Preparation And Properties Of Poly (L-lactide)-Electret Film

With the development of plastic electret materials, its application has become increasingly wide spread. Most electrets devices in our daily life, such as headphones, microphones, electret air filter and some medical electrets patches, are made of fluoric or polyolefin materials with non-biodegradablity which would bound to damage the environment no matter in what ways we dispose. Moreover, it would not merely drain more on manpower and material resources, but also bring more pains to the patients for receiving another surgery considered the undegradable electrets devices are implanted into human body. Therefore, in this paper, the biodegradable poly(1-lactic acid) was used as research object. On the basis of existing principle and method for preparation of electret, poly(1-lactic acid) electret material was prepared by corona poling and thermal poling technique, the influence of its structure, composition, processing conditions on the electret were also investigated. The main conclusions are as follows:(1) The basic raw materials were organic modified montmorillonite with strong polarity and PLLA. First, the PLLA/OMMT composite was prepared by the melt-mixing technology, then it was blown into PLLA/OMMT composite film, and the prepared membranes were charged through corona poling and thermal poling technique respectively. Moreover, the discharge behavior of PLLA-based electret was observed by the thermally stimulated discharge current TSD.(2) The dielectric constant, dielectric dissipation factor and thermal properties were studied respectively. The results showed that the glass-transition temperature of PLLA/OMMT was found to be almost the same as that of PLLA; the crystallinity of PLLA nanocomposites increased from7.34%to14.53%. The dielectric constant of PLLA/OMMT(3%) composites was slightly larger than that of PLLA, but dielectric loss tangent(tan8) was smaller than that of PLLA. This indicated that OMMT content can improve the PLLA electret properties.(3) The effect of OMMT, charging process and storage environment conditions on the electret properties were Investigated:the electret films charged in lower voltage had better charge storage stability than that of charged in higher voltage. The PLLA electret film had higher surface potential value at charging temperature of60℃and125℃, while the PLLA/OMMT(1%、3%) electret film with higher surface potential value was at room temperature and60℃. Besides, the electricity storages of those PLLA/OMMT electret films were higher than those of pure PLLA electrets films (for instance, the TSD spectrum showed that the negative peak temperature of the composite electret film was about15℃higher than that of PLLA, and the temperature which its current began to appear was about20℃higher than that of PLLA). The surface potential values of electret films deposited in an oven were higher than that deposited in the atmosphere.(4) For PVDC/PLLA electret film, the surface potential value of some samples could retain about81%of its initial value (approximately1000V) after two weeks.(5) The preliminary experiments showed that the PLLA electret film had some inhibitory effect toward E.coli.