Environmental Aspects of Plastics

Introduction

• Plastics & paper- common materials in everyday life, often used in disposable applications – major contributor for solid waste

• Plastics due to their long life- when not disposed properly, they are widely seen and often criticized

Source Reduction

• Refer to a reduction in the amount of material used in any application

• The simplest methods is to emply source reduction are – to use fewer products that cause waste– to choose size and types of products where

by waste is minimized– To reduce the material requirements of the

product (for manufacturer)

• For example;– The amount of packaging material in 1 liter drink

bottle is 40% less than material in 0.5 liter drink bottle (larger size are more efficient in using materials)

– Decrease the thickness of materials in application• PE Trash bag (when it was first introduced)- thickness

0.08 mm• LDPE introduced – thickness of trash bag is 0.05 mm• LLDPE (stronger and tougher material) – thickness is

0.025 mm• HDPE – thickness of 0.017 is available now

Source Reduction

• Plastics have a weight & volume over many other packaging materials

• Germany Society for Research for Packaging Market estimates without plastics, the cost of packaging would be double and the volume of packaging would increase by 250%

• The use of plastic packaging raises 3 problem;– Recycling of plastics– Resistance of most plastics to most form of

natural degradation– Potential harmfull off-gases when plastics are

incinerated

Recycling of Plastics

• Refers to the reprocessing and refabrication of a material by a consumer or disposal of solid waste

• This type of recycle is called postconsumer recycle (PCR)- different with recycle (generally called regrind) of the scrap from manufacturing process

• Reprocessing and refabrication of PCR involves several steps;– Collection– Handling/sorting– Reclamation/sorting– End-use fabrication

Recycling of Plastics

Recycling of Plastics

Collection• Voluntary recycling by the consumer is the

most single factor in improving recycling of all materials

• However, consumers do not sort their solid waste but rather mix all materials together

• For many plastics, the cost of virgin plastics is about the same as the cost involve in recycling- create problem in recycling process (different case with recycling of aluminium cans)

Handling & Sorting

• Involves conveying materials from the pickup point (from consumer house) to the reclamation facility

• Sorting of materials is necessary (PET bottle, HDPE waste, aluminium alloy, etc) or in broader material groupings (all metal, all plastics, etc)

• For the highest economy benefit, the HDPE and PET and other recyclable plastics must be separated from the plastics that are not to be recycle- thus considerable labour is required to pick up the recyclables by hand

• Some sorting can be done by machine, i.e. based on certain characteristics (light absorption), various plastic resins can be distinguish from the other

• Under certain condition, the mixture of several plastic type can be recycled, called as mixed recycled or comingled recycle

• To assist consumers and sorters, Society for plastic Industry (SPI) introduced recycling symbols

Handling & Sorting

Numbering system for plastic recycling

Recycling No. Abbreviation Polymer Name

PETE or PET Polyethylene Terephthalate

HDPE High-Density Polyethylene

PVC or V Polyvinyl Chloride

LDPE Low-Density Polyethylene

PP Polypropylene

PS Polystyrene

OTHEROther plastics, including acrylic, polycarbonate, polylactic acid , nylon and fiberglass.

Polymer Name Uses

Polyethylene Terephthalate

Recycled to produce polyester fibres, thermoformed sheet, strapping, soft drink bottles, reinforcement for concrete.

High-Density Polyethylene

Recycled to become various bottles, grocery bags, recycling bins, agricultural pipe, base cups, car stops, playground equipment, and plastic lumber, flower pot, toys

Polyvinyl Chloride Recycled to become pipe, fencing, and non-food bottles.

Low-Density Polyethylene

Recycled to become plastic bags, various containers, dispensing bottles, wash bottles, tubing, and various molded laboratory equipment.

Polypropylene Recycled into auto parts and industrial fibers.

PolystyreneRecycled into a wide range of products including office accessories, cafeteria trays, toys, video cassettes and cases, insulation board and styrofoam.

The coextruded plastics (more than 1 layers of plastics)….how to recycle???

Reclamation/Cleaning

• After sorted, the plastics must be chopped into small flake or shredded for further process

• Then the flakes are treated with solvents and wash to remove residual contaminants (original content & paper label)

• The flake send to the fabricators to extrude into pellets

End Uses- Sorted PCR

• The recycled material can be used in the same applications or other applications

• However, PCR plastic cannot be used in in medical and food-contacting applications due to danger of contamination and desease

• Thermoplastic- can be reheated and reprocessed many times (with minor changes in resin properties)

End Uses- Comingled PCR

• They cannot be recycled back into their original product because they usually come from different products

• The most common product is plastic wood

• Applications: home fence, park bence and table, gazebo, etc

• Process (twin screw extruder & ram injection molding): processing the commingled PCR together at a sufficient temp (to melt the majority flakes)

• Advantages of Plastic wood– Absence of the highly toxic antifungi that normally applied to

wood– Wood normally decay and need maintenance

Problem with plastic wood; the dissimilar hygroscopic characteristics of some components cause different water absorption & dimensional change (control the source stream, where the hygroscopic material should not mixed with hydrophobic materials), the cost of plastic wood is higher than untreated lumber.

Degradation

• Means that the plastic can break down into smaller molecules by natural means, biological agent or by sunlight

• In reality, some materials degrade very slowly• Some applications require that the material not

degrade, i.e. packaging material• Some applications need degradable properties,

i.e. sutures in medical applications

Landfill

• Popular since they are less expansive than other method of waste disposal

• The rubbish is simply buried in the ground• Careful control of the landfill process is required

to protect the site and its surrounding from problems like odor, fire, seepage from contaminating groundwater, etc.

• Problem with landfill, the limited space of the landfill, thus alternatives for disposal of waste are needed

• From the following data, the largest component of waste is paper product (34.1% by weight), followed by plastics (19.9%)

Example of materials in solid waste landfills by (a) volume and (b) weight (in recent year)

Incineration• Incineration or controlled burning is

another option for disposing of large percent of solid waste

• The most common purpose of burning is to generate electricity

Energy content of various solid waste materials and conventional fuels burned to generate electricity

Incineration can destroy some types of chemicals that other methods can't. It is also quicker than many other methods.

Obstacles of Recycling

• Usage of various copolymer blends (i.e. PET) from different manufacturers do not dissolve into one another when heated. Instead, they tend to phase-separate, like oil and water.

• Another barrier to recycling is the widespread use of dyes, fillers, and other additives in plastics. The polymer is generally too viscous to economically remove fillers, and would be damaged by many of the processes that could cheaply remove the added dyes. Additives are less widely used in beverage containers and plastic bags, allowing them to be recycled more frequently.