Commercial Grade Poly Research Articles

Ultrasonic evaluation of aging kinetics in amorphous polymer

The physical aging of amorphous polymers induces changes in material properties, which are challenging to detect in situ in industrial settings. Here, we present a nondestructive nonlinear ultrasonic evaluation technique that enables localized measurements of the combined effects of temperature and time in amorphous polymers, without needing to remove materials. The proposed technique is demonstrated using commercial grade poly(vinyl chloride) samples and is supported by analysis of wave–material interactions. The results show that the physical aging of the polymer is described by the Arrhenius equation with an effective activation energy of 103 kJ/mol over the analyzed temperature range.

Application of time-temperature-stress equivalence to nonlinear creep in poly(methyl methacrylate)

The uniaxial tensile creep of a commercial grade poly(methyl methacrylate)(PMMA) was measured for 4000 s at 26 ℃ and at stress levels ranging from 14 MPa to 32 MPa. Considering the influence of physical aging and rheological damage factors on the long-term creep properties of polymers, another time-temperature-stress superposition principle expression was derived. This expression as used to predict the long-term creep mechanical behaviour of PMMA. It was found that a long-term creep compliance master curve considering physical aging and damage agrees well with actual long-term creep test results.

Friction spot welding of PMMA with PMMA/silica and PMMA/silica-g-PMMA nanocomposites functionalized via ATRP

In the present study, the feasibility of Friction Spot Welding (FSpW) of a commercial-grade poly(methyl methacrylate) (PMMA) (PMMA GS) and PMMA 6N/functionalized silica (SiO2) nanocomposites was investigated. The silica nanoparticles were functionalized via atom transfer radical polymerization (ATRP) with PMMA chains to achieve a uniform dispersion in the polymer matrix. The successful functionalization of silica nanoparticles with PMMA chains via ATRP was evaluated by ATR-FT-IR and TGA measurements. Rheological investigations of the silica nanocomposites showed a plateau of the storage modulus G′ at low frequencies (0.01–0.03 rad/s) as a result of elastic particle–particle interactions. Overlap friction spot welds consisting of PMMA GS and a 2 wt% SiO2-g-PMMA nanocomposite were successfully prepared and compared to spot joints of PMMA GS welded with PMMA 6N and PMMA 6N/silica nanocomposite with 2 wt% unfunctionalized silica nanoparticles. Raman mappings of selected areas of cross-sectional plastographic specimens revealed an increased mixing behavior between the two polymer plates in the case of PMMA GS/2 wt% SiO2-g-PMMA joints. Although the joints welded with PMMA 6N/silica nanocomposites showed a reduction of 22% in lap shear strength and 21% displacement at peak load compared with the neat PMMA spot welds, they can compete with other state-of-the-art PMMA welding techniques such as thermal bonding and ultrasonic welding, which indicates the potential of friction spot welding as an alternative fabrication technology for joining future nanocomposite engineering parts.

Properties of radiation‐induced crosslinking stereocomplexes derived from poly(L‐lactide) and different poly(D‐lactide)

AbstractThe complete stereocomplexes without single crystals were obtained from a commercial grade poly(L‐lactide) (PLLA) and the sufficient low molecular weight poly(D‐lactide) (PDLA). These poly(lactide) (PLA) stereocomplex were crosslinked with triallyl isocyanurate (TAIC) by electron beam irradiation for improving their heat stability and different crosslinked samples were characterized. The organogels were formed in the irradiated stereocomplexes because of the crosslinking between the polymer chains and the crosslinker. The results indicated that 30 kGy is an optimum radiation dose for introducing the stable crosslinking network into PLA stereocomplexes. The PLLA/PDLA3 stereocomplex (L/D3) crosslinked with 3% TAIC at 30 kGy revealed the highest thermal stability. Alkaline hydrolysis and enzymatic degradation of the stereocomplex were controlled by radiation crosslinking because the alkaline solution as well as proteinase K hardly absorbed or attacked to the crosslinking network of polymer chains. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers

Application of Time-Temperature-Stress Superposition Principle to Nonlinear Creep of Poly(methyl methacrylate)

The uniaxial tensile creep of a commercial grade Poly(methyl methacrylate) was measured for 4000 seconds under various temperatures and stress levels ranging from 14 oC to 26 oC and 6 MPa to 32 MPa. The resultant creep compliance curves depart from each other for stresses beyond a critical value which varies with temperature, indicating nonlinear viscoelastic behavior. The time-temperature-stress superposition principle (TTSSP) was used to construct a smooth master compliance curve with a much longer time-scale interval from the short-term tests at higher stresses and temperatures. It is shown that the master curve covers a period of over 290 days, which is nearly 3.9 decades longer than the test duration. Moreover, it is verified that the time-temperature shift factors are dependent on stresses at which the shifts are applied, and that the time-stress shift factors are dependent on reference temperatures.

Biostability and macrophage‐mediated foreign body reaction of silicone‐modified polyurethanes

In this study, the effect of soft segment chemistry on the phase morphology and in vivo response of commercial-grade poly(ether urethane) (PEU), silicone-modified PEU (PEU-S), poly(carbonate urethane) (PCU), and silicone-modified PCU (PCU-S) elastomers were examined. Silicone-modified polyurethanes were developed to combine the biostability of silicone with the mechanical properties of PEUs. Results from the infrared spectroscopy confirmed the presence of silicone at the surface of the PEU-S and PCU-S films. Atomic force microscopy phase imaging indicated that the overall two-phase morphology of PEUs, necessary for its thermoplastic elastomeric properties, was not disrupted by the silicone modification. After material characterization, the in vivo foreign body response and biostability of the polyurethanes were studied using a subcutaneous cage implant protocol. The results from the cage implant study indicated that monocytes adhere, differentiate to macrophages which fuse to form foreign body giant cells on all of the polyurethanes. However, the silicone-modified surfaces promoted apoptosis of adherent macrophages at 4 days and high levels of macrophage fusion after 21 days. These results confirm that the surface of a biomaterial may influence the induction of apoptosis of adherent macrophages in vivo and are consistent with previous cell culture studies of these materials. This study validates the use of our standard cell culture protocol to predict in vivo behavior and further supports the hypothesis that interleukin-4 is the primary mediator of macrophage fusion and foreign body giant cell formation in vivo. The impact of these findings on the biostability of polyurethanes is the subject of current investigations. Attenuated total reflectance-Fourier transform infrared analysis of explanted specimens provided evidence of chain scission and crosslinking at the surface of all of the polyurethanes. The silicone modification did not fully inhibit the oxidative biodegradation of the polyether or polycarbonate soft segments; however, the rate of chain scission of PEU-S and PCU-S seemed to be slower than the control polyurethanes. To verify this finding and to quantify the rate of chain scission in order to predict long-term biostability, an in vitro environment that simulated the microenvironment at the adherent cell-material interface was used to accelerate the biodegradation of the polyurethanes. Polyurethane films were treated in vitro for up to 36 days in 20% hydrogen peroxide/0.1M cobalt chloride solution at 37 degrees Celsius. Characterization with attenuated total reflectance-Fourier transform infrared and scanning electron microscopy showed soft segment and hard segment degradation consistent with the chemical changes observed after long-term in vivo treatment. The biostability ranking of these four materials based on rate of chain scission and surface pitting was as follows: PEU < PEU-S PCU < PCU-S. The silicone modification increased the biostability of the PEU and PCU elastomers while maintaining the thermoplastic elastomeric properties.

Thermal properties of ion beam irradiated engineering thermoplastics

Thermal properties and recrystallization ability of commercial grade poly(para-phenylene sulphide) (PPS) and poly(ethylene terephthalate) (PET) thin foils, bombarded with 380 keV He+ ions, were studied by Differential Scanning Calorimetry (DSC) and X-ray Diffractometry (XRD). The following phenomena are observed on bombarded targets: a) decrease of the enthalpy of fusion (ΔHf ) and recrystallization (ΔHrc ) and b) decrease of the onset of the melting and recrystallization temperature. This behaviour indicates amorphisation of crystalline phases, increase of imperfections in the remaining crystallites, and loss of the recrystallization ability of the amorphous zones upon repeated thermal cycles. The amorphisation fluence, for which no crystalline regions were detected by DSC and XRD, is 2 × 1014 He+ / cm2 for PPS and 1014 He+ / cm2 for PET. However, the irradiated targets lose their ability to recrystallize at much lower fluences, around 4 × 1013 He+/cm2 for PPS and 2 × 1013 He+/cm2 for PET. The loss of crystallization ability is attributed to the presence of reactive defects on the bombarded targets which may generate crosslinks (and chain scissions) during the heating stage of the DSC run.

Thermal and Rheological Properties of Commercial-Grade Poly(Lactic Acid)s

Poly(lactic acid) is the subject of considerable commercial development by a variety of organizations around the world. In this work, the thermal and rheological properties of two commercial-grade poly(lactic acid)s (PLAs) are investigated. A comparison of the commercial samples to a series of well-defined linear and star architecture PLAs provides considerable insight into their flow properties. Such insights are valuable in deciding processing strategies for these newly emerging, commercially significant, biodegradable plastics. Both a branched and linear grade of PLA are investigated. The crystallization kinetics of the branched polymer are inferred to be faster than the linear analog. Longer relaxation times in the terminal region for the branched material compared to the linear material manifests itself as a higher zero shear rate viscosity. However, the branched material shear thins more strongly, resulting in a lower value of viscosity at high shear rates. Comparison of the linear viscoelastic spectra of the branched material with the spectra for star PLAs suggests that the branched architecture is characterized by a span molecular weight of approximately 63,000 g/mol. The present study conclusively demonstrates that a wide spectrum of flow properties are available through simple architectural modification of PLA, thus allowing the utilization of this important degradable thermoplastic in a variety of processing operations.

Syntheses and kinetics of piperazine-modified poly(vinyl chloride)s for use as fixed-site proton carrier membranes

Analytical-grade piperazine was dissolved in methanol and reacted with commercial-grade poly(vinyl chloride) powders over a range of temperatures from 25 to 64°C and times from 0.17 to 49 days. The products were aminated polymers that also contained conjugated double bonds. Chemical analysis of the resulting powders showed that up to 1.6 wt% N was possible in this solid-liquid heterogeneous reaction, although insolubility of the aminated polymer in tetrahydrofuran was always realized by 0.8 wt% N content. In those polymer formulations that were soluble, membranes were cast from solution using o-nitrophenyloctyl ether and potassium tetrakis(p-chlorophenyl)borate as the plasticizer and negatively charged sites, respectively. After conditioning, many of these fixed-site proton carrier membranes showed Nernstian pH sensitivity in potentiometric cells, independent of synthesis parameters. The nitrogen content of the aminated PVC and the pH sensitivity of the membrane correlated below a limiting nitrogen content, where Nernstian behaviour was generally observed over a range from 0.4 to 0.8 wt% N content. A three-dimensional plot over the soluble region of the polymer predicted the overall dependence of the reaction parameters, from which an activation energy (17 kcal mol−1) was determined for the substitution process. A time-temperature correspondence was demonstrated that allowed the construction of a master curve of amination in which the shift factor was of the same form as either the Williams-Landel-Ferry equation or a rearranged Doolittle equation. This format was extended to three dimensions, where the pH sensitivity is shown as a function of both the weight percentage N content and the shift factor.

Miscibility studies of polyimide/poly(ether imide) molecular composites

A new group of miscible mixtures (molecular composites) has been studied by means of differential scanning calorimetry, dielectric relaxation and dynamic mechanical techniques. Three kinds of rigid aromatic polyimides (PI) and a commercial-grade poly(ether imide) (PEI) were mixed by dissolving them in m-cresol and subsequently coagulating in methanol. The mixtures show a single glass transition temperature ( T g) in all compositions in which the T g increases with increasing PI content. These T g values are reproducible in repeated heating cycles, suggesting the true miscibility of the blends. This miscibility may be attributed to the similarity of imide structure between the rigid PI and PEI matrix. The bulk PI/PEI indeed shows improved modulus and tensile strength as compared to the pure PEI matrix.

Combustion of poly(Vinyl chloride) studied by the moving wire technique

This paper is a demonstration of the utility of the Moving Wire Technique (MWT) for studying polymer pyrolysis, ignition and burning. The polymer is coated on a support wire and transported at a uniform and controlled speed through a heat or ignition source flame. An advantage of the MWT is that residence time, as seen by an observer moving with the wire, is resolved spatially in laboratory coordinates (residence time is the ratio of distance to wire speed). This allows greater precision in measurements of composition and temperature profiles and makes it easy to obtain smaples of the solid phase. In this study, we compared reagent and commercial grade poly(vinyl chloride) (PVC). Our heat source was the wake of a flat CH4−O2−N2 flame. Excess O2 for polymer combustion was a part of the flame gases in some experiments but was confined to an adjoining flowing “atmosphere” in others. Ignition in an O2-rich source flame required a minimum of about 20% excess O2. Above this value, the O2-level had no effect on the critical surface temperatures at ignition, which were 295±5°C for the pure PVC and 370±10°C for two different brands of commercial PVC. Earlier studies with the MWT indicated that critical ignition temperatures appear to be independent of the diameter and heat capacity of the support wire, and the thickness of the polymer coating. Ignition occurred at the first appearance of flammable gas, identified as principally benzene in pyrolysis experiments. Reagent PVC emitted HCl prior to ignition but the commercial PVC did not. Quenched samples of the solid phase were collected for analysis; the quenching was accomplished by rapid cooling with cold He. A long-lived free radical was detected in the burned PVC, which was charred.

Annealing effect on the microstructure of poly(vinyl chloride)

AbstractThe effect of annealing on the microstructure of commercial grade poly(vinyl chloride) was investigated by calorimetric, X‐ray and viscoelastic measurements. The degree of crystallinity increases with increasing annealing temperature from above the glass transition temperature up to 130°C, at which point the degree of crystallinity takes on a maximum value. Also, the crystal melting temperature increases with increasing annealing temperature. Thermal analysis and X‐ray study suggest that the crystallite of poly (vinyl chloride) decomposes by thermal degradation when annealed, above 170°C. The isothermal crystallization process is analyzed using Avrami's equation employing the degree of crystallinity as a function of annealing time at various annealing temperatures. The crystallization rate has a maximum value at around 140°C. It is expected that the crystalline texture grows in the shape of a lineal‐like habit, judging from the magnitude of Avrami's constant and from a study of the X‐ray intensity distribution. The αf‐transition was observed to occur at temperatures 5 to 10°C lower than the crystalline melting temperatures for annealed specimens of poly(vinyl chloride) using a dynamic spring analysis. The αf‐transition may be attributed to thermal molecular motions with a long time scale, resulting from the cross‐link points introduced by the small crystallites.