙酯质量比为1∶3时材料的热稳定性能较佳；材料的亲水性较好，其接触角为53.28 °～76.17 °；材料具有较好的力学性能，其剪切强度、粘接强度、压缩强度及三点弯曲强度分别为1.33～1.63 MPa、1.86～3.18 MPa、60.47～88.15 MPa、 18.77～20.63 MPa；体外降解实验结果表明，随着浸泡时间变长，体系溶液pH呈下降趋势，其变化值为0.093～0.628；当PPF和丙烯酸羟乙酯质量比为3∶1时，试样的失重率和吸水率分别可达11.20%和38.27%，材料的降解速率较为缓慢；细胞毒性实验结果显示体系材料细胞毒性轻微。     

Surface Tension in Polymer Blends of Isotactic Poly(propylene) and Atactic Polystyrene

The surface tension of atactic polystyrene (PS), isotactic poly(propylene) (PP) and PS/PP‐blends, and additionally the interfacial tension between PP/PS have been measured in the temperature range between 200 and 280°C using the pendant drop method. Within the temperature range studied, the surface tension decreased linearly with increasing temperature for all systems whereas the surface tension of neat PP is approximately 7 mN/m smaller than the value of PS. The interfacial tension between PS and PP is in the range of approximately 4 mN/m and this indicates a strong incompatibility. It results a heterogeneous PP/PS blend morphology. A significant increase of the surface tension of the blends as a function of composition is observed only when the PS content exceeds 60 wt.‐%. Furthermore, microscopic observations indicate that even if the bulk matrix material is PS, a thin layer of PP can be detected by atomic force microscopy on the droplet surface used for surface tension measurements.     

Morphology,Thermal and Mechanical Properties of Poly(propylene) Fibre‐Matrix Composites

Preparation and properties of poly(propylene)‐poly(propylene) composites have been investigated. Poly(propylene) fibres of varying diameter have been incorporated in a random ethylene co‐poly(propylene). The composites prepared from the same semi‐crystalline polymer in the matrix and reinforcement have lead to inherently strong interfacial bonding between the two phases of the same polymer. The composites demonstrated enhanced stiffness, which increased with fibre diameter. The structure, thermal, static and mechanical properties of poly(propylene) long fibre reinforced random co‐poly(propylene) composites have been studied with reference to the fibre diameter. The matrix and fibre components retained their separate melting temperatures. After melting, the two phases remained separate and showed their individual crystallization temperatures on cooling, and melting temperatures on a second heating. The melting temperature of the poly(propylene) fibres increased after formation of the composites. The compression molding of the composites at a temperature below the melting temperature of the fibres caused annealing of the fibre crystals. By incorporation of long poly(propylene) fibre into random co‐poly(propylene), the glass transition, storage and static modulus have been found to be increasing and composite with the largest fibre diameter shows better properties. Transcrystallization of the matrix poly(propylene) was observed.

Optical microscopy of composites with fibre diameter 68 μm.     

Time‐Temperature Creep Behaviour of Poly(propylene) and Polar Ethylene Copolymer Blends

Polymers commonly undergo deformation under an applied stress over their lifetime; some deformations are irrecoverable once the source of stress is removed. Therefore an understanding of the response of a polymer can be achieved by investigating the viscoelastic properties using creep experiments, where the behaviour can be monitored under small deformational loads. Poly(propylene) (PP) was blended with a polar elastic, thermoplastic, poly[ethylene‐co‐(methyl acrylate)] (EMA), to toughen the matrix. EMA formed a dispersed phase in PP that maintained its strength through its crystallinity rather than crosslinking. EMA can form a compatible interface with PP through inclusion of maleated‐PP as a compatibiliser. The viscoelasticity of the PP–EMA blends, particularly the creep behaviour is an important factor if the properties of PP are to be maintained. The creep and recovery of PP–EMA blends with varying compositions were investigated under different loads and number of cycles. High EMA content provided an alternative deformation pathway due to its elastomeric properties. The experimental creep behaviour has been evaluated using the 4‐element model with some limitations evident in the viscoelastic transitional region.