Preparation And Characterization Of The Cu/LDPE Nanocomposites: A Novel Material For Use In Intrauterine Devices

Among the various contraceptive methods, intrauterine devices (IUDs), especially the copper-containing intrauterine devices (Cu-IUDs), have become one of the most popular forms for birth control throughout the world, especially the developing countries, owing to their advantages of long-lasting and high efficacy, economy, safety and reversibility. There are more than 40% of the married procreant women using IUDs for long-term pregnancy prevention in China. However, the existing Cu-IUDs have some side effects such as pain, intermenstrual bleeding and so on. These side effects are relevant to the drawbacks of the existing Cu-IUDs, i.e., the burst release of cupric ions, direct contact of the copper with endometrium, low transformation ratio of the copper and stiff deposits deposited on the copper surface et al. To avoid these deficiencies, a novel Cu-IUDs material, a polymer-based nanocomposite, has been developed in our research. This is the first one who developed the polymer-based nanocomposite as a material used in the field of births control throughout the world. LDPE is chosen as the matrix and copper nanoparticles (nano-Cu) is used as active matter of the novel Cu-IUDs material. Cu/LDPE nanocomposites were prepared successfully by extruding mixtures of pure LDPE and nano-Cu using melt-blending method in a single-screw extruder and/or hot press in a mold. Then the structure, non-isothermal crystallization behavior, thermal stability and mechanic properties, water uptake characteristics, cupric ions release characteristics and self-cleaning function were investigated in this paper. From the study of the structure of the Cu/LDPE nanocomposites, it can be seen that the nanocomposites is a simple hybrid of the pure LDPE and the nano-Cu. And porosities and nano-Cu aggregates are existed in the nanocomposites, and the nano-Cu aggregates are distributed uniformly in the polymer matrix in general. Additionally, the vinyl ether bond (R₁-O-R₂) has been found in the nanocomposites. It also can be seen that the incorporation of nano-Cu leads to the difference of crystalline morphology between the nanocomposites and the pure LDPE. From the investigation of the non-isothermal crystallization behavior of the nanocomposites, one can see that the melting temperature and the crystallinity degree decrease but the crystallization temperature increase with the increasing of the nano-Cu loading. And the crystallization temperature rages increase remarkably and crystallization temperature decrease with the increasing of cooling rate. And the crystallization temperature is higher than that of the pure LDPE at various cooling rates. All these results indicate that the nano-Cu may act as a heterogeneous nucleation for the crystallization of the LDPE matrix, and the presence of the nano-Cu may hinder the transport of the molecule chains and lead to a decrease of the crystallization growth rate of the LDPE matrix at the same time. The investigation of thermal stability shows that the thermal stability of nanocomposites is higher than that of pure LDPE and is different from that of the Cu/LDPE microcomposites. As the increasing of nano-Cu loading, the thermal stability of nanocomposites increase remarkably, and a maximum increment of 18℃is obtained in this experiment when the nano-Cu loading is about 2 wt.%. However, its thermal stability will decrease slowly when the nano-Cu loading is more than 2 wt.%. But the thermal stability of microcomposites reaches its peak at about 6 wt.% copper microparticles loading and then keeps the same level. These phenomena might be caused by the different influence of the different size of the copper particles on the diffusion of volatile decomposition products within the Cu/LDPE composites and the different effect of the interface between the different copper particles and the LDPE matrix. The results of mechanic properties of the nanocomposites show that the tensile strength of the nanocomposites is lower than that of the pure LDPE, and it decrease with the increasing of copper loading owing to the decreases of the effective surface area ratio. It also shows that the nanocomposites has excellent plasticity due to the integrative matrix of the nanocomposites, and the nanocomposites after released cupric ions completely has better mechanic properties because of the release of stress concentration. From the research of water uptake characteristic of the nanocomposites, one can see that the nanocomposites have well water absorption ability, and the water absorption ability increase with the increasing of the nano-Cu loading. When the copper loading is 25 wt.%, the water uptake ability of nanocomposites is 43.6 times larger than that of the microcomposites and 183 times higher than that of the pure LDPE. And the water uptake process of nanocomposites obeys the classical diffusion theory, i.e., the Fick law, very well. Among the various factors that affected the water uptake of the nanocomposites, the most important one is the influence of size effect of the nano-Cu. The study of the cupric ions release of nanocomposites shows that the burst release of the cupric ions can be eliminated completely, and the cupric ions can be released stably for years as we designed. And the cupric ions release rate can be effected differently by theprocess parameters of preparation: the cupric ions release rate increase with the increasing of the nano-Cu loading and keep stable with the change of the temperature, and can be effected by the pressure but its rule has not been summarized in this experiment due to the influence of the serious waves of the cupric ions release. From the analysis of morphology and elements of the surfaces of the copper sleeves, the LDPE frame of IUDs and the surface of the nanocomposites after incubated in the stimulated uterine fluid for two years, it can be seen that the surface of nanocomposite is quite different from that of the copper sleeve and is similar to that of the LDPE frame, no elements such as P, Ca et al. have been found in the surface of the nanocomposites. The surface of nanocomposites can keep clean is attributed to its hydrophobic surface which the LDPE matrix bring to the nanocomposites. All these results show that the Cu/LDPE nanocomposites can be used as a novel Cu-IUDs material competently, and its cupric ions release rate can be controlled and designed by the control of structure and the adjustment of the process parameters. The control release of cupric ions and the self-cleaning of the surface of the nanocomposites indicate that the contraception effect can be ensured and the side effects of Cu-IUDs can be abated at the same time.