Francisco J. Baltá Calleja

New aspects of thermal treatment effects on gelatin films studied by microhardness

Microhardness measurements were carried out using various treatment cycles, including heating and cooling during different treatment times at high temperatures. Two possible processes to explain the observed increase in the microhardness are proposed, namely crystallisation and crosslinking. In order to distinguish between these two alternatives, differential scanning calorimetry (DSC), wide-angle X-ray scattering (WAXS), and swelling kinetics measurements were performed. The observed decrease of crystallinity (from DSC and WAXS measurements) as well as the decrease of swelling ability with increasing temperature and duration of thermal treatment are in favour of the occurrence of crosslinking reactions during thermal treatment. It is suggested that the crosslinking, as a result of additional intra- and intermolecular condensation processes, leads to a denser chain packing in the amorphous gelatin and consequently to higher microhardness values.

Study of nanoclay blends based on poly(ethylene terephthalate)/poly(ethylene naphthalene 2,6-dicarboxylate) prepared by reactive extrusion

Abstract The success of processing compatible blends, based on poly(ethylene terephthalate) (PET)/poly(ethylene naphthalene 2,6-dicarboxylate) (PEN)/clay nanocomposites in one step by reactive melt extrusion is described. Untreated clay was first purified and functionalized “in situ” with a compound based on an organic peroxide/sulfur mixture and (tetramethylthiuram disulfide) as the activator for sulfur. The PET and PEN materials were first separately mixed in the molten state with functionalized clay. The PET/4 wt% clay and PEN/7.5 wt% clay compositions showed total exfoliation. These compositions, denoted nPET and nPEN, respectively, were used to prepare new nPET/nPEN nanoblends in the same mixing batch. The nPET/nPEN nanoblends were compared to neat PET/PEN blends. The blends and nanocomposites were characterized using various techniques. Microstructural and nanostructural properties were investigated. Fourier transform infrared spectroscopy (FTIR) results showed that the exfoliation of tetrahedral clay nanolayers is complete and the octahedral structure totally disappears. It was shown that total exfoliation, confirmed by wide angle X-ray scattering (WAXS) measurements, contributes to the enhancement of impact strength and tensile modulus. In addition, WAXS results indicated that all samples are amorphous. The differential scanning calorimetry (DSC) study indicated the occurrence of one glass transition temperature Tg, one crystallization temperature Tc and one melting temperature Tm for every composition. This was evidence that both PET/PEN and nPET/nPEN blends are compatible in the entire range of compositions. In addition, the nPET/nPEN blends showed lower Tc and higher Tm values than the corresponding neat PET/PEN blends. In conclusion, the results obtained indicate that nPET/nPEN blends are different from the pure ones in nanostructure and physical behavior.

Effect of SBS compatibilizer on the interphase boundary of polymer blends of polystyrene and natural rubber

Abstract Microhardness (H) has been used to quantitatively characterize the quality of the interphase boundary of blends of atactic polystyrene (PS) with natural rubber (NR) and the compatibilizer styrene-butadiene-styrene (SBS) block copolymer. Qualitative conclusions are drawn for the same purpose from scanning electron microscopy (SEM) observations on surface indentation. Cast films of neat PS and the blends PS/NR, PS/SBS and PS/NR/SBS were prepared from a common solvent (toluene). While neat PS shows a constant H = 175 MPa, the PS/SBS blend exhibits a gradual decrease starting from H = 130 - 140 MPa at a distance of about 100 μm from the phase boundary up to the final value of 25 MPa. For the PS/NR blend this decrease starts at about 50 μm, reaching the same final value. Owing to the elastic recovery, no indentations on the NR or SBS particles surface can be detected as confirmed by SEM. The compatibilized blend PS/NR/SBS is characterized by the thinnest phase boundary (about 25 μm) and a final H value of 75 MPa which demonstrates that the compatibilizer SBS is distributed just on the phase boundary between PS and NR. Results confirm previous findings in incompatible blends of poly(methyl methacrylate)/NR, highlighting that microindentation is a sensitive tool for studying the breadth and quality of the interphase boundary in compatibilized or non-compatibilized polymer blends and other non-homogeneous materials. This technique allows, in addition, the localization of the compatibilizer in the polymer blends.

Structure and mechanical properties of nylon 6.12 prepared by temperature slope crystallization. I. Crystallization of oriented spherulitic textures

Abstract Oriented spherulitic textures of a rod-shaped nylon 6.12 sample were crystallized by the temperature slope method. Crystallization conditions were compared by changing temperatures and growth rates. Three types of textures (negative spherulites, positive spherulites, and spherulitic aggregates) were observed by this method. The negative textures appeared when the growth rate was less than 0.1 mm/h. Crystalline orientation and mechanical properties of the textures were investigated by x-ray diffraction and micro-hardness measurements, respectively. The hydrogen-bonded (010) planes were perpendicular to the growth direction in the negative spherulite, while they were parallel to the growth direction in the positive spherulite. In the spherulitic aggregates, the b axis was parallel to the growth direction, while the (010) planes formed roughly an angle of 45° with the growth direction. Due to the orientation of the hydrogen-boned planes, the negative texture exhibited an anisotropy, with hardness va...

Structure and mechanical properties of nylon 6.12 prepared by temperature slope crystallization. II. Rolling deformation and microhardness of the oriented negative spherulite

Abstract Oriented negative spherulites of nylon 6.12 were crystallized by the temperature slope method. Rolling deformation of the negative texture was performed in three directions. The deformation mechanism of the negative spherulites was investigated by x-ray diffraction and microhardness measurements. Slip deformation between crystalline lamellae (interlamellar slip) was observed in the first stage of deformation. The results are compared with the rolling deformation of other polymer textures such as the positive spherulites of nylon 6.12 and β-phase isotactic polypropylene. In the rolling deformation of nylon 6.12, hydrogen-bonded (010) planes play an important role. For large deformations (λ > 1.5), preferential slip between (010) planes appears, resulting in a lamellar inclination of 60° and a decrease of the lamellar thickness. Microhardness measurements after rolling deformation of the oriented negative texture show good agreement with the structural analysis. The rapid decrease in the microhardn...

Nanostructural characterization of poly (vinylidene fluoride)-clay nanocomposites prepared by a one-step reactive extrusion process

Abstract Poly (vinylidene fluoride) (PVDF)-untreated clay nanocomposites were successfully prepared using an innovative one-step reactive melt extrusion process. Through specific temperature and shear conditions, the chemical reactions took place between the polymer matrix, the inorganic clay particles, and three main reactive agents: an organic peroxide, sulfur, and a specific activator led finally to the PVDF-clay nanocomposites. The materials were formulated with various amounts of clay in order to identify the best conditions, enabling to obtain the optimal particle exfoliation in the polymer matrix at the nanometric scale. The microstructure and nanostructure modifications were characterized by Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), and wide- and small-angle X-ray scattering (WAXS and SAXS). The relationship between nanostructure and mechanical behavior was investigated by tensile experiments, impact tests, and microhardness measurements. The FTIR results suggest that there is a chemical interaction between the clay and the polymer. Furthermore, the WAXS study shows that no intercalation step takes place in any composition. In addition to this, the sample with 2.5 wt.% clay could present a total exfoliation of the clay particles. The PVDF matrix is found to be exclusively of the α-form in all compositions. The final microhardness slightly increases with both nanoclay content and degree of crystallinity.

The role of crosslinking on the physical properties of gelatin based films

The crosslinking of gelatin using crosslinking agents based on condensation of the aldehyde groups and ε-amine groups present in lysine and hydroxylysine rests is a very attractive method reported recently. The present work deals with different films prepared from commercial gelatin of type B and animal origin, aiming at an improvement of physical properties. These films were modified by two plasticizing agents (glycerol, GLY, and poly (vinyl alcohol), PVA) and/or crosslinked by glutaraldehyde (GTA). The number of ε-amino groups present in the gelatin chains, before and after modification, was determined by the method of protein dosage using 2,4,6-trinitro benzene sulfonic acid (TNBS). The addition of the plasticizing and/or crosslinking agents induced a decrease in the number of ε-amino-groups due to the fact that these groups are involved in the physical and/or chemical crosslinking reactions occurring among the different components. The variation of the crosslinking ratio was studied as a function of formulation type, crosslinking nature and GTA concentration. The use of microhardness (H) in this study emphasizes the effect of the crosslinking on the improvement of the micromechanical properties. The study of differential scanning calorimetry reveals that crosslinking induces a drastic decrease of crystallinity in the samples.

Study of rheological and mechanical properties of ternary blends of iPP/LDPE/EPDM

Abstract Compatible blends of isotactic polypropylene (iPP)/low-density polyethylene (LDPE)/ethylene-propylene-diene monomer (EPDM) were prepared by reactive blending in the presence of dicumyl peroxide (DCP). The blends were characterized using different techniques: dynamical rheological analysis (DRA), differential scanning calorimetry (DSC), optical microscopy (OM) and scanning electron microscopy (SEM), dynamical mechanical thermal analysis (DMTA), viscosity and impact strength, to evaluate their properties. Results revealed that the presence of the peroxide in LDPE/EPDM blends gives rise to crosslinking reactions, as is the case in iPP/LDPE/EPDM blends. However, in the latter case, scission reactions of the iPP component also take place. As a consequence of the whole process, morphological changes arise mainly in the amorphous regions, without affecting the degree of crystallinity of the components. The mechanical properties of the blends are consequently improved, due to the crosslinked network thus formed in the blends.