§ Find ways to recycle abundant waste plastic utilizing the Scheffler solar cooker




§ As there is no garbage disposal/recycling system in place all (plastic) garbage gets burned on location causing carcinogenic fumes

§ The aim is to use abundant resources (plastic waste, sand, solar heat) to produce lacking goods (containing vessels e.g. pods, tagari, etc.)


Background Information


§ Plastics are divided into seven sub groups

§ Each plastic displays different properties in terms of melting temperature, strength and flexibility among others

§ The types most present in barefoot are PET (plastic bottles, bags), HDPE (bottle caps, medicine cotainers), LDPE (garbage/nursery bags) and candy/food wrappers for which the exact material is not known at the moment

§ PET and HDPE as well as LDPE are good recycable materials


Experiment Series

1. PET

§ melting PET with the small scheffler solar cooker

§ the result was a brittel hard plastic that stuck strongly to the heated container

§ the temperature in some spots rose so fast that the pet burned



§ melting bottle caps with the small scheffler solar cooker

§ the result was hard steardy bricket partly burned on the upper side


3. Stone Oven

§ as experiment 1. and 2. showed that the temperature development in the container was uneven

§ it was attempted to use marble plates as heat buffer

§ similtaniously it was test if and how strong melted plastic woud stick to the stone

§ the samples were tea cup (PET), bottle label (?), cookie wrapper (?), bottle cap (HDPE); from let to right, top to bottom

§ the result was that all 4 samples stuck to the stone

§ bottle label and cookie wrapper showed signs of seperation of plastic from rest material



4. Composite

§ it was attempted to reproduce a composite of melted plastic (in this case PET) and sand in the big solar cooker

§ research had brought up a ratio for plastic and sand of approxematly 30:70 [2]

§ it was assumed that this ration concerns the weight

§ during the melting process this ratio was let go, focus was set on getting any result in terms of composit at all

§ research had brought up that the sand should be ideally river sand[3] or marble dust[2] dried and pre-cooked as to eliminate all organic matter

§ the sand used in this experiment was simple dry sand from the street that was not pre-cooked

§ the (cooled down) result was a brown, strong material, slightly brittel in its whole, broken of pieces could be hammered flat

§ material had stony feeling to it

§ the produced (hot) sludge was tough and hard to work with


5. HDPE Mirror Embedding

§ Attempt to embed a mirror in an HDPE frame

§ The mold was filled with pieces of HDPE and placed in the marble stone oven

§ The stone oven was the placed in the big scheffler solar cooker

§ When the pieces were melted the oven was removed from the solar cooker and mirror was placed in the plastic. The material then was first shock cooled and then allowed to slowly cool down

§ The stone oven did not suffice to spread the heat more evenly. Some parts were close to burning while others were yet to be melted. This partly due to the spread focus of the collector

§ While cooling down the shrink of the material cracked the mirror.

§ The complicated removal of the product from the mold further broke the mirror

§ The mold is made of tin and coated with a thin protective plastic layer

§ the plastic layer stuck to the product



6. PET Composite Molding

§ attempt to produce a bigger amount of PET-sand-composite and mold it into a shallow pod

§ sand was seefed and pre-cooked

§ community was involved to watch and participate in the experiment

§ mold was an existing pod covered with newspaper to prevent sticking

§ to prevent sticking of the spatel kitchen oil was used and for curiosity reasons also added to the mixture

§ Produced sludge was tough and hard to work. This was mainly due to infirrior mixture of sand and PET as well as the uneven distribution of heat and thus the uneven melt. A significant amount of the PET did not reach melting point

§ Amount usable sludge produced was not enough to produce a pod

§ product smells of kitchen oil even more than a week after the experiment

§ product was strong and flexible but breakable by hand


7. HDPE Sticking Test

§ it was tested if HDPE would be removable from the mold even after the protecting layer had been removed during experiment 5.

§ result: it was possible to remove the samples with the help of tools

[photos lost]

8. HDPE Composite Molding

§ attempt to produce a bigger amount of HDPE-sand-composite and mold it into a shallow pod using the big scheffler solar cooker

§ same process as in experiment 6

§ HDPE (ca. 150[°C]) melts at lower temperatures than PET (ca. 250 [°C])

§ it was possible to create an amount of homogeneous sludge

§ sludge still was tough and hard to work with although better than the PET composite

§ cooled product was hard and strong yet slightly flexible

§ drop from 1.50 [m] broke a piece of


9. LDPE Compostite Molding

§ attempt to produce a bigger amount of LDPE-sand-composite and mold it into a shallow pod using the big scheffler solar cooker

§ same process as in experiment 6. and 8.

§ LDPE (ca. 110[°C]) melts at lower temperatures than PET (ca. 250 [°C]) and HDPE (ca. 150[°C])

§ it was possible to create an amount of sludge

§ sludge was less homogeneous than HDPE composite but more than PET composite

§ sludge seemed tar like

§ cooled product is quite hard yet gets very flexible and weaker with reduced thickness

§ depending on material thickness product can be pulled apart




§ recycling plastic with a solar cooker in to composite products seems possible

§ main issue at the moment is process controlling

§ heat has to be distributed more evenly

§ heating up has to be more controlled

§ the mixture of the composites has to be optimized (ratio, choosen sand)

§ in all composite experiments the sand was heated up first in order to get a more even heat distribution

§ problems mainly occured in the mixing process when a homogeneous sludge was to be formed

§ mixing and kneading helped the process

§ mixing and kneading efforts were inferior as they had to be done by hand with improvised gloves

§ best product came from HDPE composite