Thermal analysis of thermoplastic elastomers based on recycled polyethylenes and ground tyre rubber

Thermal stability and phase structure of thermoplastic elastomers (TPEs) based on post-consumer materials such as recycled lowor high-density polyethylene and ground tyre rubber (GTR) were investigated by using TG, DSC and DMTA analysis. Preliminary reclamation of GTR leads to enhancement of compatibility between polyethylene matrix and dispersed GTR particles.     

The influence of recycled material on the crystallization kinetics of thermoplastic polymers

The injection moulding of semi-crystalline thermoplastic polymers requires an exact knowledge of the thermodynamic data and of the crystallization kinetics. The behaviour of the polymer melt during rapid cooling in the mould determines, to a great extent, the quality and usability of a final product. Technical raw materials are often equipped with nucleating agents in order to obtain crystallization within the desired temperature range and at the required rate. The use of recycled material (regranulate) shows an analogous effect such as the addition of nucleating agents, i.e. crystallization begins at a higher temperature and a higher crystallization rate is detected compared to materials without added regranulate. Heat flux DSC was used to study the crystallization of polyamides, polyolefins and polyoxymethylene during cooling at various cooling rates. Although the temperature gradients and pressures which occur in the proceesing machine cannot be realised in DSC tests, the DSC results reproduce the direction of influence of the regranulate additive very clearly.     

The influence of thermoplastic elastomers on structure and crystallisation behaviour of polyolefin blends

The influence of a styrene-ethylene/butylene-styrene triblock copolymer (SEBS) on an isotactic polypropylene / polyethylene blend was investigated. For comparison binary blends with polypropylene and SEBS alone were also prepared. The blends obtained by solution mixing were characterised by small-angle x-ray scattering, light microscopy and dynamic mechanical analysis. The role of SEBS as matrix reinforcer or interfacial agent is composition dependent. Experimental data also reveal a different influence of SEBS on the binary blends than on the ternary blends containing polyethylene.     

线形低密度聚乙烯／废胶粉热塑弹性体动态硫化性能研究

利用动态硫化法制备了线形低密度聚乙烯(LLDPE)/废胶粉(GTR)热塑弹性体。重点研究了两种交联剂:硫和过氧化二异丙苯(DCP)对共混物性能的影响。加入一定量的苯乙烯-丁二烯-苯乙烯(SBS)共聚物作为增容剂。结果表明,经过DCP动态硫化后的共混物的力学性能比简单共混的共混物有明显的提高,而加入硫磺体系对共混物力学性能影响不大甚至有所下降。通过红外光谱、热分析(DSC)和扫描电镜(SEM)对共混物的热行为和表面形态研究表明,加入DCP交联剂使LLDPE、SBS和胶粉之间发生了交联反应,从而增加了胶粉颗粒与LLDPE间的界面相容性,使其热塑性弹性体的力学性能得以提高。     

Dynamic vulcanization and thermoplastic elastomers

Ageing and electrical conductivity of thermoplastic elastomers (TPE) have been studied. It is shown that incorporation of LDPE leads to more stable structure of TPE during ageing. Electrical conductivity of TPE depends on blending condition.     

Cryodilation of thermoplastic PEBA elastomers

PEBA block copolymers, poly(ether-block-amide), containing low concentrations of polyamide are thermoplastic elastomers. These materials, when strained at room temperature and then relaxed, exhibit dilation during cooling to low temperatures (ca.–10°C). This effect, of the order of 5–15%, depending on the concentration of the different blocks, is due to oriented crystallization of the soft polyether segments.     

Physical testing of thermoplastic elastomers

Consideration is given to which physical test methods are appropriate for thermoplastic elastomers, in particular choosing between the conventional methods for thermoplastics and rubbers. Possible experimental difficulties and modifications to standard procedures are discussed.     

The influence of the nanofiller on thermal properties of thermoplastic polyurethane elastomers

Pure Fe₃O₄ and Mn-doped Fe₃O₄ nanoparticles were synthesized by simple wet chemical reduction technique using nontoxic precursors. Manganese doping of two concentrations, 10 and 15%, were employed. All the three synthesized nanoparticles were characterized by stoichiometry, crystal structure, and surface morphology. Thermal studies on as-synthesized nanoparticles of pure ferrite (Fe₃O₄) and manganese (Mn) doped ferrites were carried out. The thermal analysis of the three as-synthesized nanoparticles was done by thermogravimetric (TG), differential thermogravimetric, and differential thermal analysis techniques. All the thermal analyses were done in nitrogen atmosphere in the temperature range of 308–1233 K. All the thermocurves were recorded for three heating rates of 10, 15, and 20 K min^?1. The TG curves showed three steps thermal decomposition for Fe₃O₄ and two steps thermal decompositions for Mn-doped Fe₃O₄ nanoparticles. The kinetic parameters of the three as-synthesized nanoparticles were evaluated from the thermocurves employing Kissinger–Akahira–Sunose (KAS) method. The thermocurves and evaluated kinetic parameters are discussed in this paper.     

Mechanical and thermo‐mechanical studies of double networks based on thermoplastic elastomers

A new approach to prepare and characterize double network elastomeric systems was investigated. A styrene‐ethylene‐co‐butylene‐styrene (SEBS) triblock copolymer system containing physical crosslinks was used to achieve a double network by additional crosslinking using ultra‐violet (UV) light. An ethylene–propylene–diene monomer (EPDM) terpolymer system containing chemical crosslinks was used to achieve a conventional double network using UV crosslinking. Properties from conventional monotonic tensile tests, dynamic mechanical analysis, and thermomechanical properties were investigated. These double network elastomers show a transition between competitive and collaborative behavior in their mechanical properties and lower coefficients of thermal expansion arising from a competition of the networks. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 778–789, 2010     

Reactively compatibilized and dynamically vulcanized thermoplastic elastomers based on high-density polyethylene and reclaimed rubber

Melt blending was employed to prepare thermoplastic elastomer (TPE) of reclaimed rubber (RR) and high density polyethylene (HDPE). Mechanical properties of TPE samples were improved in different methods including dynamic vulcanization and reactive blending (reactive compatibilization) during melt mixing in an internal Haake mixer. The physical and mechanical properties of the TPE blends were investigated by the dynamic mechanical analysis (DMA) and tensile tests. The thermal behavior was characterized by differential scanning calorimeter (DSC) and thermogravimetric analysis (TGA). The phase morphology of the blends was studied by scanning electron microscopy (SEM). Experimental results showed that, both static and dynamic mechanical properties of reactively-compatibilized and dynamically-vulcanized samples improved significantly compared with the virgin samples. The effect of dynamic-vulcanization and reactivecompatibilization on the mechanical properties revealed that the Young’s modulus and storage modulus increased with both improvement methods. SEM results showed that, dynamic-vulcanization and reactivecompatibilization methods improved the distribution of RR particles in HDPE matrix. Although both methods improved the thermal and mechanical properties of the HDPE/RR blends, dynamic-vulcanization was more effective and promising approach due to the higher properties of HDPE/RR blends prepared by this method.     

Synthesis of transparent thermoplastic polyurethane elastomers

Thermoplastic polyurethanes were synthesized from poly(propylene glycol)‐block‐poly(ethylene glycol) polyols and hybrid hard segments that combined at least two different chain extenders. The combination of hard segments allowed for modification of elastomer performance and processing not achievable by any single hard segment. The combination of hard segments modulated hard‐segment energies that were directly related to elastomer performance. Special attention is paid to obtaining optically transparent elastomers with this technique. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 271–278, 2004     

Synthesis of thermoplastic elastomers based on PET glycolysates: Study of their dielectric properties

Thermoplastic elastomers based on PET glycolysates were synthesized in the molten state according to a multistep process. Their chemical structures were studied (¹H NMR, triple detection, steric exclusion chromatography) as well as their thermal properties (ATG, DSC) and their morphology (AFM). Influence of hard segments composition on the different properties was investigated with the same ratio soft/hard segment. DSC study showed that these compounds had thermal properties similar to those of conventional thermoplastic elastomers (low T_g and high T_m). The association of PET with PBT segments seemed to harm the hard segments crystallization. SEC analyses showed that the compounds obtained had low molecular weights. Two factors seemed to explain the difference in properties between the compounds with and without glycolysate: a lower molecular weight of the TPE containing glycolysate, and a lower organization for materials containing both PET and PBT segments in respect to copolymer without glycolysate and containing solely PBT segments.Dielectric measurements showed properties close to those usually encountered for insulators used in electrical engineering. Glycolysate-free materials exhibited the best properties (high resistivity, low loss factor, slight variation of permittivity) and the materials exhibited interesting insulating properties (breakdown voltage up than 35 kV/mm_RMS, resistivity around 10⁹ Ωm). An improvement of the synthesis methodology with the use of catalyst might result in a significant enhancement of the dielectric properties, already promising for this type of materials.     

Ductile-to-ductile transition in dispersely filled composites based on thermoplastic polymers

The fracture mechanism for rubber-filled composites based on gutta-percha, LDPE, medium-density PE, and rubber particles has been studied. An increase in the concentration of filler particles leads to a change in the stress-strain behavior of the composites from neck propagation to homogeneous plastic deformation. For the filled composites, the criterion for the ductile-to-ductile transition is the equality of yield and draw stresses. The critical concentration of rubber particles at the ductile-to-ductile transition is controlled by the ratio between the yield stress of matrix polymer and the neck propagation stress. Transition from neck propagation to homogeneous plastic flow of the material is accomplished under two conditions: the breaking strength of the polymer matrix should be higher than the yield stress, and stretching of the composite should not be accompanied by the formation of diamond cracks. The latter condition is fulfilled when the dimensions of rubber particles are below a certain critical value, which is determined by the ductility of the matrix.     

Crystalline structure of polypropylene in blends with thermoplastic elastomers after electron beam irradiation

Isotactic polypropylene (PP) was blended in extruder with 0–50% addition of styrene–ethylene/butylene–styrene (SEBS) and styrene–butadiene–styrene (SBS) block copolymers. Granulated blends were irradiated with electron beam (60 kGy) and 1 week later processed with injection molding machine. Properties of samples molded from irradiated and non-irradiated granulates were investigated using DSC, WAXS, MFR, SEM and mechanical and solubility tests. It was found that the SEBS based systems are more resistant to irradiation in comparison to similar blends with SBS copolymer. Such behavior can be explained by the presence of double bonds in elastic SBS block. Irradiation of PP-SBS blends leads to considerable structure changes of crystalline and amorphous PP phases and elastic SBS phase. It indicates creation of new (inter)phase consisting of products of grafting and cross-linking reactions. Irradiated PP-SBS blends show significant improvement of impact strength at low temperatures.     

Solid state extrusion of thermoplastic elastomers 4

A solid state extrusion technique is applied as to produce oriented block copoly(ether ester) under various physical conditions. The morphology of the extruded samples is characterized in relation to the extrusion parameters and hard segment compositions of the polymer, using thermal analysis and X-ray methods. The lateral dimensions of the crystalline domains are found to be approximately 150 Å depending on the extrusion conditions. The statistics of the long range periodicity of the structure along the extrusion direction is in agreement with a one-dimensional two phase model, the crystalline portion of which does not vary much in thickness (35 – 45 Å). The unexpected increase in the long period and the thermal shrinkage suggest the existence of strained interlamellar amorphous chains (tie molecules). The observed variations in tensile properties are interpreted under the assumption that both the number of such tie molecules and their fully extended lengths are determined by the hard segment composition and the extrusion conditions. It is also argued that the increase in the glass transition temperature is not only a function of the composition of hard segments in the amorphous phase but also of the number of strained tie molecules.Herrn Dr. Dr. h. c. H. Hellmann zum 70. Geburtstag gewidmet.Part 3 cf. lit [11]     

Physical characterization of commercial polyolefinic thermoplastic elastomers

In this work, a systematic study of physical characterization on a series of commercial polyolefinic thermoplastic elastomers (TPEs), is reported. Formulations from different manufacturers, having a wide range of Shore hardness values (from A45 to D51), were examined using simple, inexpensive and standard laboratory methods. From this analysis, the TPE chemical composition and its relationship with hardness and tensile set—the key parameters that define the TPE performance in most of the applications—could be established.

It was found that the strategy followed by the manufacturers to design TPEs is very similar. The EPDMs used for the different formulations look similar in ethylene content and thermal properties. Therefore, the TPE bulk modulus (or hardness) is mainly controlled by the PP content. Nice elastomeric behavior was observed only in grades with a dominant proportion of EPDM, in agreement with the deformation mechanism generally accepted for this type of materials. Grades with higher hardness values—and a dominant proportion of PP—showed a mechanical response corresponding to a toughened thermoplastic, even when these grades are marketed by the producers as “thermoplastic elastomers”. Differently from conventional crosslinked elastomers, where hardness and ability to recover from highly deformed states can be simultaneously controlled by changing the degree of crosslinking, the results of this work indicate that it is very difficult to increase TPE hardness without sacrificing elastomeric properties.     

Polypropylene ionic thermoplastic elastomers: Synthesis and properties

Polypropylene ionic thermoplastic elastomers have been prepared by melt radical grafting of maleic anhydride onto polypropylene in the presence of N-bromosuccinimide followed by neutralization of the resulting elastomeric grafted polypropylene using sodium salts. Sodium hydroxide and sodium acetate were compared in aqueous solution, as anhydrous or hydrated powders. The neutralization reaction was followed by Fourier transform infrared spectroscopy, allowing the development of a method to determine the effective neutralization degree. Important physical changes were recorded upon neutralization. Especially thermal stability, shear storage modulus and complex viscosity in the flow region were largely increased as a function of the neutralization degree.     

Effect of butadiene/styrene ratio,block structure and carbon nanotube content on the mechanical and electrical properties of thermoplastic elastomers after UV ageing

Thermoplastic elastomers based on a triblock copolymer styrene-butadiene-styrene (SBS) with different butadiene/styrene ratios, block structure and carbon nanotube (CNT) content were submitted to accelerated weathering in a Xenontest, in order to evaluate their stability to UV ageing. It was concluded that ageing mainly depends on butadiene/styrene ratio and block structure, with radial block structures exhibiting faster ageing than linear block structures. Moreover, the presence of carbon nanotubes in the SBS copolymer slows down the ageing of the copolymer. The evaluation of the influence of ageing on the mechanical and electrical properties demonstrates that the mechanical degradation is higher for the C401 sample, which is the SBS sample with the largest butadiene content and a radial block structure. On the other hand, a copolymer derivative from SBS, the styrene-ethylene/butadiene-styrene (SEBS) sample, retains a maximum deformation of ∼1000% after 80 h of accelerated ageing. The hydrophobicity of the samples decreases with increasing ageing time, the effect being larger for the samples with higher butadiene content. It is also verified that cytotoxicity increases with increasing UV ageing, with the exception of SEBS, which remains non-cytotoxic up to 80 h of accelerated ageing time, demonstrating its potential for applications involving exposure to the environment.     

Effect of an anionic emulsifier on the structure of butadiene-nitrile elastomers

X-ray diffraction and TMA studies show that surfactant sodium alkyl sulfonate (C₁₅) forms one of its two LC structures (distinguished by the smallest layer periodicity) in butadiene-nitrile elastomers containing different amounts of acrylonitrile units. In this case, the surfactant serves as a structural plasticizer and facilitates a more complete selective segregation of microblocks of trans-1,4-butadiene units and, especially, of sequences of alternating trans-1,4-butadiene and acrylonitrile units.     

Comparison of the characteristics of polyurethane elastomers based on DMC- and traditional polyethers

The results of the study of replacement of traditional polyether polyols with DMC polyols based on the new DMC technology in formulas of polyurethane (PU) elastomer adhesives and sealants are presented. It is shown that the physical and mechanical characterisrics of PU elastomers are improved in many cases.