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The effect of different molecular weight of soft segments in polyurethanes on photooxidative stability

The effect of molecular weight of polyol (soft segment) and the concentration of urethane (hard segment) in segmented polyurethane elastomers on their photodegradation was investigated. Polyurethane elastomers have been prepared from 4.4′-dipheylmethane diisocyanate (MDI) and poly(oxytetramethylene) glycol (PTMO) of 1000 and 2000 molecular weight at NCOOH ratios of 21 and 41. Purified 1,4-butanediol (BD) was used as the chain extender. Mechanical, thermal, dynamic mechanical and Fourier Transform Infrared Spectroscopy (FTIR) measurements have been used for mechanical and structural studies of PUR elastomers before and after UV irradiation, for a better understanding of the role of the concentration of hard segments (urethane) and molecular weight of soft segments (polyol) in PUR. It was found that the molecular weight of soft segments as well as the NCOOH ratios have an influence on the UV stability of the examined elastomers. The photooxidative degradation is more prevalent in elastomers with lower hard segment concentration and with higher soft segment molecular weight. The correlation between the compositions of the investigated elastomers and mechanical properties, dynamic mechanical properties, physical transitions, as well as intensities of the changes of these properties after irradiation were established. The results show that with an increase of hard segment concentration in all examined polyurethane elastomers, the glass transition temperature (Tg) of the soft segment increased, the tensile strength increased and the elongation at break decreased. In irradiated polyurethane elastomers based on PTMO (1000) with the higher hard segment concentration Tg of the soft segment decreased, the opposite effect was obtained in PUR elastomer with lower hard segment concentration. Resistance to photooxidative degradation was enhanced with increase of the hard segment concentration in polyurethane elastomers based on PTMO (1000). The photooxidative degradation is more prevalent in polyurethane elastomers based on polyether with higher molecular weight PTMO (2000), than those based on polyether of molecular weight PTMO (1000), even at higher hard segment concentration.

Thermal stability of polyurethane elastomers before and after UV irradiation

In this work, we investigated the thermal degradation behavior of segmented polyurethane (PUR) elastomers before and after UV irradiation. The thermal degradation of PUR elastomers was studied over the temperature range of 25–600°C in an atmosphere of nitrogen using thermal gravimetric analysis (TGA). Four series of PUR elastomers derived from poly(oxytetramethylene)glycol (PTMO) of 1000 and 2000 molecular weight and poly(caprolactone glycol) (PCL) of 1250 molecular weight, 4,4′-diphenylmethane diisocyanate (MDI), and 4,4′-dicyclohexylmethane diisocyanate (H12MDI) and 1,4-butanediol as an chain extender were synthesized by the prepolymer method. The derivative thermogravimetric (DTG) peaks observed in the experiments indicated that PUR elastomers degraded through two steps. We attributed the first step to degradation of the hard segment. The second degradation step could be ascribed to degradation of the soft segment. We found that the PUR elastomers based on poly(ester polyol) and aromatic diisocyanate exhibit better thermal stability than that of PUR elastomers based on the poly(ether polyol) soft segment in both steps of degradation. The thermal degradation is more prevalent in PUR elastomers based on cycloaliphatic diisocyanate. The higher values of the temperature of initial decomposition (Ti) indicate a higher thermal stability of UV-exposed elastomers on the beginning of degradation. This may be due to the formation of a crosslinking structure in the presence of UV irradiation.

Thermal Degradation of Polyurethane Elastomers: Determination of Kinetic Parameters:

The objective of this study is determining the kinetic parameters of thermal degradation of polyurethane elastomers before and after UV irradiation. To determine the kinetic parameters of elastomeric polyurethane (PUR) decomposition the Freeman-Carroll method of calculation is applied. The effect of soft segment and hard segment type, soft segment molecular weight and hard segment content on the kinetic parameters of the degradation process were measured. Polyurethane elastomers were obtained from poly(oxytetramethylene) glycol, PTMO, of 1000 and 2000 molecular weight and polycaprolactone glycol of 1250 molecular weight (PCL), 4,40diphenylmethan diisocyanate (MDI) and 4,40-dicyclohexylmethane diisocyanate (H12MDI) and 1,4-butanediol as chain extender. The activation energy values obtained for PUR elastomers based on polyester soft segment were higher than those based on polyether soft segment.The PUR elastomers based on aromatic type of diisocyanate have lower activation energy values than those based on cycloaliphatic type of diisocyanate.

Effect of polymer modifiers on the properties of bitumen

This article presents an investigation about the polymer-modified bitumens (PMBs) containing styrene–butadiene–styrene (SBS) block copolymers with different structures, linear (SBS-L) and radial (SBS-R), semicrystalline copolymer ethylene–vinyl acetate (EVA), and terpolymer ethylene–butyl acrylate–glycidyl methacrylate, Elvaloy AM and Elvaloy 4170. The aim of the study was to establish the influence of the polymer type and content on the properties of PMBs for engineering applications and to evaluate the effectiveness of polymer modifiers. The results indicated that the polymer modification improved the rheological properties of bitumen, increased critical temperature, that is better resistance to permanent deformation was achieved as well as a wider temperature range in service. The degree of improvement generally increased with the polymer content but varied with the polymer type.

The influence of talc content on the thermal and mechanical properties of thermoplastic polyurethane/polypropylene blends:

The influence of different talc contents on the thermal and mechanical properties of thermoplastic polyurethane/polypropylene (TPU/PP) blends was investigated. The compatibility and crystallinity of TPU/PP and TPU/PP/T blends were determined by differential scanning calorimetry (DSC). The DSC results indicated that the addition of PP in TPU/PP blends increased glass transition temperature (T g), melting temperature (T m) and crystallinity (χ c). The addition of talc has decreased T m and χ c and increased T g and crystallization temperature (T c). The effect of talc content on T g, T m and χ c was insignificant, while T c content increased. The T g of nonfilled and talc-filled blends increased suggesting that the TPU and PP are partially compatible. Thermogravimetric analysis (TGA) showed improved thermal stability of all investigated nonfilled and talc-filled TPU/PP blends in the nitrogen atmosphere. In the air atmosphere only talc-filled TPU/PP 80/20 blends show a higher thermal stability, while thermal stability decreased for TPU/PP 50/50 and increased insignificantly for TPU/PP 20/80 blends. DSC and TGA results showed improved thermal properties of talc-filled TPU/PP blends when compared with nonfilled blends. The mechanical properties of talc-filled TPU/PP 50/50 and 20/80 blends improved in terms of tensile strength and Young’s modulus, while elongation of break decreased with the addition of talc and as the talc content increased.

Morphology and Properties of SEBS Block Copolymer Compatibilized PS/HDPE Blends

The objective of this study is to examine the influence of poly [styrene-b-(ethylene-co-butylene)-b-styrene] (SEBS) compatibilizer on the morphology and properties of atactic polystyrene/high density polyethylene (aPS/HDPE) blends. The rheological behavior of the blends melt during processing is followed. The concentration of SEBS does not significantly influence the processing parameters. The morphology is determined by SEM and TEM. aPS/HDPE/SEBS blends exhibit fine dispersion of HDPE or aPS particles in the matrix and better adhesion at the interface. Higher concentration of SEBS results in better compatibility. Transmission electron micrographs confirm existence of the SEBS interfacial layer between the aPS and the HDPE phase. This effect is stronger in the blends with higher SEBS concentration and HDPE as matrix. The mechanical properties are determined. The tensile strength decreases while the elongation at break and the impact strength increase with the SEBS content. The results prove that SEBS acts as a compatibilizer in aPS/HDPE blends and its effect is more expressed in blends with a higher SEBS content and HDPE as matrix.

Polymer modified bitumen

Abstract Standard methods of characterisation of bitumen (BIT) and polymer modified bitumen (PMB) do not provide sufficient information. We propose to rely on determination of rheological properties which are much more informative. Along theses lines, we have determined rheology before and after the rolling thin film oven test. The materials studied were BIT, BIT+linear (L), styrene–butadiene–styrene (SBS), block copolymer, BIT+radial (R) and SBS copolymer. The rheological properties of the modified binders are characterised using a dynamic shear rheometer, over wide ranges of temperatures at a fixed traffic frequency of 10 rad s−1. The SBS block copolymers increase the elasticity of the BIT at high temperatures and contribute to a better flexibility at low temperatures. Polymer modified bitumens have higher resistance to permanent deformation. After aging, the hardening of BIT and PMBs occurred and the elastic response decreases as a consequence of degradation. The determined rheological properties are in agreement with the results of conventional tests.

The Effect of Ultraviolet Irradiation On Polyurethane Solution and On Solid Polymer

The course of photodegradation of polyurethane based on tolylene diisocyanate and polyoxypropylene glycol has been studied. The influence of the physical state of the polymer and of the irradiation dose on the reactions was establ ished.

Effect of EPDM as a compatibilizer on mechanical properties and morphology of PP/LDPE blends

Blends of polypropylene (PP) and low-density polyethylene (LDPE) with and without ethylene-propylene-diene (EPDM) terpolymer as a compatibilizer were studied. Mechanical properties were chosen to estimate the compatibilization efficiency of EPDM. The interactions between phases were valued through glass transition shifts in dynamic mechanical spectra, and morphology of the blends was obtained using scanning electron microscopy. Interfacial adhesion was improved by EPDM addition. Addition of EPDM to PP/LDPE blends improved mechanical properties, especially Izod impact strength in LDPE-rich blends and with higher EPDM content.

Preparation and Characterization of Talc Filled Thermoplastic Polyurethane/Polypropylene Blends

The effect of the addition of talc on the morphology and thermal properties of blends of thermoplastic polyurethane (TPU) and polypropylene (PP) was investigated. The blends of TPU and PP are incompatible because of large differences in polarities between the nonpolar crystalline PP and polar TPU and high interfacial tensions. The interaction between TPU and PP can be improved by using talc as reinforcing filler. The morphology was observed by means of scanning electron microscopy (SEM). The thermal properties of the neat polymers and unfilled and talc filled TPU/PP blends were studied by using dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). The addition of talc in TPU/PP blends improved miscibility in all investigated TPU/T/PP blends. The DSC results for talc filled TPU/PP blends show that the degree of crystallinity increased, which is due to the nucleating effect induced by talc particles. The reason for the increased storage modulus of blends with the incorporation of talc is due to the improved interface between polymers and filler. According to TGA results, the addition of talc enhanced thermal stability. The homogeneity of the talc filled TPU/PP blends is better than unfilled TPU/PP blends.