Nano-sized particles emission during drilling and low velocity impact of silica-based thermoplastic nanocomposites

摘要

During the past decade, polymer nanocomposites have emerged as a novel andrapidly developing class of materials and attracted considerable investment in researchand development worldwide. Driven by the certainty that by the integrationof low nano ller amounts, existing material properties can be improved and moreovernew material properties can be developed. Despite the clear bene t andtherefore, increasing research, production and utilisation of nanomaterials, littleis known about how nanocomposites will perform over their whole life cycle, especiallyin the usage and end of life phase. Under the in uence of environmentalfactors such as ultraviolet light, moisture, temperature and mechanical actions,nano-sized particles can be potentially released from nanocomposites and thusmay have negative e ects on the human health and the environment.Within the scope of this work an extensive literature review has been conductedin which polymer nanocomposites are brie y introduced and release scenarios ofengineered nano-sized particles from nanocomposites during their life cycle are discussed.In the experimental part of this work silica based polypropylene, polyamideand polyurethane composites were manufactured and particle exposure mechanismduring mechanical processing and testing were monitored and analysed. A series ofcomprehensive physical characterisation techniques were utilised to assess particlesize distribution, shape, and concentration in di erent mediums, once emitted bythe solid composite materials.It was observed that during drilling of PA6 composites, the airborne particle emission rates were 10 times higher than those for the PP based composites. However,the characterisation of deposited particles showed exactly the opposite behaviour,were the total number of particles emitted by the PP based composites was 10-100times higher than those of the PA6 based composites. To the best of our knowledge,this is the rst time such work has been reported in the literature.Further, the addition of secondary ller into a polymer/glass- bre compositeschanged the micro-mechanism during crash testing and therefore controlled theenergy absorption characteristics of the composites. However, it was shown thatonce subjected to higher impact energies the geometric particle size of the releasedparticles increased from approx. 25 nm for the 530 J to approx. 60 nm for the1560 J impact. Additionally, the tensile modulus increased by 0.31 GPa and thespeci c energy absorbed during impact test increased from 20.7 kJ to 22.6 kJ byusing nano-SiO2 alternative to micro-SiO2 particles in PP/glass- bre matrix. Eventhough a respective enhancement in mechanical properties were observed by usingnano llers over micro llers, no signi cant di erence in particle emission duringimpact test were measured.Further, it could be shown that during drilling and testing, nano-sized particleswere released from all materials studied, regardless of whether they had nanoparticlesintegrated or not. In one particular case, the neat polymer matrix generatedmore nano-sized particles during drilling than the exfoliated PA6/nanoclaynanocomposite. Hence, the addition of nanoclay can have bene cial impact interms of controlled particle release. However, in general the addition of nano llersincreased the particle emission rates during drilling and impact testing of thenanocomposites. Further, the emitted nano-sized particles were not all free engineeredpristine nanoparticles but also hybrid particles consisting of matrix/nano llermaterial. A signi cant set of data was obtained during this study and hence theoutcomes sets an excellent foundation for risk assessment and life cycle analysis ofsilica based polypropylene, polyamide and polyurethane nanocomposites.