Thin polyurethane films have been widely used as erosion-resistant coatings on helicopter rotor blades. Published research has mainly focused on empirical studies that relate the mechanical properties such as rebound resilience and hardness of polyurethane to solid particle erosion resistance. However polyurethane possesses phase mixing at multiple scales and thus sand particle erosion resistance depends also on the micro structure and the phase mixing. Hence, it is very important to carry out detailed and systematic investigations to understand the step-by-step mechanism of erosion and how it relates to the polyurethane micro, meso, and macrostructure. Thermal transitions of the pristine films have been studied through Differential Scanning Calorimetry (DSC) and Dynamic Mechanical Analysis (DMA) yielding micro-scale information such as glass transition temperatures of the hard and soft segments and melting temperature of the soft segment. The next stage of our study involved sand particle erosion tests carried out at 500 mph, at an impact angle of 30 degrees. Test specimens were exposed to two different sand media at different mass loadings ranging from 0.1 to 20 g/cm^2. The tools of characterization used on the pristine polyurethane are once again used on the eroded specimens, with the goal to compare pre- and post- erosion results. The comparison of FTIR results on pre-eroded and eroded films reveal the removal of macromolecular bonds corresponding to soft segments in the micro scale. The reduction of the crystalline portion of the soft segment observed from DSC results supports the FTIR findings. Scanning electron microscopy (SEM) images of the eroded specimens are used to correlate the sequence of the damage due to erosion. The observations revealed that after initial ductile deformation of the soft segments on the surface, brittle cracks are formed on the hard segments. The increased exposure to sand particles leads to formation of fragments containing mainly soft segments with cracks in the hard segments propagating in a brittle manner. As exposure increases, cracks intersect and material on the surface gets removed which mainly contains the soft segments as revealed by the FTIR and DSC results.

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This thesis focuses on designing thermoplastic composites with high mechanical properties and a low processing temperature. Thermoplastic composites, which are used in this work, are composed of thermoplastic polyurethane (TPU) matrices and plain woven E-glass fabrics (GFs). TPUs were synthesised with large quantities of hard segments (HS), including 70% and 90%wt HS. The GF-TPU composites manufactured in this study have a melting point of around 175oC. As such, 180oC represents the processing temperature, which was used to produce GF-TPU composites. The influences of HS content and annealing treatment at 80oC on the thermal, dynamic mechanical and mechanical properties of TPU samples and GF-TPU composites with 25% fibre volume fraction (Vf) have been investigated. The highest crystallinity, storage modulus, Tg, yield strength, tensile strength and tensile modulus of all the TPU samples are seen in the TPU/90 samples annealed for 4 days. The TPU/90 samples display higher tensile properties than the TPU/70 and polypropylene (PP) samples, while the PP samples show the greatest elongation at break point. Furthermore, the tensile properties of the TPU/70 and TPU/90 samples are much higher than those of commercial TPUs. As such, annealed GF-TPU/90 composites with 25% Vf present the greatest dynamic mechanical, flexural, and tensile properties. GF-TPU/90 composites with 25% Vf show higher flexural strength than GF-PP composites or GF-polyamide 6 (PA6) composites with the same Vf. The effects of fibre surface treatments on the mechanical properties of GF and GF-TPU/70 composites with 25% Vf have also been studied in this investigation. GF treated with burn-off treatment is found to exhibit the lowest tensile properties. The interfacial adhesion between GF treated by NaOH for 0.5hrs and a TPU/70 matrix is greater than between GF treated by acetone for 5hrs and a TPU/70 matrix. Silanised GF presents greater tensile properties than desized GF. Thus, enhanced interfacial adhesion and tensile, flexural, ILSS and GIC properties are observed in the silanised GF-TPU/70 composites than in the desized GF-TPU/70 composites. GF-TPU/70 composites based on GFs treated by NaOH for 0.5hrs then sized with 0.15%wt. aminosilane display the greatest interfacial adhesion, flexural properties, ILSS and GIC, damage tolerance and impact-damage resistance. Conversely, the lowest interfacial adhesion, GIC, damage tolerance and impact-damage resistance are seen in the GF-PP composites based on 25% Vf as-received GF. There is a significant increase in the tensile and flexural properties of GF-TPU/90 composites with increasing the Vf from 25% to 50%. Moreover, the flexural strength of GF-TPU/90 composites with 50% Vf is not only higher than that of GF-EP composites or GF-vinyl ester composites with normalised 50% Vf, but is also much higher than that of GF-PP composites with 50% Vf. Despite this result, GF-TPU/90 composites with 50% Vf show the lowest fracture toughness, impact-damage resistance and damage tolerance, which are improved by adding 25% and 50%wt. of TPU/70 to the TPU/90 matrix. GF-TPU/90 composites based on a modified matrix have higher GIC, GIIC, impact-damage resistance and damage tolerance than GF-TPU/90 composites based on an unmodified matrix. The GIC, GIIC, impact-damage resistance and damage tolerance of GF-TPU/90 composites based on a modified matrix increase with increasing the percentage of TPU/70. Hence, the highest GIC, GIIC, impact-damage resistance and damage tolerance are seen in the GF-TPU/90 composites based on a modified matrix with 50%wt. of TPU/70.

In the project, our purpose is the synthesis of segmented block copolymers using novel selectively reacting bi-functional coupling agents which have recently been developed by Jakisch at al. Both couplers have one oxazoline group that reacts with carboxylic groups and one oxazinone group that reacts with hydroxyl or amino groups. It was intended to synthesize segmented block copolymers by combination of amino or hydroxyl terminated pre-polymers and carboxylic terminated chain extenders using the above mentioned coupling agents. Several prepolymers were selected such as hydroxyl terminated liquid polybutadiene (PBD-OH), hydroxyl terminated liquid natural rubber (LNR) and amino terminated liquid polybutadiene-b-acrylonitrile (PBAN) and poly(propylene glycol)-bis(2-aminopropylether) (PPO). They were selected as soft polymer segments in the segmented block copolymers aimed for. Additionally, various di-carboxylic acids were chosen as chain extenders. The resulting block copolymers are phase separated materials with a crystalline hard phase. This was demonstrated by two glass transition temperatures corresponding to the soft and hard segments and various melting regions of the hard chain extenders. For these new materials, the controlled phase separation morphology in nano-size was evidenced by TEM. A hard domain size of about 2-5 nm surrounded by a soft matrix was observed on the micro-photographs. This is consistent with the low hard segment content and the segment alternation (A-B)n in multi-block copolymers. With respect to the mechanical properties, a relationship between tensile strength and the average molar mass of the block copolymers was found out. The samples behave as rubber-like thermoplastic materials. The tensile properties depend on the degree of polymerization and the polymer distribution. The reinforcement ability of the hard domains in a physical network was achieved as expected. As a consequence, the obtained final products have mechanical properties like a typical elastomeric material.

In the project, our purpose is the synthesis of segmented block copolymers using novel selectively reacting bi-functional coupling agents which have recently been developed by Jakisch at al. Both couplers have one oxazoline group that reacts with carboxylic groups and one oxazinone group that reacts with hydroxyl or amino groups. It was intended to synthesize segmented block copolymers by combination of amino or hydroxyl terminated pre-polymers and carboxylic terminated chain extenders using the above mentioned coupling agents. Several prepolymers were selected such as hydroxyl terminated liquid polybutadiene (PBD-OH), hydroxyl terminated liquid natural rubber (LNR) and amino terminated liquid polybutadiene-b-acrylonitrile (PBAN) and poly(propylene glycol)-bis(2-aminopropylether) (PPO). They were selected as soft polymer segments in the segmented block copolymers aimed for. Additionally, various di-carboxylic acids were chosen as chain extenders. The resulting block copolymers are phase separated materials with a crystalline hard phase. This was demonstrated by two glass transition temperatures corresponding to the soft and hard segments and various melting regions of the hard chain extenders. For these new materials, the controlled phase separation morphology in nano-size was evidenced by TEM. A hard domain size of about 2-5 nm surrounded by a soft matrix was observed on the micro-photographs. This is consistent with the low hard segment content and the segment alternation (A-B)n in multi-block copolymers. With respect to the mechanical properties, a relationship between tensile strength and the average molar mass of the block copolymers was found out. The samples behave as rubber-like thermoplastic materials. The tensile properties depend on the degree of polymerization and the polymer distribution. The reinforcement ability of the hard domains in a physical network was achieved as expected. As a consequence, the obtained final products have mechanical properties like a typical elastomeric material.