Investigation On Mixing Extrusion And Foaming Of Biodegradable PBS/PLA Blends

In this dissertation,poly(butylene succinate)/poly(lactic acid)(PBS/PLA)blend samples(93/7,85/15,80/20,70/30,60/40 and 50/50)were prepared by mixing extrusion using a single-screw extruder.The phase morphologies,rheological properties,thermal properties,crystal structure,mechanical properties and degradation properties of the prepared samples were studied and the relationship of “rheological behaviors–phase morphologies–properties” was investigated.Then,PBS and some PBS/PLA blend samples were foamed in a batch process.The effect of PLA content and foaming condition on the cellular structure of foamed samples was analyzed,and the oil-water separation property of the foamed PBS/PLA blend sample was studied for extending the application of PBS.The phase morphologies of the PBS/PLA blend samples were developed from droplet to co-continuous when increaseing PLA contents from 7 to 50 wt%.The rheology test showed that the addition of PLA induced higher complex viscosity of PBS.The PBS/PLA blend samples with 40 or 50 wt% PLA exhibited strong shear thinning behavior.In the low frequency region,the storage modulus(G′)of the PBS/PLA blend samples increased with increaseing PLA contents,while the G′ of the PBS/PLA(50/50)blend sample decreased because of the reduced interface area between PBS and PLA phases.The addition of PLA had almost no influence on the crystal structure of PBS.PLA microdomains had a heterogeneous nucleating effect on the crystallisation of PBS,resulting in reduced crystal size.However,adding higher PLA contents(50 wt%)reduced the crystallization temperature of the PBS phase.The mechanical test showed that the PBS/PLA(93/7)blend sample exhibited higher elastic modulus and tensile strength than PBS.At a foaming temperature(Tf)of 120 °C,adding low PLA contents(7,15 or 20 wt%)obviously improved the foaming properties of the PBS.Microcells were developed with more uniform distribution,more regular shape,and smaller diameter(with a mean value of about 10 μm)for all the foamed blend samples.That was attributed to improved storage modulus,complex viscosity and especially melt strength of the PBS induced by added PLA.Moreover,the cell diameters for the foamed blend samples exhibited a much narrower distribution and followed Gaussian distribution,resulting from good dispersion of the PLA microdomains.Further,the effect of the Tf on the cellular structure of microcellular samples of the PBS and the blend with 15wt% PLA was investigated.It turned out that adding 15wt% PLA shifted the lower Tf limit of the PBS from 115 to 110°C,and obviously improved the cellular structure uniformity and decreased the cell diameters for the foamed samples prepared at relatively high Tfs(120 and 125°C).When the Tf and foaming pressure were set at 125 °C and 18 MPa respectively,the foamed PBS/PLA(93/7)blend sample exhibited relatively regular microcells with 35.3% opening ratio.The foamed PBS/PLA blend sample has lipophilic-hydrophobic characteristic(the water and oil contact angles were 126.0° and 0°,respectively)and high oil sorption quality(Mobiltherm,14.0 g/g),which endowed it with relatively excellent oil-water separation property.