# Changes in Fabric Surface Pilling under Laser Ablation

^{1}

^{2}

^{3}

^{*}

## Abstract

**:**

## 1. Introduction

- extraction of loose threads from the yarn that makes up the fabric
- the generation of pills, also called combing the fibers
- pill growth
- shaping the structure of the pills
- changes inside the core and ligament of pills
- detachment of pills.

## 2. Materials and Methods

#### 2.1. Textile Characteristic

^{2}and were considered to have a high degree of resistance to unwanted pilling. They differed in terms of the chemical composition of the fibers. Knit fabric F1 was made entirely of polyamide, F2 was a mixture of polyester and polyacrylonitrile in ratio of 65:35, respectively, and F3 was cotton with an almost 32% polyamide admixture.

#### 2.2. Process of Laser Modification

#### 2.3. Methods of Pilling Assessment

- Manual test T1, in which the knitted fabric was rubbed with the speed 23–25 cm/s for 15 s with a harsh hard fiber brush at a constant pressure of 2 N controlled by a strain gauge;
- Manual test T2, in which the knitted fabric was rubbed with the speed 23–25 cm/s for 15 s with an unglazed ceramic plate at a constant pressure of 1 N;
- Martindale’s test MT, carried out in accordance with the Polish Norm introducing the International Norm PN-EN ISO 12945-2: 2002 standard [18] for 5000 friction cycles, at a constant pressure of 100 N, diameter 20 cm.

#### 2.4. Textile Image Acquisition

#### 2.5. Assessment of Pilling Texture

_{P}located above the fabric surface and regarded as a separated image J(x,y,z). We have described the detection principle of this layer in a previous article [19].

_{P}located above the fabric surface.

_{OTSU}(I) is evaluated based on the intensities of the denoised image I(x,y,z). The thresholding in Equation (4) determines the fraction f

_{P}of pixels with brightness similar to the fabric layer. This corresponds to the outlying fibers of pilling in the L

_{P}layer. The fraction f

_{P}is evaluated as

_{P}∈ L

_{P}belongs to the layer L

_{P}and V

_{P}is the volume of the layer expressed in voxels.

_{B}as another fabric pilling measure. This feature of the image texture increases with J

_{B}image space filled by protruding fibers, which also increases J

_{B}internal complexity. The fractal dimension is evaluated for the boundary image J

_{E}obtained as the exclusive disjunction of J

_{B}and its morphological erosion with the spherical structuring element ${S}_{E}$ of the unit radius (Equation (6)) [49,50].

_{E}is computed for each box of size ${\u03f5}_{i}=s,s/2,s/4,\dots ,2$ starting with the initial size s equal to the smallest image dimension rounded to the power of two.

#### 2.6. Statistical Analysis

_{p}and f

_{D}for the sample groups. It was also used to determine whether any of the group means were significantly different statistically depending on the laser power used. ANOVA analysis was preceded by verification of the data series for the assumptions of normality in the value distribution and the homogeneity of variance, using the Shapiro–Wilk test [54] and the Brown–Forsythe test [55], consecutively, at a level of significance α = 0.05. The omega-squared (ω²) coefficient was used as an effect size measure to describe the part of the variance in the pilling indicator that is explained by the predictor (laser power used for fabric treatment) [56].

## 3. Results

_{P}defined in Equation (5) and the fractal dimension f

_{D}described in Equation (9).

_{P}and f

_{D}descriptors, where F(5,30) = 17.75, p < 0.000001, ω

^{2}= 0.70 and F(5,29) = 27.07, p < 0.000001, ω

^{2}= 0.78. Among the fabrics tested, the observed effect size index ω

^{2}reaches the highest value in the case of the polyester fabric, indicating a strong relationship between laser ablation and the occurrence of pilling symptoms.

^{2}= 0.45 and F(6, 48) = 8.47, p < 0.0001, and ω

^{2}= 0.41 for the f

_{P}and f

_{D}descriptors, respectively. The values of the ω

^{2}effect coefficient indicate that fabric modification with the laser explains 45% of the pixel fraction variability and 41% of the pilling layer fractal dimension variability observed in the OCT images.

^{2}= 0.60. The decrease in the fractal dimension was very small (2%), and no statistically significant downward trend was observed.

_{P}F(5, 14) = 3.93, p < 0.0473, ω

^{2}= 0.30 and f

_{D}F(5, 14) = 6.93, p < 0.0052, and ω

^{2}= 0.52. The effect size ω

^{2}measure indicates that surface modification by the laser explains 30% of pixel fraction variability and 52% of fractal dimension changeability. This may suggest that the fibers become more resistant to breakage with increasing laser power, and thus the self-cleaning by this polyester fabric is less effective during intensive testing.

## 4. Conclusions

## Author Contributions

## Funding

## Conflicts of Interest

## References

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**Figure 1.**Mechanism of pilling formation, (

**a**) threads emerge from inside the fabric; (

**b**) extraction of loose threads; (

**c**) pills are generated; (

**d**) fabric behavior after laser treatment (melted, connected threads).

**Figure 2.**Mode of operation of the laser during textile modification: $D=26\mathsf{\mu}\mathrm{m}$—laser beam diameter, $x\approx 0.99D$—beam offset assuming O = 0.01 (according to Equation (1)).

**Figure 3.**Microscopic photos and optical coherence tomography (OCT) cross-sections of the laser-modified surface of F1: (

**a**,

**c**)—camera view, (

**b**,

**d**)—OCT view; upper row (

**a**,

**b**)—0 W, lower row (

**c**,

**d**)—16 W.

**Figure 4.**Pilling scale as described in standard PN-EN ISO 12945-2:2002 [18].

**Figure 6.**Flowchart of the applied algorithm: I—acquired fabric OCT image; J—image of the pilling layer L

_{P}; J

_{B}—result of image J binarization, J

_{E}—image of J

_{B}boundary objects.

**Figure 7.**Pilling grade of textiles determined after the Martindale test MT, based on the five-point rating scale (PN-EN ISO 12945-2:2002) [18].

**Figure 8.**Perspective view of the fabric surface and two-dimensional fabric cross-section obtained by OCT, illustrating the appearance of pilling phenomena after abrasion tests T1 and MT. Fabric samples not subjected to laser treatment and subjected to laser ablation with 14 W laser power. The scale of volumetric images is common to all sub images.

**Figure 9.**Plots of the texture descriptors of the pilling layer of the tested fabrics subjected to laser ablation, including both mean feature values and approximated trend lines for the fiber pixel fraction (

**left column**) and fractal dimension (

**right column**), as the laser power increased. Samples: (

**a**), (

**b**) and (

**c**)—fabrics F1, F2, and F3; not pilled samples (NP), after manual abrasion test T1 and test T2, after Martindale test (MT).

Name | Composition | Type | Surface Mass |
---|---|---|---|

(g/m^{2}) | |||

F1 | 100% polyester | single jersey, left–right weave | 240 |

F2 | 65% polyester, 35% polyacrylonitrile | Lacoste blue | 240 |

F3 | 68% cotton, 32% polyamide | smooth knit, left–right weave | 240 |

Wavelength | Pulse Duration | Pulse Energy | Pulse Frequency | Hatching Distance | Scan Speed | Beam Diam. | |
---|---|---|---|---|---|---|---|

(nm) | (ns) | (µJ) | (µHz) | (µm) | (mm/s) | (µm) | |

range | 1060 | 15–220 | 88–198 | 35–290 | 10–40 | 200–2000 | 26 |

test | 1060 | 220 | 88–198 | 35 | 10 | 400 | 26 |

Energy | (µJ) | 88 | 110 | 121 | 132 | 154 | 165 | 176 | 188 | 198 |

Power | (W) | 8 | 10 | 11 | 12 | 14 | 15 | 16 | 17 | 18 |

**Table 4.**Analysis of variance (ANOVA) of the pixel fraction for textiles after laser modification and the Fisher least significant difference (LSD) test for linear trend. NP—not pilled samples, T1, T2—manual abrasion tests, MT—Martindale test. * denotes the Brown–Forsythe correction of F-statistic, n.s. not significant data.

Textile | Test | ANOVA Results | Fisher LSD Test | |||
---|---|---|---|---|---|---|

F | P | ω² | F | p | ||

F1 | T1 | 17.749 * | <0.000001 | 0.699 | 60.940 | <0.000001 |

T2 | 4.670 * | 0.0094 | 0.372 | 9.887 | 0.0020 | |

MT | 3.932 * | 0.0473 | 0.304 | 2.579 | 0.0653 | |

F2 | T1 | 8.555 | <0.00001 | 0.452 | 46.904 | <0.000001 |

T2 | 3.690 | 0.0040 | 0.218 | 10.280 | 0.0012 | |

MT | 2.357 | 0.0871 | 0.279 | 0.973 | 0.1703 | |

F3 | T1 | 5.004 | 0.0022 | 0.543 | 0.843 | 0.1853 |

T2 | 6.005 | 0.0008 | 0.597 | 6.034 | 0.0122 | |

MT | 1.758 | 0.2988 | 0.194 | n.s. | n.s. |

**Table 5.**Analysis of variance (ANOVA) of the fractal dimension for textiles after laser modification and the Fisher LSD test for linear trend. NP—not pilled samples, T1, T2—manual abrasion tests, MT—Martindale test. * denotes the Brown–Forsythe correction of F-statistic, n.s. not significant data.

Textile | Test | ANOVA Results | Fisher LSD Test | |||
---|---|---|---|---|---|---|

F | P | ω² | F | p | ||

F1 | T1 | 27.069 * | <0.000001 | 0.782 | 76.610 | <0.000001 |

T2 | 2.655 * | 0.0698 | 0.222 | n.s. | n.s. | |

MT | 6.926 * | 0.0052 | 0.518 | 5.387 | 0.0179 | |

F2 | T1 | 8.475 * | <0.0001 | 0.415 | 26.452 | <0.00001 |

T2 | 4.012 | 0.0024 | 0.244 | 7.869 | 0.0036 | |

MT | 1.084 | 0.4241 | 0.026 | n.s. | n.s. | |

F3 | T1 | 3.953 | 0.0074 | 0.467 | 0.529 | 0.2382 |

T2 | 5.546 * | 0.0081 | 0.484 | 2.586 | 0.0614 | |

MT | 0.989 * | 0.5298 | 0.018 | n.s. | n.s. |

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**MDPI and ACS Style**

Korzeniewska, E.; Gocławski, J.; Sekulska-Nalewajko, J.; Walczak, M.; Wilbik-Hałgas, B.
Changes in Fabric Surface Pilling under Laser Ablation. *Sensors* **2020**, *20*, 5832.
https://doi.org/10.3390/s20205832

**AMA Style**

Korzeniewska E, Gocławski J, Sekulska-Nalewajko J, Walczak M, Wilbik-Hałgas B.
Changes in Fabric Surface Pilling under Laser Ablation. *Sensors*. 2020; 20(20):5832.
https://doi.org/10.3390/s20205832

**Chicago/Turabian Style**

Korzeniewska, Ewa, Jarosław Gocławski, Joanna Sekulska-Nalewajko, Maria Walczak, and Bożena Wilbik-Hałgas.
2020. "Changes in Fabric Surface Pilling under Laser Ablation" *Sensors* 20, no. 20: 5832.
https://doi.org/10.3390/s20205832