title: The processing, production and improvement of hemp-fibre reinforced polypropylene composite materials

authors: Beckermann, Gareth

abstract: Increasing worldwide environmental awareness is encouraging scientific research into the development of cheaper, more environmentally friendly and more sustainable construction and packaging materials. Natural fibre reinforced thermoplastic composites are strong, stiff, lightweight and recyclable, and have the potential to meet this need. Industrial hemp fibre is amongst the strongest of the natural fibres, and possesses a similar specific strength and stiffness to Eglass, but with additional benefits such as low cost and low production energy requirements.
The favourable mechanical properties of hemp, however, have yet to be transferred successfully to thermoplastic-matrix based composite materials. The main objective of this research was to produce an improved hemp-fibre reinforced polypropylene composite material by optimising the fibre strength, fibreprocessing methods, composite-processing methods and fibre-matrix interfacial bonding.
To obtain the strongest and stiffest fibres for use in composites, an investigation was performed on a crop of New Zealand grown hemp to determine the effects of plant growth duration on fibre strength and stiffness. By conducting single fibre tensile tests on retted hemp fibre, it was discovered that the optimum cultivation time was 114 days, producing fibres with an average tensile strength of 671 MPa, and a Young's modulus of 40 GPa. It was also found that the retting process considerably reduced the tensile strength and stiffness of the hemp fibres.
Biological fibre-treatments using 3 varieties of fungi were then used to modify the surface morphology of hemp fibres, so that the adhesion between the fibres and a polypropylene matrix could be improved. It was found, however, that these treatments severely degraded the fibres, and reduced their tensile properties to such an extent that they were deemed unsuitable for use as composite reinforcements.
An investigation was then conducted to determine a suitable fibre treatment method to remove lignin and other non-structural constituents from the fibre wall, to separate the fibres from their fibre bundles, and to retain the fibre strength. Various alkali treatments were used, and a treatment consisting of fibre digestion in a 10% NaOH solution with a maximum processing temperature of 160°C and a hold time of 45 minutes, was found to provide the best combination of fibre strength retention, lignin removal and fibre separation.
Finally, the alkali treated fibres, polypropylene and a maleated polypropylene (MAPP) coupling agent were compounded using a twin-screw extruder, before being injection moulded into composite tensile test specimens. A range of composites with differing fibre and MAPP weight contents were then produced and tensile tested. It was found that the addition of 2% MAPP greatly improved the tensile strength and interfacial bonding of the 30% fibre composites, while only moderate improvements were observed for the 40% fibre composites. An increase in the fibre content from 0% to 40% greatly improved the stiffness of the composites. The most successful composite produced consisted of 40% long alkali treated fibres with 2% MAPP, and had a tensile strength and Young's modulus of 39 MPa and 4.4 GPa respectively.

text: The processing, production and improvement of hemp-fibre reinforced polypropylene composite materials Increasing worldwide environmental awareness is encouraging scientific research into the development of cheaper, more environmentally friendly and more sustainable construction and packaging materials. Natural fibre reinforced thermoplastic composites are strong, stiff, lightweight and recyclable, and have the potential to meet this need. Industrial hemp fibre is amongst the strongest of the natural fibres, and possesses a similar specific strength and stiffness to Eglass, but with additional benefits such as low cost and low production energy requirements.
The favourable mechanical properties of hemp, however, have yet to be transferred successfully to thermoplastic-matrix based composite materials. The main objective of this research was to produce an improved hemp-fibre reinforced polypropylene composite material by optimising the fibre strength, fibreprocessing methods, composite-processing methods and fibre-matrix interfacial bonding.
To obtain the strongest and stiffest fibres for use in composites, an investigation was performed on a crop of New Zealand grown hemp to determine the effects of plant growth duration on fibre strength and stiffness. By conducting single fibre tensile tests on retted hemp fibre, it was discovered that the optimum cultivation time was 114 days, producing fibres with an average tensile strength of 671 MPa, and a Young's modulus of 40 GPa. It was also found that the retting process considerably reduced the tensile strength and stiffness of the hemp fibres.
Biological fibre-treatments using 3 varieties of fungi were then used to modify the surface morphology of hemp fibres, so that the adhesion between the fibres and a polypropylene matrix could be improved. It was found, however, that these treatments severely degraded the fibres, and reduced their tensile properties to such an extent that they were deemed unsuitable for use as composite reinforcements.
An investigation was then conducted to determine a suitable fibre treatment method to remove lignin and other non-structural constituents from the fibre wall, to separate the fibres from their fibre bundles, and to retain the fibre strength. Various alkali treatments were used, and a treatment consisting of fibre digestion in a 10% NaOH solution with a maximum processing temperature of 160°C and a hold time of 45 minutes, was found to provide the best combination of fibre strength retention, lignin removal and fibre separation.
Finally, the alkali treated fibres, polypropylene and a maleated polypropylene (MAPP) coupling agent were compounded using a twin-screw extruder, before being injection moulded into composite tensile test specimens. A range of composites with differing fibre and MAPP weight contents were then produced and tensile tested. It was found that the addition of 2% MAPP greatly improved the tensile strength and interfacial bonding of the 30% fibre composites, while only moderate improvements were observed for the 40% fibre composites. An increase in the fibre content from 0% to 40% greatly improved the stiffness of the composites. The most successful composite produced consisted of 40% long alkali treated fibres with 2% MAPP, and had a tensile strength and Young's modulus of 39 MPa and 4.4 GPa respectively.

year: 2004

title: High performance aligned short natural fibre - Epoxy composites

authors: Pickering, Kim L.

abstract: Aligned short harakeke fibre (New Zealand flax) mats were produced using dynamic sheet forming, impregnated with epoxy resin, then pressed and cured on a compression moulder to manufacture composite materials. These composites were found to have significantly higher tensile properties than planar random oriented short fibre composites; the tensile strength (136 MPa) obtained for the composites is higher than any seen in the literature to date for short natural fibre composites. Fibre orientation was not affected by fibre content despite the higher processing pressure required and fibre orientation factors obtained from Modified Rule of Mixtures equations for Young's modulus and tensile strength were found to be similar.

text: High performance aligned short natural fibre - Epoxy composites Aligned short harakeke fibre (New Zealand flax) mats were produced using dynamic sheet forming, impregnated with epoxy resin, then pressed and cured on a compression moulder to manufacture composite materials. These composites were found to have significantly higher tensile properties than planar random oriented short fibre composites; the tensile strength (136 MPa) obtained for the composites is higher than any seen in the literature to date for short natural fibre composites. Fibre orientation was not affected by fibre content despite the higher processing pressure required and fibre orientation factors obtained from Modified Rule of Mixtures equations for Young's modulus and tensile strength were found to be similar.

year: 2016-02-01

title: Local Cryo-history: Redefining the creation, transformation and circulation of Aotearoa’s nineteenth century glacier knowledge

authors: Annandale, Claudi - Ann

abstract: The creation, transformation and dissemination of knowledge constantly shapes the narrative of glacier history. However, the intersecting layers that human encounters with the frozen environment, Indigenous knowledge, and popular thought add to glacier histories is often overlooked. By analysing the trends and intellectual traditions that emerged in nineteenth century New Zealand, a period defined as glaciology's 'classical' era of study, this thesis aims to broaden the Southern Alps’ local science-focused glacier discourse.   

Māori, for example, possessed unique mātauranga (knowledge) that was documented through Europeans employing local guides to accompany them across the Southern Alps. This mātauranga shaped some encounters nineteenth-century scientists, surveyors, and travellers had with Kā Tiritiri o te Moana’s glacier environment. New Zealand scholars like Julius von Haast and James Hector, on the other hand, further refined their understanding of New Zealand glaciers through the transnational exchange of knowledge and intellectual debates. A combination of Enlightenment rationalism and Romantic aesthetic also influenced popular glacier narratives that emerged during the nineteenth century. For example, the imagination of journalists, mountaineers and travellers reflected the broader cultural trends that circulated from Europe to New Zealand before their knowledge was disseminated to the public.  

By interrogating mātauranga Māori, formal scientific study, and popular settler imagination about glaciers, this thesis redefines New Zealand’s nineteenth-century glacier history as inherently multilayered through the circulation, creation, transformation and dissemination of glacier knowledge. In doing so, it highlights glaciers not only as physical entities defined by scientific study but as ideas shaped by diverse knowledge systems, cultural perceptions, and historical contingencies.

text: Local Cryo-history: Redefining the creation, transformation and circulation of Aotearoa’s nineteenth century glacier knowledge The creation, transformation and dissemination of knowledge constantly shapes the narrative of glacier history. However, the intersecting layers that human encounters with the frozen environment, Indigenous knowledge, and popular thought add to glacier histories is often overlooked. By analysing the trends and intellectual traditions that emerged in nineteenth century New Zealand, a period defined as glaciology's 'classical' era of study, this thesis aims to broaden the Southern Alps’ local science-focused glacier discourse.   

Māori, for example, possessed unique mātauranga (knowledge) that was documented through Europeans employing local guides to accompany them across the Southern Alps. This mātauranga shaped some encounters nineteenth-century scientists, surveyors, and travellers had with Kā Tiritiri o te Moana’s glacier environment. New Zealand scholars like Julius von Haast and James Hector, on the other hand, further refined their understanding of New Zealand glaciers through the transnational exchange of knowledge and intellectual debates. A combination of Enlightenment rationalism and Romantic aesthetic also influenced popular glacier narratives that emerged during the nineteenth century. For example, the imagination of journalists, mountaineers and travellers reflected the broader cultural trends that circulated from Europe to New Zealand before their knowledge was disseminated to the public.  

By interrogating mātauranga Māori, formal scientific study, and popular settler imagination about glaciers, this thesis redefines New Zealand’s nineteenth-century glacier history as inherently multilayered through the circulation, creation, transformation and dissemination of glacier knowledge. In doing so, it highlights glaciers not only as physical entities defined by scientific study but as ideas shaped by diverse knowledge systems, cultural perceptions, and historical contingencies.

year: 2025