Low Saturation Of The Ppo-pla-based Biodegradable Polyurethane Materials

Environmental protection is one of the tasks of vital importance in the 21st century.The huge consumption of plastics and synthetic fibres has caused serious "white pollution" problems in the natural environment.Since 1980s,with the aim of reducing environmental pollution,people have started to develop biodegradable polymers and products as a substitute for general plastics.Poly(lactic acid)(PLA) has been one of the degradable polymers that attract the most attention of researchers.Poly(lactic acid),also called polylactide,is an essentially novel green material because of the sufficient and renewable resources of lactic acid.In addition,PLA is biodegradable and its producing procedure is pollution free.PLA can be processed by many methods,such as extrusion,spinning,biaxially oriented,injection and blow molding.PLA products have good biocompatibility, brightness,clarity,touch feeling,and also reasonable fungus resistance,flame resistance,and anti-UV properties.Therefore,PLA products are widely used as packaging materials,fibres,and bonded yarn fabrics.However,PLA is brittle and of low impact resistance.Experiments show that the defects can be modified by copolymerizing PLA with other materials,and variable degradability and lower production costs can also be realized.In this work,triarm block or random copolymers were synthesized from domestic novel low unsaturated poly(propylene oxide)(PPO) orε-caprolactone(CL) together with PLA.The condensed matter of PLA segments is adjusted by the soft PPO or PCL segments.Furthermore,novel environmental friendly degradable polyurethane(PU) materials were investigated, including PPO-b-PLLA or PPO-b-PDLLA based partially degradable PU foams, PPO-b-PLLA based fully degradable PU foams,and PLLA-r-PCL based fully degradable PU foams.The main contents of this work are as follows.(1) Fourier transform infrared(FTIR),gel permeation chromatography(GPC), matrix-assisted laser desorption/ionisation-time of flight mass spectrometry (MALDI-TOF MS),proton nuclear magnetic resonance(¹H-NMR),and ¹³C nuclear magnetic resonance(¹³C-NMR) were carried out to investigate the chemical structure and composition of the domestic novel low unsaturated polyether polyols,which were synthesized by continuous process using double metal cyanide complex catalysts.The molecular structure of low unsaturated polyether polyols were characterized and compared with the general polyether polyols.Differential scanning calorimetry(DSC) and thermogravimetric analysis(TGA) were measured to evaluate the thermal properties of the polyether polyols.Basic data were provided for further developing of new materials.(2) The synthesis of flexible PU foams from low unsaturated polyether polyols by one-stage process using water as blowing agent were investigated.The processing technic was found to be a good solution to the problem of collapse during the foam forming process from low unsaturated polyether polyols.The microphase morphology of flexible PU foams were investigated by attenuated total reflectance(ATR)-FTIR and DSC.The results show that both microphase mixing and microphase separation between the hard segments of urethane or urea and the soft segments of polyether present in flexible PU foams,while the microphase mixing is dominating.The mechanical tests show that both the tear propagation resistance and compression hardness of flexible PU foams made from low unsaturated polyether polyols are better than those of general flexible PU foams.(3) Triarm low unsaturated PPO-b-PLA copolymers of different PO/LA molar ratios and condensed matter were synthesized by ring-opening polymerization of L-lactide or DL-lactide using low unsaturated PPO triols as macromolecular initiator and stannous octoate as catalyst.FTIR,GPC,and ¹H-NMR were used to investigate the chemical structure and chain composition.It is proved that the copolymers all present narrow molecular weight distribution(PDI～1.0-1.1).It was shown by DSC and wide angle X-ray diffraction(WAXD) that PPO-b-PLLA copolymers with isotactic PLLA segments are crystalline materials,and the crystallinity decreases with decreasing the PLLA segments length,whereas,PPO-b-PDLLA copolymers having atactic PDLLA segments are amorphous.The thermal stability of PPO-b-PLA copolymers was improved by introducing PLLA or PDLLA segments according to the results of TGA experiments,and PLLA segments were found to have a stronger effect than PDLLA segments.(4) PPO-b-PLA based partially degradable and fully degradable PU foams were synthesized.It was found by ATR-FTIR and DSC that the PLA segments improve the microphase mixing in PPO-b-PLA based PU foams.In addition,the contribution of PDLLA segments to the microphase mixing is greater than that of PLLA segments. The extent of microphase mixing in PPO-b-PLLA based fully degradable PU foams is greater than that in PPO-b-PLA based partially degradable PU foams.Atomic force microscope(AFM) was also used to examine the microphase morphology of PU foams.The results show that microphase separation of urethane or urea takes place in pure PPO foams.As for PPO-b-PLLA based partially degradable PU foams, microphase separation of PLLA segments is observed besides that of urethane or urea. No microphase separation is observed in PPO-b-PDLLA based partially degradable PU foams.The mechanical property tests show that PPO-b-PLA based partially degradable PU foams exhibit high performance in both tear propagation resistance and tensile properties.The tear propagation resistance,tensile,and rebound resilience properties of PPO-b-PDLLA based partially degradable PU foams are better than those of PPO-b-PLLA based partially degradable PU foams.Alkaline hydrolysis experiments prove that the degradability of PPO-b-PLA based PU foams increases with increasing PLA content,and the degradability of PPO-b-PDLLA based partially degradable PU foams is greater than that of PPO-b-PLLA based partially degradable PU foams.And the degradation rate and extent of PPO-b-PLA based fully degradable PU foams are far greater than those of PPO-b-PLA based partially degradable PU foams under alkaline hydrolysis condition.In contrast,pure PPO foams are non-degradable under the alkaline hydrolysis condition.Enzymatic degradations prove that PPO-b-PLA based fully degradable PU foams are degradable under enzymatic degradation condition,whereas the degradation behaviors of PPO-b-PLA based partially degradable PU foams are not obvious.(5) Triarm PLLA-r-PCL random copolymers with various monomer molar ratios were synthesized by ring-opening polymerization of L-lactide andε-CL using glycerol as initiator and stannous octoate as catalyst.FTIR,GPC,and ¹H-NMR were used to investigate the chemical structure and chain composition.It is confirmed that the copolymers are random copolymers,and the chemical structure and the chain composition of the copolymers are as expected as the initial molecular design.In addition,PLLA-r-PCL based fully degradable PU foams were synthesized from PLLA-r-PCL copolymers.It is found by ATR-FTIR and DSC that a slight microphase separation exists in this material.The mechanical property tests show that PLLA-r-PCL based PU foams exhibit high hardness.Moreover,PLLA-r-PCL based PU foams exhibit great degradability under both alkaline hydrolysis and enzymatic degradation condition.