| The Polylactic Acid（PLA）has many advantages, such as easily available raw materials,good physical and chemical properties, complete biodegradable and harmless, which make ithas important significance in reducing environmental pollution, saving oil resources andreducing greenhouse gas effect. The PLA is becoming one of the most prospective greenenvironmental protection materials. The PLA materials have been introduced into the area ofdesertification combating, and achieved promising effects on desertification prevention andtreatment.Various patterns of the PLA sand barriers were laid on the dune of Ulanbuh desert and MuUs sandland and regularly sampled. The change of physical, chemical, thermal properties andsurface morphology of different part of PLA sand barriers with the increased laying time weremeasured, the process and laws and the main impact factors of the degradation of PLA sandbarriers were analyzed and revealed. Combined with laboratory simulation and field test, thepolish resistance properties of PLA sand barriers were evaluated and the empirical evaluationequation was established. The improvement measures for the sand leakage in the application ofPLA sand barriers were proposed and verified. The main conclusions are as follows:（1）The loss ratio of bursting strength,single yarn breaking strength and weight increasedwith the laying time, and reached to48.28%,78.77%and23.05%after5years, respectively.Their variation speed were inconformity.（2）The degradation degree of different part of the barrier body ranked in the descendingorder as windward part, top part, leeward part and the ground part. The difference of thedegradation degree for4parts of barrier body decreased with the increase of laying time, whichindicated that the wind-sand activity was the most important impact factor for the degradationof PLA sand barriers, following as light and soil water, the impact of environmental factorsdecreased with the increase of time. （3）The degradation degree of the exposed part of sand barriers was higher than theground part in Ulan buh desert, and the difference was significant. While the difference of thedegradation degree between the two parts in Mu Us Sandland was small, which indicated thatthe impact intensity of the wind-sand activity and light and soil water varied in different studyarea. The degradation degree of PLA sand barriers in growing season (May to October) andnon-growing season (November to following March) half year were different, and thedegradation degree in in growing season was higher than in non-growing season, whichindicated that the environment difference such as the wind-sand activity and light and soilwater between the sampling time impacted the degradation degree of sandbag barriers（4）The FT-IR analysis showed that there were no generation and disappear of new or oldfunctional groups, which indicated that the PLA sandbag barriers were stable in the sand area.The results of FTIR analysis showed that the–CH vibrated significantly, which indicated thatthe long time exposure to the light was one of the important factors that impact the degradationof PLA. The measurement of relative molecular weight showed that the relative molecularweight of PLA sand barriers decreased with the increase of time, the average value haddecreased33.96%. The distribution of relative molecular weight was becoming wider, theaverage value had decreased6.63%.which means that the degradation degree of PLA wasaggravating. The half life of the PLA sand barriers’ service life was predicted to be about8.5athrough the establishment of first order kinetics model.（5）The DSC thermal analysis results showed that with the extension of time, the glasstransition temperature of the PLA sand barriers first increased then decreased. Meanwhile, themelting point decreased, the melting enthalpy and crystallinity increased. All these indicatedthe degradation degree of PLA sand barriers was increasing with the extention of laying time,but it was still in the amorphous zone degradation stage.（6）The results of scanning electron microscope showed that the structures of barriers’yarns were destroyed with the extension of time. The demolishment of fiber surfacetransformed from strip peeling off to groove block off even to crack. It can be estimated that the PLA sand barriers were in the initial stage and medium stage of degradation. Theaccelerated degradation stage did not reached. The bursting strength loss rate of PLA sandbarriers was25.06%after being laid2years, while the bursting strength loss rate of7conventional chemical fiber materials varied from47.68%to100%, which indicates that thePLA sand barriers has the advantages of degradation resistence and they are suitable for beingwidely used in the sandy area（7）Due to the comprehensive effect of environmental factors, the degradation degrees ofthe PLA sandbarriers distributed on the different part of dune were different. The sand barrierslocated on the top of dunes and in the middle part of windward slope suffered the severestdegradation, followed as the bottom parts of windward and leeward slope, the middle part ofthe leeward slope suffered the least severe degradation. All the sand barriers laid on thewindward side suffered severer degradation than that laid on the leeward side.Overall, thedegradation degrees of the sand barriers distributed on different part of windward slope wereseverer than that of on leeward slope. There are no obvious differences in the degradationprocess of PLA sand barriers among different laying patterns. The experiment of sand bury inthe lowland showed that the degradation degrees varied with the difference of water content,the difference was becoming larger with the increase of burying time, which indicated that thesoil water content was an important factor that affects the PLA sand barriers degradation.（8）Boiled for1.5min in the100℃water, the fabric density of PLA sand barrierssignificantly increased, meanwhile the pore diameter of the fabric reduced significantly.Thenumber of coils reached93per5cm after boiling. The situation of the sand leakage of PLAsand barriers improved significantly, and the leakage amount of sand reached78.5%. Theimpact on the chemical and thermal properties and surface morphology was little. Whereas thelength of the fabric significantly reduced, the fineness of single yarn decreased slightly, so didthe width and the weight of fabric. |
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