Stick to It


Modern Pioneer - - Contents - By James E. House & Kathy A. House

Choos­ing the right ad­he­sive for the job

We don’t of­ten stop to con­sider how of­ten we need to join to­gether dif­fer­ent pieces of ma­te­rial. Whether you’re build­ing a piece of wood fur­ni­ture, re­pair­ing a bro­ken gar­den­ing tool or putting to­gether a new flintlock ri­fle, it’s im­por­tant to know the best way to make a join hold firm for the long haul. If the ob­jects be­ing joined are me­tals, then weld­ing, sol­der­ing and nuts and bolts are ef­fec­tive. If the pieces be­ing joined are wooden, then nails, screws and glues are stan­dard bin­ders. Sewing binds to­gether fab­ric or leather. For most ap­pli­ca­tions, though, we all reach for some sort of ad­he­sive or glue.

When it comes to prac­ti­cal de­vel­op­ments in mod­ern chem­i­cal sci­ence, ad­he­sives have re­ceived the lion’s share of im­prove­ments. If you go into a craft, hard­ware or build­ing-sup­ply store, you’ll see lit­er­ally dozens of ad­he­sives on dis­play. There are spe­cialty prod­ucts de­signed for use with wood, fab­ric, china or glass. There are also two-part ad­he­sives. An­other ad­he­sive that’s cur­rently avail­able is con­duc­tive and pri­mar­ily is used to join elec­tri­cal wires. If you need to join it, there’s an ad­he­sive for the job.

The Gen­er­als

For gen­eral use with pa­per or wood, there are nu­mer­ous glues avail­able. In­cluded in th­ese are com­mon white glues, rub­ber ce­ment, etc. Many of th­ese types of glues con­tain a sol­vent that evap­o­rates and leaves the ad­he­sive in place. Oth­ers con­tain com­pounds that form bonds to the ob­jects be­ing at­tached. Pres­sure-sen­si­tive ad­he­sives are used in ap­pli­ca­tions that re­quire an ob­ject such as a stamp to at­tach where it is placed. Glues that are ap­plied hot are used in glue guns, and both the glues and ap­pli­ca­tors are avail­able in stores that range from build­ing sup­pli­ers to gas sta­tions and de­part­ment stores. Pop­u­lar glues in the gen­eral cat­e­gory in­clude Elmer’s Glue-all, Dev­con, Lepage and many other brands. Some are de­signed es­pe­cially for glu­ing plas­tics and have long been as­so­ci­ated with build­ing mod­els.

The Su­pers

A fam­ily of glues of­ten re­ferred to as “su­per” glue have been pop­u­lar for many years. Su­per Glue is a reg­is­tered trade­mark of Su­per Glue Cor­po­ra­tion, but there are nu­mer­ous glues that have sim­i­lar char­ac­ter­is­tics. Most con­tain a class of com­pounds known as cyanoacry­lates, with methyl cyanoacry­late be­ing the most com­mon. The com­pounds have been known for many years, but their use as ad­he­sives be­gan about 50 years ago. Al­though Su­per Glue re­mains pop­u­lar, nu­mer­ous other brands are avail­able.

Su­per glues are avail­able in liq­uid and gel forms, usu­ally in tubes that al­low a small amount to be squeezed out at the time of ap­pli­ca­tion. One of our fa­vorites is the easy-to-use Loc­tite gel. It doesn’t run from the point of ap­pli­ca­tion, and it bonds strongly and quickly. One neg­a­tive at­tribute of su­per glue is that if some ends up where it shouldn’t (like on fin­gers), it will not wash off. How­ever, nail pol­ish re­mover (ace­tone) ef­fec­tively re­moves it.

“If you go into a craft, hard­ware or build­ing­sup­ply store, you’ll see lit­er­ally dozens of ad­he­sives on dis­play.”

Su­per glues bond to most sur­faces, which makes them a first choice for many uses. The con­tain­ers are small and easy to carry in a re­pair kit, tool­box or back­pack. One disad­van­tage is that they de­te­ri­o­rate quickly (even in the con­tain­ers), so it’s not un­com­mon to pick up a tube that was used some time ago, only to find that noth­ing is left, or that it has be­come a small brick.

“… you can eas­ily make a glue that works very well us­ing only a few com­mon kitchen items.”

The Heav­ies

Some­times an ad­he­sive is needed that not only binds two ob­jects to­gether, but also per­mits an ob­ject to be re­shaped. In such cases, the ad­he­sives that con­sist of two com­po­nents are the usual choice. Two-part epoxy-type glues con­sist of a resin and a hard­ener that are mixed im­me­di­ately be­fore use. A class of com­pounds known as epox­ides con­sti­tute the resin, and the hard­en­ers in­clude com­pounds such as amines, al­co­hols, or­ganic acids or phe­nols. When the two parts are mixed, a re­ac­tion oc­curs in which the epox­ide com­pounds are linked to form a rigid poly­mer. This re­ac­tion is re­ferred to as cur­ing or crosslink­ing.

Be­cause of the many dif­fer­ent epoxy com­pounds and crosslink­ing agents, there is a wide range of epoxy glues. Some are quick­set­ting, whereas oth­ers re­quire con­sid­er­able time for the cur­ing process to com­plete. In some cases, ad­di­tives such as glass fibers or pow­dered me­tals are in­cluded to in­crease strength. The epoxy glues are ver­sa­tile and are good choices when some­thing re­ally needs to be “welded” to­gether with­out a welder. This is es­pe­cially true of larger ob­jects, and the re­sult is a rigid piece so strong that some can even be ma­chined or shaped. J-B Weld prod­ucts are of this type. By choos­ing dif­fer­ent in­gre­di­ents, epoxy glues are avail­able in a wide range of prop­er­ties. Such ad­he­sives are used in many industrial ap­pli­ca­tions.

Make Your Own

There are times when a project must be com­pleted, but a trip to the store is im­prac­ti­cal.

In that case, you can eas­ily make a glue that works very well us­ing only a few com­mon kitchen items. One such prod­uct is some­times re­ferred to as “milk glue” be­cause one of its in­gre­di­ents is skim milk, which con­tains ca­sein (milk protein), a prod­uct used in many glues. This glue is a gen­eral-pur­pose ad­he­sive that cre­ates a very strong bond with por­ous sur­faces such as wood, pa­per or card­board.

Not only does home­made glue work well, it’s eas­ily made from wa­ter, vine­gar, skim milk and bak­ing soda. The process be­gins by com­bin­ing ½ cup of skim milk with 2 ta­ble­spoons of vine­gar. The mix­ture is stirred for one minute, then al­lowed to set for two min­utes. The solid curds that form are re­moved by plac­ing a pa­per-towel-lined strainer over a bowl to al­low the liq­uid to pass through. Af­ter the liq­uid has drained for about five min­utes, the pa­per towel con­tain­ing the solids is re­moved and squeezed to force out the re­main­ing liq­uid. The solid is placed in a bowl, and 2 ta­ble­spoons of wa­ter are added and blended with a fork.

Af­ter the lumps are bro­ken up, 2 tea­spoons of bak­ing soda are slowly added, and the mix­ture is stirred un­til the foam­ing (caused by the re­ac­tion be­tween vine­gar and bak­ing soda) stops and all lumps are bro­ken up. At this point, the glue is a thick, white semiliq­uid. It should be stored in an air­tight con­tainer, and it can be thinned by adding a small amount of wa­ter.

Don’t be de­ceived by think­ing that this sounds too sim­ple to be good. This stuff works! Ca­sein-based glues have been used for cen­turies in wood­work­ing. We have even joined small flat sticks end to end with sur­pris­ing strength in the bond. When ap­plied to broader sur­faces and clamped un­til dry, a very strong bond is ob­tained.

What to Glue

Ad­he­sives of­fer many ad­van­tages over other join­ing meth­ods. One is that you can glue ob­jects such as wood, fab­ric or leather to­gether where sewing isn’t fea­si­ble. When it comes to con­sumer ad­he­sives, we never had it so good.

“Two-part epoxy­type glues con­sist of a resin and a hard­ener that are mixed im­me­di­ately be­fore use.”

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