Thermogravimetric, Morphological and Infrared Analysis of Blends Involving Thermoplastic Starch and Poly(ethylene-co-methacrylic acid) and Its Ionomer Form

This study focuses on the thermal properties and structural features of blends consisting of thermoplastic starch (TPS) and poly(ethylene-co-methacrylic acid) copolymer (EMAA) or its ionomer form (EMAA-54Na). The aim is to investigate how carboxylate functional groups of the ionomer form intervene in blends compatibility at the interface of the two materials and how this impacts their properties. Two series of blends (TPS/EMAA and TPS/EMAA-54Na) were produced with an internal mixer, with TPS compositions between 5 and 90 wt%. Thermogravimetry shows two main weight losses, indicating that TPS and the two copolymers are primarily immiscible. However, a small weight loss existing at intermediate degradation temperature between those of the two pristine components reveals specific interactions at the interface. At a mesoscale level, scanning electron microscopy confirmed thermogravimetry results and showed a two-phase domain morphology, with a phase inversion at around 80 wt% TPS, but also revealed a different surface appearance evolution between the two series. Fourier-transformed infrared spectroscopy analysis also revealed discrepancies in fingerprint between the two series of blends, analysed in terms of additional interactions in TPS/EMAA-54Na coming from the supplementary sodium neutralized carboxylate functions of the ionomer.

Influence of Surface Chemistry of Fiber and Lignocellulosic Materials on Adhesion Properties with Polybutylene Succinate at Nanoscale

The production of bio-based composites with enhanced characteristics constitutes a strategic action to minimize the use of fossil fuel resources. The mechanical performances of these materials are related to the specific properties of their components, as well as to the quality of the interface between the matrix and the fibers. In a previous research study, it was shown that the polarity of the matrix played a key role in the mechanisms of fiber breakage during processing, as well as on the final properties of the composite. However, some key questions remained unanswered, and new investigations were necessary to improve the knowledge of the interactions between a lignocellulosic material and a polar matrix. In this work, for the first time, atomic force microscopy based on force spectroscopy measurements was carried out using functionalized tips to characterize the intermolecular interactions at the single molecule level, taking place between poly(butylene succinate) and four different plant fibers. The efficiency of the tip functionalization was checked out by scanning electron microscopy and energy-dispersive X-ray spectroscopy, whereas the fibers chemistry was characterized by Fourier-transform infrared spectroscopy. Larger interactions at the nanoscale level were found between the matrix and hypolignified fibers compared to lignified ones, as in control experiments on single lignocellulosic polymer films. These results could significantly aid in the design of the most appropriate composite composition depending on its final use.

Time/Molecular Weight Superposition to Describe the Behavior of Controlled-Rheology Polypropylenes

Polypropylene resins issuing from polymerization reactors are degraded by peroxides in subsequent reactive extrusion processes to improve their processability. This operation reduces their molecular weight and, thus, their viscosity and elasticity. In a previous study, a series of homo- and copolymer polypropylenes of different molecular weight distributions were prepared by twin-screw extrusion and characterized by oscillatory rheometry. It was shown that their behavior could be described by Carreau–Yasuda equations, possibly with a yield stress, in which all parameters depended on the weight average molecular weight. By using these experimental data, it is show in the present study that a time/molecular weight superposition allowed for a drastic reduction in the number of parameters to be considered in order to precisely describe the viscous behavior of these materials. This concept was then validated by applying it to various experimental data from the bibliography.

Optimization and Scale-Up of Twin-Screw Reactive Extrusion: The Case of EVA Transesterification

Despite its complexity, reactive extrusion is continuously developing for the production of new and performing materials. Due to the strong coupling between flow, rheology and chemistry, optimizing this process for a given reaction remains a difficult task. Moreover, the scale-up from the laboratory to the production scale is another crucial question, which cannot be solved by conventional techniques. In this paper, we show how the use of numerical modeling may help answer these complex questions by providing realistic solutions, rapidly and without excessive costs. The example of a transesterification reaction was chosen because this reaction has been carefully characterized in previous studies. The reaction kinetics and the kinetic constants are well known and the modeling of this reactive extrusion process has proved to be realistic and accurate.

Transesterification of Ethylene Acetate Copolymer in a Twin Screw Extruder

The chemical modification of poly(ethylene-co-vinyl acetate) with a primary aliphatic n-alcohol in a modular co-rotating twin screw extruder was investigated. The purpose was to build a theoretical model, able to predict the extent of conversion along the screw axis. First, the influence of operating conditions (throughput, screw speed, barrel temperature and initial reactant concentrations) on the EVA copolymer conversion was experimentally examined. Then, the extent of conversion was computed by coupling flow simulation and reaction kinetics. Theoretical and experimental results were found in good agreement, what allows the prediction of the reaction extent as a function of the processing conditions.

Electromyographic study of stomatognathic system muscles during chewing of different materials

OBJECTIVE

The aim of this study was to compare the behavior of the major chewing muscles (anterior temporalis, masseter and suprahyoid muscles) by using two commercial chewing gums (A and B) and two insipid materials (cotton ball and Parafilm M) through analysis of electromyographic signals.

METHOD

Ten female young adult subjects, aged from 18 to 27 years, with normal occlusion and no history of craniomandibular disorder were studied The masticatory activity was performed with the subjects comfortably sat so that the Frankfurt plane was parallel to the floor. Electromyographic exams were carried out using bipolar surface passive mini-electrodes positioned on the anterior temporalis, masseter, and suprahyoid muscles. The subjects were guided to chew bilaterally and simultaneously each one of the materials, in aleatory sequence. For the study of the masticatory activity the electromyographic signals were processed through rectification, linear envelope and normalization, so that the coefficient of variation obtained from the procedure was comparatively analyzed. All data were submitted to analysis of variance (uni- and multi-varied).

RESULTS

The results of this study indicated that the best materials for electromyographic studies on the chewing were Parafilm and cotton ball because they demonstrated the smallest coefficients of variation.

CONCLUSION

In addition, Parafilm showed the best palatability. In a general way, these materials are indicated for the accomplishment of electromyographic exams, since they demonstrated a smaller coefficient of variation as compared to the other materials.

Electromyographic analysis of fatigue in temporalis and masseter muscles during continuous chewing

The aim of this study was to evaluate the electromyographic changes in the anterior temporalis and masseter muscles after fatigue induced by continuous chewing. Surface electrodes were placed bilaterally over the anterior temporalis and masseter muscles of 31 subjects with normal dentition. Recordings were taken every minute from the beginning of chewing to the exact moment the volunteer reported subjective sensation of fatigue in the jaw muscles. The length of endurance period (fatigue threshold) was measured to each subject, as well as the average amplitude and duration of activation phase and duration of relaxation phase through electromyographic recording of each muscle. The average endurance period was about 500 s. No significant change occurred on the average amplitude of activation phase meanwhile the duration of both the activation and relaxation phase diminished after fatigue.

EMG activity of the orbicularis oris and mentalis muscles in children with malocclusion, incompetent lips and atypical swallowing--part II

The EMG activity of the orbicularis oris (upper and lower), and of the mentalis muscles was verified during several movements of the lips, in 18 children ageing from 8 to 12 years, divided into three groups: one with normal occlusion, and two with class II division 1, with atypical swallowing and/or incompetent lips and who had received no orthodontic treatment. In blowing through a straw the muscular activity of the orbicularis oris and the mentalis was significantly greater in the incompetent lips group. The mentalis presented moderate activity in the competent lips group and negligible in normal occlusion. In puffing out of the cheeks, the malocclusion groups developed marked activity of the orbicularis oris and very marked activity of the mentalis, while the normal occlusion presented moderate and negligible activities, respectively. In pursing of the lips, only the incompetent lips group presented a very marked activity of the lower segment. The compression of the lips against the teeth revealed a marked activity of the upper segment of the orbicularis oris in the groups of malocclusion and the mentalis presented greater activity in the competent lips group. The reciprocal compression of the lips presented a hyperactivity of the three muscles.

EMG activity of the orbicularis oris and mentalis muscles in children with malocclusion, incompetent lips and atypical swallowing--part I

The function and the level of activity of the orbicularis oris (upper and lower), and of the mentalis muscles were verified electromyographically in resting position and in several movements and carried out in 18 children aged 8-12 years, divided into three groups: one with normal occlusion, and two with Class II division 1, with atypical swallowing and/or incompetent lips, who had received no orthodontic treatment. It was observed that, in a resting position with the lips separated, there was no activity in any of the muscles. When there was a contact of the lips, action potentials were recorded in the muscles studied, in those individuals with incompetent lips. In the movements of sucking either through a straw or a pacifier and the thumb, there were no differences among the groups. The incompetent lips group presented very marked muscle activity of the lower orbicularis oris and mentalis in the movement of sucking a lollipop. In deglutition of saliva, the orbicularis oris presented slight activity, and the mentalis, moderate. In deglutition of water, the mentalis presented very marked activity, whereas, the upper and lower orbicularis oris presented moderate and marked activities, respectively.