Research Division Summer Placement 2011

Shawn Jackson Supervisors: Dr Stephen Pickering and Dr Richard Brooks

Lightweight Sandwich Panels from Recycled Materials

Recycled Material A range of different recyclate was provided, prepared by different process (Hammer mill for specimens 1 to 4 and cutting mill for 5 and 6) and from different sources. The specimens are classified by Volume Fraction and Fibre Length.

Specimen 5 was selected, although Specimen 1 has longest fibres it is still not above the critial length (≈5.5mm) it mixes very poorly, Specimen 5 has the highest volume fraction and mixes far better.

Introduction & Objectives An industrial partner has developed a patented machine called the LEAP Machine (Layered Engineering Active Polymer) which is a low energy moulding process that uses recycled thermoplastic powders. The aim of the project is to incorporate the recycled glass fibres into the skins of these structures in order to provide reinforcement, reduce weight and reduce cost by reducing the amount of polymer used.

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me

Frac

tion

(%)

Leng

th (m

m)

Recyclate Characterisation

Average Length Volume Fraction

Conclusions From the research carried out, it is has been concluded that the LEAP machine is possible destination for the recycled material at the moment. Although the material mixes and moulds well with the polymer, it does not significantly enhance the properties of the polymer, this is due to the large void content in the skins that can only be reduced by applying pressure during moulding. Further research into this is needed to determine the minium pressure to achieve good consolidation and modify the LEAP Machine to make this possible.

Moulding The amount of fibre in the mixture was increased from zero up to a maximum of 30% recyclate by weight, above this the polymer failed to retain the recyclate as shown in the right hand image below.

30% Recyclate Panel Most Successful 50% Recyclate Panel

Testing Bending tests of panels and Tensile tests of just the skins were performed to determine the stiffness and strength of the skins. Initial tests showed that the fibres were not giving much reinforcement so the void content was analyzed using microscopy (example images shown in bottom left corner). The results were 14.16% and 20.54% void content in the 20% and 30% recyclate skins respectively. This is very high as expected so Compression moulded skins were produced to reduce void content and see what may be achievable with good consolidation.

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Pure Polymer 20% Recyclate 30% Recyclate CompressionMoulded 20%

CompressionMoulded 30%

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ific

Youn

g’s M

odul

us (k

N·m

/kg)

Youn

g’s M

odul

us (G

Pa)

& P

eak

Stre

ss (x

10 M

Pa)

Mechanical Properties of Skins

Youngs Modulus Peak Stress Specific Young's Modulus

Microscopy Images showing voids in 30% Skin (Top) and 20% Skin (Bottom)

The results show that the stiffness of the skins has been increased by the introduction of the recycled fibres and despite slightly increased density the specific stiffness has also increased however the peak stress was decreased. This is because the fibres used are shorter than the critical length.

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ss, σ

(MPa

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Strain, ε

Stress Strain Graphs Comparing Skins

Pure Polymer20% LEAP30% LEAP20% Comp.30% Comp.

Specimen 1 Specimen 5

1mm

1mm