Strength of bed nets as function of denier, knitting pattern, texturizing and polymer

Abstract

BackgroundBursting strength is a standard method for evaluating mosquito net strength. This article suggests that tension strength with one grab and one hook better represent how holes are generated in bed nets in real life.MethodsMeasurements of bursting strength and tension strengths in the two directions are analysed for eight model nets created for the study. The nets were made in the most commonly used denier (75 and 100 D) and mesh (156 holes/inch2) for multifilament polyester yarns, texturized or not, and with 4 or 6 sided holes. All were made from one polyester quality. Data was arranged in a randomized, complete block design and analysed for significant variables and their interactions. Data was then subjected to regression analyses using net square metre weight as a weighting factor with stepwise removal of variables. This revealed how the four textile variables interacted and allowed for making predictions for the strength of commercial nets in polyester or polyethylene.ResultsFor the model nets, higher denier provided higher bursting strength and tension strengths, texturizing weakened nets and four-sided holes were stronger than six-sided holes. Even when compensating for square metre weight, 100 D nets are stronger than 75 D nets. Results for the commercial polyester net nets are less clear, probably because of different qualities of polyester. Tensile strength: a 75 denier net knitted tightly to provide the same square metre weight as a standard 100 denier net therefore does not obtain the same strength. Polyethylene nets are made of mono-fibre yarns and, therefore, have higher tension strength in both directions than multifilament polyester nets. For bursting strength results overlap for 100 denier yarns of both yarn types. As a class, commercial polyethylene nets are stronger than commercial polyester net whatever method is used for evaluation.ConclusionTension strength measured in the length and width directions of the net using one hook and one clamp provide new relevant data as this method more closely imitates the cause of tear holes in nets as they occur in real life use. Using this methodology, the commercial monofilament yarn polyethylene nets are significantly stronger than the commercial multifilament polyester nets. This test method should be applied for nets used for years in the field.

Physical integrity and residual bio-efficacy of used LLINs in three cities of the South-West region of Cameroon 4 years after the first national mass-distribution campaign

“…However little information exists on the physical durability of LLINs in the field; and few malaria control programmes to date have systematically monitored the performance of LLINs in terms of physical durability after mass distributions [10]. Aside for net fabric [11] and fibre weight or denier [12], other factors that influence physical deterioration are the house environment (house wall material, bed type and construction), socio economic status (SES) and the bed net maintenance behaviour (general handling, washing and repair) [13, 14]. …”

Physical condition and maintenance of mosquito bed nets in Kwale County, coastal Kenya

“…Nevertheless, various researchers have variably estimated the useful life of bed nets to be up to four years [4,5] As a result of the insecticidal effect on mosquitoes, insecticide treated nets have slightly longer useful life than untreated nets [4,5,23]. Regardless of insecticide treatment status, the rate at which holes appear on the net may be predisposed by net fabric [24] and fibre weight or denier [5]. Other factors that influence physical deterioration are the house environment (house wall material, bed type and construction), social economic status (SES) and the bed net maintenance behaviour (general handling, washing and repair) [6,9].…”

Comparative functional survival and equivalent annual cost of three long lasting insecticidal net (LLIN) products in Tanzania

“…While it is possible to encourage users to retain their damaged but still insecticidal nets through behavioural change communication (BCC) a more effective strategy will be to distribute more physically durable LLINs. 22 LLINs are the largest single item on the global malaria control budget. Most are distributed through mass campaigns.…”