Easy care, wrinkle-resistant cotton fabrics are one of the most widely manufactured and commonly used products in the world. Every individual on Earth uses these products every day of his/her life. Wrinkle recovery performance of untreated cotton fabric is poor because creases can be stabilized by intermolecular hydrogen bonds that easily break and reform in a creased configuration within the fiber during wetting/drying of the fabric. It's the same as what happens to spaghetti when it's boiled, then dried. When wet, the cotton cellulose (a polymer almost identical to the starch in spaghetti) becomes flexible. But when dried, it retains the shape in which it has been dried, due to the re-formation of hydrogen bonds.


To improve end-use performance, formaldehyde-based stabilizers are used to replace many of the hydrogen bonds in cellulose with permanent stronger covalent bonds called "crosslinks" that won't break when the fiber becomes wet. The original formaldehyde-containing crosslinkers from the mid 1900's suffered from poor stability, degraded strength (tear, tensile, and abrasion), and possible degradation of fabric during washing/drying. Even worse, they released airborne formaldehyde, a known human carcinogen. Later, a more stable crosslinker called DMDHEU became the industry standard. DMDHEU reduced many of these problems but notably did not completely eliminate the carcinogenic formaldehyde release.


Many alternatives to DMDHEU have been proposed and studied, but they all have eventually failed to be widely adopted for several reasons, i.e. environmental, health and safety issues; high cost; lower wrinkle recovery performance; strength degradation; and difficulty of application. These alternatives have mostly been low-molecular-weight reactive materials that could easily become airborne, thus releasing reactive pollutants that could affect the consumer in much the same way as formaldehyde.


We are stabilizing fabric for wrinkle resistance by a completely different chemical route that does not involve volatile materials that can become airborne and affect the consumer. Our basic strategy is to give cellulose an electrical


charge to make it "ionic" charged, then to treat it with high molecular weight polyelectrolyte polymers of opposite charge to lock the charged cellulose sites together with ionic (not covalent) crosslinks. This provides improved wrinkle recovery angle performance and also produces a consumer product with no hazardous chemical release. Our ionic crosslinks are intermediate in strength as shown in the following list (strength given in kilocalories per mol of bonds):



BOND TYPE

TYPICAL BOND STRENGTH

Hydrogen bonding (untreated cellulose)

1

Ionic crosslinking

(our method)

10

Covalent bonds (commercial crosslinkers)

30


We are investigating several methods ways to apply ionic crosslinking including the following:

Make the cellulose anionic (negative) then use polycation (positive) to crosslink

Make the cellulose cationic (positive) then use polyanion (negative) to crosslink

Make the cellulose anionic (negative), then cationic (positive) simultaneously

Make a pre-condensate from anionic (negative) any cationic (positive) material, then react with cotton

We have developed optimized methods for making cellulose ionic, either + or charged, using chloroacetic acid or 3-chloro-2-hydroxy-propyl trimethyl ammonium chloride. The first is indicated in Figure 1 below.

 


Our initial investigations were based on making the fabric anionic (negative charged) with chloroacetic acid, then treating with various polycations such as cationized chitosan, cationized glycerin, and others. These fabrics showed great improvement in crease angle performance when the fabric is in its wet state. This is important in reducing wrinkling during washing when the fabric is wet. However, we did not achieve very much improvement in wrinkling in the dry state, which corresponds to wrinkling during wear. We have investigated numerous chemical routes to anionic and cationic cellulose, as well as various ionic crosslinking agents, as shown in Figure 2.





 

In spite of our best efforts, we have still not solved the dry wrinkle recovery problem, but work continues in that area. Much of the work centers on an attempt to improve the distribution of crosslinks throughout the fibers of the sample, or to actually form the crosslinks when the fiber is in its dry state. To study this we are using laser confocal microscopy (LSCM), which gives accurate 3-dimensional information about the distribution of ionic sites, as indicated below in Figure 3. LSCM was used to investigate how anionic groups were distributed along the fabric surface and across the fiber cross-section. It appears that we are producing carboxymethylation evenly across the complete cross-section of the fibers. The intensity plot below shows that the reaction occurs typically over the entire cross-section uniformly.



In addition we are evaluating the possibility of improving the durability of certain non-durable topical finishes, such as fire retardant finishes. Some of these are ionic materials that might be bound to the cellulose by ionic attractions. If they can be bound, they will become permanent and durable. This is an area of study that we are pursuing.


During this year, the following students participated in the project: Adham Tabba, Pruthesh Vargantwar, and Kiran Goli. Also the following faculty participated: Peter Hauser, Brent Smith, and Mohamed Hashem.


We have had contact with numerous industrial, academic and governmental individuals, through presentations, publications and individual discussions, according to the following table.



Contacts

Academic

Industrial

Governmental



12

4


For more information, see our project website at

http://www.ntcresearch.org/projectapp/?project=C04-NS01Figure



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