Volume 34, Issue 1

Poly(ethylene terephthalate) (PET) resin is one of the most widely used thermoplastics, especially in packaging. Due to thermal and hydrolytic degradations, recycled PET (RPET) exhibits poor mechanical properties and lacks moldability. The effects of adding chain extender (CE) and nanoclay to RPET were investigated. Melt blending of RPET with CE was performed in a thermokinetic mixer (K-mixer). The blended materials were then prepared via solid and microcellular injection molding processes. The effects of CE loading levels and the simultaneous addition of nanoclay on the thermal and mechanical properties and cell morphology of the microcellular components were noted. The addition of 1.3% CE enhanced the tensile properties and viscosity of RPET. The higher amount of CE (at 3%) enhanced the viscosity, but the margin of improvement in mechanical properties diminished. While the solid RPET and CE blends were fairly ductile, the samples with nanoclay and all microcellular specimens showed brittle fractural behavior. Finally, nanoclay and the increase of CE content decreased the average cell size and enlarged the cell density of the microcellular samples.

In this article, a new rotational extrusion processing system was adopted for manufacturing of polybutene-1 (PB-1) pipes, and the effects of mandrel rotation speed on their structures and mechanical performances were studied. The experimental results showed that besides the conventional axial extrusion flow field, a hoop shear stress field imposed to the melt, which was generated by the introduction of mandrel rotation, could lead the combined stress apart from the axial direction of the pipes to induce the molecular orientation deviated from the axial direction. Thus, the axial orientation of PB-1 was restrained, which was revealed by thermal shrinkage measurements and polarized infrared spectra. Moreover, it was also found and confirmed by scanning electron microscopy and two-dimensional wide-angle X-ray diffraction that orientation mainly existed in the amorphous region rather than the crystal region. Differential scanning calorimetry tests showed that the mandrel rotation could facilitate the formation of more perfect crystals and higher crystallinity. As a result, compared with the PB-1 pipe produced by conventional extrusion, the hoop strength of the PB-1 pipes manufactured at a mandrel rotation speed of 8 rpm increased from 20.2 to 24.9 MPa, achieving a mechanical balance in both axial and hoop directions.

The effect of the molecular weight and testing rate on shear strength of epoxidized natural rubber (ENR 25)-based adhesives with statistical model was investigated using gum rosin as the tackifying resin. Toluene and polyethylene terephthalate (PET) were used as the solvent and substrate, respectively, throughout the study. A SHEEN hand coater was used to coat the adhesive on the substrate at a coating thickness of 120 μm. All the adhesion properties were determined by a Lloyd Adhesion Tester operating at different rates of testing. Result shows that shear strength increases up to an optimum molecular weight of 6.5×10 4 ENR 25. Shear strength increases with coating thickness, an observation that is ascribed to the increasing amount of adhesive present in the coating layer, which enhances the shear resistance of the adhesive. It also increases with increase in rate of testing, a phenomenon that is associated with the viscoelastic response of the adhesive.

The direct incorporation of ground tire rubber (GTR) as a waste rubber into a virgin polymer matrix causes a remarkable reduction in its mechanical and performance properties. In this work, maleic anhydride-grafted natural rubber (MA-g-NR) was employed as a compatibilizer to improve the interaction between a natural rubber (NR) matrix and GTR. The effect of MA-g-NR on curing characteristics, rheological behavior, morphology, and performance properties of the NR-GTR blend was studied using an oscillating disk rheometer, rheomechanical spectroscopy (RMS), scanning electron microcopy (SEM), and tensile and abrasion testing. The obtained results by RMS and SEM tests revealed better adhesion between NR and GTR in the presence of MA-g-NR. Using up to 8 parts of MA-g-NR caused an increase in the curing rate index, and a remarkable increase in mechanical properties and abrasion resistance was observed, which was comparable to or even better than the virgin vulcanizate.

Multiwalled carbon nanotube (MWCNT) reinforced chlorobutyl elastomer nanocomposites were prepared. The morphology of nanocomposite samples has been studied from scanning electron microscopy (SEM). The effect of MWCNT loadings on mechanical properties shows increase in tensile strength, hardness, and modulus and decrease in elongation at break with MWCNT loadings, which can be attributed toward better chlorobutyl-MWCNT interaction. At higher filler loading, the rate of increase slowly decreases. The above explanation was also verified from bound rubber (BdR) measurements, showing increase in BdR contents with MWCNT loading. Swelling of the nanocomposites in chloroform, benzene, and trichloroethylene was measured and found to be dependent on both MWCNT concentration and the type of solvent used. The degree of swelling, diffusion coefficient, and penetration rate was calculated. The effect of solvent on swelling properties at different periods of time shows that the degree of swelling increases with time and decreases with concentration of MWCNT loading. Dynamic mechanical properties of nanocomposites have been studied as a function of temperature (from -100°C to 100°C) at a constant frequency of 1 Hz and 1% strain. The effect of MWCNT loading on storage modulus, loss modulus, and loss tangent has been studied. The nonlinearity in tan δ and storage modulus and loss modulus was explained on the basis of MWCNT-elastomer interaction. The smooth Cole-Cole plots explain the nonlinearity in the nanocomposites as well as good distribution of MWCNT in the elastomer matrix.

The nonisothermal crystallization behaviors of virgin isotactic polybutene-1 (iPB-1) and iPBn (iPB-1 containing a nucleating agent that owns acid amides structure; iPB/Mult920=100/0.5, mass ratio) were studied by means of differential scanning calorimetry (DSC). Modified Avrami theories (Ozawa method) and Mo method were used to analyze the DSC date. The results show that both methods are suitable to describe the crystallization process of iPB-1 and iPBn. Addition of 0.5% (mass ratio) nucleating agent can give rise to the nucleation effect, which increases the crystallization temperature ( T c ) and the rate of crystallization of iPB-1, decreases the activation energy of crystallization (Δ E ), and increases the crystallization rate of iPB-1 under the actual conditions.

Nanocomposites consisting of polyamide 6 (PA6) matrix with epoxidized natural rubber-50 (ENR-50) and organoclay-modified montmorillonite (OMMT) were prepared by melt blending in a twin-screw extruder followed by injection molding. The influence of varying amounts (0–6 phr) of OMMT loadings on ENR-50 (10 wt.%) toughened PA6 nanocomposites was examined. Morphological characterizations and mechanical and thermal properties of the blend and nanocomposites were investigated. The addition of OMMT resulted in an increase in tensile strength and modulus, while impact strength and elongation at break reduced. Thermal study revealed no significant change in thermal properties with OMMT loadings. Exfoliated structure was observed from X-ray diffraction (XRD) patterns for <4 phr OMMT and was confirmed by transmission electron microscopy (TEM) images.

The effects of nanometer calcium carbonate content and tensile rate on the tensile properties of the filled polycaprolactone (PCL) composites were investigated. There was a certain reinforcing effect of the filler on the PCL resin. The tensile modulus increased nonlinearly, and the tensile strength also increased with increase of the filler weight fraction. When the filler weight fraction was kept constant, the tensile modulus and tensile strength increased slightly with increasing tensile rates. By comparing the experimental results with those determined from the tensile yield strength theory, the interfacial adhesion between the filler and matrix was found to be relatively strong; it should be one of the reasons for the good reinforcing effect.

In the present investigation, low density polyethylene (LDPE)/organoclay nanocomposites with various clay contents (1–7 wt%) were prepared via a melt mixing technique, using two different compatibilizers with various contents; low molecular weight trimethoxysilyl-modified polybutadiene (Organosilane) and low molecular weight oxidized polyethylene (OxPE). The effects of incorporation of compatibilizers and clay contents on the mechanical and thermal properties of the nanocomposites were investigated. The dispersibility of silicate clay in the nanocomposites was investigated by transmission electron microscopy (TEM). It was found that organosilane yielded better clay dispersion and a more exfoliated structure compared with the OxPE. Rheological behavior of the samples was examined by a dynamic oscillatory rheometer in the linear viscoelastic region. The organosilane compatibilized system conferred higher tensile strength, yield strength and tensile modulus than those of an uncompatibilized system, and even higher than those of the OxPE compatibilized case. The crystallization behaviors of uncompatibilized and compatibilized nanocomposites were investigated using differential scanning calorimetry (DSC). DSC results indicated that the addition of compatibilizers increased the crystallization temperature (T c ) as a result of heterogeneous nucleation effect of clay on LDPE.

Novel photopolymerizable formulations, able to photopolymerize with a dual mechanism (cationic and radical), were developed and characterized as potential resins for stereolithography (SL) process. The influence of the presence of organically modified boehmite nanoparticles on the properties of the photopolymerizable mixtures was also analyzed. The main properties required for a liquid SL resin are a high reactivity and a low viscosity. All of the experimental formulations produced, even in the presence of boehmite nanoparticles, are able to satisfy these significant requirements. Physical-mechanical and thermal properties of the photocured samples, obtained starting from the experimental formulations, were finally measured. The cured nanocomposite bars show a high transparency, confirming the good dispersion of the nanofiller in the polymeric matrix and possess improved glass transition temperature (T g ) and mechanical performances, compared to the unfilled system and to a commercial stereolithographic resin. These results suggest the possibility of using the novel nanofilled photopolymerizable suspensions in the stereolithographic apparatus to build, not only esthetical, but also functional prototypes.

The cubic equation of state (CEoS) is a powerful method for calculation of the vapor-liquid equilibrium (VLE) in polymer solutions. Using CEoS for both the vapor and liquid phases allows one to calculate the non-ideality of polymer solutions based on a single EoS approach. In this research, VLE calculations of polypropylene glycol (polypropylene oxide) [PPG(PPO)]/solvent solutions were carried out. In this approach, eight models containing Peng-Robinson-Stryjek-Vera (PRSV) and Soave-Redlich-Kwong (SRK) CEoS separately combined with four mixing rules, namely van der Waals one-fluid mixing rule with one adjustable parameter (vdW1), van der Waals one-fluid mixing rule with two adjustable parameters (vdW2), Wong-Sandler (WS), and Zhong-Masuoka (ZM) were applied to calculations of bubble point pressure. For a better correlation, the adjustable binary interaction parameters existing in any mixing rule were optimized. The results were very acceptable and satisfactory. The results of absolute average deviations (%AAD) between computed results and experimental bubble point pressure data were calculated and presented. Although the capability of two CEoS had a good agreement with experimental data and illustrated the correct type of phase behavior in all cases, the performance of the PRSV+vdW2 was more reliable than the other models.