Space City Skeptics

The Official Blog of the Houston Skeptic Society

Archive for May 26th, 2009

Paper or Plastic?

with 7 comments

(This is a brief overview of the manufacture of paper and of plastic, and is not intended to be comprehensive, or a chemistry class.)

How do you answer?  If you give what you think is the ‘correct’ answer, you say ‘paper’ or you’ve brought your own bags.  Let’s examine that choice.

The paper bags used in grocery stores begin in the forest, with the timber industry.  Even though trees are a renewable source, there is more to producing new paper than planting new trees.  The paper industry is one of the dirtiest industries around.   The chemicals used in the paper pulp process include sulfur, bleaches, and acids.  The process uses huge quantities of water, which must be treated and cleaned, a process which also uses chemicals.  According to a representative of the Texas Commission on Environmental Quality, paper manufacturing also receives a larger number of complaints than refineries on ‘nuisance odors ‘ which is a term meaning that the facilities emit very strong, disagreeable odors, as unpleasant to live near as a feedlot.   Processing facilities must control odors to the same extent that they must control pollutant emissions. Odor is a non-trivial pollution problem.

Paper has a limited ability to be recycled.  On each trip through recycling, paper must be chopped and shredded, which shortens the fiber length.  Eventually, the fibers become too small to use and must be discarded into landfill, as do many of the manufacturing byproducts from paper manufacture.

What about plastic?  Grocery stores bags are made of polyethylene, which begins as the ethane component of natural gas.  The primary emission from polyethylene manufacture is from natural-gas fired heaters, which supply heat or steam for the process.  Natural gas is the cleanest burning fuel, and natural gas wells are clean and low-profile – a valve sticking up out of the ground as opposed to the ‘pumping units’ associated with oil wells.  The conversion of ethane into polyethylene is close to 99% efficient.  The feedstocks for ethylene are basically ethane – clean and odorless, and steam.  Additionally, polyethylene can be recycled almost infinitely.  Even though the molecular weight of the polymer chains will change with recycling, it’s still plastic and can be reused.   It is also inert- in some locations, polyethylene has been chopped into sand-sized bits and incorporated into heavy clay soils, to lighten them as you would do with sand.

The manufacture of polyethylene requires about 6% of the water that paper manufacture requires.  As our population grows and the supply of fresh water becomes increasingly scarce, industrial usage of water becomes an important consideration in the chain.

Transportation adds more cost to the paper product than to plastic.  Paper is heavier, so trucking costs, for a given ‘carrying capacity’ of the bag, are higher, as is the amount of pollution from the gasoline needed to transport the denser product.

Frequently, the public’s attitudes and beliefs about environmental consequences of our choices are shaped by sound bites and pictures from the media.  Pictures of sea turtles with a plastic grocery bag stuffed into their throat, or a sea mammal with a set of six-pack rings caught around its head, are moving and emotional.  These items do end up in the oceans, due to sloppy handling.  However, legible newspapers from 70 years ago have also been mined from landfills. Searches on the EPA’s website will turn up studies showing that the TOTAL environmental impact from the manufacture and long-term landfill storage of paper bags exceeds that of plastic bags – from the mining of the raw materials (trees or natural gas), through manufacture including energy requirements, pollutants, water use, and hazardous wastes, to the volume of a bag in the landfill.

As skeptics, we must look at the entire picture.  The issue is more complicated than I can discuss in a short blog post, but critical thinking skills can be used on these issues just as readily as they can on issues of quackery and pseudoscience.   I posted this article in a slightly different format on a well-known skeptic website a few months ago, and was attacked for either being a shill for Al Gore or a shill for Big Oil. I’m not sure how I can be both at the same time, but it shows the knee-jerk reaction of people on hot-button issues.  Although most people wanted to disagree with my statement that plastic is a better choice (as compared to paper), the only evidence given was that sometimes “bags end up in the ocean and get caught on bird beaks or swallowed by whales”.  This is true, but the answer is not to ban plastic over paper, but to handle any bag properly through reuse, recycling, and proper disposal.

The option with the least environmental impact is to carry reusable shopping bags, or carry personal bags.  However, if you are faced with a choice between paper or plastic, plastic is the environmentally responsible decision.

Written by Geek Goddess

May 26, 2009 at 4:02 pm