Valdis Kalkis

Assessment of skeletal muscle fatigue of road maintenance workers based on heart rate monitoring and myotonometry

ObjectiveThis research work is dedicated to occupational health problems caused by ergonomic risks. The research object was road building industry, where workers have to work very intensively, have long work hours, are working in forced/constrained work postures and overstrain during the work specific parts of their bodies. The aim of this study was to evaluate the work heaviness degree and to estimate the muscle fatigue of workers after one week work cycle. The study group consisted of 10 road construction and maintenance workers and 10 pavers aged between 20 and 60 years.MethodsPhysical load were analyzed by measuring heart rate (HR), work postures (OWAS) and perceived exertion (RPE). Assessments of the muscles strain and functional state (tone) were carried out using myotonometric (MYO) measurements. The reliability of the statistical processing of heart rate monitoring and myotonometry data was determined using correlating analysis.ResultsThis study showed that that road construction and repairing works should be considered as a hard work according to average metabolic energy consumption 8.1 ± 1.5 kcal/min; paving, in its turn, was a moderately hard work according to 7.2 ± 1.1 kcal/min. Several muscle tone levels were identified allowing subdivision of workers into three conditional categories basing on muscle tone and fatigue: I – absolute muscle relaxation and ability to relax; II – a state of equilibrium, when muscles are able to adapt to the work load and are partly able to relax; and III – muscle fatigue and increased tone. It was also found out that the increase of muscle tone and fatigue mainly depend on workers physical preparedness and length of service, and less – on their age.ConclusionWe have concluded that a complex ergonomic analysis consisting of heart rate monitoring, assessment of compulsive working postures and myotonometry is appropriate to assess the work heaviness degree and can provide prognosis of occupational pathology or work-related musculoskeletal disorders for the workers under different workload conditions. These results can also be used when deciding on necessary rest time and its periodicity.

Thermomechanical and adhesive properties of radiation-modified polymer composites for thermosetting products

Gamma-irradiated blends of polyethylene (PE) with ethylene-propylene-diene copolymer (EPDM) and a thermotropic liquid-crystalline polymer (LCP) are investigated at absorbed radiation doses not exceeding 150 kGy (10 kGy=1 Mrad). The temperature dependences of elastic moduli, tension diagrams at a temperature above the melting point of the crystalline phase of PE, and long-term strain recovery curves for oriented test specimens are presented. The kinetics of thermal relaxation and shrinkage stresses in previously oriented composite specimens upon their heating and cooling is investigated. Data on the influence of LCP additions on the adhesive interaction of the compositions with steel are obtained. The peculiarities of thermomechanical and adhesion properties of these composites are discussed taking into account the morphologic and calorimetric data obtained.

Studies on Morphology, Rheological, Mechanical, and Thermorelaxation Properties of Chemically and Radiation Modified Polyethylene/Ethylene Propylene-Diene Copolymer Blends

Experimental studies of the blends consisting of chemically and radiation modified polyethylene and ethylene -propylene -diene copolymers have been carried out. Measurements of crystallinity, microhardness, strength-deformation, viscoelastic, adhesive and thermorelaxation properties, as well as electron microscope observations, have shown that the blends chemically vulcanized by a special elastomer phase crosslinking system has a typical biphasic structure within the entire composition range with characteristics specific for rubber. Subsequently, radiation vulcanized blends where crosslinking takes place in both disperse phases, formation of chemical bonds between these phases and fibrillation of molecular structures is observed. Consequently, it can be stated that radiation treatment shows the best properties of the blends in comparison with chemical vulcanization. Therefore, materials formed by such a systcm can be successfully used, e.g., as elastic and adhesive active thermosetting materials if the polymer is previously oriented.

Features of thermomechanical properties of radiation-modified blends of high-density polyethylene with liquid-crystalline copolyester

The present paper surveys the investigation results of gamma-irradiated blends of high-density polyethylene (PE) with thermotropic liquid-crystalline polymer (LCP). The LCP used was a liquid crystalline copolyester of 40% poly(ethyleneterephthalate) with 60% p-(hydroxybenzoic acid). The LCP content in the blends was 0,5, and 10 wt.%. The constituents were blended with the use of a single-screw extruder. The samples were prepared by compression molding and irradiated by a Co60 γ-radiation source in an inert atmosphere (argon) to relatively low absorbed doses (up to 200 kGy; 1 Mrad=10 kGy). Morphological, thermal, and mechanical properties in a wide temperature range were investigated for the irradiated and nonirradiated samples. The effects of gamma-irradiation and LCP addition on the thermomechanical behavior of PE are discussed. It was found that the LCP addition affected significantly the stress-strain behavior of PE at temperatures above the melting point. The features of thermorelaxation properties of the PE/LCP blends previously irradiated and oriented, particularly thermorelaxation and residual shrinkage stresses at isometric heating and cooling, were also established. The results obtained testify that the LCP addition makes it possible to improve considerably the thermosetting properties of irradiated PE.

Prediction of the Stress-Relaxation Behavior of Thermoshrinkable Radiation-Modified Polymer Materials

The results of investigating nonirradiated and gamma-irradiated (to an absorbed dose of 150 kGy) specimens of an ethylene-octene copolymer are presented. The thermal properties (melting endotherm and crystallization exotherm) are determined by the method of differential scanning calorimetry. The behavior of the material in short-term tension is discussed. The primary attention is given to the temperature-time dependence of the mechanical properties of the materials under creep and stress relaxation. The long-term stress relaxation is predicted from short-term creep tests at elevated temperatures using the temperature-time correspondence principle. The results obtained indicate that the material investigated may be used for thermoshrinkable polymer products with long-term serviceability.

Manufacturing, structure and properties of recycled polyethylene terephthalate /liquid crystal polymer/montmorillonite clay nanocomposites

Polyethylene terephthalate (PET)/liquid crystal polymer (LCP)/monthmorillonite clay (MMT) compositions were obtained by melt mixing. Their mechanical, structural, rheological and thermal properties were investigated.

The Significance of Early Multidisciplinary Rehabilitation in Health Promotion for Workers with VDT Suffering from NSAH Complaints

METHODS The study was performed over a period of one year. Twenty offi ce workers aged 40,2 yrs. (±SD 8,1) participated. We selected participants who had suffered from pain between 2 to 5 years (without sick-lists) and who had had physical pain at least 6 8 times during one month working with VDT. The workers questionnaire was utilized. The pain level in NSAH and the effectiveness of rehabilitation after successfully completing the programme was determined using Visual Analogue Scale (VAS). Rehabilitation was carried out for 9 months and consisted of various physical activities. The autogenic training (AT) method was applied in order to learn the technique of self relaxation and self positive control. Muscles tension was measured with MYOTON-3 device before, during and at the end of rehabilitation. Life quality was assessed before and after rehabilitation using the Quality Of Life Scale.

Properties of radiation‐modified blends of polyethylene with elastomers and liquid crystalline copolyester

The results are given on the effect of γ-irradiation on properties of blends of high and low-density polyethylene (HDPE, LDPE) with elastomers -ethylene/propylene/diene rubber (EPDM) and chlorinated polyethylene (CPE), and thermotropic liquid crystalline polymer (LCP). The morphological, thermal, mechanical properties (including thermosetting properties) and adhesion properties of blended composites were investigated. A special attention was paid to the applicability of the blends as thermosetting materials (TSM). The LCP used was a copolyester of poly(ethylene terephthalate) with p-(hydroxybenzoic acid) in the ratio 40: 60. It was found that addition of LCP essentially influenced the thermomechanical and adhesion properties of PE composites, irradiated up to the absorbed dose 150 kGy, as well as the dimensional stability of thermosetting products, made from polyethylene/elastomer mixtures. The results show that such ternary blends considerably improve the exploitation conditions of irradiated polyethylene and useful thermosetting materials can be obtained.

New Thermoshrinkable Materials of Radiation Modified Polypropylene-Elastomer Composites with Cross-Linking Agents

In this work, electron beam modified heterogeneous composites of isotactic polypropylene (PP) with chlorinated polyethylene (CPE) have been investigated. The PP/CPE blend composites with an excess of elastomer (30/70 wt%) have been modified with trimethylolpropane triacrylate (TMPTA) and bisphenol-A-dimethacrylate (BPDMA) cross-linking agents and have been irradiated with accelerated electrons up to ionizing radiation doses from 25 to 150 kGy. The internal stresses characterizing the thermoshrinkage properties (TMP) thermorelaxation stresses formed in thermal heating and the residual stresses resulting in the process of full setting and cooling of materials have been investigated for radiation cross-linked oriented (extended up to 100%) composite samples. The dependence of cross-linking efficiency and the TMP characteristics of PP/CPE heterogeneous blends have been compared to properties of a low density polyethylene (LDPE), which has been commonly used as thermoshrinkable material (TSM) in polymer industry. It has been proved that the radiation-chemically modified PP multiphase composites with elastomers and the crosslinking promoters are comparable perspective materials for creation thermoshrinkable materials with higher or similar thermoshrinkage properties compared to currently exploited TSM.

Radiation-chemically modified PP/CNT composites

Abstract In this work, the authors studied the effects of electron beam (EB)-induced changes in stress-strain characteristics, heat shrinkage stresses, and structure characteristics on polypropylene (PP) composites containing bisphenol-A-dimethacrylate (BPDMA) as the radiation sensitizer and different contents of multi-walled carbon nanotube (CNT) filler (0–2 wt.%). The effect of stearic acid (SA) as the surface modifier on the improvement of CNT dispersion in the PP matrix was also studied. Initially, PP blends with different contents (up to 10 wt.%) of BPDMA were prepared to determine the effective concentration of the sensitizer for the modification of the PP matrix. PP/BPDMA composites and blends filled with CNTs were irradiated up to 25–50 kGy of radiation doses. The properties of unirradiated compositions and those modified by EB, were compared. Radiation-induced changes were confirmed by gel fraction and by the changes in Fourier transform infrared spectroscopy spectra. The results showed an increase in Young’s modulus, yield strength, and thermal-relaxation stresses for the irradiated PP/CNT compositions grafted with 3 wt.% of BPDMA and compatibilized with SA.