The influences of the glass transition temperature

the crystallization behavior and the hydrogen bond strength on the thermal expansion behavior of four types of aliphatic polyamides were studied in details by thermal expansion test

differential scanning calorimetry (DSC)

wide-angle X-ray diffraction (WAXD) and Fourier transform infrared spectroscopy (FTIR).DSC and X-ray diffraction results showed that the coefficient of linear thermal expansion (CLTE) of crystalline part is lower than that of amorphous part for different types of aliphatic polyamides.However

the influences of the melting temperature and crystallinity of the aliphatic polyamide on CLTE are not clear.Polyamide 56 (PA56) owning a higher glass transition temperature and a lower ratio of methylene/amide groups (CH2/CONH) shows a much lower CLTE value than other aliphatic polyamides.Further experimental results showed that when all of these specimens were prepared under the same procedure and conditions

a linear relationship between CH2/CONH ratio or glass transition temperature and CLTE could be obtained for the aliphatic polyamide systems.It was found that a further decrease in CLTE could be achieved either by increasing Tg or by decreasing the CH2/CONH ratio of the polyamide chains.FTIR results confirmed that the density and strength of hydrogen bonds are the key factors influencing the thermal expansion behavior of aliphatic polyamides.