Study On Blending Modification Technology Of Polybutyrolactam And Polylactic Acid

Bio-based Polybutyrolactam(PA4)is regarded as the only biodegradable nylon in the world,which possesses superior mechanical properties,gas barrier properties,and heat resistance.Nevertheless,its high density of amide bonds in the molecular chain leads to the strong hygroscopic and weak water vapor barrier properties.Polylactic acid(PLA)is a bio-based degradable material with a wide range of sources,mature applications.Its hydrophobic groups in the molecular chain leads to excellent water barrier properties.However,there are some defects,such as its high brittleness,low gas barrier properties and poor heat resistance that limit its current use.In the present contribution,bio-based degradable materials with high barrier properties are obtained by blending PA4 and PLA,which provides not only new materials but new ideas for the application of PA4 and PLA in the field of environmental-friendly food packaging.Firstly,suitable co-solvent trifluoroethanol(TFE)was screened out for preparing of PA4/PLA blend films,and the compatibility of blends systems was explored under different blending conditions.When the blending ratio of PA4/PLA is 10/90,the barrier properties are excellent,and the oxygen transmission coefficient is 14.45×10-15 cm3·cm/(cm2·s·Pa),which is 68%lower than that of PLA.The water vapor transmission coefficient is 1.38×10-13 g·cm/(cm2·s·Pa),which is 47%lower than that of PA4.However,the mechanical properties of the blends decreased when compare with the pure component,because of the poor compatibility of the two components.X-ray diffraction(XRD)results show that the polymer components crystallized separately,indicating that the two components are incompatible in the crystallization zone.Differential scanning calorimetry(DSC)was used to obtain the melting enthalpy(?H)of PLA in the blends to calculate its crystallinity.It is found that blending with 10%of PA4 promoted crystallization of PLA.The increase in crystallinity improved the barrier performance of blendsSecondly,TPU(Thermoplastic polyurethane)and(O-acylated chitosan)were used as compatibilizers to modify the PA4/PLA blends.Among them,the effect of TPU is more obvious.When the amount of TPU is between 10%and 15%,the interface of the blends becomes blurred,and the combination between the two phases is closer,which improve the compatibility in the blend films.However,the addition of OCS has no significantly influence on the phase separation of the blends.The results of the blended materials show that the addition of OCS reduces the elongation at break,and the blends become more brittle.TPU significantly improves the mechanical properties of the blends.When the addition amount of TPU is 15%,the elongation at break is increased by 10 times compared with the control group.Barrier performance tests show that the addition of both compatibilizers decreases the oxygen transmission coefficient.The oxygen barrier coefficient reaches the minimum value when the TPU content is 10%,which is lower with an order of magnitude than the control group;when the amount of OCS is 3%,the oxygen barrier coefficient is the smallest in the blend system,and 37%reduction of the control group.Finally,hydrogen bonding was introduced into PA4/PLA blending system through methylol graft modification of PA4.The effect of hydroxymethyl grafting degree on the compatibility of blends was explored.Introducing methylol group to PA4 significantly improves the mechanical properties of the blended material.The elongation at break of the PA4/PLA blends raises up from 1.33%to 164.42%by modification.Stress-strain curves show that the brittle materials are transformed into plastic ones.The oxygen barrier properties of the blends with methylol grafting degree less than 10.80%are improved,especially for that methylol degree of 7.93%,whose oxygen transmission coefficient is the lowest.Infrared spectroscopy proved that there is obvious hydrogen bonding between N-hydroxymethyl PA4 and PLA.The surface morphology of the blended film was analyzed,and it is found that with the increase in the degree of methylol grafting,the phase separation phenomenon is significantly weakened,the surface roughness of the film is greatly reduced,which indicates that the blends have good compatibility in microscopic dimensions.XRD results show that the hydroxymethyl modification of PA4 partially destroies its crystalline structure and increases the amorphous structure,but the crystalline form of the blend components did not change.The results of DSC analysis show that with the increase in the degree of hydroxymethylation,the crystallinity of PLA in the blended material decreased,due to the intermolecular hydrogen bonding hindered PLA crystallization.The above results indicate that the hydroxymethyl modification of PA4 successfully introduces intermolecular hydrogen bonding in the blending system,and improves the compatibility of the blends,the properties of the blended materials achieved an obvious enhancement.