<TITLE: Lactic Acid Based Hot Melt Adhesives: Preparation and Properties
ACADEMIC DOMAIN: technology
DISCIPLINE: materials engineering
EVENT TYPE: doctoral defence presentation
FILE ID: UDEFP010
NOTES: continued in UDEFD010

RECORDING DURATION: 10 min 50 sec

RECORDING DATE: 25.4.2003

NUMBER OF PARTICIPANTS: unknown

NUMBER OF SPEAKERS: 1

S1: NATIVE-SPEAKER STATUS: Finnish; ACADEMIC ROLE: research student; GENDER: male; AGE: 31-50>


<S1> adhesive material is is a substance capable of holding materials to- together by surface attachment er getting more close to this thesis the definition of hot melt adhesive is an adhesive that is applied on it's molten state and it forms bond after cooling a solid state , with the adhesive er it is generally so that the adhesive , must wet the surface so it must be applied in in it's liquid state and er it forms a bond in a solid state and with the other adhesive types transition from fluid to solid happens either by evaporation of carrier or solvent or by chemical cure <P:12> hot melt adhesive , market can be described so that er there are fairly new adhesive types er among the others in 1950s the market share of the hot melt adhesive was almost zero per cent and today it's close to 20 per cent of the adhesive market value hot melt adhesives are still growing more than the other other er adhesive types and the reason for for that is is is here that the speed of the bond formation is is very fast so there is no time needed for evaporation of of solvent or carrier fluid , on the other hand because of this no volatile organic compounds V-O-Cs are produced so they are environmentally very safe and also for the workers very safe they also require small space in the transportation or or the storage stage because they are 100 per cent adhesive material also the application equipment is very simple er in industrial application it is normally required a drying tunnel er but in the case of hot melt adhesive it is not so , er <COUGH> where are the hot melt adhesive used , we can say that er they have a small segment in the fur- er furniture sector so for example it's banding of the of the this kind of tables is done with the hot melt adhesives , er also in the book binding for example this thesis is is made with E-V-A based adhe- hot melt adhesive then quite big amount is the pressure sensitive sector which means this kind of permanently tacky adhesives for example used in tapes , disposables which means for example diapers it's it's a big market for hot melt adhesives and finally the biggest sector is in the packaging industry , and er world wide the packaging industry uses over 650,000 tons of hot melts , annually and and typical samples i can show you , what's have been done with hot melt adhesives er this looks like survival kit for technical student but anyhow these are put together with hot melt adhesives and maybe some familiar p- packages to you so mostly they are used in case and carton assembly and sealing <P:07> we can say that almost without exception packaging hot melt adhesives are based on er polyethylene vinyl acetate copolymer E-V-A er with the E-V-A we have vinyl acetate part here and and the ethylene part here and depending on the length of the ethylene chain the vinyl acetate content can be determined and normally it's about range of 30 per cent the problem with E-V-A is is that er it is based on oil-based raw materials and it's non-degradable so very stable er synthetic system , and going mo- more closely to the packaging field , so most of the packages are based on cellulosics and er er cellulose is by nature renewable and biodegradable material and if there is a moisture barrier needed for for this kind of application in other words er plastic films so the trend is also toward biodegradable coatings , er on the other hand biodegradation of the package according to the E-N norm includes all it's components er including adhesives plastic films used in the in the package , er , in the packaging recycling as as you all know the the paper material is is er very strongly recycled which means that er the paper is repulped to fibres and new paper is made out of the recycled fibres if any hot melt residuals as they always are present in the in the paper making process after the recycling they can cause interruptions in the process meaning that er er this sticky contamina- er contaminants can can er make interruptions in in the paper paper line they can cause printing problems it's not guaranteed that er er printing inks will adhere on to to hot melt surface and of course they can ruin the aesthetics of the paper meaning that you have these kind of brown spots on the on the paper surface . so there is a need to develop a new new type of hot melt adhesive and er and er polylactic acid is is very promising candidate for this , lactic acid exist in two two forms L and D depending on on the place of this methyl group , er L form is naturally occurring in animal organism er for for the for the er technical pur- purposes lactic acid is obtained by fermentation from starch so it's renewable raw material , of course we cannot use lactic acid as such er in the ad- adhesive making but we have to polymerise it to make it er poly- polylactic acid suitable polymer for for hot melt adhesive er it can be polymerised through two routes so either direct polycondensation from the lactic acid to polylactic acid or other way er doing this intermediate delac- lactide and with the ring opening polymerisation make it er polylactide er the first route the simplified route has disadvantage that er that er it doesn't favour very long long polylactide chain structure so so if we want very high molecular weight polymer we have to use this more complex route in the ad- adhesive application the polycondensation route er proves to be enough , PLA is known to degrade through hydrolysis typical to aliphatic polyesters and and er this degradation mechanism is er favourable in in the repulping er point of view because of the of the water used in in the process and it is known to er bio- biodegrade totally er polylactide is currently used in by abso- absorbable surgical implants and this thesis incla- includes the first scientific papers published about PLA based hot melt adhesives <P:08> professors <NAME S2> and <NAME S3> as the opponents appointed by the department of material engineering please present your criticism of this thesis </S1>
