title: Performance of Hemp-Fibre Reinforced Polypropylene Composite Materials

authors: Beckermann, Gareth

subjects: composite materials

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 available, and possesses a similar specific stiffness to E-glass, 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 composite materials.  The aim of this thesis was to achieve a greater understanding of the various parameters that contribute to composite strength and stiffness, and to manipulate these parameters in order to produce an improved hemp fibre reinforced polypropylene composite material.  

Hemp fibre was alkali treated at elevated temperatures in a small pressure vessel with either a solution of 10wt% NaOH or 5wt% NaOH / 2wt% Na2SO3.  Single fibre tensile tests were performed on treated and untreated fibres, and it was found that the NaOH/Na2SO3 treatment produced the strongest and stiffest fibres with a good level of fibre separation.  Lignin tests revealed that both alkali treatments were effective in the removal of lignin from hemp fibre, and XRD analysis showed that both alkali treatments resulted in increases in the hemp fibre crystallinity index.  TGA and DTA analysis showed that the alkali fibre treatments improved the thermal stability of the treated hemp fibre when compared to the untreated fibre.

Alkali treated hemp fibre, polypropylene and a maleic anhydride modified polypropylene (MAPP) coupling agent were compounded in a twin-screw extruder, and injection moulded into composite tensile test specimens.  A range of composites with different fibre and MAPP contents were produced and tested.  Tensile tests revealed that the optimum composite consisted of polypropylene with 40wt% NaOH/Na2SO3 treated hemp fibre and 4wt% MAPP, and had a tensile strength of 50.5 MPa and a Young's modulus of 5.31 GPa, respectively.  

The effect of MAPP on the fibre/matrix interface of NaOH/Na2SO3 treated hemp fibre/polypropylene composites was assessed by means of the single fibre fragmentation test.  A composite consisting of NaOH/Na2SO3 treated fibres in a matrix of 4wt% MAPP and polypropylene was found to have a critical fibre length of 0.83mm and an interfacial shear strength of 16.1 MPa.  The effects of MAPP on the composite fracture mechanisms were evaluated by means of SEM microscopy.  TGA and DTA analysis showed that untreated hemp fibre composites and NaOH/Na2SO3 treated hemp fibre composites, each with a matrix of 4% MAPP and polypropylene, were less thermally stable than the polypropylene matrix alone.

The Bowyer-Bader model was used to model the strength of an injection moulded composite with a normal fibre length distribution, consisting of 40wt% NaOH/Na2SO3 treated fibre, 4% MAPP and polypropylene.  A theoretical composite tensile strength of 149 MPa was obtained from the model, based on the assumption that all the fibres were axially aligned in the composite.  

Composites with long, axially aligned fibres were produced using a novel solution mixing technique, where the polymer matrix and MAPP coupling agent were dissolved in a solvent and then precipitated inside an aligned fibre mat.  Significant improvements in tensile strength and Young's modulus were achieved for solution mixed composites compared to composites produced by means of extrusion and injection moulding.  The strongest solution mixed composite had a tensile strength of 84.7 MPa, and consisted of 56wt% NaOH/Na2SO3 treated fibre, 4% MAPP and polypropylene; and the stiffest injection moulded composite had a Young's modulus of 16.0 GPa, and consisted of 63wt% NaOH/Na2SO3 treated fibre, 4% MAPP and polypropylene.

text: Performance 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 available, and possesses a similar specific stiffness to E-glass, 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 composite materials.  The aim of this thesis was to achieve a greater understanding of the various parameters that contribute to composite strength and stiffness, and to manipulate these parameters in order to produce an improved hemp fibre reinforced polypropylene composite material.  

Hemp fibre was alkali treated at elevated temperatures in a small pressure vessel with either a solution of 10wt% NaOH or 5wt% NaOH / 2wt% Na2SO3.  Single fibre tensile tests were performed on treated and untreated fibres, and it was found that the NaOH/Na2SO3 treatment produced the strongest and stiffest fibres with a good level of fibre separation.  Lignin tests revealed that both alkali treatments were effective in the removal of lignin from hemp fibre, and XRD analysis showed that both alkali treatments resulted in increases in the hemp fibre crystallinity index.  TGA and DTA analysis showed that the alkali fibre treatments improved the thermal stability of the treated hemp fibre when compared to the untreated fibre.

Alkali treated hemp fibre, polypropylene and a maleic anhydride modified polypropylene (MAPP) coupling agent were compounded in a twin-screw extruder, and injection moulded into composite tensile test specimens.  A range of composites with different fibre and MAPP contents were produced and tested.  Tensile tests revealed that the optimum composite consisted of polypropylene with 40wt% NaOH/Na2SO3 treated hemp fibre and 4wt% MAPP, and had a tensile strength of 50.5 MPa and a Young's modulus of 5.31 GPa, respectively.  

The effect of MAPP on the fibre/matrix interface of NaOH/Na2SO3 treated hemp fibre/polypropylene composites was assessed by means of the single fibre fragmentation test.  A composite consisting of NaOH/Na2SO3 treated fibres in a matrix of 4wt% MAPP and polypropylene was found to have a critical fibre length of 0.83mm and an interfacial shear strength of 16.1 MPa.  The effects of MAPP on the composite fracture mechanisms were evaluated by means of SEM microscopy.  TGA and DTA analysis showed that untreated hemp fibre composites and NaOH/Na2SO3 treated hemp fibre composites, each with a matrix of 4% MAPP and polypropylene, were less thermally stable than the polypropylene matrix alone.

The Bowyer-Bader model was used to model the strength of an injection moulded composite with a normal fibre length distribution, consisting of 40wt% NaOH/Na2SO3 treated fibre, 4% MAPP and polypropylene.  A theoretical composite tensile strength of 149 MPa was obtained from the model, based on the assumption that all the fibres were axially aligned in the composite.  

Composites with long, axially aligned fibres were produced using a novel solution mixing technique, where the polymer matrix and MAPP coupling agent were dissolved in a solvent and then precipitated inside an aligned fibre mat.  Significant improvements in tensile strength and Young's modulus were achieved for solution mixed composites compared to composites produced by means of extrusion and injection moulding.  The strongest solution mixed composite had a tensile strength of 84.7 MPa, and consisted of 56wt% NaOH/Na2SO3 treated fibre, 4% MAPP and polypropylene; and the stiffest injection moulded composite had a Young's modulus of 16.0 GPa, and consisted of 63wt% NaOH/Na2SO3 treated fibre, 4% MAPP and polypropylene.

year: 2007

title: Biopolymer foams from Novatein thermoplastic protein and poly(lactic acid)

authors: Walallavita, Anuradha Sammani

subjects: Biopolymer

abstract: Novatein is the only commercial thermoplastic protein made from bloodmeal, a highly denatured protein and a readily available by-product of the meat processing industry. One of the major limitations of Novatein is its hydrophilic nature and loss of plasticizer during processing which leads to poor mechanical properties. To address these issues, Novatein has been blended with another biodegradable polymer with good mechanical properties, polylactic acid (PLA).  

Blending two components can lead to poor mechanical properties of the blend due to weak interfacial adhesion and thermodynamic incompatibility. These problems can be overcome with the use of a compatibilizer which helps to stabilize the interface by coalescence suppression of the dispersed domains. In this work, itaconic anhydride grafted PLA (PLA-g-IA) was chosen as a compatibilizer for Novatein-PLA blends because IA is extremely stable when reacted with proteins and less harmful compared to maleic anhydride. 

Reactive extrusion was used to blend different proportions of Novatein and PLA and the compatibilizing effects of itaconic anhydride was examined. Results showed that fewer agglomerated Novatein particles and less phase separation was visible in the presence of compatibilizer. At 50-50 Novatein/PLA, the absence of compatibilizer produced a dispersed morphology which caused the material to disintegrate in chloroform. Upon the addition of itaconic anhydride, the 50-50 blend stayed intact which was thought to be a result of co-continuous morphology. Incorporating 50 wt.% of PLA-g-IA improved the tensile strength of Novatein by 42% and impact strength by 36%. The effect of compatibilizer was evident in wide-angle x-ray scattering. Three phases were detected in the absence of compatibilizer: crystalline Novatein, amorphous Novatein, and amorphous PLA phases. With compatibilizer, the blend was moving toward two phases: crystalline Novatein, and an amorphous blend of Novatein and PLA. Itaconic anhydride grafted PLA improved miscibility between Novatein and PLA, which lead to the fabrication of Novatein-PLA foams.

Foaming Novatein is a new area of study which has never been investigated before. The foamability of a material depends on the ability of the material to withstand the stretching forces during bubble growth and hold the newly formed cellular structure. The low melt strength of Novatein, however, make it difficult to induce a cellular structure in the proteinous bioplastic. Therefore, the foaming ability of Novatein can be improved by blending with PLA, which can successfully be foamed using a batch process with carbon dioxide as the blowing agent.

Various compositions of Novatein/PLA were batch foamed with and without compatibilizer. Results showed that pure Novatein cannot form a cellular structure at a foaming temperature of 80°C, however, in a blend with 50 wt.% PLA, micro cells formed with a higher cell density (8.44x1021 cells cm-3) and smaller cell sizes (3.36 µm) compared to pure PLA and blends with higher amounts of PLA. A further reduction in cell size and increase in cell density was observed upon the addition of compatibilizer due to the higher crystallinity of grafted PLA. The co-continuous morphology obtained upon the addition of compatibilizer led to the development of foams with more uniform cell sizes, which was stable for cell nucleation even at high temperatures.

text: Biopolymer foams from Novatein thermoplastic protein and poly(lactic acid) Novatein is the only commercial thermoplastic protein made from bloodmeal, a highly denatured protein and a readily available by-product of the meat processing industry. One of the major limitations of Novatein is its hydrophilic nature and loss of plasticizer during processing which leads to poor mechanical properties. To address these issues, Novatein has been blended with another biodegradable polymer with good mechanical properties, polylactic acid (PLA).  

Blending two components can lead to poor mechanical properties of the blend due to weak interfacial adhesion and thermodynamic incompatibility. These problems can be overcome with the use of a compatibilizer which helps to stabilize the interface by coalescence suppression of the dispersed domains. In this work, itaconic anhydride grafted PLA (PLA-g-IA) was chosen as a compatibilizer for Novatein-PLA blends because IA is extremely stable when reacted with proteins and less harmful compared to maleic anhydride. 

Reactive extrusion was used to blend different proportions of Novatein and PLA and the compatibilizing effects of itaconic anhydride was examined. Results showed that fewer agglomerated Novatein particles and less phase separation was visible in the presence of compatibilizer. At 50-50 Novatein/PLA, the absence of compatibilizer produced a dispersed morphology which caused the material to disintegrate in chloroform. Upon the addition of itaconic anhydride, the 50-50 blend stayed intact which was thought to be a result of co-continuous morphology. Incorporating 50 wt.% of PLA-g-IA improved the tensile strength of Novatein by 42% and impact strength by 36%. The effect of compatibilizer was evident in wide-angle x-ray scattering. Three phases were detected in the absence of compatibilizer: crystalline Novatein, amorphous Novatein, and amorphous PLA phases. With compatibilizer, the blend was moving toward two phases: crystalline Novatein, and an amorphous blend of Novatein and PLA. Itaconic anhydride grafted PLA improved miscibility between Novatein and PLA, which lead to the fabrication of Novatein-PLA foams.

Foaming Novatein is a new area of study which has never been investigated before. The foamability of a material depends on the ability of the material to withstand the stretching forces during bubble growth and hold the newly formed cellular structure. The low melt strength of Novatein, however, make it difficult to induce a cellular structure in the proteinous bioplastic. Therefore, the foaming ability of Novatein can be improved by blending with PLA, which can successfully be foamed using a batch process with carbon dioxide as the blowing agent.

Various compositions of Novatein/PLA were batch foamed with and without compatibilizer. Results showed that pure Novatein cannot form a cellular structure at a foaming temperature of 80°C, however, in a blend with 50 wt.% PLA, micro cells formed with a higher cell density (8.44x1021 cells cm-3) and smaller cell sizes (3.36 µm) compared to pure PLA and blends with higher amounts of PLA. A further reduction in cell size and increase in cell density was observed upon the addition of compatibilizer due to the higher crystallinity of grafted PLA. The co-continuous morphology obtained upon the addition of compatibilizer led to the development of foams with more uniform cell sizes, which was stable for cell nucleation even at high temperatures.

year: 2018

title: Creating an environment to inform, build, and sustain a Māori health research workforce

authors: Barrett, Nikki Maree

subjects: Kaupapa Māori

abstract: Ensuring the growth and development of the Māori health research workforce is key to achieving health equity for Māori and enabling positive change for all New Zealanders. The purpose of this study was to identify enablers and barriers to research for Māori staff in a large health organisation, and to understand how research is developed and undertaken. A Kaupapa Māori mixed-methods study was undertaken, using an electronic survey comprised of quantitative data and open-ended responses delivered to all Māori staff at the Waikato District Health Board. Following the survey were 10 one on one interviews. Survey data were analysed using descriptive statistics and open-ended responses summarised. A descriptive thematic analysis was undertaken of the interview data. Each of the interview responses was coded and five themes emerged. Frontline Māori staff affirmed their desire to conduct, design, and undertake health research. Challenges to staff included a lack of information on research opportunities, unclear processes for initiating research, and lack of support and resource. The evidence from participants provides insights into Māori health research priorities, considerations for those wanting to undertake research, and solutions for informing, building, and sustaining the Māori health research workforce.

text: Creating an environment to inform, build, and sustain a Māori health research workforce Ensuring the growth and development of the Māori health research workforce is key to achieving health equity for Māori and enabling positive change for all New Zealanders. The purpose of this study was to identify enablers and barriers to research for Māori staff in a large health organisation, and to understand how research is developed and undertaken. A Kaupapa Māori mixed-methods study was undertaken, using an electronic survey comprised of quantitative data and open-ended responses delivered to all Māori staff at the Waikato District Health Board. Following the survey were 10 one on one interviews. Survey data were analysed using descriptive statistics and open-ended responses summarised. A descriptive thematic analysis was undertaken of the interview data. Each of the interview responses was coded and five themes emerged. Frontline Māori staff affirmed their desire to conduct, design, and undertake health research. Challenges to staff included a lack of information on research opportunities, unclear processes for initiating research, and lack of support and resource. The evidence from participants provides insights into Māori health research priorities, considerations for those wanting to undertake research, and solutions for informing, building, and sustaining the Māori health research workforce.

year: 2023