Enzymatic Modification Of PET Fiber With Lipase Prepared From Aspergillus Oryzae

Poly(ethylene terephthalate) fiber is a polyester formed by ethyleneglycol reacting with terephthalate, it exhibits some drawbacksinfluencing its wearing comfort, like static charges and hydrophobicity.To improve these drawbacks, it is necessary to modify PET fiber/fabric.As a mild and environmentally friendly way as well asdemonstrating no damages to the original good properties of PETfiber/fabric, enzymatic modification of PET fiber/fabric came into sightin the last several years. According to the stage of enzymaticmodification of PET fiber/fabric up to now, there are several problemsneeded to solve. Firstly, enzymes used were often purchased fromcompanies and had no pertinences for modification of PET fiber/fabric,so activities of enzymes to PET were rather low and treatment resultswere far to industrial application, new more efficient enzymes areneeded to explore. Secondly, mechanism of enzymatic modification ofPET had not been studied. To solve these problems, the authors considerthat it should cultivate enzymes purposely for modification of PET atfirst. In this paper, aiming at enzymatic modification of PET, a lipasewas obtained by screening strains, optimizing culture conditions,purifying and partial characterizing. PET sample was treated with thelipase and the modification results were evaluated by analyzinghydrolysis products, carboxyl groups on PET surface and physicalproperties of PET such as hydrophlicity, anti-static ability and cationic dyeing ability. Effects of temperature, surfactants and crystallinity ofPET on the enzymatic modification of PET were discussed. To estimatethe lipase objectively, four other enzymes were also used to treat PETsample. Detailed research ways, steps and results are as the followings.By solid-plate method first and then liquid incubation, Aspergillusoryzae 1 was screened out for its most potential for lipase productionfrom four strains.Effects of carbon sources and their concentrations, nitrogen sourcesand their concentrations, surfactants and their concentrations,incubation temperature, beginning pH value of the liquid culture mediumand aeration (rotating speed) on lipase production from Aspergillusoryzae 1 were studied. Purposely, three additives, bis(2-hydroxyethyl)terephthalate, diethyl p-phthalate or PET short fiber was added into theculture medium, their effects on lipase production and mycelium weightas well as on hydrolysis of diethyl p-phthalate were studied. It turnedout that diethyl p-phthalate depressed lipase production and growth ofthe strain, PET short fiber had no evident effect on andbis(2-hydroxyethyl) terephthalate stimulated lipase production from thestrain. Lipase preparation cultivated ("induced") withbis(2-hydroxyethyl) terephthalate could catalyze hydrolysis of diethylp-phthalate, while lipase preparation cultivated with PET short fiber orcultivated with no additives had no effect on diethyl p-phthalate. Theoptimal culture medium for lipase production from Aspergillus oryzae 1contained 2．0%(v/v) Vogel's Medium N, 0．5% maltose, 0．5% peptone,1．0% olive oil, 0．032% Peregal O, 0．01% bis(2-hydroxyethyl)terephthalate, beginning pH 6．0, culture temperature 30℃, rotatingspeed 160rpm and culture time 84h.Aspergillus oryzae 1 lipase was purified by ammonium sulfateprecipitation and gel filtration. The optimal saturation of ammonium sulfate was 80%, the lipase was purified 2．92 fold after precipitated by80% saturated ammonium sulfate, the yield was 72% and the specificlipase activity came to 118, 421U/g. After gel filtration by a SuperdexG-75 column, the lipase was purified 11．9 fold and the yield was about25%, the specific lipase activity was 481,500U/g. SDS-PAGE identifiedthat the lipase was pretty pure.The optimal pH of the lipase activity was 7．0 and the lipase waspretty stable at pH7．0; the lipase activity was relatively high between 35℃～45℃and the optimal temperature was 40℃; in aqueous solution,the lipase had a high thermal stability, its activity remained about 50%after incubation at 55℃for 24h; Ca²⁺ and Mg²⁺ stimulated whereasEDTA strongly inhibited the lipase activity, from which it could beconcluded that the lipase was a metal enzyme: JFC, Peregal O andmaltose had protective effects on the lipase stability and they could beused together with the lipase during PET treatment.Lipase preparation from Aspergillus oryzae could act on ester bondson the surface of PET fiber. Under catalysis of the lipase preparation,hydrolysis products of PET fibers were probably mono(2-hydroxyethyl)terephthalate or mixture of terephthalic acid and mono(2-hydroxyethyl)terephthalate. After the lipase modification, there were more carboxylgroups on the treated PET fabric surface that resulted in interacting withmore cationic dyes; increased hydrophilicity and antistatic ability ofPET samples were found based on moisture regain, water contact angleand static half decay time.The appropriate temperature for the lipase treatment of PET was 55℃. Adding JFC, Peregal O or increasing the lipase concentrationfacilitated the modification results of PET. Amorphous area in PET fiberwas more susceptible for lipase attack. The optimal condition for thelipase treatment of PET included bath ratio 40, 9．0U/ml or 12．6U/ml lipase concentration, 0．5g/L JFC, pH7．0, treatment temperature 55℃,rotation speed 100rpm and treatment time 24h. After treated under theoptimal condition, water contact angle of PET fabric decreased from 75°to 69°, static half decay time decreased from 8．40s to about 8．00s.In order to estimate effects of Aspergillus oryzae 1 lipase on PETobjectively, Rhizopus oryzae esterase, Hog pancreas lipase, Lipase L andcutinase J were also used to treat PET. It turned out after PET samplewas treated with Hog pancreas lipase, lipase L or cutinase J, itsantistatic ability, hydrophilicity and cationic dyeing ability almostunchanged. After PET was treated by Rhizopus oryzae esterase solution,its water contact angle decreased from 75°to 67°, static half decay timedecreased from 8．40s to 7．45s, dyeing ability with various cationic dyeimproved to different degrees.According to results in this paper, we described a simple model ofPET enzymatic modification with lipase. 1) PET is a linear polymer ofbig molecular, lipase is difficult to penetrate inside of it, so enzymaticmodification only happens on the PET surface and doesn't affectstrength of PET. 2) As a result of enzymatic catalysis, PET polymersegment is off PET bulk; this PET segment is also a substrate for enzymeas well and can be catalyzed by enzyme to a smaller segment till it turnsto the final hydrolysis product. The hydrolysis products were probablymono(2-hydroxyethyl) terephthalate or mixture of mono(2-hydroxyethyl)terephthalate and terephthalic acid. 3) In PET bulk, amorphous area ismore susceptible for lipase attack, because ester bonds in amorphousarea are more mobile, they can access and bind with the active site oflipase more easily. 4) Enhancing mobility of PET facilitates enzymaticmodification of PET.Wang Xiao-hua (Textile chemistry and dyeing and finishingengineering)...