Bio-processing of polyester fabrics
Enzymatic hydrolysis on synthetic fibers enhances the hydrophillicity and solves the concerns regarding the environmental issues of the textile industry. Lipase hydrolyses ester linkages in Polyethylene Terephthalate (PET) and produces polar hydroxyl and carboxylic groups.
This study aims to know the effect of enzyme treatment on the weight loss of polyester fabrics. The study also investigates the effect of enzyme treatment on the surface modification of the fabrics.
Further the functional group’s presence before and after treatments and the effect of enzyme treatment on the improvement of dye uptake are studied. The test results show that enzymatic process creates less surface damage, weight loss and improved moisture regain dye uptake and shear properties.
Keywords: enzymatic hydrolysis, Polyethylene Terephthalate, weight loss, shear properties
Polyethylene terephthalate (PET) is one of the most commonly used synthetic fibers . Major advantages of PET are high strength, stretch resistance, washability, wrinkle resistance and abrasion resistance [2, 3].
However, PET has undesirable properties such as pilling, static and lack of dyeability associated with its hydrophobic nature. PET fiber has low moisture regain about 0.4% . The most conventional and industrially way to modify polyester fabrics is an alkaline treatment [5, 6, 7]. but alkaline treatment effects on strength of polyester fabrics.
A recent alternative is the use of enzymes in surface modification [8, 9, 10]. Studies about the enzymatic treatment of polyester have been focused on biodegradation of aliphatic polyester using a lipase, and biological synthesis of polymer with enzymes [11, 12].
Only a few studies have been reported regarding enzymatic modification of PET fabric . Improvement hydrophilicity of polyesters by hydrolysis of ester bonds has been reported . These studies focus that the applicable enzymes are lipases and polyesterases.
Lipase is known to hydrolyze water-insoluble esters or triglycerides composed of long-chain fatty acids . Thus, the application and studies about lipases in textile processing have been focused on detergent. If enzymes can hydrolyze ester linkage in PET fabrics, polar hydroxyl (-OH) and carboxyl (-COOH) groups will be formed on the surface of PET fabrics.
As a result, moisture regains and wettability will improve due to the forming of hydrophilic groups on PET fabrics. Carboxyl and hydroxyl groups on PET fabrics can be evaluated through dyeability of disperse dyes.
Materials and methods
In the present work 100%, polyester fabric is taken to know the effect of enzyme treatment on the structural modifications. The fabric specifications and treatment conditions are given in table 1.
The fabrics are subjected to washing treatment to eliminate the presence of impurities as well as finishes. The fabrics are treated with enzymes with varying concentrations, treatment time as well as temperature. The fabrics selected for the experiments are subjected to alkali treatment as well as lipase treatment with different concentrations namely 5%, 10%, and 15%.
The fabrics are dyed with different shade percentages namely 1%, 2%, and 5% on weight of the fabric. The treated fabrics are dyed using disperse dye with carrier method for polyester. The fabric weave is a plain weave the chemicals used in this work was laboratory grade reagents.
|Table 1: Materials specifications|
|Fabric type||Linear density||Ends/inch||Picks/inch||Thickness (mm)||GSM|
|Polyester (100%)||75*150 D||120||94||0.18||82|
Results and discussions
3.1 Influence of lipase treatment on weight loss of polyester fabrics
|Table 2: Effect of lipase treatment on weight loss of polyester|
|Alkaline treated weight loss (%)||7.14%||12%||22%|
|Lipase treated weight loss (%)||2%||2.6%||4.6%|
It is understood from table 2 that the increase in concentration of enzyme causes increase in weight loss in both the cases. The weight loss is very high for alkaline treated whereas the loss in weight of lipase treated is very low for the similar concentrations.
3.2 Effect on absorbency
|Table 3: Influence of lipase treatment on absorbency of polyester|
|Fabric type||Wicking height (Cm)||Drop test (Sec)|
|Alkaline treated fabric||5.9||3.5|
|Enzyme treated fabric||6||2.8|
|Dyed alkaline treated||6.0||3.4|
|Dyed lipase treated fabric||7||3.0|
From table 3 it is understood that lipase treated samples are having higher absorbency characteristics compared with the untreated fabrics and alkaline treated fabrics.
3.3 Effect of lipase treatment on surface characteristics of polyester fabrics
The enzyme treated polyester and blended samples are analyzed through a Scanning Electron Microscope (SEM) to know the effect of enzyme treatment on the surface etching.
The fabric samples are magnified to (5000X).The SEM photographs of the Alkaline treated, lipase treated samples are magnified to understand the effect of treatments respectively. The extent of damage is shown in figure 1.
3.4 Effect of lipase treatment on moisture regain
The fourier transform infra-red spectroscopy tests reveal the additional functional groups due to alkaline and enzymatic hydrolysis. The addition of hydroxyl groups in polyester is responsible for the hydrophillicity.
The following comparative FT-IR spectrum reveals the modification in the functional chains which are responsible for the property changes.
From Figure 2 it is noted that the following additional groups are present in the treated fabrics. The group’s presence is identified as aromatic ring, alkynes, esters, hydrogen-bonded and carboxylic acids.
The stretching in the region of 3600-3200 is responsible for the hydrophillicity of lipase and alkaline hydrolyzed polyester. The stretching is very high in the case of lipase hydrolyzed polyester which makes the enzyme-treated more hydrophilic. It is also noted the presence of basic functional groups inherent in the polyester materials.
3.5 Effect of lipase treatment on water vapor permeability of polyester
|Table 4: Water vapor permeability of lipase treated polyester|
|Treatment type||Sample code||Water vapor permeability(gms/m2/day)|
|Untreated polyester fabric (100%)||PU||1260|
|Alkaline treated polyester fabric||PA||1660|
|Lipase treated polyester fabric||PL||1980|
|Dyed alkaline treated||PAD||1820|
|Dyed lipase treated fabric||PLD||2761|
From table 4 it is understood that the alkaline and lipase treated polyester fabrics are having improved water vapor permeability when compared with the untreated polyester fabrics. It is mainly due to the degradation of chain links and the addition of hydroxyl groups.
3.6 Effect of enzyme treatment on dye uptake of polyester fabrics
The alkaline treated, lipase treated and dyed fabrics are tested by reflectance type spectrophotometer to know the K/S values. These values help to understand the difference in luster as well as color values. The treatment offers better dye uptake which enhances the color values.
|Table 5: Polyester fabric K/S values|
|Type of treatment||Sample code||Wave length(nm)/ K/S Value|
|Alkaline treated dyed||PAD||3.904||5.897||4.167||1.503||0.169||0.023||0.014|
|Lipase treated dyed||PLD||4.021||5.79||3.685||1.318||0.146||0.018||0.012|
From table 5 it is understood that lipase treated fabrics shows higher reflectance values and lower K/S values. A similar trend is observed in dyed fabrics. This clearly shows that treatment enhances the dye uptake of the polyester fabrics.
3.7 Effect of enzyme treatment on the low-stress mechanical properties of polyester
The Kawabata evaluation tests are carried out for lipase treated and untreated fabrics of polyester. Compression and shear properties are evaluated since it reveals the effectiveness of the enzyme treatment.
|Table 6: Effect of lipase treatments on compression and shear properties of polyester|
|Fabric type||Treatment type||Sample code||LC||WC(gf cm/cm2)||RC(%)||G(gf/cm. deg)||2HG(g/cm)||2HG5(g/cm)|
|Dyed alkaline treated||PAD||0.304||0.070||42.06||0.57||0.78||2.20|
|Dyed lipase treated||PLD||0.308||0.064||54.69||0.59||0.66||2.13|
|WC- Compression Energy RC- Compression Resilience LC-Linearity of Compression Thickness|
From Table 6 it is understood that lipase treatment reduces the linearity of compression and compression energy in polyester and the blends.
The compression resiliency enhances for polyester fabrics whereas in polyester/cotton blends the effect is not much noticed due to the presence of blend component. The enzyme treatment makes the fabric much softer and it retains its original shape as quickly as possible while applying low-stress load.
It is possible to infer that lipase treatment makes the polyester fabric with low shear rigidity which indicates that the fabric will conform to three-dimensional structures while applying low stress.
Lipase enzyme attacks the polymer chain, which causes a mild etching offers low weight loss due to surface level etching. The treated fabrics are having improved water vapor permeability when compared with the untreated polyester fabrics.
It is mainly due to the degradation of chain links and the addition of hydroxyl groups and enhances the dye uptake of the polyester fabrics.
The compression resiliency enhances for polyester fabrics makes the fabric much softer and it retains its original shape as quickly as possible while applying low-stress load and makes the polyester fabric with low shear rigidity.