Thermomechanical Behavior Of Poly Research Articles

Role of Surface-Treated Silica Nanoparticles on the Thermo-Mechanical Behavior of Poly(Lactide)

Surface-treated fumed silica nanoparticles were added at various concentrations (from 1 to 24 vol%) to a commercial poly(lactide) or poly(lactic acid) (PLA) matrix specifically designed for packaging applications. Thermo-mechanical behavior of the resulting nanocomposites was investigated. Field Emission Scanning Electron Microscopy (FESEM) micrographs revealed how a homogeneous nanofiller dispersion was obtained even at elevated filler amounts, with a positive influence of the thermal degradation stability of the materials. Modelization of Differential Scanning Calorimetry (DSC) curves through the Avrami–Ozawa model demonstrated that fumed silica nanoparticles did not substantially affect the crystallization behavior of the material. On the other hand, nanosilica addition was responsible for significant improvements of the storage modulus (E′) above the glass transition temperature and of the Vicat grade. Multifrequency DMTA tests showed that the stabilizing effect due to nanosilica introduction could be effective over the whole range of testing frequencies. Sumita model was used to evaluate the level of filler dispersion. The obtained results demonstrated the potential of functionalized silica nanoparticles in improving the thermo-mechanical stability of biodegradable matrices for packaging applications, especially at elevated service temperatures.

Conformational Entropy as a Means to Control the Behavior of Poly(diketoenamine) Vitrimers In and Out of Equilibrium

AbstractControl of equilibrium and non‐equilibrium thermomechanical behavior of poly(diketoenamine) vitrimers is shown by incorporating linear polymer segments varying in molecular weight (MW) and conformational degrees of freedom into the dynamic covalent network. While increasing MW of linear segments yields a lower storage modulus at the rubbery plateau after softening above the glass transition (Tg), both Tg and the characteristic time of stress relaxation are independently governed by the conformational entropy of the embodied linear segments. Activation energies for bond exchange in the solid state are lower for networks incorporating flexible chains; the network topology freezing temperature decreases with increasing MW of flexible linear segments but increases with increasing MW of stiff segments. Vitrimer reconfigurability is therefore influenced not only by the energetics of bond exchange for a given network density, but also the entropy of polymer chains within the network.

Influence of cornstarch on thermomechanical behavior of poly(vinyl) chloride bioplastics

ABSTRACTThe diverse and ubiquitous consumption of polymers urges the necessity to make these materials easily available. However, the excessively used petrochemical‐based polymers such as poly(vinyl) chloride (PVC) are nonbiodegradable, which is a motivation to modify it with “green” alternatives. In the present study, PVC (Mw = 48 000 g mol−1) has been incorporated with cornstarch (CS) to synthesize a series of 25 samples of bioplastics in addition to blank polymer samples. The films of five various thicknesses (0.1, 0.2, 0.3, 0.5, and 1.0 mm) have been synthesized using in situ polymerization. Each sample of pure PVC film and bioplastic has been induced with different concentrations of CS in the range of 1–5 wt %. The synthesized samples were subjected to the structural characterization by using Fourier transform infrared. Thermogravimetric analysis has demonstrated the three‐step degradation with the improved stability of 250 °C. The 3% concentration of CS has shown the optimum storage modulus (E′) of 1 660 MPa from dynamic mechanical analysis and Tan δ as 0.50. The swelling test performed using water has shown an induction of hydrophilicity in PVC up to 4%. CS‐induced bioplastics can be a potential ecofriendly alternative of conventional polymers. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48493.

Melt rheology and thermomechanical behavior of poly(methyl methacrylate)/reduced graphene oxide nanocomposites

Thermomechanical and rheological behavior of poly(methyl methacrylate) (PMMA)/reduced graphene oxide (RGO) nanocomposites prepared via in situ polymerization using sheet casting method was investigated. Scanning electron microscope and transmission electron microscope were used to study the microstructure of nanocomposites in terms of dispersion of RGO and polymer–RGO interaction. The thermomechanical properties were investigated using dynamic mechanical analyzer, and it was found that the incorporation of RGO sheets into PMMA matrix resulted in an increase in both storage modulus and glass transition temperature (Tg) as compared with neat PMMA. Storage modulus showed an increase of 40% and 46% at a loading of 0.5 and 1.0 wt% RGO, respectively. The glass transition temperature showed an increase of 20°C (104°C for neat PMMA) at RGO loading of 2.0 wt% (124°C for sample PMMA‐2.0). The complex viscosity and moduli (storage and loss) as a function of angular frequency also showed an increase with increasing amount of RGO. A significant increase in melt viscosity of PMMA observed in case of sample having 0.5 wt% RGO (sample PMMA‐0.5) could be due to the formation of interconnected network of RGO in PMMA matrix and can be considered as rheological percolation threshold. A drop in the crossover frequency was registered with increase of RGO loading that does not directly correlate with the percolation threshold concentration, representing an increase in solid‐like behavior. Secondly, the complex viscosity did not change with RGO loading at higher frequency, which showed that the short‐range PMMA relaxations were unaffected by RGO. Copyright © 2015 John Wiley & Sons, Ltd.

Effect of Fiber Surface Treatments on Thermo-Mechanical Behavior of Poly(Lactic Acid)/Phormium Tenax Composites

In the present study, Phormium Tenax fiber reinforced PLA composites were processed by injection molding and twin screw compounding with a fiber content ranging from 10 to 30 wt%. Three surface treatment methods have been used to improve the Phormium Tenax fiber-matrix interfacial bonding that are as follows: (1) aqueous alkaline solution, (2) silane coupling agent, and (3) a combination of alkaline and silane treatment. The mechanical, thermal and morphological properties of the resulting composites were investigated. The results have shown that the moduli of surface treated fiber reinforced composites are lower than the ones obtained for untreated composites (as a consequence of the decrease in fiber modulus caused by the chemical treatments) and no significant increase in strength was observed for any of the composites compared to neat PLA. SEM micrographs of composite fractured surfaces confirmed an improvement in the interfacial strength, which was insufficient nonetheless to significantly enhance the mechanical behavior of the resulting composites. Results from thermogravimetric analysis and differential scanning calorimetry suggest that surface treatment of Phormium affects the ability of PLA to cold crystallize, and the thermal stability of the composites at the different fiber contents was reduced with introduction of alkali and silane treated Phormium fibers.

High-rate thermomechanical behavior of poly(vinyl chloride) and plasticized poly(vinyl chloride)

A combined experimental and analytical investigation was carried out in order to develop predictive capabilities for the rate-dependent behavior of poly(vinyl chloride) (PVC) and a dioctyl phthalate (DOP)-plasticized PVC, with focus on predicting the thermo-mechanically coupled behavior under high rates of deformation. The two materials were studied experimentally using both dynamic mechanical analysis (DMA) and compression testing over a wide range of strain rates (10 -4 s -1 to 2000 s -1 ). DMA testing revealed both an α-transition and a low-temperature β-transition (-56°C) in the neat PVC; the incorporation of 20wt% DOP in PVC reduced the α-transition temperature by 54°C, and also suppressed the β-transition peak. In compression testing, rate-sensitivity transitions were observed in both the neat PVC and the PVC-20wt% DOP compound. The transition in PVC is attributed to the shift of the β-transition, whereas the transition in the 20wt% DOP blend is due to the rubbery-to-glassy transition as the deformation rate goes from low to high. A constitutive model for the finite strain deformation of amorphous polymers, introduced elsewhere [1,2] and tailored here for the two material systems of interest, is shown to capture the large deformation stress-strain behavior at all rates tested.

Thermomechanical behavior of poly(vinyl alcohol) and sugar cane bagasse composites

AbstractFibers from renewable resources are gaining interest for use as fillers in hybrid composite materials. Particularly waste material such as sugar cane bagasse offer large availability, biodegradability, and low cost. Influence of single components on composite material properties is an important parameter to be evaluated. Composites of poly(vinyl alcohol) (PVA) at 88 and 98% saponification degrees and sugar cane bagasse (B) were prepared by casting water suspensions of the components and characterized for their dynamic mechanical behavior. The storage modulus below and above the glass transition and the shape of the relaxation process are strongly influenced by the amount of B. Good adhesion was observed at the lignocellulosic fiber–synthetic polymer interface. Urea and glycerol are able to plastify the PVA/B composites thus giving rise to a decrease of the glass transition temperature and to a widening of the glass transition temperature gap. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 426–432, 2004

Cold‐drawing (necking) behavior of polycarbonate as a double glass transition

AbstractThe thermomechanical behavior of poly(bisphenol A carbonate) (PC) undergoing cold‐drawing (necking) over a large range of temperature and strain rate has been studied. The cold‐drawing of PC has been described from a material particle perspective in terms of true stress and strain relationships. The isothermal draw stress is shown to be a material parameter, and the true stress‐strain behavior of necked material above the true drawing stress follows conventional treatment by rubber elasticity. Cold‐drawing is described as a double glass transition: first, a transition from an isotropic glass to an isotropic rubber at the yield point, then, on unloading after stretching of a rubbery mesophase, a transition from an oriented rubber to an oriented glass.

Thermomechanical behavior of poly(vinyl chloride) in the process of degradation

The thermomechanical behavior of poly(vinyl chloride) (PVC) was investigated during its thermal degradation by using torsional braid analysis. In thermomechanical behavior as a function of temperature, the relative rigidity Gr decreased initially with increasing temperature, then began to increase passing through a minimum at about 200°C, and finally decreased at 340°C. Increase in Gr from 200°C was caused by formation of a conjugated polyene chain accompanied by dehydrochlorination and by crosslinking reaction, and decrease in Gr at 340°C was related to scission reactions of the crosslinking network by oxidation. In the change in logarithmic decrement Δ, three peaks were observed: at 90°C, coinciding with the glass transition of the polymer; at about 200°C, due to the melting transition of crystallites, and at about 300°C, due to a loss of mechanical energy in the rheological transition of the polymer from a liquid state to a glassy state passing through a viscoelastic region. The thermomechanical properties of PVC with different molecular weights were also measured, and the effect of molecular weight Gr and Δ are discussed. In isothermal measurements of the relative rigidity in air, exponentially increasing curves were observed as a function of time. These curves were analyzed kinetically as a first-order reaction, and an activation energy of 22.7 kcal/mole was obtained.

Apparatus for torsional braid analysis by a digital data analyzer

AbstractAs apparatus for torsional braid analysis (TBA), which is a variant of the torsional pendulum technique, a new method for recording the damped wave electrically, using an electric mater as a transducer, is described. In order to process a large volume of data, an instrument to print out digitally the amplitude and period of oscillation has been developed. The thermomechanical behavior of poly(vinyl chloride) is presented so as to demonstrate the use of the present TBA apparatus.

Thermomechanical Behavior of Poly(ethylene Glycol Methacrylate) and Poly(diethylene Glycol Methacrylate)

AbstractThe influence of the length of side groups on the thermomechanical behavior of poly‐(ethylene glycol methacrylate), poly(diethylene glycol methacrylate), and their copolymers was studied. It was found that the hydroxyl endgroups increase the viseosity of these polymers compared to poly(propyl methacrylate) and poly(hexyl methacrylate); the increasing length of the side chains lowers the differences between the mechanical behavior of the poly(alkyl methacrylates) and poly(glycol methacrylates). The thermomechanical curves are sufficiently sensitive to determination of the fundamental mechanical characteristies of network polymers with very small differences of network density. A relation was obtained between the physical degree of crosslinking of poly‐(ethylene glycol methacrylate) and poly(diethylene glycol methacrylate) and the content of the crosslinking agent based on thermomechanical measurements, and the assumption has been expressed, that the physical degree of crosslinking can be partly influenced by the supermolecular structure of the polymers.