The Process of Making Trees into Plastic

Eastman Chemical Company Website 13may01

From Trees to Plastic
Trees to Cellulose 4.78 lb of wood chips = 1 lb of cellulose
Cellulose to Ester 0.59 lb of cellulose = 1 lb of ester
Ester to Plastic 0.92 lb of ester = 1 lb of plastic
Trees to Plastic2.60 lb of wood chips = 1 lb of plastic

From Trees to Cellulose

In the process of converting trees to cellulose, little is wasted. The bark is removed before pulping and is used as fuel for the conversion process itself. The tree is chipped and then cooked in a digester to separate cellulose fibers. Lignins and resins produced at this stage can also be used for other chemical products or as fuel.

The resulting pulp of alpha cellulose and hemicellulose is treated with various bleaching chemicals to reduce the hemicellulose content and remove the last traces of lignins and resins. At this stage, the pulp is clean and white. It is pressed to remove water, then dried and wound onto rolls. This is the high-quality, high-alpha cellulose used to manufacture cellulose esters for plastics. Only the highest-quality pulps are used for Tenite cellulosics

From Cellulose to Ester

Cellulose esters are made by reacting high-purity cellulose with selected acids and anhydrides in a multistage process. The choice of acids and anhydrides determines the chemical composition and properties of the final Tenite cellulosic plastic; the cellulosic plastics—acetate, butyrate, and propionate—are chemically different.

In esterification and hydrolysis, the cellulose, acids, and anhydrides are reacted under controlled catalyst concentrations and temperatures to determine the chemical make-up and viscosity of the cellulose ester. A viscous solution—the cellulose ester dissolved in acid—is formed at this stage. The solution then undergoes ultrafine filtration to remove traces of unreacted cellulose fibers and by-products. This ultrafine filtration is critical in making high-quality material required for injection molding and extrusion applications. Then, in a process known as precipitation, the cellulose esters are separated from the viscous solution of water and acids as a solid powder. Following precipitation, the cellulose esters are washed to remove residual acids, then dried.

From Ester to Plastic

Cellulose ester, plasticizer, and additives are compounded in the final manufacturing step to produce the finished cellulosic plastic.

Pulp End Use	Pulp Quality
Plastic Ester Fiber Acetate Ester Industrial Filament Rayon Textile Filament Rayon Rayon Staple Cellophane Fluff Paper	Highest Lowest

A fully formulated Tenite cellulosic plastic will contain one of the three base esters and a variety of additives (such as plasticizers, heat stabilizers, slip agents, and ultraviolet inhibitors) compounded into a homogeneous mixture. To ensure high-quality formulations, each additive passes separate quality tests before it is used.

A custom compounder of cellulosics since 1932, Eastman produces Tenite acetate, butyrate, and propionate in a variety of formulations and plasticizer content ranging from 3% to 35% in 3.2-mm (1/8-in.) pellets for molding and extrusion.

The emphasis given to continual quality improvement and controlling variables in manufacturing results in quality Tenite cellulosics.

At Eastman, focused operator teams use a structured approach to standardize processes by identifying key variables and specifying desired operating ranges. Statistical Process Control (SPC) and other advanced evaluation tools generate the data that bring variables under control and provide consistent quality within an order and from order to order.

• Dedicated lines for plasticizers
  A good example of data-driven innovation is the use of dedicated plasticizer charging lines. These dedicated lines include highly accurate metering pumps that make precise control of the plasticizer/ester blend a reality.
• Near infrared (NIR) technology
  (accurately measures plasticizer content during compounding) A method to reduce variability and permit real-time control is provided through NIR technology. The plasticizer content of a formula is quickly and precisely determined, confirming that a mixture is properly compounded. NIR offers reduced variability and is a more accurate test than the conventional flow temperature test.
• Twin screw compounding
  Twin screw compounding provides improved extrusion finish and processibility for Tenite cellulosics.
• Quality processes
  Tenite cellulosics are manufactured under quality processes that are ISO 9002 certified, which means they are manufactured to the same standards every time.

Tenite cellulosic plastics, the first of the modern thermoplastics, have been used for more than 60 years because they:

• Have an excellent balance of properties, including toughness, hardness, strength, surface gloss, clarity, chemical resistance, and a warm feel.
• Are available in a variety of formulas, plasticizer levels, and additives.
• Are easily molded, extruded, and fabricated.
• Are resistant to attack or change by a wide variety of common household, industrial, and medical chemicals.

Tenite cellulosic plastics, noted for their excellent balance of properties, are available in a variety of formulas and plasticizer levels and can be tailored to the requirements of the user.

Mechanical
Tenite acetate, butyrate, and propionate are specified by the percentage of plasticizer.

The mechanical properties of Tenite cellulosic plastics differ with plasticizer level. The type and amount of plasticizer affects the mechanical properties of the plastic. Lower plasticizer content yields a harder surface, higher heat resistance, greater rigidity, higher tensile strength, and better dimensional stability; higher plasticizer content increases impact strength.

Electrical
Electrical properties of Tenite acetate, butyrate, and propionate are similar. All have a high dielectric constant, good dielectric strength and volume resistivity, and a high dissipation factor.

Color
Tenite acetate, butyrate, and propionate are available in natural, clear, selected ambers or smoke transparents, and black translucent. Color concentrates are available in a range of let-down ratios in the following formulas: Tenite acetate 100, Tenite butyrate 200, and Tenite propionate 300.

Tenite cellulosic plastics are characterized by exceptional resistance to chemically induced stress cracking. Tenite cellulosics are resistant to attack or change by a wide variety of common household, industrial, and medical chemicals such as toothpaste, aliphatic hydrocarbons, bleach, detergents/soaps, ethylene glycol, salt solutions, vegetable and mineral oils, alcohols, and lipids.

Tenite cellulosics are noted for their outstanding processibility. These cellulosics are easily molded, extruded, or fabricated. They are unique in their ability to accept various types of secondary fabrication including solvent polishing, cutting, cementing, drilling, and decorating. Figure 1 illustrates their exceptional versatility. In addition, clean scrap can be reprocessed, minimizing waste and systems costs.

Cellulosics are frequently chosen not only for their good balance of properties and ease of processing but also for their extraordinary appearance characteristics.

Special formulations of Tenite butyrate and propionate for outdoor applications or formulations that meet FDA regulations are available.

Tenite Acetate
Ophthalmic Sheet
Tool Handles

Tenite Butyrate
Automotive and Furniture Trim
Displays and Profiles
Pen Barrels
Tool Handles
Toys and Sporting Goods

Tenite Propionate
Appliance Parts
Cosmetic and Personal Care Containers
Film and Tubing for Packaging
Healthcare Supplies
Ophthalmic and Optical Safety Frames
Toothbrush Handles
Sunglasses

The HT series formulations in Tenite acetate, butyrate, and propionate demonstrate that it is possible to improve a classic. The basic composition of cellulosics is unchanged; however, HT formulations are superstabilized for processing at the higher melt temperatures used for injection molding and extrusion. Tests show a dramatic improvement in the impact strength of a part when its melt temperature is increased. During initial compounding and in end-use processing, color stability of HT formulations is superior to that of standard formulations, which may permit the use of more regrind.

Testing with the HT formulations also produced a measurable improvement in weld-line strength, the most important factor in the overall strength of a molded part.

Public concern about protecting the environment is increasing. Air, land, and water pollution, excessive energy consumption, solid waste management, and recycling are major issues worldwide. Eastman is also concerned about these issues and is committed to providing sound solutions to these problems through its people, technology, and resources.

Eastman aggressively promotes Responsible Care^®,¹ a Chemical Manufacturers Association initiative focused on improving performance in many areas, including community awareness, emergency response, distribution, pollution prevention, employee and process safety, and product stewardship. Eastman continually looks for ways to reduce waste, manufacture and transport its products more safely, protect employees and the community, and communicate with its neighbors.

¹Responsible Care^® is a registered service mark of the Chemical Manufacturers Association.

Recycling

Consistent with its sense of product stewardship, Eastman supports plastic recycling. Eastman is recognized as a leader in environmental initiatives, as exemplified by the company's pioneering advocacy of recycling and its innovative technology that returns post-consumer PET plastic back to its original chemistry. Recycling is a valid waste management strategy for high-volume disposable goods.

Because of the durable, nondisposable nature of cellulosic end products, recycling of Tenite cellulosic plastics is currently not an issue.

It is important to recognize that recycling represents only one facet of an integrated plan for combating the solid waste management dilemma. Eastman also supports source reduction, incineration, and municipal composting as valuable technologies in reducing the amount of material destined for landfills.

Formula Guide

¹ Contains lubricant for extrusion
² Contains mold release
³ Standard inventory clears
⁴ HT series formula
Bold numbers = Meets FDA requirements when supplied in FDA color numbers. (For Tenite proplonate 350, only plasticizer contents of 14% or less meet FDA requirements.)

Property	Unit	ASTM Method	Acetate 105–35	Butyrate 264–10	Propionate 360–12
Specific Gravity		D 792	1.26	1.19	1.20
Tensile Strength @ Yield [50 mm/min (2 in./min)]	MPa	D 638	22.8	33.1	31.7
	psi		3,300	4,800	4,600
Elongation @ Break [50 mm/min (2in./min)]	%	D 638	30	50	45
Flexural Modulus [1.27 mm/min (0.05 in./min)]	MPa	D 790	1,300	1,400	1,400
	105 psi		1.9	2.0	2.1
Flexural Yield Strength [1.27 mm/min (0.05 in./min)]	MPa	D 790	33	46	41
	psi		4,800	6,600	6,000
Izod Impact Strength, Notched, @ 23oC (–40oC) [3.2 mm × 12.7 mm (1/8 in. × 1/2 in.) specimen]	J/m	D 256	235 (59)	240 (96)	416 (107)
	ft·lbf/in.		4.4 (1.1)	4.5 (1.8)	7.8 (2.0)
Deflection Temperature [conditioned 4h @ 70oC (158oF)]
1.82 MPa (264 psi)	oC (oF)	D 648	57 (135)	74 (165)	75 (167)
0.455 MPa (66 psi)	oC (oF)		70 (158)	85 (185)	83 (181)

Classifications: A = Injection Molding   E = Extrusion

source: http://www.eastman.com/Online_Publications/ppc100d/ppc100d02.htm