ABSTRACT. improved mechanical stability, wrinkle recovery angles and durable press performance,

Transcription

1 ABSTRACT BILGEN, MUSTAFA. Wrinkle Recovery for Cellulosic Fabric by Means of Ionic Crosslinking. (Under the direction of Peter auser and Brent Smith.) When treated with formaldehyde-based crosslinkers, cellulosic fabrics show improved mechanical stability, wrinkle recovery angles and durable press performance, but N-methylol treatment also causes fabrics to lose strength and later to release formaldehyde, a known human carcinogen. We have discovered that ionic crosslinks can stabilize cellulose using high or low molecular weight ionic materials which do not release hazardous reactive chemicals, but at the same time provide improved wrinkle recovery angles as well as complete strength retention in treated goods. We have varied polyelectrolyte, the ionic content of fabrics, and various features of the application procedure to optimize the results and to develop an in-depth fundamental physical and chemical understanding of the stabilization mechanism.

2 WRINKLE RECVERY FR CELLULSIC FABRIC BY MEANS F INIC CRSSLINKING by MUSTAFA BILGEN A thesis submitted to the Graduate Faculty of North Carolina State University in partial fulfillment of the requirements for the Degree of Master of Science TEXTILE CEMISTRY Raleigh 2005 APPRVED BY: Dr. Peter auser (Chair) Dr. Brent Smith (Co-Chair) Dr. Charles Boss (Minor)

3 DEDICATIN This thesis is dedicated to my family and my wife, Nicole, who supported me with constant love and caring and inspired my interest in studying textile chemistry. ii

4 BIGRAPY Mustafa Bilgen was born in December 1, 1978 in Erdemli, Turkey. e graduated from Erzurum Science igh School in June e received the Bachelor of Science degree in Textile Engineering from Department of Engineering and Architecture, Uludag University, Bursa, Turkey in July After he graduated he worked as a dyeing and finishing supervisor in Akay Textile Dyeing & Finishing Company for one year before he started to help his father for taking care of the family business. e came to North Carolina State University in January 2004, to continue his education and started his master program in Textile Chemistry under the direction of Dr. Brent Smith and Dr. Peter auser. iii

5 ACKNWLEDGEMENTS I would like to thank to the National Textile Center and North Carolina State University for their financial support. I also would like to thank to my advisors, Dr. auser and Dr. Smith, for their crucial help and patience during my research and preparation of my thesis. iv

6 LIST F CNTENTS LIST F TABLES viii LIST F FIGURES x 1. INTRDUCTIN LITERATURE REVIEW Cellulose chemistry Cellulosic fabric s nature of wrinkling Durable Press finishing of cotton Urea-Formaldehyde derivatives Melamine-Formaldyhe derivatives Methylol derivatives of cyclic ureas Effects of formaldehyde based DP finishes on cellulose Recent developments in non-formaldehyde DP applications Ionic crosslinking Preparation of quaternized polymers Chitosan and its reaction with CTAC Reaction of Cellulose with CTAC Carboxymethylation of cellulose Proposed Research EXPERIMENTAL PRCEDURES Test Materials Equipments Application procedures Pad dry cure Pad batch Exhaustion Analysis and physical property tests Nitrogen analysis FT-IR analysis NMR analysis Wrinkle recovery angles Tensile strength Whiteness index Stiffness Reaction of cellulose with chloroacetic acid Reaction of Cellulose with CTAC Synthesis of compounds Molecular weight determination of chitosan Depolymerization of chitosan and characterization Reaction of chitosan with CTAC Reaction of glycerin and ethylene glycol with CTAC v

7 3.7.5 Reaction of cellobiose and dextrose with CTAC Preparation of fabric samples Crosslinking of carboxymethylated cellulosic fabric Treatment with cationic chitosan Treatment with cationic glycerin Treatment with cationic cellobiose, cationic dextrose and cationic ethylene glycol Treatment with calcium chloride and magnesium chloride Crosslinking of cationic cellulosic fabric Treatment with PCA and BTCA Treatment with EDTA, NTA and EDTA Treatment with oxalic acid, citric acid and malic acid RESULTS & BSERVATINS AND DISCUSSIN Wrinkle recovery angles of conventional durable press finished fabrics Wrinkle recovery angles of polycation treated anionic cellulosic fabrics Wrinkle recovery angles of cationic chitosan treated fabrics Application of paired t-test analysis on cationic chitosan treatments Wrinkle recovery angles of cationic glycerin treatments Wrinkle recovery angles of cationic cellobiose and cationic dextrose treated fabrics Wrinkle recovery angles of calcium chloride and magnesium chloride treated fabrics Discussion of wrinkle recovery angles for polycation treatments Wrinkle recovery angles of polyanion treated cationic cellulosic fabrics Wrinkle recovery angles of PCA and BTCA treated fabrics Wrinkle recovery angles of EDTA, NTA and EDTA treated fabrics Wrinkle recovery angles of oxalic acid, citric acid and malic acid treatments Discussion of wrinkle recovery angles for polyanion treatments Strength data Tensile strength of conventional durable press finished fabric Strength data of polycation treated anionic cellulosic fabrics Strength data of polyanion treated cationic cellulosic fabrics Discussion of strength data of untreated and treated fabrics CIE whiteness index data CIE whiteness index of conventional durable press treated fabric CIE whiteness index of polycation treated anionic cellulosic fabrics CIE whiteness index of polyanion treated cationic cellulosic fabrics Discussion of whiteness index of untreated and treated fabrics Stiffness data Stiffness of conventional durable press treated fabrics Stiffness data of polycation treated anionic cellulosic fabrics Stiffness data of polyanion treated cationic cellulosic fabrics Discussion of stiffness data of untreated and treated fabrics vi

8 5. CNCLUSINS RECMMENDATINS FR FUTURE WRK LIST F REFERENCES APPENDIX Wrinkle recovery angles Breaking strength CIE whiteness index Stiffness Nitrogen analysis vii

9 LIST F TABLES Table 3.2 Results for carboxymethylation of cellulosic fabrics Table 3.3 Scheme of intrinsic viscosity measurement for the low viscosity chitosan Table 3.4 Properties of the Low Viscosity chitosan Table 3.5 The intrinsic viscosity and M v of depolymerized chitosans Table 4.1 Paired t-test results for dry wrinkle recovery angles of cationic chitosan treated fabrics Table 4.2 Paired t-test results for wet wrinkle recovery angles of cationic chitosan treated fabrics Table 4.3 Paired t-test results for dry/wet wrinkle recovery angles of Ca ++ and Mg ++ treated fabrics Table 4.4 Paired t-test results for dry/wet wrinkle recovery angles of PCA and BTCA treated fabrics Table A.1 Dry and wet wrinkle recovery angles for molecular weight of 3.2 x 10 4 g/mole cationic chitosan treated fabrics Table A.2 Dry and wet wrinkle recovery angles for molecular weight of 1.4 x 10 5 g/mole cationic chitosan treated fabrics Table A.3 Dry and wet wrinkle recovery angles for molecular weight of 6.11 x 10 5 g/mole cationic chitosan treated fabrics Table A.4 Dry and wet wrinkle recovery angles for molecular weight of 1.4 x 10 5 g/mole cationic chitosan treated fabrics by exhaustion method Table A.5 Dry and wet wrinkle recovery angles for cationic glycerin treated fabrics Table A.6 Dry and wet wrinkle recovery angles for cationic glycerin treated fabrics by exhaustion method Table A.7 Dry and wet wrinkle recovery angles for cationic cellobiose and cationic dextrose treated fabrics Table A.8 Dry and wet wrinkle recovery angles for calcium chloride and magnesium chloride treated fabrics Table A.9 Dry and wet wrinkle recovery angles for PCA treated fabrics Table A.10 Dry and wet wrinkle recovery angles for BTCA treated fabrics Table A.11 Dry and wet wrinkle recovery angles for EDTA treated fabrics Table A.12 Dry and wet wrinkle recovery angles for NTA treated fabrics Table A.13 Dry and wet wrinkle recovery angles for EDTA treated fabrics Table A.14 Dry and wet wrinkle recovery angles for oxalic, malic and citric acid treated fabrics Table A.15 Breaking strength data for molecular weight of 3.2 x 10 4 g/mole cationic chitosan treated fabrics Table A.16 Breaking strength data for molecular weight of 1.4 x 10 5 g/mole cationic chitosan treated fabrics viii

10 Table A.17 Breaking strength data for molecular weight of 6.11 x 10 5 g/mole cationic chitosan treated fabrics Table A.18 Breaking strength data for cationic glycerin treated fabrics Table A.19 Breaking strength data for calcium chloride and magnesium chloride treated fabrics Table A.20 Breaking strength data for PCA treated fabrics Table A.21 Breaking strength data for BTCA treated fabrics Table A.22 Whiteness index data for molecular weight of 3.2 x 10 4 g/mole cationic chitosan treated fabrics Table A.23 Whiteness index data for molecular weight of 1.4 x 10 5 g/mole cationic chitosan treated fabrics Table A.24 Whiteness index data for molecular weight of 6.11 x 10 5 g/mole cationic chitosan treated fabrics Table A.25 Whiteness index data for CG treated fabrics Table A.26 Whiteness index data for calcium and magnesium chloride treated fabrics -140 Table A.27 Whiteness index data for PCA treated fabrics Table A.28 Whiteness index data for BTCA treated fabrics Table A.29 Stiffness data for molecular weight of 3.2 x 10 4 g/mole cationic chitosan treated fabrics Table A.30 Stiffness data for molecular weight of 1.4 x 10 5 g/mole cationic chitosan treated fabrics Table A.31 Stiffness data for molecular weight of 6.11 x 10 5 g/mole cationic chitosan treated fabrics Table A.32 Stiffness data for cationic glycerin treated fabrics Table A.33 Stiffness data for calcium chloride and magnesium chloride treated fabrics 144 Table A.34 Stiffness data for PCA treated fabrics Table A.35 Stiffness data for BTCA treated fabrics Table A.36 Nitrogen analysis data for molecular weight of 3.2 x 10 4 g/mole cationic chitosan treated fabrics Table A.37 Nitrogen analysis data for molecular weight of 1.4 x 10 5 g/mole cationic chitosan treated fabrics Table A.38 Nitrogen analysis data for molecular weight of 6.11 x 10 4 g/mole cationic chitosan treated fabrics Table A.39 Nitrogen analysis data for cationic glycerin treated fabrics ix

11 LIST F FIGURES Figure 2.1 Molecular structure of a cellulose polymer chain Figure 2.2 Crystalline and amorphous structure of cellulose Figure 2.3 Molecular structure of DMDEU Figure 2.4 Molecular structure of BTCA Figure 2.5 Reaction of chitosan with CTAC in alkaline conditions Figure 2.6 Reaction of cellulose with CTAC in alkaline conditions Figure 2.7 Molecular structure of carboxymethyl cellulose Figure 3.1 Reactions of cellulose with CAA that impart an anionic character Figure 3.2 Reactions of cellulose with CTAC that impart a cationic character Figure 3.3 uggins plot of ή sp /c versus c for the cationic chitosan Figure 3.4 Reaction of chitosan with CTAC Figure 3.5 Conductometric titration curve of cationic chitosan Figure 3.6 FTIR spectrum of deacetylated chitosan Figure 3.7 FTIR spectrum of cationic chitosan Figure NMR spectrum of deacetylated chitosan Figure NMR spectrum of -substituted and N-substituted cationic chitosan Figure 3.10 Reaction of glycerin with CTAC Figure 3.11 Crosslinked anionic cellulose with calcium Figure 3.12 Crosslinked cationic cellulose with BTCA Figure 4.1 Effect of carboxyl content and concentration on dry wrinkle recovery angles of cationic chitosan treated fabrics Figure 4.2 Effect of carboxyl content and concentration on wet wrinkle recovery angles of cationic chitosan treated fabrics Figure 4.3 Effect of carboxyl content and concentration on %Nitrogen content of cationic chitosan treated fabrics Figure 4.4 The relationship between %Nitrogen content of the fabrics and dry/wet wrinkle recovery angles Figure 4.5 Effect of molecular weight of chitosan and concentration on dry wrinkle recovery angles of cationic chitosan treated fabrics Figure 4.6 Effect of molecular weight of chitosan and concentration on wet wrinkle recovery angles of cationic chitosan treated fabrics Figure 4.7 Effect of carboxyl content and concentration on dry wrinkle recovery angles of cationic glycerin treated fabrics Figure 4.8 Effect of carboxyl content and concentration on wet wrinkle recovery angles of cationic glycerin treated fabrics Figure 4.9 Effect of carboxyl content and concentration on %Nitrogen content of cationic glycerin treated fabrics Figure 4.10 The relationship between %Nitrogen content of the fabrics and dry/wet wrinkle recovery angles x

12 Figure 4.11 Effect of carboxyl content on dry wrinkle recovery angles of calcium and magnesium treated fabrics Figure 4.12 Effect of carboxyl content on wet wrinkle recovery angles of calcium and magnesium treated fabrics Figure 4.13 Effect of %Nitrogen fixed and concentration on dry wrinkle recovery angles of PCA treated fabrics Figure 4.14 Effect of %Nitrogen fixed and concentration on wet wrinkle recovery angles of PCA treated fabrics Figure 4.15 Effect of %Nitrogen fixed and concentration on dry wrinkle recovery angles of BTCA treated fabrics Figure 4.16 Effect of% Nitrogen fixed and concentration on wet wrinkle recovery angles of BTCA treated fabrics Figure 4.17 Effect of %Nitrogen fixed and concentration on dry wrinkle recovery angles of EDTA treated fabrics Figure 4.18 Effect of %Nitrogen fixed and concentration on wet wrinkle recovery angles of EDTA treated fabrics Figure 4.19 Effect of treatment on dry wrinkle recovery angles Figure 4.20 Effect of treatment on wet wrinkle recovery angles Figure 4.21 Effect of carboxyl content and concentration on breaking strength of the cationic chitosan (molecular weight of 1.4 x 10 5 g/mole) treated fabrics Figure 4.22 Effect of carboxyl content and concentration on breaking strength of the cationic glycerin treated fabrics Figure 4.23 Effect of carboxyl content and concentration on breaking strength of the calcium and magnesium treated fabrics Figure 4.24 Effect of %Nitrogen content and concentration on breaking strength of the PCA treated fabrics Figure 4.25 Effect of %Nitrogen content and concentration on breaking strength of the BTCA treated fabrics Figure 4.26 Effect of treatment on breaking strength Figure 4.27 Correlation between wet wrinkle recovery angles of cationic chitosan (molecular weight of 1.4 x 10 5 g/mole) treatment and tensile strength Figure 4.28 Correlation between wet wrinkle recovery angles of PCA treatment and tensile strength Figure 4.29 Effect of carboxyl content and concentration on whiteness index of the cationic chitosan (molecular weight of 1.4 x 10 5 g/mole) treated fabrics Figure 4.30 Effect of carboxyl content and concentration on whiteness index of the cationic glycerin treated fabrics Figure 4.31 Effect of carboxyl content and concentration on whiteness index of the calcium chloride and magnesium chloride treated fabrics Figure 4.32 Effect of %Nitrogen fixed and concentration on whiteness index of the PCA treated fabrics xi

13 Figure 4.33 Effect of %Nitrogen fixed and concentration on whiteness index of the BTCA treated fabrics Figure 4.34 Effect of treatment on whiteness index Figure 4.35 Effect of carboxyl content and concentration on stiffness of the cationic chitosan (molecular weight of 1.4 x 10 5 g/mole) treated fabrics Figure 4.36 Effect of carboxyl content and concentration on stiffness of the cationic glycerin treated fabrics Figure 4.37 Effect of carboxyl content and concentration on stiffness of the calcium chloride and magnesium chloride treated fabrics Figure 4.38 Effect of %Nitrogen fixed and concentration on stiffness of the PCA treated fabrics Figure 4.39 Effect of %Nitrogen fixed and concentration on stiffness of the BTCA treated fabrics Figure 4.40 Effect of treatment on stiffness xii

14 1. INTRDUCTIN The textile market has shown an interest in the demand for easy care, wrinkleresistant for cellulosic fabrics over the years. Untreated cellulose has poor recovery, because cellulose is stabilized by hydrogen bonds within and between cellulose chains. Moisture between the polymer chains can invade the cellulose structure and can temporarily release the stabilizing hydrogen bonds and hydrogen bonds in cellulose experience frequent breaking and reforming when extended and newly formed hydrogen bonds tend to hold cellulose chain segments in new positions when external stress is released. Preventing wrinkling of cellulosic fabric can be accomplished by the crosslinking of polymer chains, thus making intermolecular bonds between chains that water cannot release. In a typical durable-press (DP) treatment, some hydrogen bonds are replaced with covalent bonds between the finishing agent and the fiber elements. Because covalent bonds are much stronger than hydrogen bonds, they can resist higher external stress. ence, treated cellulose has a higher initial modulus and better elastic recovery. After the external force is released, the energy stored in the strained covalent bonds provides the driving force to return chain segments back to their original positions. Formaldehyde-based cellulose crosslinking was a very important textile chemical breakthrough of the 1930's, and is still the basis for a vast array of modern finished cotton products today. N-methylol crosslinkers have the biggest use in durable press finishing. They give fabrics crease resistance, shrinkage control, anti-curl, and durable press, but 1

15 they also impart strength loss and release formaldehyde, a known human carcinogen. [1] Today s textile industry has for a long time been searching for durable press finishes that can give same results as formaldehyde based finishes, but cause less strength loss and no formaldehyde release. For example, polycarboxylic acids and citric acid have been used with varying degrees of success. [2, 3] We have developed multiple methods of forming ionic crosslinks to give nonwrinkle effects to cellulosic fabric. [4] These includes, (1) treatment of cellulose with an anionic material and reacting with a polycation, (2) treatment of cellulose with a cationic material and then application of a polyanion, (3) treatment of cellulose with a precondensate of an ionic reactive material and a polyelectrolyte of the opposite charge. The performance of crosslinkers can be measured by dry and wet wrinkle recovery angle (WRA). Dry WRA is important for outerwear clothing to help resist dry wrinkling during wearing, but wet WRA is more important for bedding which is almost never ironed and must resist wrinkling during laundering. We observed simultaneous enhancements of both wet and dry WRA as well as significant strength gain and excellent washing durability. Polyelectrolytes are strongly bond and thus do not desorb during laundering. The chemicals are common industrial reactants and do not have unusual safety or environmental issues. Processes use existing equipment and no high temperature curing is necessary. In addition, ionic crosslinks may have other important advantages, such as antimicrobial activity and enhanced dyeability. 2

16 2. LITERATURE REVIEW 2.1 Cellulose chemistry We can only understand chemical as well as physical properties of cellulose by the knowledge of both chemical nature of the cellulose molecules and their structural and morphological arrangement in the solid, mostly fibrous, state. For example reactivity of the functional sites in the cellulose molecules and structural characteristics of polymers such as; inter- and intramolecular interactions, and size of crystallites and fibrils. These structural characteristics of the cellulosic polymers influence the physico-mechanical properties utilized in the textile industry. The largest part of the cellulosic polymers used for textile substrates comes from cotton. Cotton is a soft fiber that grows around the seeds of the cotton plant. The fiber is most often spun into thread and used to make a soft, breathable textile. Cotton is a valuable crop because only about 10% of the raw weight is lost in processing. [5] nce traces of wax, protein, etc. are removed, the remainder is a natural polymer of pure cellulose. This cellulose is arranged in a way that gives cotton unique properties of strength, durability, and absorbency. After scouring and bleaching, cotton is 99% pure cellulose. [6] Cellulose is a macromolecule made up of anhydroglucose units united by 1, 4, oxygen bridges as shown in Figure 2.1. The anhydroglucose units are linked together as beta-cellobiose; therefore, anhydro-beta-cellobiose is the repeating unit of the polymer chain. The number of these repeat units that are linked together to form the cellulose polymer is referred to as the degree of polymerization and is between 1000 and [7] 3

17 Cellulose n Figure 2.1 Molecular structure of a cellulose polymer chain The cellulose chains within the cotton fibers tend to be held in place by hydrogen bonding. These hydrogen bonds occur between the hydroxyl groups of adjacent molecules and are more prevalent between the parallel, closely packed molecules in the crystalline areas of the fiber as shown in Figure 2.2. [8] Figure 2.2 Crystalline and amorphous structure of cellulose The chemical characters of the cellulose molecules are determined by the sensitivity of the three-hydroxyl groups, one primary and two secondary, in each repeating cellobiose unit of cellulose, which are chemically reactive groups. These groups can undergo substitution reactions in procedures designed to modify the cellulose fibers such 4

18 as esterification and etherification or in the application of dyes and finishes for crosslinking. The hydroxyl groups also serve as principal sorption sites for water molecules. Directly sorbed water is firmly chemisorbed on the cellulosic hydroxyl groups by hydrogen bonding. [8] f particular interest in the case of cellulosic fibers is the response of their strength to variations in moisture content. Generally, in the case of regenerated and derivative cellulosic fibers, strength decreases with increasing moisture content. In contrast, the strength of cotton generally increases with increased moisture. The contrast seen between the fibers in their response to moisture is explained in terms of intermolecular hydrogen bonding between cellulose chains and their degree of crystallinity. [8] 2.2 Cellulosic fabric s nature of wrinkling The textile market has shown an interest in the demand for easy care, wrinkleresistant for cellulosic fabrics over the years. Improvements in crease angle recovery property are obtained by chemical treatments, which improve the ability of fibers to maintain configurations in which they are treated. [9] Untreated cellulose has poor recovery, because hydrogen bonds in cellulose experience frequent breaking and reforming when extended, and newly formed hydrogen bonds tend to hold cellulose chain segments in new positions when external stress is released. In a typical durable-press treatment, some hydrogen bonds are replaced with covalent bonds between the finishing agent and the fiber elements. Because covalent bonds are much stronger than hydrogen bonds, they can resist higher external stress. ence, treated cellulose has a higher initial 5

19 modulus and better elastic recovery. After the external force is released, the energy stored in the strained covalent bonds provides the driving force to return chain segments back to their original positions. owever, chemical treatment on cellulose also causes the loss of mechanical properties. [10] The classical explanation to this problem is that traditional crosslinks are too rigid to allow cellulose chain segments to move. 2.3 Durable Press finishing of cotton Durable press is shaping a garment and then treating it in such a way that after wearing and washing it will return to its pre-set shape. In order to produce non-wrinkle cellulosic fabrics the durable press finishing has been developed. The original process for the production of crease resistant fabrics was developed in [11] DP finishes have been marketed ever since. Durable press is accomplished by resin treatments. The main purpose of resin treatments is to overcome a serious drawback of cellulosic fabrics, for example their ease of wrinkling, which requires ironing after washing. [12] Ideally, a DP finished fabric will wash and dry to a completely smooth state. The usual method of production of crease resistant fabric consists of padding fabric trough a crosslinking agent along with a catalyst and other additives, drying at o C followed by curing at o C for 2-3 minutes. [13] The resulting fabric has the ability of recovering from creases both when fabric is wet and dry. The selection of crossslinking agents for DP finishing is important. There are a large number of cross linker available. Some of the most common reagents are urea-formaldehyde derivatives, melamine- 6

20 formaldehyde derivatives and methylol derivatives. All of these reagents used for DP of cellulosic fabric with varying degrees of success Urea-Formaldehyde derivatives The first widely used crosslinking agent for DP finishing was urea-formaldehyde adducts. These products are mostly prepared at the finishing plant; also precondensate are available in the market. The treatment of fabrics with urea-formaldehyde resin involves padding the fabric through precondensate and an acid catalyst, drying, curing and washing. The advantages of urea-formaldehyde resins are the low cost and high efficiency. The disadvantages are poor stability of the agent, poor durability and imparting chlorine retention to the fabric. The chlorine retention is due to the presence of the N groups which react with chlorine from the bleach or laundry bath. [14, 15, 16] The reaction of N groups and chlorine produces hydrochloric acid and it is a strong acid that causes tendering and yellowing of cellulose Melamine-Formaldyhe derivatives The most commonly used melamine product is trimethylol melamine. It has good stability and durability. Trimethylol-melamine is more expensive than urea-formaldehyde. It picks up and retains chlorine, it also yellows the bleached fabric but the fiber degradation due to strong acid is avoided because of basicity of the compound. [17, 18] 7

21 2.3.3 Methylol derivatives of cyclic ureas These compounds are also referred to as fiber reactants, because they only react with the cellulose instead of themselves. As a result insoluble resin on the surface of the fabric is absent hence the finished fabric have a softer hand. The members of this group are: (a) Dimethylol ethylene urea (DMEU) has high reaction efficiency and low price. [19] It can produce high wrinkle recovery angles at low add-ons. The finish with DMEU is sensitive to acids and can be destroyed by acid treatment during laundering. (b) Dimethylol propylene urea (DMPU) is suitable for white goods, since it does not produce yellowing on heating. [20] Another advantage of it is that not giving any odor. But the finish is not susceptible to chlorine retention damage. It is more expensive than others in the group. (c) Dimethylol dihydroxy ethylene urea (DMDEU) as shown in Figure 2.3. It is the most commonly used DP finish agent and gives excellent crease angle recovery. [21, 22] N N DMDEU Figure 2.3 Molecular structure of DMDEU 8

22 It shows some chlorine retention therefore it is not recommended for white goods. It does not effect the lightness of the dyes hence it is dominating the colored garments durable press finishing Effects of formaldehyde based DP finishes on cellulose Formaldehyde-based N-methylol reagents are the most common DP reagents. But these reagents produce losses in tensile strength of cotton due to depolymerization of cellulose chains. Cellulose depolymerization occurs with a polycarboxylic acid or a Lewis acid, which are catalysts for formaldehyde based resins. As a result they cause a high degree of depolymerization. A direct correlation between tensile strength loss of the treated cotton and the molecular weight of cellulose was found. [23] Severe tensile strength loss is a major disadvantage of DP finished cotton fabrics, and it continues to be the major obstacle for DP applications. Most of the studies of mechanical strength of durable press finished cotton fabrics in the past have focused on changes in the gross properties of cotton fabrics, such as tensile strength and abrasion resistance. Another disadvantage of N-methylol reagents is later formaldehyde release. In recent years there have been extensive efforts to find non-formaldehyde alternatives due to increasing concern with health risks associated with formaldehyde. n the other hand, the final textile products not only have to be eco-friendly, but also have to be produced by clean technologies. Crosslinking of cellulose with N-methylol crosslinking agents to impart wrinkle-resistance, shrink proofing, and smooth drying properties by virtue of chemical reaction with cellulosic hydroxyl groups to form covalent crosslinks in the interior of 9

23 cellulosic fibers have successfully been done. owever, at the present time, presence of formaldehyde in the finished product, working atmosphere, as well as in wastewater streams is considered as highly objectionable due to the mutagenic activity of various aldehydes, including formaldehyde. [24] 2.4 Recent developments in non-formaldehyde DP applications Extensive research has attempted to develop nonformaldehyde crosslinking agents to replace N-methylol compounds that release formaldehyde during production and storage, which is proven to be carcinogenic. [25] Durable press finishing, used to overcome wrinkling problems in cotton fabric for some years, involves chemical crosslinking agents that covalently crosslink with hydroxyl groups of adjacent cellulose polymer chains within cotton fibers. This crosslinking not only results in the fabric's wrinkle resistance, but also in discoloration and impairment of fabric strength and of other mechanical properties. The early chemical agents used for crosslinking with cellulose were mostly formaldehyde and formaldehyde derivatives, which can form ether bonds with cellulose. DMDEU is the most widely used crosslinking agent because it provides good durable press properties at a lower cost and an acceptable level of detrimental effects on fabric strength and whiteness compared to other N-methylol agents. owever, fabric treated with DMDEU tends to release formaldehyde vapors during processing, storage, and consumer use. Because formaldehyde is toxic to human beings, several attempts have been made to replace it with formaldehyde-free crosslinking agents. 10

24 Several polycarboxylic acids have served as durable press agents. Carboxylic groups in polycarboxylic acids are able to form ester bonds with hydroxyl groups in cellulose. The main advantages of polycarboxylic acids are that they are formaldehydefree, do not have a bad odor, and produce a very soft fabric hand. BTCA (1.2,3,4- butcnetetracarboxylic acid) is the most effective polycarboxylic acid for use as a durable press agent as shown in Figure 2.4. In the presence of sodium hypophosphite monohydrate as catalyst, BTCA provides almost the same level of durable press performance and finish durability with laundering as the conventional DMDEU reactant, but its high cost may be an obstacle to a mill's decision to use it as a replacement for the conventional durable press reactant. As with DMDEU, fabrics treated with polycarboxylic acids generally lose their strength, [26] probably due to excess crosslinking with cellulose chains. This may be tackled by using long-chain polycarboxylic acids, which can be obtained through copolymerization of two unsaturated polycarboxylic acids. BTCA satisfies many desirable requirements such as durability to laundering and durable press performance. Crosslinking of cellulose molecules with BTCA increases fabric wrinkle resistance at the expense of mechanical strength. [27] 11

25 C C C C BTCA Figure 2.4 Molecular structure of BTCA Severe tensile strength loss diminishes the durability of finished cotton garments. The factors involved in strength loss of cotton fabric treated with BTCA include acid catalyzed degradation of cellulose molecules and their crosslinking. The common catalysts for polycarboxylic acids are phosphorous-containing compounds, although their use has disadvantages such as high cost, strength loss and raises some environmental concerns. In order to decrease strength retention other catalysts have been proposed; among these is boric acid, [28] which was added to increase strength of the treated fabrics. With this treatment, durable press properties were similar to those obtained with sodium hypophosphite; moreover the mechanical resistance improved. A previous study [29] indicated that cellulosic fabric treated with a copolymer made with maleic and acrylic acids possesses the same level of wrinkle resistance as with BTCA, while tensile strength retention improves slightly. Another disadvantage of polycarboxylic acid finishing is yellowing of the treated fabric. It is proposed that the use of a copolymer between acrylic and maleic acids as a durable press finishing agent can improve crease angle recovery for cotton fabric. [29] owever, the copolymer treatment does not provide as good tensile strength and whiteness as DMDEU. 12

26 Chitosan citrate has been evaluated as non-formaldehyde durable press finish to produce wrinkle-resistance and antimicrobial properties for cotton fabrics. [30] The carboxylic groups in the chitosan citrate structure were used as active sites for its fixation onto cotton fabrics. The fixation of the chitosan citrate on the cotton fabric was done by the padding of chitosan citrate solution onto cotton fabrics followed by a dry - cure process. The factors affecting the fixation processes were systematically studied. The antimicrobial activity and the performance properties of the treated fabrics, including tensile strength, wrinkle recovery, wash fastness and whiteness index, were evaluated. The finished fabric shows adequate wrinkle resistance, sufficient whiteness, high tensile strength and more reduction rate of bacteria as compared to untreated cotton fabric. A non-polluting system of applying an easy-care finish to cotton fabrics has been proposed. [31] The new formulation is based on an aqueous system of BTCA-chitosansodium hypophosphite and was applied by the traditional pad-dry-cure method to an Egyptian poplin. The variables studied were the concentrations of BTCA and chitosan, the time and temperature of polymerisation. The study also included a comparison with other traditional or recommended systems. The treated fabric was tested for crease recovery angle, resistance to traction, elongation to breakage, rigidity, wetability, whiteness, nitrogen content and dyeability. It was concluded that the new formulation gave comparable if not better results than the traditional treatments. 13

27 2.5 Ionic crosslinking Ionic crosslinking has been used in the polymer industry for various applications. It is an alternative to covalent crosslinks. It is well known that the thermal resistance, durability, abrasion resistance, chemical resistance, etc., of a polymer are improved by crosslinking. For example, acrylic copolymer sizes have been used for improving the weaving properties of polyester filament warps. [32] Acrylic sizes produce good abrasion resistance, high strength, good adhesion and easy removability. But when exposed to high humidity many of the acrylics absorb water and cause blocking on the beam. In order to improve the stability of acrylic sizes divalent cations are used for reduction of the moisture regain. Calcium and magnesium ions were used [32] for reducing the water sensitivity of sizes. These cations form ionic crosslinks between the polymer chains and stabilize the structure against moisture. Also these crosslinks improved the strength properties of the polymer film. The copolymer of propylene and maleic anhydride is also crosslinked by ionic bonding. It is considered that the ionic crosslinking by maleic anhydride groups is possible by using not only of magnesium hydroxide but also of other metal compounds. Magnesium 12-hydroxy stearate, zinc oxide, and zinc sulfide were chosen for ionic crosslinking. Accordingly, by changing the kind and content of the metal compounds, the viscosity can be freely controlled. Considering also other rheological characteristics, these ionically crosslinked compounds are assumed to show ideal flow processabilities except for the extrudate appearance [33,34] 14

28 A series of siloxane-based liquid-crystalline elastomers were synthesized by using ionic crosslinking agents containing sulfonic acid groups. The ions aggregated in domains forces the siloxane chains to fold and form an irregular lamellar structure. Ionic aggregates and liquid crystalline segments may be dispersed among each other to form multiple blocks with increasing ionic crosslinking content. [35] In a previous work [36] a vulcanized carboxylated nitrile rubber compound was prepared using a mixed crosslinking system employing a mixture of zinc peroxide and sulphur accelerators as vulcanizing agents to produce ionic and covalent structures. Because of the existence of carboxyl groups in the polymeric chain, crosslinked polymers of ionic nature can be obtained when a bivalent metal oxide, such as zinc oxide, is used as a crosslinking agent. Ionic vulcanized compounds with properties equal to or better than those produced using sulphur accelerators can also be obtained in the same way using metal peroxides. Polyurethanes are a versatile class of materials; their end applications dictate the structure and morphology during synthesis. From the prepolymer stage through chain extension and in the required cases of final crosslinking, there are many ways to influence the final characteristics of the polyurethanes. Crosslinked networks are obtained through ionic crosslinking and the different approaches produce cationic, anionic and Zwitter ionic polyurethanes. These networks find a variety of applications as coatings, adhesives, shoe soles, and vibration damping materials. [37] 15

29 2.6 Preparation of quaternized polymers Conversion to quaternary ammonium salts gives products whose degree of ionization is p-independent. Such polymers can be prepared by reaction of polymers with 3-chloro-2-hydroxypropyl trimethyl ammonium chloride (CTAC) Chitosan and its reaction with CTAC Chitosan is the deacetylated form of chitin, poly [β-(1 4)-2-deoxy-Dglucopyranose], is the second most abundant natural polymer next to cellulose. Chitosan is a linear copolymer composed mainly β-(1 4)-2-amino-2-deoxy-D-glucopyranose and partially β-(1 4)-2-acetamido-2-deoxy-D-glucopyranose residues. [38] Chitosan can be dissolved in diluted acids by being protonated to soluble polyammonium salt. ydroxyl and amino groups of chitosan can react with epoxides by a ring opening reaction in either present of a base or neutral conditions. These reactions were performed previously. [4, 39] Kim at al performed the reaction between chitosan and CTAC at neutral conditions. They proved by FTIR and 1 -NMR that the product they produced had a degree of substitution larger than 60% and substitutions formed at N 2 sites. Because the hydroxyl groups of chitosan are not sufficiently nucleophilic under neutral conditions, N-substituted cationic chitosan can be obtained under neutral conditions. n the other hand; in alkali conditions the hydroxyl groups of chitosan are nucleophilic therefore reaction of chitosan and CTAC produce -substituted cationic chitosan. asem at al performed the reaction under highly alkaline (p=11-12) conditions and they believe that the product was -substituted cationic chitosan and soluble at 16