DOCSUN Silk Lab Reference Report

Micro-Structural Analysis and Physicochemical Properties of 6A Grade Silk

Q: Why does 6A grade silk have a pearlescent luster?

SEM analysis shows that 6A grade mulberry silk fibers have a rounded triangular prism-like cross-section. This geometry refracts incoming light at multiple angles, contributing to the natural pearlescent appearance of silk.

Q: How does the microscopic structure of silk differ from cotton?

Silk fibers show a relatively smooth longitudinal surface and a compact triangular cross-section, while cotton fibers show a collapsed lumen and twisted ribbon-like morphology. These structural differences help explain their different friction, moisture and optical behavior.

Q: Is silk fibroin scientifically considered biocompatible?

Published biomedical literature reports that properly degummed silk fibroin has a strong biocompatibility record. The immunogenicity of raw silk is mainly associated with sericin, which is removed during degumming.

Q: Why do natural fibers usually generate less static electricity than polyester?

Natural fibers such as silk and cotton contain hydrophilic groups and retain more moisture than polyester. Absorbed water molecules can help form conductive pathways for charge dissipation, while hydrophobic synthetic fibers tend to accumulate charge.

Published: February 19, 2026 | Updated: June 28, 2026 | Research format: SEM morphology, digital microscopy, literature review and laboratory validation.

This Silk Lab report summarizes SEM observations, third-party test evidence, comparative fiber analysis and published scientific references related to 6A grade mulberry silk.

1. Abstract

To examine the material characteristics of 6A grade mulberry silk, DOCSUN Silk Lab integrates scanning electron microscopy (SEM), digital optical microscopy, independent GTTC laboratory reports and a review of established biomedical literature. The following report focuses on fiber morphology, optical behavior, friction, hygroscopicity, electrostatic behavior and biological safety.

2. Microscopic Morphology (SEM Analysis)

SEM observation allows the cross-sectional and longitudinal structure of silk fibroin to be examined at a scale that is not visible in ordinary product photography. The two views below help explain both the optical character and tactile profile of mulberry silk.

SEM cross-section of DOCSUN 6A mulberry silk showing rounded triangular prism structure — **Figure 1:** SEM cross-section of DOCSUN 6A mulberry silk showing a rounded triangular prism-like geometry. See Section 4 for GTTC-certified report pages.

Longitudinal SEM view confirming smooth scale-free mulberry silk surface — **Figure 2:** Longitudinal SEM view confirming a smooth, scale-free surface along the silk fiber.

Optical refraction: The non-round cross-sectional geometry of silk behaves as a natural prism. Incoming light is refracted at multiple angles, contributing to the characteristic pearlescent luster of silk.

Surface topography: The longitudinal view shows a relatively smooth fiber surface, without wool-like scales or cotton-like convolutions. This morphology is relevant to friction and tactile smoothness.

3. Comparative Study I: Silk vs. Cotton

Cotton is also a natural fiber, but its morphology differs significantly from silk. Cotton fibers show a collapsed lumen and twisted ribbon-like surface, which affect moisture absorption, surface friction and visual finish.

Cotton cross-section showing collapsed lumen moisture reservoir — **Figure 3:** Cotton cross-section showing the collapsed lumen, a structure associated with moisture absorption.

Cotton longitudinal view showing twisted ribbon structure — **Figure 4:** Cotton longitudinal structure showing twisted ribbon-like convolutions.

Analysis: Cotton's hollow lumen and twisted morphology increase hygroscopic behavior and surface irregularity. By contrast, silk's smoother and more compact structure helps explain its lower surface drag and different optical appearance.

4. Independent Laboratory Validation (GTTC)

The microstructural observations above are supported by physical samples submitted to Guangzhou Inspection Testing and Certification Group Co., Ltd. (GTTC), a CNAS-accredited testing authority with ilac-MRA mutual recognition.

100% Mulberry Silk - GTTC Test Report No. 260049838

Applicant: Docsun Home and Living Co., Ltd. | Test standard: GB/T 36422-2018 | Accreditation: CNAS L10314 | Report issue date: 2026-03-03.

GTTC silk report page showing longitudinal SEM section of DOCSUN mulberry silk — Longitudinal SEM section: smooth, scale-free surface confirmed.

GTTC silk report page showing cross-section of 6A grade mulberry silk — Cross-sectional SEM section: rounded triangular prism-like geometry confirmed.

100% Cotton - GTTC Test Report No. 260049836

Applicant: Docsun Home and Living Co., Ltd. | Test standard: GB/T 36422-2018 | Accreditation: CNAS L10314 | Report issue date: 2026-03-03.

GTTC cotton report page showing longitudinal SEM section of cotton reference — Longitudinal SEM section: twisted ribbon-like cotton structure observed.

GTTC cotton report page showing cross-section of cotton reference sample — Cross-sectional SEM section: kidney-shaped and collapsed lumen morphology observed.

Test results are valid for the submitted samples under GTTC standard terms. Full reports may be requested for verification. Authenticity verification: Silk report code CMLI-6466-04; cotton report code HTSH-1021-44. Official portal: www.gttctech.com.

5. Comparative Study II: Silk vs. Polyester

SEM analysis reveals structural morphology, while digital optical microscopy helps visualize surface reflection and weave behavior. The following images compare natural mulberry silk with synthetic polyester satin.

Digital microscopy of mulberry silk showing diffuse reflection — **Figure 5:** Mulberry silk under digital microscopy. Diffuse reflection creates a soft, pearlescent optical effect.

Digital microscopy of polyester synthetic fiber showing specular reflection — **Figure 6:** Polyester synthetic satin under digital microscopy. Specular reflection produces a sharper glare.

Luster quality: Silk's irregular natural texture and triangular prism-like cross-section scatter light, while polyester's smoother synthetic surface reflects light more directly.
Thermal and airflow behavior: The natural irregularity of silk fibers can support micro-scale air pathways, while mechanically uniform synthetic fibers tend to form a denser barrier.

6. Physical Properties: Friction, Hygroscopicity and Electrostatics

6.1 Tribology: Coefficient of Friction

The tactile smoothness of silk can be evaluated using tribological methods such as tribometers and atomic force microscopy (AFM). Literature on silk fibroin films reports nano-scale surface smoothness and substantial friction reduction under hydrated conditions.

Nano-scale smoothness: De Giorgio et al. (2024) report that regenerated silk fibroin films can exhibit surface roughness (Ra) below 10 nm, reducing sliding resistance at the contact interface^[2].

Hydration lubrication: Under hydrated conditions, silk fibroin can form a water-mediated lubrication layer, with reported coefficient of friction values as low as 0.02-0.10 in selected test conditions^[1].

Table 1: Tribological Performance Data Matrix
Test Subject	Friction Coefficient Range	Performance Benchmark
Silk fibroin film vs. glass - dry	0.25-0.40	Moderate protective coating behavior
Silk fibroin film vs. glass - hydrated	0.02-0.10	Reported as approaching biological lubrication conditions
Silk fibroin suture vs. tissue	30%-50% lower than cotton in selected contexts	Lower tissue abrasion profile
Nanofiber surface roughness (Ra)	< 10 nm	Nano-scale smooth interface

6.2 Electrostatics and Hygroscopicity

Synthetic materials such as polyester are prone to static accumulation because of low moisture regain. In contrast, natural fibers such as silk and cotton contain hydrophilic groups that can bind water molecules and support charge dissipation.

According to Jain et al. (2023) and Hutton et al. (1949), silk fibroin contains polar amino acids and nano-pores that attract water molecules through hydrogen bonding^[3]^[4]. This intrinsic hydration contributes to electrostatic balance under daily contact conditions.

Table 2: Hygroscopicity and Electrostatic Potential Comparison
Material	Moisture Regain	Electrostatic Potential	Key Factors
Mulberry silk fibroin	Approx. 11% (reported range 10%-30%)	Approx. 100-200 mV under daily light friction; approx. 1-2 kV in high-intensity tests	Hydrophilic amino acid groups and nano-pores support moisture absorption and charge dissipation.
Cotton	Approx. 8.5%	Approx. 55-60 mV under daily light friction; below 1.5 kV in high-intensity tests	Abundant hydroxyl groups provide strong hydrophilicity and rapid charge leakage.
Polyester	Approx. 0.4%	Approx. 240-270 mV under daily light friction; above 3.6 kV in high-intensity tests	Low moisture absorption prevents effective charge dissipation, allowing static accumulation.

Note: Low-pressure tests at mV level more closely simulate daily light friction such as fabric-to-skin contact. High-intensity kV tests simulate laboratory rotary friction conditions^[6].

7. Biological Safety: Immunogenicity and Clinical Validation

Scientific literature generally attributes the immunogenic potential of raw silk primarily to sericin. After degumming, the remaining silk fibroin is widely studied as a biocompatible material in biomedical contexts.

Biomaterial classification: Silk fibroin has been used in surgical sutures and tissue scaffolds, and is discussed in biomedical literature as a clinically relevant material^[2].
Low inflammatory response: Purified silk fibroin is reported to induce limited inflammatory cytokine release compared with sericin-containing samples in selected studies^[2].
Cell viability: In vitro studies report high cell viability on silk fibroin substrates, supporting its biocompatibility in controlled test conditions.

Repair-oriented immune response: De Giorgio et al. (2024) discuss silk fibroin scaffolds in relation to immune microenvironment modulation, including pathways associated with M2 macrophage polarization in tissue repair contexts.

Metabolic safety: Silk fibroin can be enzymatically degraded into amino acid components, avoiding some degradation pathways associated with synthetic polymers.

8. Frontier Applications: Silk in Regenerative Medicine and Technology

Beyond textiles, silk fibroin is being studied as a foundational biomaterial for regenerative medicine, bioelectronics and smart textile systems. The research directions below are included to contextualize why silk is considered a high-value natural protein material.

8.1 Bone Tissue Engineering

Li et al. (2022) review silk fibroin scaffolds for bone tissue engineering, noting mechanical support from beta-sheet crystalline regions and the potential to support bone marrow stromal cell behavior^[7].

8.2 Transient Bioelectronics

In organic bioelectronics, silk fibroin is valued for optical transparency, dielectric properties and biodegradability. Researchers are exploring transient sensors that can dissolve after completing their function^[2]^[3].

8.3 Meniscal and Soft Tissue Replacement

Warnecke et al. (2017) reported friction behavior of silk fibroin scaffolds for meniscal replacement, including lubrication performance under biologically relevant conditions^[1].

8.4 Moisture-Responsive Smart Textiles

Jia et al. (2019) demonstrated moisture-sensitive behavior in silk fiber systems, opening research directions for humidity-responsive textile structures^[5].

9. Scientific References

Warnecke, D., et al. "Friction properties of a new silk fibroin scaffold for meniscal replacement." Tribology International 107 (2017).
De Giorgio, G., et al. "Silk Fibroin Materials: Biomedical Applications and Perspectives." Bioengineering 11.2 (2024).
Jain, S., et al. "Silk and its composites for humidity and gas sensing applications." Frontiers in Chemistry 11 (2023).
Hutton, E. A., et al. "The Moisture Regain of Silk: Adsorption and Desorption of Water by Silk at 25 degrees C." Textile Research Journal (1949).
Jia, et al. "Moisture Sensitive Smart Yarns and Textiles from Self-Balanced Silk Fiber Muscles." Advanced Functional Materials (2019).
"Electrostatic Properties of Clothing Fabrics Suitable for Different End-Uses." ResearchGate (2020).
Li, M., et al. "A Comprehensive Review on Silk Fibroin as a Persuasive Biomaterial for Bone Tissue Engineering." International Journal of Molecular Sciences 23 (2022).

10. Frequently Asked Questions

Why does 6A grade silk have a pearlescent luster?

SEM analysis shows that 6A grade mulberry silk fibers have a rounded triangular prism-like cross-section. This geometry refracts incoming light at multiple angles, contributing to the natural pearlescent appearance of silk.

How does the microscopic structure of silk differ from cotton?

Silk fibers show a relatively smooth longitudinal surface and a compact triangular cross-section, while cotton fibers show a collapsed lumen and twisted ribbon-like morphology. These structural differences help explain their different friction, moisture and optical behavior.

Is silk fibroin scientifically considered biocompatible?

Published biomedical literature reports that properly degummed silk fibroin has a strong biocompatibility record. The immunogenicity of raw silk is mainly associated with sericin, which is removed during degumming.

Why do natural fibers usually generate less static electricity than polyester?

Natural fibers such as silk and cotton contain hydrophilic groups and retain more moisture than polyester. Absorbed water molecules can help form conductive pathways for charge dissipation, while hydrophobic synthetic fibers tend to accumulate charge.

From Lab to Living Room

The material observations above help explain why 6A grade mulberry silk is used in skin-contact home textiles such as pillowcases.

Explore Products Engineered with 6A Silk

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