Structure And Properties Of Polyamide 6/High Density Polyethylene/Clay Composites

The dissertation consists of two parts. First, study on HDPE/clay and PA6/clay nanocomposites; second, the compatibilizaion effect of clay on PA6/HDPE and PA6/PEAA blends. All composites were prepared via melt compounding.1. Study on the HDPE/clay and PA6/clay nanocompositesFor HDPE/clay and PEAA/clay composites, the size and concentration of free-volume in composites were investigated by PALS, and the relationship between free-volume properties and modulus was studied. The results indicated that most of the clay platelets are not intercalated in HDPE, resulted in lower modulus of the composites. In comparison, clay exfoliated and dispersed in PEAA better than that in HDPE matrix, resulting in more interfaces and higher free volume strength (I₃). Consequently, the modulus of the composites increased.For PA6/Clay composites, the dispersion of clay and the properties were investigated by XRD, SEM, TEM, and DSC. The results showed that the clay was exfolicated and dispersed well in PA6. At low shear rate, the viscosity of PA6 decreased with the addition of clay. However, when the shear rate was larger than 3000 s^-1, the viscosity of PA6/clay was higher than pure PA6. Moreover, the effect was little when 1-4 phr clay was added in PA6. Because of finer dispersion of clay in PA6 and good interaction between PA6 and clay, the clay layers prevented the mobility of PA6 chain segments in certain extent and reduced the crystallization temperature.2. Compatibilizaion effect of clay on PA6/HDPE and PA6/PEAA blendsFor PA6/HDPE system, the compatibilization effect of clay was analyzed according to four factors: (1) Clay content. The HDPE domain size decreased dramatically with the increment of clay content. XRD and TEM results showed that the clay platelets mainly dispersed in PA6 phase and enriched around the interface between PA6 and HDPE. With the increment of clay content, the clay layers which enriched around the interface increased and the thickness of interface also increased.(2) Processing parameters (including rotation speed and mixing time). The variation of rotation speed: for PA6/HDPE (70/30) blend, the HDPE domain size was the smallest when the rotation speed was 40 rpm. With the increment of rotation speed, the HDPE domain size increased. Adding 4 phr clay into this blend, the morphology began to be stable at 40 rpm or faster. The variation of mixing time: for PA6/HDPE blend, with the increment of mixing time, the HDPE domain size decreased. For PA6/HDPE/1 phr clay, HDPE domain size decreased, however, with the increment of mixing time, the HDPE domain size also decreased. When adding more clay into this blend and mixed same time, the HDPE domain size decreased further, and with the increment of mixing time, the domain size began to be stable. (3) The composition of PA6/HDPE. The HDPE domain size (PA6/HDPE-90/10 and 70/30) was lager than that of PA6 in HDPE/PA6=90/10 and 70/30 blends for the blends without clay. When adding 2 phr clay into these blends, the dispersed domain size decreased to a similar level. (4) PA6's viscosity. The higher is the PA6's viscosity, the smaller the HDPE domain size is. However, when adding 4 phr clay into these blends, the HDPE domain size decreased to a similar level.For PA6/PEAA system, there were strong interaction between PA6, PEAA and clay. The clay was exfolicated and dispersed well in PA6/PEAA blend, and partial clay sheets enriched around the interface. With the increment of clay content, the PEAA domain was elongated and finally formed co-continuous morphology. Because of the fine dispersion of clay and its strong interaction with PA6 and PEAA, the tensile modulus increased dramatically. The dispersed clay platelets prevented the mobility of PA6 chain and induced the decrement of crystallization temperature and crystallinity. The increment of amorphous portion also induced the compatibility of HDPE and PA6.Whether PA6 was the continuous phase or not, the interaction between clay and the matrix was the most important reason that determines the compatibilization effect of clay. Lipatov theory was used to analyze the compatibilization mechanism.