Effect of dissolution-based recycling on the degradation and the mechanical properties of acrylonitrile-butadiene-styrene copolymer

A dissolution-based recycling technique for acrylonitrile-butadiene-styrene copolymer (ABS) is proposed, and the effects of repeated recycling cycles are studied measuring changes in chemical structure, melt viscosity, and tensile and impact properties. Acetone as solvent, 0.25 g/ml concentration, room temperature and 40 min for dissolution have been found to be the most reliable recycling parameters. FTIR, DSC and MFI results have shown that the dissolution-based recycling itself does not degrade the ABS. However, TGA analysis suggests that during the dissolution some stabilizers are probably eliminated, and consequently degradation takes place in the following injection moulding step. Darkening of recycled ABS is attributed to the butadiene degradation, pointed out by FTIR results. Otherwise, the chemical structure of the SAN matrix has not been modified, but its molecular weight has been reduced. The modulus of elasticity is not affected even after four recycling cycles. However, yield stress and impact strength decrease after the first recycling cycle, and remain constant in the following steps.     

Tuning the mechanical properties and degradation properties of polydioxanone isothermal annealing

Polydioxanone (PPDO) is synthesized by ring-opening polymerization of p-dioxanone, using stannous octoate as the catalyst. The polarized optical micrograph (POM) shows thes pherulite growth rate of PPDO decreases with an increase in the isothermal crystallization temperature. PPDO is compression-molded into bars, and PPDO bars are subjected to isothermal annealing at a range of temperatures (Ta = 50, 60, 70, 80, 90, and 100 °C), and correspond to three different annealing times (ta = 1h, 2h, 3h). The effect on PPDO is investigated by using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), X-ray diffraction (XRD), and scanning electron microscopy (SEM). With an increase in Ta and ta, the grain size and the degree of crystallinity also increase. Meanwhile, the tensile strength is significantly improved. The PPDO bars (90 °C, 2 h) reach the maximum crystallinity (57.21%) and the maximum tensile strength (41.1 MPa). Interestingly, the heat treatment process does not result in serious thermal degradation. It is observed that the hydrolytic degradation of the annealed PPDO is delayed to some extent. Thus, annealed PPDO might have potential applications, particularly in the fields of orthopedic fixation and tissue engineering.     

Modeling mechanical properties of polyhydroxyalkanoate during degradation in animal tissue

Polyhydroxyalkanoates (PHAs) are a family of biodegradable and biocompatible polymers produced by several species microorganisms that possess favorable mechanical properties (e.g. strength and elongation properties). Different types of PHA polymers have been used in medical applications. However, in order to better understand the use of this polymer in the different applications, a thorough understanding of the kinetics of in vivo degradation is one of the major requirements. In this study, poly(3‐hydroxybutyrate) (PHB) was subcutaneously implanted in mice and incubated for 2, 4, 8, or 16 weeks. After removal from the animal, the strength, elongation, mass loss, and enthalpy of the PHB were tested for each time point. From these data, a mathematical model was generated by Rayleigh's method of dimensional analysis, where polymer strength over tissue contact time could be predicted. To prove the model, previous data obtained by our group were used: poly(3‐hydroxybutyrate‐co‐3‐hydroxyhexanoate) [P(HB‐co‐HHx)] incubation in the presence of human embryonic kidney cells (HEK). It was found that the developed model was aligned with experimental results, could predict the strength of the polymer when in contact with cells, and the predicted strength follows the trend of the experimental data. Also, the dimensionless constant (K) value associated with the model is different for both experiments, where this constant, produced via experimental data, is used for construction of a homogeneous equation. Copyright © 2017 John Wiley & Sons, Ltd.     

Effect of the flow field on the mechanical degradation of molten polystyrene

Degradation tests have been carried out on a polystyrene sample using various capillaries of different length (L) to diameter (D) ratio and entrance angle. The extent of degradation depends on the length to diameter ratio becoming larger and larger with increasing length of the capillary. However, even when L/D approaches zero degradation still occurs to some extent.It may thus be inferred that degradation occurs both in the capillary and in the converging flow preceding the entrance of the melt to the capillary. Runs with a conical die lubricated to eliminate any shearing effects show that the elongational flow is mainly responsible for the mechanical degradation in the converging flow.On the basis of an approximate analysis, one may say that the breakage of C-C links is possible in elongational flow.     

Effect of mechanical activation on structural-chemical properties of phosphorites

Effect of mechanochemical activation of mono-and mid-fraction of phosphorites from the Burenkhan deposit was studied by IR and ESR spectroscopies in vibration and planetary mills. Original Russian Text ? B.G. Sukhov, D. Enkhtuyaa, Zh. Amgalan, T.I. Vakul’skaya, L.N. Novikova, Zh.G. Bazarova, B.G. Bazarov, 2007, published in Zhurnal Prikladnoi Khimii, 2007, Vol. 80, No. 6, pp. 881–886.     

Structure development and change in properties of polymers during mechanical degradation

The effects of ultrasonic irradiation, high speed stirring and vibro-, jet- or pan-milling on structure and change in properties of polymers were studied in hopes of gaining an innovative route to enhance the processability and properties of polymer materials via polymer stress reaction. A brief survey of ongoing research work done by the author and his colleagues is given in this paper.     

Effect of degradation on electronic properties of polymer solar cells

We present here the effect of degradation on electronic properties of polymer solar cells. Investigations were performed on two types of solar cells based on the bulk‐heterojunction network of poly(3‐hexylthiophene) and phenyl [6,6] C₆₁ butyric acid methyl ester, one with slow degradation whereas other with faster degradation. Samples were prepared in identical conditions with controlled atmosphere, but for faster degradation, one of the samples was exposed to ambient air (rich in O₂ and H₂O molecules) before deposition of top metal electrode. The sample with slow degradation showed linear degradation in short circuit current density (J_sc), whereas the sample with faster degradation exhibited exponential degradation in J_sc. Linear degradation happens due to degradation in the active layer only whereas the exponential degradation is because of through degradation of the solar cell. The effect of degradation is investigated on different diode parameters. Because of different degradation processes in the two samples, the variations in diode parameters with time are different. Copyright © 2013 John Wiley & Sons, Ltd.     

Effect of aminoglycoside on mechanical properties of zwitterionic phospholipid vesicles

The effect of the aminoglycoside (streptomycin) incorporation on the nanomechanical properties of pure dipalmitoylphosphatidylcholine (DPPC) vesicles was studied using atomic force microscope (AFM) on mica surface. The vesicles were prepared by extrusion and adsorbed on the mica surface. The forces, measured between an AFM tip and the vesicle, presented that the breakthrough of the tip into the vesicles occurred two times. Each breakthrough represented each penetration of the tip into each bilayer. Force data prior to the first breakthrough were fitted well with the Hertzian model to estimate Young's modulus and bending modulus of the vesicles. It was found that the Young's modulus and bending modulus were not varied with the incorporation of AGs (streptomycins) up to the 1:1 AG/DPPC vesicle system. This result may suggest that the AGs do not lead to the disruption of DPPC packing.     

Effect of water on the mechanical properties of collagen films

The effect on water on mechanical properties of collagen films has been studied. The S-shaped sorption isotherm is separated into an adsorption curve C₁ and a solution curve C₂. From the C₂ curve, a value of 0.8 is calculated for the Flory-Huggins interaction parameter χ₁. The dynamic shear modulus G′, loss modulus G″, and loss tangent tan δ determined as functions of water content indicate two dispersions at low and at high water content. The region of water content from about 0.05 to 0.1 g/g, G′ decreases suddenly, G″ has a peak, and tan δ increases, corresponds to the region where the C₂ component of sorption becomes detectable. Another dispersion occurs at water contents above 0.2 g/g. A composite curve can be obtained by shifting stress-relaxation curves obtained at different humidities along the log time axis. When only the C₂ component of sorbed water is taken into account, the shift factor a_c is explained by a relation of Fujita and Kishimotos' based on free-volume theory. Shift factor for the relaxation curves of wool fibers, except for an initial part at times of less than 1 sec, are described by the same equation. The parameter β in the equation has the same value of 0.16 for both collagen and wool.     

Synthesis,properties, and fungal degradation of castor-oil-based polyurethane composites with different cellulose contents

Different contents of bonded cellulose were dispersed in a matrix of castor-oil-based polyurethane to produce composites with high susceptibility to fungal attack. We chose to bond the cellulose filler with free diisocyanate, to increase the crosslinking density. Measurements indicated physical and chemical interactions between the polyurethane matrix and cellulose filler. The cellulose network significantly enhanced the interfacial adhesion and thus improved the thermal stability and Young’s modulus of the composites. The influences of the amount of cellulose on the surface chemical structure, surface morphology, and mechanical properties after fungal attack were also investigated. The tensile strength and elongation at break of these composites substantially decreased after exposure to fungus. These composites with high content of renewable raw materials present an optimal balance of physical properties and biodegradability, with potential applications as ecofriendly biomaterials.     

The effect of NDGA-modified etchant on the enzymatic degradation resistance and mechanical properties of collagen matrix

Bio-modified etchant can significantly improve the biostability of demineralized dentin collagen matrix, which validates the concept of etch-andcrosslink in dentin bonding.     

Effect of magnesium methacrylate on the mechanical properties of EVM vulcanizate

High performance ethylene-vinyl acetate copolymer (EVM) vulcanizate was obtained by directly blending EVM with magnesium methacrylate (MDMA) at a high level. The mechanical properties and crosslink density of the peroxide-cured EVM vulcanizates were investigated. Dynamic mechanical thermal analysis (DMTA) was used to study dynamic properties of EVM reinforced by MDMA. The results showed that the commercial MDMA can greatly improve the modulus at 100% and tensile strength of the EVM vulcanizates, while retaining their high elongation at break. DMTA results revealed that the glass transition temperature (T_g) of the vulcanizate shifted to lower temperature with the increase of MDMA loading. Fourier transform infrared (FTIR) spectrum indicated that the double bonds in MDMA reacted after peroxide curing. Crosslink density analysis showed that EVM vulcanizate contained both ionic bonds and covalent bonds. Ionic crosslinks greatly increased with increasing amount of MDMA and dicumyl peroxide (DCP).     

Effect of fiber treatment on mechanical properties of polypropylene-wood fiber composites

Polypropylene (PP) was reinforced with chemi-thermomechanical (CTMP) pulp and wood flour. Different chemical treatment of the fiber a) polyethylene-poly-(phenyl isocyanate), b) silane A-172 and c) epolene was carried out to improve the bonding between the polymer and fiber. PP reinforced with CTMP pulp and wood flour showed a decrease in stress values as the concentration of fiber increased in the composite. Tensile modulus generally increased with filler loading and was not much affected by fiber treatment. Experimental results of the composites were compared with theoretically predicted values.     

Effect of solvents on the cryogenic dynamic mechanical properties of polystyrene

Young's modulus and mechanical damping of 15 organic liquids in polystyrene have been measured from 4°K to 250°K. The concentration was generally in the range from 10 to 15%, but the polystyrene–toluene system was investigated over the range from 0 to 16%. Some liquids cause the 40°K damping peak of polystyrene to disappear, other liquids do not. Seven of the liquids which cause the disappearance of the 40°K peak give rise to new large damping peaks at the temperature expected for the secondary glass transition temperatures of the liquids, that is, at 0.77 T_g of the liquids. Some of the liquids produced large unexplained damping peaks at temperatures above the expected glass transition temperatures T_g of the liquids. It is suggested that the γ peak in polystyrene is caused by styrene monomer.     

Effect of cerium on electrochemical and mechanical properties of aluminum-iron alloys

Effect of cerium on the corrosion-electrochemical and mechanical properties of aluminum alloys with an iron content of up to 3% was studied in order to use secondary aluminum in development of sacrificial formulations.     

Sub-micron scale mechanical properties of polypropylene fibers exposed to ultraviolet and thermal degradation

Nanoindentation using atomic force microscopy (AFM) was conducted to investigate the affect of accelerated ultraviolet (UV) and thermal degradation on the mechanical properties of polypropylene fibers. The affect of degradation on Young’s modulus across fiber cross-sections was investigated with progressive nanoindentation from the surface to the center of the fiber. UV degradation initially increases the Young’s modulus both at the center and the surface of the fibers until 120 h of exposure with the increase being more rapid at the surface. Moduli started to decrease beyond 120 h of exposure. Wide angle x-ray scattering shows an increase of crystallinity up to 120 h of exposure and total destruction of crystallinity at 144 h. Infrared spectra showed the formation of carbonyl bonds with UV exposure. To investigate thermal degradation, the fibers were exposed to 125 °C for four weeks. Young’s modulus increased near the surface after four weeks exposure. These results support the idea that surface degradation may lead to embrittlement of textile fibers.     

Effect of branching on the degradation behaviour and caloric properties of PVC

Nine different PVC samples with defined chlorine content and degree of branching have been investigated. The aim of the work was the influence of these parameters on some caloric properties as well as the degradation behaviour and the degradation products. As expected, the heat of combustion decreases with increasing chlorine content. As determined by simultaneous thermal analysis/mass spectrometry, the volatile degradation products of the pyrolysis in nitrogen atmosphere vary. The higher the chlorine content, the higher the amount of chlorinated degradation products and the lower the amount of polycyclic aromatic hydrocarbons (PAH). A higher number of branching promotes the formation of alcylated aromatic hydrocarbons.     

Thermal Degradation,Flame Retardance and Mechanical Properties of Thermoplastic Polyurethane Composites Based on AluminumHypophosphite简

Aluminum hypophosphite （AP） was used to prepare flame-retarded thermoplastic polyurethane （FR-TPU） composites, and their flame retardancy, thermal degradation and mechanical properties were investigated by limiting oxygen index （LOI）, vertical burning test （UL-94）, thermogravimetric analysis （TGA）, cone calorimeter （CC） test, Fourier transform infrared （FTIR） spectroscopy, scanning electron microscopy （SEM） and tensile test. TPU containing 30 wt% of AP could reach a V-0 rating in the UL-94 test, and its LOI value was 30.2. TGA tests revealed that AP enhanced the formation of residual chars at high temperatures, and slightly affected the thermal stability of TPU at high temperatures. The combustion tests indicated that AP affected the burning behavior of TPU. The peak of heat release rate （PHRR）, total heat release （THR） and mass loss rate （MLR） greatly reduced due to the incorporation of AP. The tensile test results showed that both the tensile strength and the elongation at break slightly decreased with the addition of AP. The digital photos and SEM micrographs vitrified that AP facilitated the formation of more compact intumescent char layer. Based on these results mentioned above, the flame-retarding mechanism of AP was discussed. Both the self-charring during the decomposing process of AP and its facilitation to the charring of TPU led to the great improvement in the flame retardancy of TPU.     

The mechanical degradation of polystyrene

The catastrophic failure of a polymeric material is preceded by a number of complex, partially understood events occurring on the molecular level. These events range from the flow of ordered regions to the cleavage of primary bonds in the chain. In recent years, stress-induced bond cleavage in polymers has received increased attention, many authors nothing the presence of free radicals and/or volatile products released upon fracture; a free-radical decomposition mechanism involving up to 10³ molecules per chain rupture also has been postulated. A special tensile stress–strain and shear apparatus was developed and located inside the ion-source housing of a time-of-flight mass spectrometer to characterize the volatile products released during mechanical degradation of polystyrene. Volatile compounds evolved during stress and fracture of polystyrene were monitored either continuously or by z-axis modulated oscilloscopic display. The polystyrene was purified by two methods: vacuum outgassing and fractional reprecipitation. Large amounts of styrene evolved from both the as-received and outgassed samples; however, essentially none was observed from the reprecipitated samples. Previous reports on monomer evolution during mechanical stress of polystyrene may be the result of residual monomer and not mechanical degradation products. The product of the surface density of primary radicals and the chain length for unzipping is less than 3 × 10¹⁰ radicals/mm² indicating a maximum radical concentration of approximately 10¹⁰ radicals/mm².