The Preparation Of PPDO/PLLA Sheath-core Composite Monofilaments And The Study Of Performance

With the continuous development of biotechnology,biodegradable materials are playing a more and more important role in the medical field.Polydioxanone(PPDO)has excellent flexibility and degradability.It has been widely used to produce medical sutures.However,the price of PPDO suture is relatively high.Polylactic acid(PLLA)has large production and low cost,but it is rarely used as a suture alone because of its lack of flexibility.In this paper,PPDO/PLLA composite monofilament was made from PPDO and PLLA.The crystallinity,orientation degree,strength and elongation and section morphology of monofilament and the degradation properties of composite monofilament were studied.First,PPDO monofilament and PLLA monofilament were prepared.In the first process of drawing PPDO monofilament and PLLA monofilaments,found with the increasing of draw ratio,sonic orientation factor and mechanical properties of two kinds of monofilaments are improved.When the draft ratio is 6 times,the mechanical properties of filament spinning line are great and the stability of spinning wire is high.With the increase of drawing temperature,the orientation degree and fracture strength of the two monofilaments were increased and then decreased.The orientation degree and fracture strength of PPDO monofilament are maximum at 60?.The orientation degree and fracture strength of PLLA monofilament orientation are maximum from 70? to 80?.In the second drawing process of PPDO monofilament,found that with the increase of temperature,filament orientation,crystallinity and tensile strength increased first and then decreased,which the maximum is 75?;With the increasing of draw ratio,degree of orientation and mechanical properties of the filaments are improved.When the draft ratio is 1.3 times,the mechanical properties of filament spinning line are great and the stability of spinning wire is high.Two kinds of PPDO/PLLA sheath-core composite monofilaments were prepared by using PPDO and PLLA as core layer respectively.The optimum material barrel temperature is 175?,the composite nozzle temperature is 175?,the drag ratio is 6 times,and the drafting temperature is selected from 60? to 80?.It is found that with the increase of drafting temperature,the orientation and fracture strength of two kinds of core drafting increased first and then decreased,and they all reached the maximum at 70?.And under the same temperature conditions,the orientation degree and fracture strength of PLLA-PPDO monofilament are always slightly higher than that of PPDO-PLLA monofilament.Through the observation of optical microscope,it is found that the cross section of the composite monofilament is round,the core of the skin is close,there is no obvious crack,and the structure of the skin core is clear.The DSC test found that when the drafting temperature was 70?,the two components' crystallinity of the PLLA-PPDO sheath-core composite monofilament was slightly larger than that of the PPDO-PLLA monofilament.In the process of in vitro degradation,the weight loss and water absorption of PPDO/PLLA sheath-core composite monofilaments decreased with the time increased.Meanwhile,the relative viscosity and pH of PBS solution decrease obviously.PLLA-PPDO monofilament has a small change in initial performance due to the protective effect of PLLA.The mechanical properties test showed that the strength retention rate and elongation at break of the two monofilaments were decreased with time increased gradually.The strength retention rate of PLLA-PPDO monofilament is relatively lower than that of PPDO-PLLA monofilament at the early stage of degradation.The elongation at break of PLLA-PPDO monofilament is larger than that of PPDO-PLLA monofilament at the early stage of degradation.DSC test shows that with the increase of degradation time,the melting enthalpy and crystallinity of PPDO and PLLA increased when the PPDO/PLLA sheath-core composite monofilaments was in the first heating curve,indicating that hydrolysis took place in amorphous region first;With the increase of degradation time,the crystallization temperature and melting temperature of PPDO and PLLA decreased when the PPDO/PLLA sheath-core composite monofilaments was in the second heating curve.Meanwhile,the enthalpy of crystallization and the enthalpy of melt become larger.SEM tests show that with the increase of the degradation time,PPDO-PLLA filament surface changed significantly.When the degradation time is 35 days,almost all the filament surface is full of holes,cracks and degradation of debris produced by the degradation.Meanwhile,the change of PLLA-PPDO monofilament surface with degradation time is not obvious in the degradation test time.