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ABSTRACT:Intercalated nanocomposites of poly(ethylene terephthalate) (PET) and layered silicate (ME) were prepared by a two-step polymerization process: a melt polymerization of bis(2-hydroxyethyl)terephthalate and a subsequent solid-state polymerization. Two kinds of cationic surfactants, dodecyltriphenylphosphonium bromide (C 12 TP) and 10-[3,5-bis(methoxycarbonyl)phenoxy]decyltriphenylphosphonium bromide (IP10TP) were employed as compatibilizers. The dispersibility of ME in PET was investigated by X-Ray diffraction analysis and optical polarization microscopy. The thermal and dynamic mechanical behavior of the nanocomposites was compared with that of pure PET and a PET/ME composite. By utilizing IP10TP as the compatibilizer, better dispersion of ME into the PET matrix could be achieved. The obtained PET/IP10TP/ME nanocomposite showed a higher tensile storage modulus compared with those of pure PET, PET/ME, and PET/C 12 TP/ME, especially in the temperature range above the glass transition temperature.KEY WORDS Nanocomposites / Poly(ethylene terephthalate) / Layered Silicates / Compatibilizer / Dynamic Mechanical Property / Much attention has been paid to polymer/layered silicate nanocomposites because remarkable improvements can be expected in mechanical, thermal, and physicochemical properties over their base polymers or conventional composites. 1-4 Development of poly(ethylene terephthalate) (PET)/layered silicate nanocomposites is highly desired because of their practical importance. [5][6][7] We have recently reported the preparation of PET/expandable fluorine mica (ME) nanocomposites via an in-situ polymerization method utilizing a novel reactive compatibilizer, 10-[3,5-bis(methoxycarbonyl)phenoxy]decyltriphenylphosphonium bromide (IP10TP, Scheme 1). 8 The obtained nanocomposites showed a high flexural modulus compared with that of pure PET. However, the molecular weight of PET in the nanocomposites was found to be low for practical applications, probably due to the high viscosity during the melt polymerization. A solid-state polymerization (SSP) process can be applied to increase the average molecular weight of PET without being affected by the viscosity of the reactants. [9][10][11] In the SSP process, the crystallized PET prepolymer is heated at a temperature below the crystalline melting point (T m ) but well-above the glass transition temperature (T g ) under a flow of inert gas or under vacuum. The hydroxyethyl end groups of the PET prepolymer are considered to be concentrated into the amorphous region during the crystallization process. The transesterification reaction between the chain ends leads to the high-molecular-weight PET.In the present study, we applied the SSP process to prepare PET/IP10TP/ME nanocomposites with a suitable molecular weight. A PET/ME composite with dodecyltriphenylphosphonium bromide (C 12 TP, Scheme 1) was prepared in order to determine the effect of the functional groups of IP10TP on the final properties of the PET nanocomposites. Pure PET and a PET/ME composite without ...

Subjective ratings of pure tones at low and infrasonic (3–40 Hz) were obtained on a set of semantic-differential-type scales and were analysed by factor analysis. From the results, it was concluded that there are three main factors in the human response to the stimulus sound, these are 1) sound pressure, 2) vibration, and 3) loudness. In order to predict the human responses from the physical variables of the sound stimuli, prediction equations were derived for each of the three factors. Also, equal sensation contours for the factors were obtained. From these results, a new evaluation method for the psychological effects is proposed, which considers the multidimensional aspects of human perception at loww and infrasonic frequencies.

A psychophysical experiment was conducted to investigate an evaluation method for the combined effects of infrasound and audible noise. In the experiment, subjective rating of 80 mixed noise stimuli were obtained from 15 subjects on 22 semantic-differential-type scales. The stimulus noise conditions were mixtures of one of eight pure tones at 5, 10, 20, and 40 Hz and one of eight 1/3 octave band noises with centre frequencies 63, 125, 250, and 500 Hz. The rating data were subjected to a principal component analysis and yielded two principal components, these were interpreted as the perceptual components of infrasound and audible noise respectively. On the basis of this result, a psychophysical model was proposed to make two-dimensional predictions of subjective ratings from the physical variables of the noise stimuli. Following this model, a best weighting curve, in combination with the A-weighting curve and their regression weights, were estimated. The results showed that the psychological model successfully described the rating data.

SUMMARYIn order to investigate sensory thresholds and to make subjective evaluations of low frequency pure tones in noise sufferers who complain of annoying environments in their everyday life, sound pressure levels of sensory thresholds and subjectively acceptable maximum SPL levels for a living room were measured in a low frequency chamber. These measurements involved a psychophysical experiment using eleven pure tones at low frequencies from 10Hz to 100 Hz as stimuli, and the psychophysical method of subject adjustment was used for the measurements. Twelve members of the noise-sufferer's society in Japan participated as subjects (referred to as participants in the measurement experiment). The results show that all the participants' acceptable maximum sound pressure levels were relatively low, and nearly equal to their sensory thresholds. These results are characteristic of the participants and differ from the previous results obtained from the other adults.

The hearing threshold for low frequency (LF) tones was measured in a pressure field to investigate the effects of ageing on hearing sensitivity. Participants were young adults around 20 years old and older adults over 60. Measurement results showed that the older listeners had a higher threshold, on average, than the young listeners. The difference of median thresholds between these two groups was about 10 dB at every measurement frequency. Furthermore, hearing abnormalities other than age-related hearing loss showed no great effect upon the LF thresholds. Comparison of LF thresholds and audiograms (i.e. mid and high frequency hearing) of the older listeners revealed only moderate correlation between them. These results suggest that older people retain good hearing sensitivity in the LF region, in contrast to their often-degraded sensitivity at higher frequencies. Therefore, in LF noise evaluation, we should carefully regard the possibility that older listeners can perceive a low level LF noise.