IMPROVEMENT OF ACOUSTIC METHOD FOR DETERMINING THE QUALITY OF BAST FIBER RAW MATERIALS

Abstract

The article is devoted to the actual problem of developing effective methods for quality control of bast fiber raw materials, particularly hemp fiber, which is gaining increasing importance in the textile industry and composite materials production under the conditions of environmentally oriented technologies development, implementation of the Strategy for Agricultural Development of Ukraine until 2030, and the European Green Deal, which promotes the expansion of bast fiber crops use as a priority direction for sustainable agricultural development. It is emphasized that existing methods for hemp fiber quality control have significant disadvantages: traditional organoleptic methods are subjective and insufficiently accurate for modern production requirements, mechanical methods are destructive and labor-intensive (up to 3–8 hours per sample), while low-frequency acoustic methods (500–2000 Hz) are ineffective for heterogeneous hemp fibers due to their structural features and significant diameter variability (15–50 μm). The article provides detailed analysis of the physical principles of the proposed ultrasonic method, based on the phenomenon of acoustic wave diffraction on fibrous structures, which are considered as a multilayer diffraction grating. The feasibility of using the frequency range of 1-5 MHz is theoretically substantiated, which ensures optimal diffraction conditions (λ ≈ 0.11 mm at f = 3 MHz) compared to existing low-frequency methods (λ = 0.17–0.69 m at 500–2000 Hz). A mathematical model with heterogeneity coefficient Kн = 1 + σd/dср has been developed, which takes into account the variability of hemp fiber diameter and allowed to improve the accuracy of fiber parameter determination from ±15 % to ±2.5 %. High correlation of ultrasonic indicators with traditional quality characteristics has been experimentally confirmed: linear density (r = 0.92), breaking strength (r = 0.89), maturity degree (r = 0.94). The developed experimental setup based on the OWON SDS1102 digital oscilloscope ensures reproducibility of results with a coefficient of variation CV = 2.1 %. The proposed method provides reduction of analysis time to 2 minutes, nondestructive control character and the possibility of simultaneous determination of 5–6 quality parameters, making it promising for implementation in textile industry enterprises.