Saturday, January 17, 2015

REINFORCED PLASTICS -- DEFINITIONS


Definition:
1.      Reinforced plastics
The term refers to the polymer products reinforced with fibrous reinforcements in the form of discrete fibers, fiber strands or woven or non woven fabrics.

2.      FRP or GRP: Fiber glass reinforced plastics
Earlier the term referred almost exclusively to the parts made with polyester resins and glass fibers. Now thermoplastic resins are also included as they are also reinforced with glass fibers and molded by injection molding in the same manner as other non reinforced thermoplastics. Hence these materials are also described as FRP.

3.      Low pressure reinforced plastics
It is the term used for parts made with polyester resins. Because they can be cured at no or very low pressures (0-50 psi since volatiles are not given off). Exotic fibers mainly used with epoxy resins include Boron, Graphite, Silicon carbide and improved glass fibers.

ADDITIVES USED TO MAKE PLASTIC BIODEGRADABLE



MODIFYING AGENTS
Various modifying agents are used with polymers to obtain certain specific properties. These modifiers are known to be microbial nutrients. This includes some lubricants and plasticizers. With the large number of destructive agents and the adaptability of each, it is highly probable that there are no plasticizers that are completely free from fungal or bacterial attack. Some are readily used by the microorganism as the source of carbon. As the microorganisms grow, they secrete digestive enzymes which accelerate the degradation process of the film by advancing the mycelial growth. The destruction of polymer by plasticizer results in tack and exudation, embrittlement, weight loss and discoloration.
Polyolefins in their unmodified form exhibit excellent resistance to biological destruction. When these polymers are compounded with additives or plasticizers the biological decomposition varies in degree and also is of various types. Plasticizers are substances that are added to plastic compounds to improve their flexibility, extensibility and processibility. Deterioration of the polymer by microorganisms is chemical, involving changes in composition and breaking of chemical bonds. It is the result of enzymes produced by the microorganisms. Various plasticizers that exhibit higher susceptibility towards microbial attack are: acetals, butyrates, laurates, oleates, sebacates, epoxidized oil, epoxidized tallate esters, polyester, glycolates, stearates, abiotic acid derivatives, aliphatic acid derivatives, aliphatic alcohols, n-phthalic acid derivatives, rcinoleates, succinic acid derivatives. Vegetable oils like tung oil, linseed oil, soy bean oil, cottonseed oil, castor oil, dehydrated castor oil, ground nut oil, etc, also exhibit higher susceptibility towards microbial attack.

Tuesday, November 18, 2014

FACTORS AFFECTING DEGRADATION



Synthetic polymers are inherently resistant to biological attack. But susceptibility to biodegradation varies and is affected by:
ADDITIVES
Various compounding ingredients may have nutritive value for microorganisms and hence may invite microbial attack. Most of the plasticizers, lubricants, thickening agents, starch and cellulose fillers are susceptible to microbial attack.
PLASTICIZERS
Plasticizer tends to force the chain apart, giving them greater freedom of movement and also reducing van der Waals’ forces between the chains. All plasticizers are affected by fungal or bacterial attacks. Susceptibility of microbial attack increases as the plasticizer level increases.
THE TYPE OF CHEMICAL BOND
Various chemically degradable polymer bonds are: polycyanoacrylates, polyanhydrides, polyketals, polyorthoesers, polyacetals, poly (2-hydroxy-esters), poly (E-caprolactone), polyphosphazenes, polyB-Hydroxyesters, polyamino carbonates, polypeptides, polycarbonates, polyphosphate esters.
WATER UPTAKE
The hydrolysis of the polymer backbone requires water. Degradation rates increase when the hydrophilic component contents are increased.
CRYSTALLINITY AND MOLECULAR WEIGHT
Crystalline polymers degrade slower than amorphous polymers. High molecular weight leads to slower degradation.
PH
pH changes can modify hydrolysis rates by orders of magnitude.
COPOLYMER COMPOSITION
The presence of variety of functional groups having different hydrolysis rates affects degradability.
ENZYMATIC DEGRADATION
Biodegradable polymers can be hydrolyzed passively or actively via enzymatic catalysis.

MEASURING BIODEGRADABILITY OF POLYMERS



TEST METHODS TO ASSESS BIODEGRADABILITY OF POLYMERS:
Enormous work is being carried out in the field of biodegradable polymers. Hence the researchers must be aware of the Standard Test methods available for the measurement of the degree of degradation. A range of International Standards, and Test methods are developed specifically for biodegradability. Laboratory test protocols are usually evaluation of environmental degradation under simulated conditions to which a particular polymer will be exposed on disposal. Correlation with real world exposure is more difficult for biodegradation than photo degradation because the environment for biodegradation widely differ in microbial composition, pH, temperature, moisture, etc. hence cannot be readily reproduced. In early years, the only tests to establish biodegradability were related to the microbial growth, weight loss, tensile and other physical properties losses. These all are indirect measurements of biodegradation often leads to results that are difficult to reproduce from laboratory to laboratory, giving rise to confusion on the susceptibility to biodegradation of a given polymer.
 STANDARD ORGANISATIONS FOR TESTING:
There are number of International Standards, and Test methods, developed specifically for biodegradability, product safety, and also for compost derived products.
The main International Organizations that have established standards or testing methods are:
à American Society for Testing and Materials (ASTM) (www.astm.org); (ASTM D 638, 1980).
à European Standardization Committee (CEN) (www.cenorm.be);
à International Standards Organization (ISO) (www.iso.org);
à Institute for Standards Research (ISR),
à German Institute for Standardization (DIN); and
à Organic Reclamation and Composting Association (ORCA) (Belgium).
American Society for Testing and Materials (ASTM) methods
à ASTM D5988-03: Standard Test Method for Determining Aerobic Biodegradation in Soil of Plastic Materials or Residual Plastic Materials after Composting. This test method determines the degree and rate of aerobic biodegradation of synthetic plastic materials (including formulation additives that may be biodegradable) in contact with soil, or a mixture of soil and mature compost, under laboratory conditions.
à ASTM D5526-94(2002): Standard Test Method for Determining Anaerobic Biodegradation of Plastic Materials under Accelerated Landfill Conditions. This test method determines the degree and rate of anaerobic biodegradation of plastic materials and mixtures of household waste in an accelerated-landfill test environment.
GROWTH RATINGS G-21-70 AND GZZ-76:
In these test the resistance of plastics to fungal and bacterial growth is assessed. Fungi like aspergillus niger, pennicillium at 28-30°C temperature at 85% RH for 21 days is used. Bacteria like pseudomonas aeruginosa incubated at 35-57°C for minimum 21 days are used. After suitable time the growth is assessed in terms of % surface covered. The test gives quick results. It is easy to do and give indication of biodegradation. But it is not conclusive for biodegradation of polymer.
International Standards Organization (ISO): (www.iso.org) European biodegradable plastics are currently assessed by ISO 14855, which is a controlled aerobic composting test and ISO 14851 and ISO 14852 are biodegradability tests specifically designed for polymeric materials.
ISO 846 (1978):It specifies the use of a mixture five strains of fungi over a period of at least 28 days at 30 ±2°C and 95-100% RH. The results of attack are measured by visual examination for growth. Method A is used to determine the ability of plastics to act as the carbon and nitrogen source for the growth of microorganisms. Method B is used to determine the fungi toxic properties of plastics.
Compost Toxicity Tests: For a comprehensive assessment of toxicity associated with compost applications, plastics can be tested on both plant and animal species. A number of polyester types were tested including a plasticized cellulose acetate, an aliphatic polyester, polyhydroxybutyrate-co-hydroxyvalerate and polycaprolactone. Cell culture medium with serum was used as the extraction medium.
Plant Phytotoxicity Testing: While a product may not negatively impact plant growth in the short term, over time it could become phytotoxic due to the build-up of inorganic materials, which could potentially lead to a reduction in soil productivity. For this reason some manufacturers use plant phytotoxicity testing on the finished compost that contains degraded polymers. Phytotoxicity testing can be conducted on two classes of flowering plants. These are monocots (plants with one seed leaf) and dicots (plants having leaf with two seeds). Representatives from both of these classes are typically used in toxicity testing - summer barley to represent monocots and cress to represent dicots. Tests involve measuring the yield of both of these plants obtained from the test compost and from control compost.
Animal Toxicity Test: Animal testing is generally carried out using earthworms (as representative soil dwelling organisms) and Daphnia (as representative aquatic organisms). Earthworms are very sensitive to toxicants. Since earthworm feeds on soil, they are suitable for testing the toxicity of compost. In the acute toxicity test, earthworms are exposed to high concentrations of the test material for short periods of time. Earthworms are exposed to soil and compost in varying amounts. Following 14 days of exposure, the number of surviving earthworms is counted and weighed and the percent survival rate is calculated. The earthworms are exposed to several mixture ratios of compost and soil mixtures. Compost worms are used for testing the toxicity of biodegradable plastic residues. These worms are very sensitive to metals such as tin, zinc, and heavy metals and high acidity. For this test worms are cleaned and accurately weighed at intervals over 28 days. The compost worm toxicity test is considered to be an accurate method. The toxicity test can establish whether degradation products present in liquids pose any problem to surface water bodies. In the test, Daphnia are placed in test solutions for 24 hours. After exposure the number of surviving organisms is counted and the percent mortality is calculated.
SOIL BURIAL TEST BS 4618 SEC.4.5 1974: Soil burial is a traditional way to test samples for degradation because of its similarity to actual conditions of waste disposal. It lacks reproducibility because of the difficulties in controlling climatic factors and the population of various biological systems that are involved. Generally the samples are buried in soil for periods of up to two years. At the end of the resting period, changes in properties like loss in weight, mechanical strength, shape etc. are studied. It provides qualitative indication of biodegradation.
 Difference Between Standards for Biodegradation: The main point of differentiation between the various international standards is the percentage of biodegradation required for compliance. This is an important issue that is under discussion at ISO level.
Table  Standards Compliance Requirements
Standard
Biodegradation Requirement
DIN
60% 6 MONTHS
ASTM
60% 6 MONTHS
CEN
90%  No specific time is mentioned
OECD
60% 28 days

Tuesday, September 16, 2014

ENVIRONMENTAL EFFECTS OF BIODEGRADABLE POLYMERS


Plastic shopping bags have advantages and disadvantages when compared to alternatives such as paper bags. All disposable bags are problematic from an energy use and disposal perspective.

Advantages

The durability, strength, low cost, water and chemicals resistance, welding properties, lesser energy and heavy chemicals requirements in manufacture, fewer atmosphere emissions and light weight are advantages of plastic bags. Many studies comparing plastic versus paper for shopping bags show that plastic bags have less net environmental effect than paper bags, requiring less energy to produce, transport and recycle; however these studies also note that recycling rates for plastic are significantly lower than for paper. Plastic bags can be incinerated in appropriate facilities for waste-to-energy. Plastic bags are stable and benign in sanitary landfills. Plastic carrier bags can be reused as trash bags or bin bags.

Disadvantages

Our main concerns with plastic shopping bags:
1.                  Plastic bag littering and associated indiscriminate waste disposal and consumer behavior.
2.                  Resource consumption issues, including reduction, reuse and recycling.
3.                  Plastic degradability issues relating to littering and resource use.
4.                  Social issues, community education and awareness, and consumer perceptions.
5.                  Plastic bags are made of petrochemicals, a nonrenewable resource.
6.                  Plastic bags are flimsy and often do not stand up as well as paper or cloth.
7.                  When disposed of improperly, they are unsightly and represent a hazard to wildlife.
8.                  Conventional plastic bags are not readily biodegradable under any normal circumstance.
9.                  Plastic bags can cause unsupervised infants to suffocate.