A review on the limitations of natural fibres and natural fibre composites with emphasis on tensile strength using coir as a case study

Natural fibres such as coir, jute, flax, and hemp have been considered for technical applications. These fibres, though with some desirable qualities such as low density and environmental compatibility, possess the common property of non-uniformity along their length and, as a result, variable diameter and variable cross-sectional area. Several other factors, such as gauge length, fibre species and origin, strain rate, method of extraction of the fibres, porosity and pore size distribution, have been identified to influence the tensile strength of natural fibres and limit their applications in composites. Besides, several authors have used different diameters for the same type of natural fibre, such as coir, resulting in significant inconsistency in the tensile properties. For the same type of coir fibre, and from tensile strength reports from ten authors, an average tensile strength of 120.97 ± 42.30 MPa was obtained. The average number of fibres used in most cases for the tensile test was less than the requirement for natural fibres. All these factors were addressed with the aim of improving the overall properties of natural fibres and their composites.

Effect of post-production vermicompost and thermophilic compost blending on nutrient availability

Composting is a common waste management strategy for recycling nutrients from organic household or agricultural wastes. However, thermophilic (e.g. windrow) composting and vermicomposting (using earthworms) produce different nutrient and enzyme profiles. Vermicompost is purported to have greater fertility benefits, but is also more expensive than thermophilic compost. The objective of this study was to examine a novel approach to designing organic fertility amendments by blending mature vermicompost and thermophilic compost. To examine the effect of blending, vermicompost was admixed to thermophilic compost at 20, 50 and 70 % by mass, with and without the addition of coir (cocopeat). Electric conductivity, water-extractable, immediately available N, P and K were measured. Vermicompost and coir synergistically affected the availability of these nutrients. Synergistic effects were between 15 and 40 % for total inorganic N in blends with coir. Without coir, synergism occurred only at vermicompost additions ≥50 %. Synergism for available P and K was present in all blends and ranged from 10% to 35%. Electrical conductivity measurements suggest that blending affected compost within three days of starting the incubation. The activity of five of seven measured enzymes were linearly and positively related to the fraction of vermicompost in the blend. Blending mature composts with differing properties may be another tool, in addition to adjusting feedstock and process parameters, to affect positively the fertility properties of composts.

Comparison of rockwool and coir for greenhouse cucumber production: chemical element, plant growth, and fruit quality

Replacing rockwool with more sustainable materials, such as coir, is an effective measure to improve the sustainability of soilless cultivation in the greenhouse. To comprehensively assess the feasibility of coir before using it widely, coir was compared to rockwool as a cucumber cultivation substrate to evaluate its performance on mineral elements in the substrates, drainage, and in the plants. Plant growth, amino acids, and flavor substances of cucumber fruits were also compared between the two substrates. Compared to rockwool, coir significantly increased the LAI and yield of cucumber crops as well as contents of Ca, Mg, S, Cl and Zn in leaves and fruits. Contents of P, K, Ca, Mg, Cl, Zn, and B in the substrate were higher for coir while those of Fe, Cu, and Mn in the drainage lower. Moreover, coir also significantly increased contents of amino acids (His, Leu, Ile, Phe, Lys, Asp, Glu and Pro) and flavor substance (TC, PS, TP, CLL, CuB, and LA) in cucumber fruits. Our results demonstrated the potential of coir as a replacement of rockwool to improve sustainability of soilless cultivation in the greenhouse.